exposure from aerial applications of sulfometuron methyl using best
management practices.

Input type

Input value

Justification

Aircraft

Air Tractor AT-401

Commonly used aircraft. Typical size and weight.  Aircraft type does not
greatly affect drift.

Boom length

76.3% of wingspan

Recommended to reduce drift and increase application efficiency.
Greater boom lengths generate more drift.  3/4 wingspan should be
specified on the label.

Release (boom) height

15 ft.

Estimated upper bound under normal conditions.  Should be specified on
labels with no-spray zones.

Flight lines

20

Approximate standard scenario field size.

Swath width

60 ft.

Typical.  Does not greatly affect drift.

Swath displacement

fraction (as a fraction of  the swath width)

fine: 0.6833

Swath offset is good application practice.  The value used results in
50% deposition at the edge of the field.

Drop size

Distribution

Fine (ASAE definition)

Dependent upon product.

Spray material

50% water

50% nonvolatile

Dependent on tank mix.  Calculate nonvolatile rate based on the portion
of the tank mix which is not easily evaporated (e.g. the fraction that
is not water or high vapor pressure solvent).

Wind speed

(at 2 meters above the surface.	15 mph

Typical wind speed varies greatly with geographic region and other
factors.  Ten mph is an adequate, high drift, input for many areas.
Model runs for the plains states may require higher wind speeds.  Wind
speed limitations should be specified on the label.

Humidity

50%

Conservative input adequate for much of the US.  Extreme values may
significantly affect drift levels under certain conditions.

Temperature

86 degrees F

Conservative input adequate for much of the US.  Extreme values may
significantly affect drift levels under certain conditions.

Table   SEQ Table \* ARABIC  20 .  Estimated percentage of sulfometuron
methyl spray drift from ground or aerial applications at various
distances from a treated field.

Distance Down Wind (Feet)	[A] Ground Application (low boom)	[B] Ground
Application (high boom)	[C] Aerial (following many label
Recommendations)	[D] Aerial

(high-end exposure scenario)

	Percent	Percent	Percent	Percent

0	102.0	106.0	50.00	77.35

50	1.77	5.00	17.12	38.32

100	0.95	2.48	9.79	25.11

200	0.51	1.20	4.69	14.07

500	0.21	0.39	1.92	5.40

750	0.13	0.22	1.39	3.82

900	0.11	0.17	1.24	3.32

Table   SEQ Table \* ARABIC  21 .  Estimated amount of sulfometuron
methyl spray drift from ground or aerial applications at various
distances from a field treated with  the maximum labeled rate of 0.375
lb ai/A.

Distance Down Wind (Feet)	[A] Ground Application (low boom)	[B] Ground
Application (high boom)	[C] Aerial (following many label
Recommendations)	[D] Aerial

(high-end exposure scenario)

	Lbs ai/A	Lbs ai/A	Lbs ai/A	Lbs ai/A

0	0.3822	0.3956	0.1874	0.2900

50	0.0066	0.0187	0.0642	0.1437

100	0.0036	0.0093	0.0367	0.0941

200	0.0019	0.0045	0.0176	0.0527

500	0.0008	0.0015	0.0072	0.0203

750	0.0005	0.0008	0.0052	0.0143

900	0.0004	0.0006	0.0046	0.0125

The AgDRIFT results illustrate the importance of droplet size in
controlling spray drift. Using larger droplet sizes, such as coarse or
extremely coarse spraying, reduces the downwind drift to adjacent areas
compared to when medium or fine spraying is used. Reducing boom height
during application and applying when wind speeds are between 3 and 10
mph are also important in controlling drift.

Residue Studies

Environmental residue studies can also provide useful information
regarding the potential exposure of terrestrial wildlife receptors.
This data can be used to corroborate modeling results or to provide
additional insights into chemical fate with respect to exposure.  For
sulfometuron methyl, no studies are available; all estimates of exposure
are based on modeling efforts

Uncertainties and Limitations for this Exposure Assessment

Limitations In Knowledge Of Actual Use Patterns

Knowledge on the specific regions of use of sulfometuron methyl is
limited.  The use pattern of sulfometuron methyl does not lend itself to
easy characterization geographically: There are a variety of vegetation
management uses on sites that are less clearly defined than agricultural
crops and have disjoint or unusual treatment area configurations (e.g.,
as with rights of way and railroad uses, or industrial site grounds).

Practical limits on usage rates long-term at particular sites may
different from legally allowable use levels (e.g., usage is highly
unlikely to occur every year at a particular site even though this is
allowable under the label language).

Variability In Sulfometuron Environmental Persistence

Sulfometuron methyl persistence is significantly affected by soil or
water chemistry and may not always easy to predict from typically
available soil / water property data alone.  A clearer picture of the
range of variability in sulfometuron methyl persistence in the
environment would require environmental fate studies on a greater
variety of soils / waters / sediments with a greater range of pH levels
and other soil properties. This is particularly true for the aerobic
soil and anaerobic aquatic metabolism studies.

Exposure To Sulfometuron Methyl Degradates

Limitations in environmental fate data for the degradates made specific
modeling for exposure to each of the degradates very problematic. The
data on individual degradates, environmental persistence and mobility is
insufficient to model each compound separately.  This may not provide
realistic estimates with the PRZM / EXAMS models which utilize a
receiving pond with no turnover or outflow of residues. If any of the
degradation products of sulfometuron methyl should be found to be of
toxicological concern at potential environmental exposure levels, than
additional data and exposure assessment specific to the degradates of
concern would be needed.

ECOLOGICAL EFFECTS CHARACTERIZATION

In screening-level ecological risk assessments, the ecological effects
characterization describes the types of effects a pesticide can
potentially produce in an animal or plant.  The toxicity data used in
the effects characterization for sulfometuron methyl are derived
primarily from registrant-submitted toxicity studies that are conducted
(and reviewed) according to OPP test guidelines.  These “guideline”
studies are also supplemented by data reported in the USEPA ECOTOX
database that have met Agency criteria for acceptability.

Toxicity testing reported in this section does not include all species
potentially affected by sulfometuron methyl usage.  Only a few surrogate
species for fish, aquatic invertebrates and birds are used to represent
all species in the United States.  For mammals, effects are typically
extrapolated from laboratory rat studies.  Also, neither reptiles nor
amphibians are tested, although data from reptiles and amphibians may be
available from the literature as reported in ECOTOX.  In absence of such
data, the risk assessment assumes that avian and reptilian and
terrestrial-phase amphibian sensitivities to the chemical are similar.
A similar assumption is made for fish as surrogates for aquatic-phase
amphibians.  Terrestrial plant data are derived from the vegetative
vigor and seedling emergence tests, typically conducted on 10
agricultural crop species, and do not account for potential chronic or
reproductive effects.  Lack of plant reproduction data is particularly
relevant to sulfometuron methyl because some data suggest plant
reproduction may be more sensitive to sulfonylurea herbicide exposure
compared to growth and endpoints measured in the seedling emergence and
vegetative vigor tests (Fletcher et al, 1993). For aquatic plants, five
aquatic plant species (1 vascular, 4 nonvascular) are used to represent
potential toxicity to all aquatic plant species.

Most of the studies with non-target organisms were conducted with
sulfometuron methyl technical (i.e., > 90% purity).  These studies
provide the effects basis for risk estimation.  Registrant-submitted
studies of the acute, oral toxicity of end use product (Oust®) were
available only for rats.  Other toxicity studies of end- use product
were obtained from ECOTOX for selected aquatic invertebrates and
terrestrial plants.  Details of each of the guideline and literature
studies of sulfometuron methyl effects on non-target organisms are
provided in “  REF _Ref178405615 \h  APPENDIX H: Ecological Effects
Data Summaries .”

Toxicological information on the primary degradates of sulfometuron
methyl (e.g., pyrimidine amine, pyrimidine-ol, saccharin, sulfonamide)
appears very limited.  Specifically, no guideline toxicity studies with
ecologically relevant endpoints (e.g., growth, reproduction,
development, survival) were identified for the primary degradates of
sulfometuron methyl.  Based on literature searches conducted with
ECOTOX, toxicological studies were identified only for one major
degradate (saccharin).  Of the nine saccharin studies identified in
ECOTOX, all were considered inapplicable to the ecological risk
assessment because they lack evaluation of saccharin effects using
ecologically relevant endpoints (e.g., survival, growth, reproduction,
development).  This finding is not surprising given the role of
saccharin as a sugar substitute and the corresponding toxicological
focus on measures of effect that pertain to human health (e.g.,
biochemical, organ-level, mutagenicity and carcinogenicity assays).  A
summary of the ecological toxicity studies involving the saccharin
metabolite of sulfometuron methyl is provided in “  REF _Ref178405615
\h  APPENDIX H: Ecological Effects Data Summaries .”  Appendix J
contains the results of the ECOTOX literature search with respect to
those studies found to be acceptable to ECOTOX but not OPP for the
purposes of this risk assessment.

  REF _Ref178148115 \h  Table 22  contains a summary of the most
sensitive ecological effects endpoints used in this risk assessment.  As
expected, the acute toxicity of sulfometuron methyl to animals is very
low (slightly to practically non-toxic) while its toxicity to plants is
very high.  This finding is consistent with the mode of action of
sulfometuron methyl (inhibition of ALS) and is similar to toxicity
findings from other sulfonylurea herbicides.

Table   SEQ Table \* ARABIC  22 .  The Most Sensitive Endpoints Used In
The Sulfometuron Methyl Screening-Level Risk Estimation.

Environment	Taxa	Type of Risk	Type of Endpoint	Endpoint	Units	MRID

Aquatic	Freshwater Fish	Acute	LC50	> 148	mg ai/L	435018-02

Chronic	NOAEC	Data gap

(A)

	Freshwater Invertebrates	Acute	EC50	> 150	mg ai/L	435018-03

Chronic	NOAEC	 97	mg ai/L	416728-06(A)

	Saltwater Fish	Acute	LC50	> 45

mg ai/L

416728-03

	Saltwater Invertebrates	Acute	EC50	> 38.2

mg ai/L

416728-04

	Plants	Non-Listed	EC50	0.48	µg ai/L	435385-03

Listed	NOAEC	0.21	µg ai/L	435385-03

Terrestrial	Avian	Acute	LD50	> 4650	mg ai/kg-bw	245375

Acute	LC50	> 4600	mg ai/kg-diet	00071414

	Mammalian	Acute	LD50	> 5000 	mg ai/kg-bw	430892-01

Chronic	NOAEC	 > 300   	mg ai/kg-bw/d	78798

	Plants	Non-Listed	EC25	1.8 x 10-5	lb ai/A	435385-01(A)

Listed	EC5 (B)	9.9 x 10-7	lb ai/A	435385-01(A)

(A) Toxicity value was revised after a re-review and analysis of the
study results in 2007.

(B) EC5 was used for estimating effects to listed (endangered)
terrestrial plants because the NOAEC equaled or exceeded the EC25, as
discussed in the terrestrial effect characterization section.

Aquatic Effects Characterization  tc \l3 "1.     Aquatic Effects
Characterization

Freshwater Fish, Acute

Acute toxicity studies with the technical grade active ingredient (TGAI)
were required for two freshwater fish species for sulfometuron methyl.
Preferred test species are bluegill sunfish (warm water fish) and
rainbow trout (cold water fish).  Based on results from preliminary
range finding tests, definitive toxicity tests were not required for
bluegill or rainbow trout (i.e., LC50 >200 mg ai/L).  Therefore,
toxicity ‘limit’ tests were conducted at a single test concentration
of 150 mg ai/L (bluegill, MRID 435018-01; rainbow trout, 435018-02).

Results from these studies are summarized in   REF _Ref178151784 \h  \*
MERGEFORMAT  Table 23  and indicate that sulfometuron methyl is
practically non-toxic to freshwater fish on an acute toxicity basis.  No
mortality was reported in the test concentration of 150 mg ai/L
(nominal) and measured concentrations were within 80-120% of nominal
concentrations in both tests.  To prevent formation of insoluble
precipitate, the pH of test solutions were buffered w/ addition of
sodium hydroxide, which resulted in pH values that exceeded guideline
recommendations (up to pH 9.0).  The authors report no formation of
precipitate or solubility problems in test solutions and no mortality in
pH buffered controls. The pH range deviation is therefore considered a
necessary byproduct of increasing the solubility of the test chemical.
All other test guideline deviations are considered minor. These studies
are  classified as acceptable and meet the guideline requirements for an
acute toxicity study with  warm water and cold water fish.

Table   SEQ Table \* ARABIC  23 .  Freshwater Fish Acute Toxicity of
Sulfometuron Methyl.

Guideline

Species 	% ai	96-hour

LC50 (mg/L) 	Toxicity Category	MRID No.

Author/Year	Study Classification

72-1	Bluegill sunfish

(Lepomis macrochirus)	99.6	> 150	Practically

 non-toxic	435018-01

Brown (1994a)	Acceptable

72-1	Rainbow  trout

(Oncorhynchus mykiss)	99.6	> 148	Practically

non-toxic	435018-02

Brown (1994b)	Acceptable

Freshwater Invertebrates, Acute

The toxicity of sulfometuron methyl to freshwater invertebrates is
indicated by a 48-hr acute toxicity test with the water flea, Daphnia
magna  (MRID 435018-03;   REF _Ref178151938 \h  Table 24 .  As observed
with freshwater fish, no mortality was observed in a range finding test
up to 200 mg ai/L or the follow-up toxicity limit test at 150 mg ai/L.
Buffering of test solutions was required to prevent formation of
precipitates which resulted in a greater pH range (8.4-9.0) than
recommended (7.2-7.6).  No mortality was observed in the 150 mg/L
treatment or in the negative control.  One daphnid died in the pH
adjusted control (mortality 3%).  The test concentration was measured
and found to be 100% of nominal. The pH range deviation is therefore
considered a necessary byproduct of increasing the solubility of the
test chemical.   This study was originally classified as
‘supplemental’ by EFED in 1995 because of concerns over chemical
composition of the dilution water.  A re-review of this study in
conjunction with other data on the dilution water from a separate study
with the same lab indicates that it is acceptable.  A detailed study
review and explanation of the study reclassification are provided in “
 REF _Ref178405615 \h  APPENDIX H: Ecological Effects Data Summaries
.”

Table   SEQ Table \* ARABIC  24 .  Freshwater Invertebrate Acute
Toxicity of Sulfometuron Methyl.

Guideline

Species 	% ai	48-hour

LC50 (mg/L) 	Toxicity Category	MRID No.

Author/Year	Study Classification

72-2	Water flea

(Daphnia magna)	99.6	> 150	Practically

 Non-toxic	435018-03

Brown (1994c)	Acceptable(1)

(1) reclassified as acceptable for this risk assessment, see   REF
_Ref178405615 \h  \* MERGEFORMAT  APPENDIX H: Ecological Effects Data
Summaries  for details.

Estuarine and marine Fish, Acute

The toxicity of sulfometuron methyl to estuarine and marine fish is
indicated by a 96-hr acute toxicity test with the sheepshead minnow,
Cyprinodon variegatus conducted at nominal concentrations ranging from
15 to 100 mg ai/L (MRID 416728-03,   REF _Ref178152097 \h  \*
MERGEFORMAT  Table 25 .  The LC50 based on measured concentrations from
this study was found to be greater than 45 mg ai/L.  No mortality or
observable signs of sublethal effects occurred in the study except for
one dead fish (5%) at 8.2 mg/L (measured).

This study was re-reviewed for this risk assessment and found to contain
several significant deficiencies which render its classification as
supplemental.  Specifically, measured concentrations ranged widely from
test initiation to termination (4 to 7 times), which is believed due to
the formation of an observable precipitate in test solutions.  This
occurred despite buffering of the dilution water to an initial pH of 8.5
(pH ranged thereafter from 7.4 to 8.5).  Although these deficiencies
could render the study classification as “unacceptable,” it is
considered to provide some useful information in this risk assessment
(i.e., an indication of a lack of toxicity at or near solubility limits
in test solutions).  Furthermore, when viewed in the context of
screening level EECs (i.e., a maximum peak concentration of 0.031 ppm in
water,   REF _Ref178044350 \h  Table 15 ), the bioavailable (dissolved)
portion sulfometuron methyl would have to be approximately 1500-fold
lower than the highest measured test concentration (~45 ppm) in order
for risks to be evident.  Therefore, this study is classified as
supplemental but is not recommended for repeat testing at this time
because a repeat test would be highly unlikely to alter the risk
assessment conclusions.

Table   SEQ Table \* ARABIC  25 .  Estuarine/Marine Fish Acute Toxicity
of Sulfometuron Methyl.

Guideline

Species 	% ai	96-hour

LC50 (mg/L) 	Toxicity Category	MRID No.

Author/Year	Study Classification

72-3	Sheepshead minnow

(Cyprinodon variegatus)	99.1	> 45	> Slightly

 toxic	416728-03

Ward and Boeri (1990a)	Supplemental(1)

(1) Reclassified as supplemental for the purposes of this risk
assessment.  See   REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H:
Ecological Effects Data Summaries  for additional study details.

Estuarine and marine Invertebrates, Acute

The toxicity of sulfometuron methyl to estuarine and marine
invertebrates is indicated by acute toxicity tests with mysid shrimp,
Mysidopsis bahia, and embryo/larvae of the eastern oyster, Crassostrea
virginica.  For mysids, a 96-h assay was conducted at nominal
concentrations ranging from 15 to 100 mg/L.  The 96-h LC50 based on
measured concentrations from this study was found to be greater than
44.8 mg ai/L.  No mortality or observable signs of sublethal effects
occurred in the study at any test concentration or the control.  For
oysters, a 48-h assay was conducted on embryos at the same nominal
concentrations as used for mysids.  The 48-h EC50 based on measured
concentrations for this study was found to be greater than 38.2 mg ai/L.
 No mortality occurred and 99% of the surviving control oysters were
normal.

A re-review of both the mysid and oyster studies indicates they have
several significant deficiencies which render their classification as
supplemental.  Specifically, measured concentrations of sulfometuron
methyl ranged widely from test initiation to termination (3X to 13X in
the mysid tests; 3X in the oyster test) and were substantially below
nominal concentrations.  The low % nominal is believed due to the
formation of an observable precipitate in test solutions.  In the mysid
test, low % nominal occurred despite buffering of the dilution water to
an initial pH of 8.5 (pH ranged thereafter from 7.6 to 8.5).  In the
oyster test, pH ranged from 7.7 to 8.0.  The pH range in both the mysid
and oyster tests extended beyond the recommended range for test
guidelines (7.7-8.0 for euryhaline shrimp; 8.0-8.3 for stenohaline
oysters).

Although these deficiencies could render both study classifications as
“unacceptable,” they are considered to provide some useful
information in this risk assessment (i.e., an indication of a lack of
toxicity at or near solubility limits in test solutions).  Furthermore,
when viewed in the context of screening level EECs (i.e., a maximum peak
concentration of 0.031 ppm in water,   REF _Ref178044350 \h  Table 15 ),
the bioavailable (dissolved) portion sulfometuron methyl would have to
be approximately 1300-fold lower than the highest measured test
concentration (~ 40 ppm) in order for risks to be evident.  Therefore,
this study is classified as supplemental but is not recommended for
repeat testing at this time because a repeated test would not likely
affect the risk assessment conclusions.

Table   SEQ Table \* ARABIC  26 .  Freshwater Invertebrate Acute
Toxicity of Sulfometuron Methyl.

Guideline

Species 	% ai	96-hour

LC50 or 48-h EC50 (mg/L) 	Toxicity Category	MRID No.

Author/Year	Study Classification

72-3	Mysid shrimp(1)

(Mysidopsis bahia)	99.1	> 44.8	> Slightly

 toxic	416728-04

Ward and Boeri (1990c)	Supplemental (2)

72-3	Eastern oyster(1)

(Crassostrea virginica)	99.1	> 38.2	> Slightly

 toxic	416728-05

Ward and Boeri (1990b)	Supplemental(2)

(1) 96-h LC50 applies to mysids; 48-h EC50 applies to oyster.

(2) Reclassified as supplemental for the purposes of this risk
assessment.  See   REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H:
Ecological Effects Data Summaries  for additional study  details.

Freshwater Fish, Chronic

No acceptable or supplemental data on the chronic toxicity of
sulfometuron methyl to freshwater fish were available.  A chronic, early
life-stage toxicity test was conducted in 1982 to determine the effect
of sulfometuron methyl on fathead minnow embryo hatching, larval
survival, and growth (MRID 423857-04; Accession No. 249796), however
upon further review, this study was classified as unacceptable.

Freshwater Invertebrate, Chronic

The chronic toxicity of sulfometuron methyl to freshwater invertebrates
is indicated by a 21-day life cycle test conducted on the water flea,
Daphnia magna (MRID 416728-06;   REF _Ref178404187 \h  \* MERGEFORMAT
Table 27 ).  Daphnids (<24-h old) were exposed to six concentrations of
sulfometuron methyl ranging from 0.1 to 100 mg/L (nominal) in a
static-renewal system.  In order to promote solubility of the test
substance, the pH of the stock solutions of the 25 mg/L and 100 mg/L
treatments were adjusted with NaOH to pH 8.5.  Both a negative and
pH-adjusted controls were included. Mean measured concentrations were
close to nominal concentrations (i.e., within 20%), thus indicating that
variability in test concentrations was well within the acceptable limits
of 1.5X.  Survival and growth (length) were not affected at any test
concentration.  Reproduction, as measured by the number of neonates
produced/daphnid, was not significantly different from negative controls
in any treatment (ANOVA, 0.05).  Although the Dunnett’s multiple
comparison test indicated a marginally significant difference in the 24
mg/L treatment (mean measured concentration), it is not considered
statistically valid to apply means testing when ANOVA results indicate
lack of significant differences among treatments.  Furthermore, an
inconsistent concentration-response relationship is indicated by the
lack of a significant reduction in daphnid reproduction at 97 mg/L (the
highest treatment tested).  Therefore, the NOAEC for daphnid
reproduction is re-interpreted as 97 mg/L (unbounded) and the LOAEC is >
97 mg/L.  This study is classified as acceptable and meets the guideline
requirements for a chronic study using a freshwater invertebrate.

Table   SEQ Table \* ARABIC  27 .  Freshwater Aquatic Invertebrate
Chronic Toxicity for Sulfometuron Methyl.

 tc "Table IIIC-9.  Freshwater Aquatic Invertebrate Chronic Toxicity for
Flazasulfuron  " \f E

Species/

Static Renewal	% ai	21-day NOAEC / LOAEC (mg/L)(1)	Endpoints Affected
MRID No.

Author (Year)	Study Classification

Water flea

(Daphnia magna)	99.1	97 / >97	Reproduction	416728-06

Baer (1990)	Acceptable

(1) NOAEC and LOAEC were re-analyzed as part of this risk assessment.
See Appendix H for additional study details.

Aquatic Animal Sublethal Effects: Formulated Product  and Degradate
Toxicity  tc \l5 "(3).       Sublethal Effects

No signs of toxicity or sublethal effects were observed in the acute or
chronic toxicity tests of sulfometuron methyl that were described
previously in this Exposure Characterization (considering acceptable and
supplemental studies).  This is not surprising, given that sulfometuron
methyl is practically nontoxic on an acute toxicity basis.

Two studies of the toxicity of sulfometuron methyl in formulated product
(e.g., Oust®) to aquatic animals were identified and discussed further
below.  The first study, Naqvi and Hawkins (1989) exposed four genera of
field-collected microcrustaceans (Diaptomus sp. Eucyclops sp., Alonella
sp., and Cypria sp.) to sulfometuron methyl from the Oust® formulated
product at nominal concentrations of ranging from 100 to 2500 mg/L for
48-h.  Consistent, monotonic exposure-response relationships across the
six treatments occurred for all four species and 48-h LC50s (probit
analysis) were reported as follows:

Species	Test Chemical	48-h LC50 (mg/L)

(95% confidence limits)	Classification	Reference

Diaptomus sp.

Oust®

(~93% ai)	1315 (1207-1524)	supplemental	Naqvi and Hawkins (1989)

Eucyclops sp.

1320 (1154-1536)

Alonella sp.

802 (475-928)

Cypria sp

2241 (1744-4517)

This study is classified as supplemental primarily because test
concentrations were not measured in the study and the field collected
test organisms were provided a relatively short application period
(96-h) vs. the 7-d minimum acclimation period recommend for freshwater
invertebrate testing.  Furthermore, organisms were not positively
identified to the species level, thus indicating that more than one test
species may have been tested in each study.  Finally, the study authors
do not indicate whether nominal concentrations were adjusted to reflect
the percent active ingredient in the formulated product.  Assessment of
the relative acute toxicity of sulfometuron methyl as technical grade
and in formulated to aquatic animals is somewhat uncertain because LC50
and EC50 values were not achieved for the technical grade herbicide
(e.g., EC50 and LC50 varied from >38 to >150 mg ai/L).  However, results
from the Naqvi and Hawkins (1989) study indicate that sulfometuron
methyl formulated in Oust® is practically nontoxic to aquatic
microcrustaceans.  Thus, the comparative toxicity of technical grade
sulfometuron methyl and sulfometuron methyl formulated at least appear
similar in terms of both ingredients being practically nontoxic to
aquatic invertebrates.

The second study was submitted by the registrant (DuPont) per FIFRA
Section 6(a)2 requirements on July 1, 1991.  In this study, Romaire
(1984) evaluated the acute toxicity of Oust® (% ai not reported) to
juvenile red swamp crayfish, Procambarus clarkii. A static, acute
toxicity study was conducted for 96 hours in 4 replicate aquaria (5
crayfish/aquarium) at 8 test concentrations ranging from 0 to 10,000 mg
ai/L.  Analytical measurements of sulfometuron methyl were not taken
during the study.  The authors report that the 96-h LC50 was > 5,000 mg
ai/L for sulfometuron methyl and mortality did not exceed 50% in any
test treatment.  However, review of this study indicates that it is
unacceptable because dissolved oxygen levels dropped precipitously
throughout the study in test concentrations where mortality was
observed, despite periodic aeration of test solutions.  Dissolved oxygen
levels repeatedly reached levels as low as 2.1 mg/L or approximately 25%
saturation, which is well below ASTM recommendations of 60% saturation.
Because the effect of dissolved oxygen on crayfish mortality could not
be separated from the possible effects of sulfometuron methyl, this
study is not considered scientifically sound for the purposes of
describing the acute toxicity of sulfometuron methyl to juvenile
crayfish.

Regarding the aquatic toxicity of sulfometuron methyl degradates to
aquatic animals, a literature search conducted in May, 2007 of EPA’s
ECOTOX database revealed no acceptable or supplemental studies that
described the toxicity of major sulfometuron metabolites: pyrimidine
amine, pyrimidine-ol, saccharin, and sulfonamide. A list of studies
considered acceptable to ECOTOX but not OPP is provided in “  REF
_Ref179621877 \h  APPENDIX J: Ecological Effects Studies Rejected by OPP
.”

 Field Studies tc \l5 "(4).       Field Studies

No field studies (e.g., mesocosm and microcosm studies) were found
concerning the aquatic toxicity of sulfometuron methyl, either based on
OPP guidelines or from the aforementioned search of the ECOTOX database.

Aquatic Plants

Aquatic plant toxicity studies using the TGAI are required to establish
the toxicity of sulfometuron methyl to non-target aquatic plants (  REF
_Ref178154109 \h  Table 28 ).  Studies in five species are required for
herbicides: freshwater green alga (Selenastrum capricornutum),
blue-green algae (Anabaena flos-aquae), a freshwater diatom (Navicula
pelliculosa), a marine diatom (Skeletonema costatum), and duckweed
(Lemna gibba).  Of the four non-vascular species tested, the green alga
is the most sensitive non-vascular aquatic plant.  This finding is
consistent with the toxicity of flazasulfuron, another sulfonylurea
herbicide with the same mode of action (DP Barcodes: D302482, D302484;
EFED New Chemical review dated 4/11/2007).

The EC50 (reduction in cell density) for S. capricornutum is 4.6 µg
ai/L and the NOAEC is 0.63 ug ai/L.  At the LOAEL of 1.3 μg/L, growth
was reduced approximately 20%, while the cell growth at the NOAEC showed
a slight increase relative to controls.  These toxicity values are based
on reported nominal concentrations.  Although the study authors indicate
that samples were taken for analytical measurement and would be analyzed
“if deemed necessary,” results from chemical analysis were not
provided in the study report. At these concentrations, solubility of the
test compound is not expected to be problematic.

Preliminary tests with the two diatom species indicated that Tier II
tests would not be necessary.  Based on results from Tier 1 tests,
growth (cell density) of neither diatom was affected significantly
relative to controls at measured concentrations of 370 μg/L and 410
μg/L (i.e., the maximum values calculated for sulfometuron methyl
applied directly to a 6 inch deep pond.  Measurements at test initiation
and termination indicate stability of sulfometuron methyl in the test
solutions.

A tier 2 test was conducted on the freshwater blue-green algae, Anabaena
flos-aquae, at measured test concentrations ranging from 14 to180 μg/L.
 Measurements at test initiation and termination indicate stability of
sulfometuron methyl in the test solutions.  An EC50 of  41.6 μg/L (cell
density) is calculated for Anabaena and a NOAEC of <14 μg/L (lowest
test concentration).  This NOAEC corresponds to a 20% reduction in cell
growth relative to controls.  This study is considered scientifically
sound but classified as supplemental because a NOAEL was not determined.

The 14-day EC50 and NOAEC for the freshwater vascular plant (duckweed)
for frond count (the most sensitive endpoint tested) are 0.48 and 0.21
μg/L, respectively, based on exposure to measured concentrations
ranging from 0.13 to 1.05 μg/L. Frond counts were reduced 4% at the
NOAEC and 20% at the LOAEC.  Measurements at test initiation and
termination indicate stability of sulfometuron methyl in the test
solutions.

Except for the test with blue-green algae, the toxicity studies of
aquatic plants (  REF _Ref178154109 \h  \* MERGEFORMAT  Table 28 ) are
classified as acceptable and meet the guideline requirements for
toxicity tests with aquatic vascular and nonvascular plants. Toxicity
values for the most sensitive species (green algae and duckweed) will be
used to calculate risk quotients.

 tc \l4 "b.     Aquatic Plants

Table   SEQ Table \* ARABIC  28 .  Non-target Aquatic Plant Toxicity for
Sulfometuron Methyl.

Species	% ai	EC50/ NOAEC

(µg/L)	Endpoints Affected	MRID No.

Author (Year)	Study Classification

Vascular Species: Duckweed

Duckweed

(Lemna gibba)	95.7	0.48 / 0.21	Frond Count	435385-03

Kannuck (1995)	Acceptable

Non-Vascular Species: Algae and Diatoms

Green Algae (1)

(Selenastrum capricornutum)	99.1	4.6 / 0.63	Cell Density	416801-02

Hobert (1990)	Acceptable

Blue-green Algae(1)

(A. flos-aquae)	99.2	41.6 / <14	Cell Density	435385-02

Thompson (1994)	Supplemental

Fresh Water Diatom (2)

(Navicula pelliculosa)	99.2	>370	Cell Density	435385-02

Thompson (1994)	Acceptable

Salt Water Diatom(2)

(Skeletonema costatum)	99.2	>410	Cell Density	435385-02

Thompson (1994)	Acceptable

(1) Tier II definitive test

(2) Tier I screening  test

Terrestrial Effects Characterization tc \l3 "2.     Terrestrial Effects
Characterization

Acute Effects on Birds

An acute oral toxicity study using the technical grade of the active
ingredient is required to establish the acute toxicity of sulfometuron
methyl to birds.  The preferred guideline test species is either mallard
duck (a waterfowl) or bobwhite quail (an upland gamebird).  An acute
oral toxicity study with the mallard indicates sulfometuron methyl is
practically non-toxic on an acute basis, with a reported oral LD50
>4,650 mg ai/kg-bw (  REF _Ref178155491 \h  Table 29 ). No mortality
occurred in any treatment and birds appeared normal throughout the 14-d
test period.  Food consumption varied widely across treatments, but did
not exhibit a dose-dependent trend. Weight gain/loss also did not
exhibit a dose-dependent trend within or across sexes.  Weight gain in
females may have been confounded by induction of the egg laying cycle by
the photoperiod used.  Lack of acute oral toxicity to birds is
consistent with testing results from other sulfonylurea herbicides
(e.g., flazasulfuron, rimsulfuron). The guideline requirement (71-1) is
fulfilled for an acute oral toxicity study with birds for sulfometuron
methyl and the study (Accession No. 245375) is classified as acceptable.

Table   SEQ Table \* ARABIC  29 .  Avian Acute Oral Toxicity for
Sulfometuron Methyl.

Species	% ai	LD50

(mg ai/kg-bw)	Toxicity Category	Accession No.

Author (Year)	Study

Classification

Mallard duck

(Anas platyrhynchos)	>93	>4,650	Practically

non-toxic	245375

Dudeck and Bristol (1981)	Acceptable

Two dietary studies are required to establish the subacute dietary
toxicity of sulfometuron methyl to birds.  The preferred test species
are mallard duck and bobwhite quail.  The submitted data indicates that
sulfometuron methyl is practically nontoxic to mallard and quail when
administered via subacute, dietary exposure.  The 8-day acute dietary
LC50 values for bobwhite quail and mallard are > 5,620 mg ai/kg-diet and
> 4,600 mg ai/kg-diet, respectively (  REF _Ref178155558 \h  Table 30 .
There was no mortality, signs of clinical toxicity, or abnormal behavior
reported in the studies.  The guideline (71-2) is fulfilled for a
subacute dietary study with birds. The studies (Accession No. 246409 and
MRID 71414) are classified as acceptable.

Table   SEQ Table \* ARABIC  30 .  Avian Subacute Dietary Studies for
Sulfometuron Methyl.

Species	% ai	8-Day LC50

(mg ai/kg-diet)	Toxicity Category	MRID No.

Author (Year)	Study Classification

Northern bobwhite quail

(Colinus virginianus)	95.2	>5,620	Practically

non-toxic	246409 (1)

Beavers and Fink (1981)	Acceptable

Mallard duck

(Anas platyrhynchos)	92	>4,600	Practically

non-toxic	71414

Hazelton Laboratories Inc (1980)	Acceptable

(1) Accession number.

Acute Effects on Mammals

Wild mammal testing is required by the Agency on a case-by-case basis,
depending on the results of lower tier laboratory mammalian studies,
intended use pattern and pertinent environmental fate characteristics.
In most cases, rat or mouse toxicity values obtained from the Agency's
Health Effects Division (HED) substitute for wild mammal testing.  For
sulfometuron methyl, the acute toxicity of sulfometuron methyl
(technical grade active ingredient) is indicated by an acute, oral
toxicity study with the rat (MRID 43089201;   REF _Ref178155676 \h
Table 31 .  In this study, 5 male and 5 female rats were administered a
single oral dose of 5000 mg ai/kg-bw technical grade sulfometuron methyl
(approx. 100% a.i.) in corn oil via gavage.  Rats were observed for
mortality, signs of ill health, pharmacologic and toxicological effects
for 14 days after dosing.  No mortality occurred at 5,000 mg ai/kg-bw
and no clinical signs of toxicity were observed that were related to
sulfometuron methyl exposure. Male and females continued to gain weight
throughout the study.  An acute, oral LD50 value of >5000 mg ai/kg-bw
was determined from this study, indicating that sulfometuron methyl is
categorized as practically non-toxic (toxicity category IV) to small
mammals on an acute oral basis.  This finding is consistent with lack of
acute oral toxicity observed with other sulfonylurea herbicides to rats
(e.g., flazasulfuron).  This study is considered acceptable and
satisfies the guideline requirement (81-1) for an acute toxicity study
with mammals.

Table   SEQ Table \* ARABIC  31 .  Mammalian Acute Toxicity for
Sulfometuron Methyl.

Species	% ai	Toxicity	Affected Endpoints	MRID No.

Author (Year)	Toxicity Category

Rat

(Sprague-Dawley)	~100	LD50 > 5,000 mg ai/kg bw  (males/females)
Survival, weight gain, gross organ pathology	43089201

Dashiell and Sarver (1990)	IV

Acute Effects on Terrestrial-phase Amphibians, Reptiles and Beneficial
Insects

exposed at 5 treatments ranging from 13 to 100 μg ai/bee and included a
solvent and negative control (MRID 416728-10;   REF _Ref178155745 \h
Table 32 ).  Results indicate that sulfometuron methyl is practically
non-toxic to bees on an acute contact basis.  The contact 48-h LD50 for
sulfometuron methyl is >100 µg ai/bee.  Cumulative mortality and
immobility ranged from 4-8% in the controls to 0-2% in the treatments.
No overt signs of toxicity were observed in the study.  The guideline
(141-1) is fulfilled (MRID 416728-10).

Table   SEQ Table \* ARABIC  32 .  Non-Target Insects - Acute Contact
Toxicity for Sulfometuron Methyl.

Species	% ai	LD50

(µg ai/bee)	Toxicity Category	MRID No.

Author (Year)	Study Classification

Honey Bee

(Apis mellifera)	~100	>100 (contact)	Practically

non-toxic

416728-10

Hoxter and Smith (1990)	Acceptable

No acceptable or supplemental terrestrial-phase amphibian or reptile
toxicity studies were submitted or located in the open literature based
on a search of the ECOTOX database.

Chronic Effects on Birds

Avian reproduction studies using the TGAI are required for pesticide
registration if birds may be subject to repeated or continuous exposure
to the pesticide, especially preceding or during the breeding season.
The preferred test species are mallard duck and bobwhite quail.  No data
(71-4 guideline or literature studies) were available on the
reproductive toxicity of sulfometuron methyl to birds.

Mammals,  Reproductive Effects

A combined 2-generation reproduction/oncogenicity study and 2-year
chronic reproduction study with rats exposed to sulfometuron methyl was
submitted to the agency (MRID 423857-05 and 423857-06).  However, study
authors had to abandon the study on about day 200 due to disease of the
test organisms that was not related to exposure and the study was
classified as unacceptable by HED.  The developmental toxicity study
with rat (MRID 00078796) was also classified as unacceptable by HED.
Since no acceptable mammalian reproduction or developmental toxicity
study was available with the rat for sulfometuron methyl, the
developmental toxicity study with the rabbit (Accession No. 78798) was
used in this risk assessment (  REF _Ref178566541 \h  Table 33 ).

In this study, rabbits were administered doses of 0, 30, 100, or 300
mg/kg/day from gestation days (GD) 6-18 and examined at GD 29.  There
were no mortalities and no treatment-related clinical signs or
macroscopic findings.  A slight decrease in maternal body weight
occurred during the gestation period (GD 6-18) but this was judged
biologically insignificant.  There were no treatment related effects on
fetal or maternal endpoints measured, including external, visceral or
skeletal malformations, frequency of resorptions, live fetuses, or dead
fetuses, or on the number of litters, sex ratio, or post-implantation
loss.  The developmental LOAEL was not observed.  The developmental
NOAEL is 300 mg/kg/day (highest dose tested).   According to the data
evaluation record provided by HED, this study is acceptable but does not
fulfill the guideline requirement for a developmental toxicity study
with rabbits because dose levels were not considered high enough to
adequately assess developmental toxicity.

Table   SEQ Table \* ARABIC  33 .  Mammalian Developmental Toxicity of
Sulfometuron Methyl .

Species

	% ai	Test

Type	Toxicity1	Affected Endpoints	Accession  No.

Author (year)

Rabbit

(New Zealand White)	100	Developmental	NOAEL = 300 mg ai/kg/day (highest
test dose)

LOAEL > 300 mg ai/kg/day 	None	78798

Serota (1981)

Terrestrial Animal Sublethal Effects, Formulated Product and Degradation
Products  tc \l5 "(3).      Sublethal Effects

No sublethal effects were reported in either the avian dose or dietary
acute toxicity studies for birds.  However, data on the chronic toxicity
of sulfometuron methyl to birds (and therefore, data on other potential
sublethal effects) were not available.  For mammals, no clinical signs
of toxicity or abnormal behavior were noted in the acute toxicity study
(MRID 43089201).  No acceptable data on the chronic toxicity of
sulfometuron methyl to mammals were available.  Therefore, other
potential sublethal effects resulting from chronic exposure could not be
evaluated.  Based on the developmental toxicity study of sulfometuron
methyl to rabbits, no signs of sublethal toxicity were evident
(Accession No. 78798).

Formulated pesticide products may contain a number of other ‘inert’
ingredients that alter their toxicity compared to the technical grade
active ingredient (e.g., resulting in greater toxicity).  For
sulfometuron methyl, data on the oral toxicity of formulated products
were available for one species of terrestrial animal (rat;   REF
_Ref178495898 \h  Table 34 ).  Results from this study indicate that the
formulated product DPX-T5486-87 is practically nontoxic to laboratory
rats, with a LD50 of >5,000 mg ai/kg-bw.  No clinical signs of toxicity,
weight loss or gross legions were observed in this study.  This study
satisfied guideline requirements for acute oral toxicity with rats and
is considered acceptable.

Table   SEQ Table \* ARABIC  34 .  Mammalian Acute Toxicity to
Sulfometuron Methyl in Formulated Product: DPX-T5486-87

Species	% ai	Toxicity	Affected Endpoints	MRID No.	Toxicity Category

Rat

(Sprague-Dawley)	74%	LD50 > 5,000 mg ai/kg bw  (males/females)	Survival,
weight gain, gross organ pathology	44874103	IV

Except for saccharin, no toxicity information was available on the other
major degradation products of sulfometuron methyl (e.g., pyrimidine
amine, pyrimidine-ol, sulfonamide).  Data on the toxicity of saccharin
that met ECOTOX and OPP screening criteria were available for nine
studies (Appendix J).  However, further review of these data indicates
they do not contain information on endpoints that are considered
ecologically relevant (i.e., closely related to the assessment endpoints
of survival, growth, reproduction and development).  These studies
mostly focused on saccharin as it relates to human health effects (e.g.,
carcinogenicity, mutagenicity, organ level endpoints, biochemical
endpoints).  The remaining ecologically-oriented saccharin studies
evaluated the efficacy of saccharin as a deterrent to insect pest
damage, fungal infection or its role as an attractant to aquatic life. A
list of these studies with rationale for their rejection is provided at
the end of “  REF _Ref179621877 \h  APPENDIX J: Ecological Effects
Studies Rejected by OPP .”

Field Studies

 tc \l5 "(4).      Field Studies

Data from field studies of the effects of sulfometuron methyl on
terrestrial animals were not available to evaluate effects at organism,
population or community levels of biological organization (e.g.,
population size/growth rate, age-class structure, or species richness).

 Terrestrial Plants tc \l4 "b.     Terrestrial Plants

Terrestrial plant Tier 2 seedling emergence and vegetative vigor studies
are required for all low dose pesticides (those with the maximum use
rate of 0.5 lbs ai/acre or less) and for any pesticide showing a
negative response equal to or greater than 25% in Tier 1 studies.  Tier
2 terrestrial plant toxicity studies were conducted to establish the
toxicity of sulfometuron methyl to non-target terrestrial plants.  The
recommendations for seedling emergence and vegetative vigor studies are
for testing of (1) six species of at least four dicotyledonous families,
one species of which is soybean (Glycine max), and the second of which
is a root crop, and (2) four species of at least two monocotyledonous
families, one of which is corn (Zea mays).

For sulfometuron methyl, six dicots (sugar beet, rape, tomato, pea,
cucumber and soybean) and four monocots (onion, corn, wheat, sorghum)
were tested using the Tier 2 protocols for effects on seedling emergence
and vegetative vigor.  Tier 1 tests were not conducted since preliminary
testing indicated all plants would be promoted to Tier 2 testing.  Test
durations were 14 days and 21 days for the seedling emergence and
vegetative vigor studies, respectively.  Depending on the species and
test, seven to eleven treatments were used with application rates ranged
from 0.0000017 to 0.5625 lb ai/acre.  For this risk assessment, a
re-review and statistical analysis was conducted on the Tier 2 toxicity
data from the more sensitive test species in both the seedling emergence
and vegetative vigor tests.  All statistical comparisons were made to
negative controls (previous analyses in the DER made comparisons to
solvent controls even though negative and solvent controls were not
significantly different).  For calculation of the EC25 and EC05,
nonlinear regression was conducted using the methods of Bruce and
Versteeg (1992).  In situations where the NOAEC was found to be greater
than or equal to the EC25, the EC05 was used for the comparison with
threatened and endangered species.

Results for the most sensitive endpoints and species with monocots and
dicots indicate that seedling emergence and vegetative vigor are
impacted at exposures well below the maximum application rate of 0.375
lb ai/acre for sulfometuron methyl (  REF _Ref178157054 \h  Table 35 ).
For seedling emergence, the EC25 of 1.9 x 10 -4 lb ai/acre for the most
sensitive monocot (sorghum) is about a factor of 5 greater than the EC25
of 3.2 x 10 -5 lb ai/acre for the most sensitive dicot (sugar beet).
The maximum application rate of 0.375 lb ai/acre exceeds these EC25
values for sorghum and sugar beet by approximately 2,000 and 10,000
times, respectively.  For 9 of the 10 test species, a comparison of EC25
values indicates that species sensitivity is within a factor of 20
(based on summary data presented by McKelvey, 1995).  This indicates
that the most sensitive test species is not an outlier in terms of its
relative sensitivity.  The EC05 and NOAEC for the sorghum and sugar beet
are 4.3 x 10-5 and 2.9 x 10-5, respectively.  A consistent, declining
monotonic exposure-response curve was observed for sugar beet, while
that for sorghum was monotonic following an increase in mean shoot
height of 24% in the lowest test treatment and 2% in the next lowest
treatment relative to the negative control.  Because the statistical
method of Bruce and Versteeg (1992) uses a pooled response from the
non-monotonic portion of the dose-response curve for calculating ECx
values, the actual mean response associated with the EC05 for sorghum is
slightly higher than the mean response observed for controls, rendering
it a relatively conservative toxicological value.

Results from the vegetative vigor study indicate the most sensitive
monocot (corn) and dicot (soybean) are impacted at somewhat lower levels
compared to the seedling emergence study.  The EC25 values for corn and
soybean (shoot dry weight) are 3.7 x 10-5 and 1.8 x 10-5, respectively.
The maximum application rate for sulfometuron methyl is approximately
10,000 and 20,000 times these EC25 values.  Because the NOEC exceeded
the EC25 values for both species, the EC05 is used for risk assessment
with threatened and endangered species.  The EC05 values for corn and
soybean are 8.4 x 10-6 and 9.9 x 10-7, respectively. For all 10 test
species, a comparison of EC25 values indicates that species sensitivity
differences are within a factor of 20 (based on summary data presented
by McKelvey, 1995).  This indicates that the most sensitive test species
is not an outlier in terms of its relative sensitivity.  A consistent,
declining monotonic exposure-response curve was observed for corn and
soybean in the vegetative vigor test.

Table   SEQ Table \* ARABIC  35 .  Summary of Most Sensitive Tier II
Terrestrial Non-target Plant Seedling Emergence and Vegetative Vigor
Toxicity Data for Sulfometuron Methyl.

Most Sensitive Species

EC25

(lb ai/A)

NOAEC/[EC05]*

(lb ai/A)	Endpoint

Affected	MRID No.

Author/year	Study Classification

Seedling Emergence

Monocots

Sorghum	1.9 x 10 -4 	4.3 x 10 -5   (*)	shoot height 	435385-01

McKelvey (1995)	Acceptable

Dicots

sugar beet	3.2 x 10 -5	2.9 x 10 -5	shoot dry wt

Acceptable

Vegetative Vigor

Monocots	435385-01

McKelvey (1995)

	Corn	3.7 x 10 -5	9.9 x 10 -7  (*)	shoot dry wt

Acceptable

Dicots

Soybean	1.8 x 10 -5	8.4 x 10 -6  (*)	shoot dry wt

Acceptable

* The NOAEC value is above or equal to the EC25 or below the lowest
concentration, therefore, an EC05 is used instead.

RISK CHARACTERIZATION

Risk characterization provides the final step in the risk assessment
process.  In this step, exposure and effects characterization are
integrated to provide an estimate of risk relative to established levels
of concern (LOCs).  The results are then interpreted for the risk
manager through a risk description and synthesized into an overall
conclusion.

Risk Estimation - Integration of Exposure and Effects Data  tc "A.
  Risk Estimation - Integration of Exposure and Effects Data " \l 2

Risk characterization integrates EECs and toxicity estimates and
evaluates the likelihood of adverse ecological effects to non-target
species.  For sulfometuron methyl, a deterministic approach is used to
evaluate the likelihood of adverse ecological effects to non-target
species.

In this approach, risk quotients (RQs) are calculated by dividing
estimated environmental exposures (EECs) by acute and chronic
ecotoxicity values for non-target species.

Risk Quotient (RQ) =  Exposure Estimate/Toxicity Estimate

RQs are then compared to levels of concern (LOCs).  These LOCs are
criteria used to indicate potential risk to non-target organisms and the
need to consider regulatory action.  LOC exceedence is interpreted to
mean that the labeled use (or proposed use) of the pesticide has the
potential to cause adverse effects on non-target organisms.  LOCs
currently address the following risk presumption categories:

(1) acute - potential for acute risk to non-target organisms which may
warrant regulatory action in addition to restricted use classification,

(2) acute restricted use – potential for acute risk to non-target
organisms, but may be mitigated through restricted use classification,

(3) acute endangered species – endangered species may be potentially
affected by use,

(4) chronic risk – potential for chronic risk may warrant regulatory
action, endangered species may potentially be affected through chronic
exposure,

(5) non-endangered plant risk -  potential for effects in non-target
(non-endangered) plants, and

(6) endangered plant risk – potential for effects in endangered
plants.

Currently, EFED does not calculate formal risk quotients to assess
chronic risk to plants or acute or chronic risks to non-target insects.
However, these endpoints are evaluated on a case-by-case basis as data
allow.

Risk presumptions, along with the calculation of the corresponding RQs
and LOCs, are tabulated below:

Table   SEQ Table \* ARABIC  36 .  Risk Presumptions for Aquatic
Animals.

Risk Presumption	RQ 	LOC

Acute Risk	EEC(1)/LC50 or EC50	0.5

Acute Restricted Use	EEC/LC50  or EC50	0.1

Acute Endangered Species	EEC/LC50  or EC50	0.05

Chronic Risk	EEC/NOAEC	1

(1)  EEC units in (mg/L or µg/L) in water

Table   SEQ Table \* ARABIC  37 .  Risk Presumptions for Terrestrial
Animals.

Risk Presumption	RQ 	LOC

Acute Risk	EEC(1)/LC50 or LD50/sqft(2) or LD50/day(3)	0.5

Acute Restricted Use	EEC/LC50 or LD50/sqft or LD50/day

 (or LD50 < 50 mg/kg)	0.2

Acute Endangered Species	EEC/LC50 or LD50/sqft or LD50/day	0.1

Chronic Risk	EEC/NOAEC	1

Acute Endangered Terrestrial Invertebrate	EEC(4)/LD50 (4)	0.05

(1)   EEC units are in ppm diet

(2)        mg/sqft

LD50 * wt. of bird

(3) mg of toxicant consumed/day

           LD50 * wt. of bird

(4) EEC = ppm in small insects; LD50 = ug/g  bw (ppm)

Table   SEQ Table \* ARABIC  38 .  Risk Presumptions for Plants.

Risk Presumption	RQ	LOC

Terrestrial Plants in Terrestrial and Semi-Aquatic Areas:

Non-Endangered Species	EEC(1)/EC25	1

Endangered Species	EEC/EC05 or NOAEC	1

Aquatic Plants:

Non-Endangered Species	EEC(2)/EC50	1

Endangered Species	EEC/EC05 or NOAEC	1

(1)  EEC units in lbs ai/acre

(2)  EEC units in  µg/L or mg/L in water

Non-target Aquatic Animals and Plants

 tc "1.         Non-target Aquatic Animals and Plants " \l 3

A summary of the toxicity values used to derive risk quotients for
aquatic animals and plants is provided in   REF _Ref178452513 \h  Table
39  below.

Table   SEQ Table \* ARABIC  39 .  Endpoints Used for Estimating Risks
of Sulfometuron Methyl to Aquatic Animals and Plants.

(1) tc "Table IVA-4.  Summary of Selected Endpoints for Aquatic Toxicity
Studies " \f D

Organism Group	Toxicity	Units	MRID #

Freshwater fish, LC50 	> 148 	mg ai/L	435018-02

Freshwater invertebrate EC50	> 150	mg ai/L	435018-03

Marine/estuarine fish LC50	> 45	mg ai/L	416728-03

Marine/estuarine invertebrate (mollusk - oyster) EC50	> 38	mg ai/L
416728-04

Chronic freshwater fish NOAEC	Data gap

Chronic freshwater invertebrate NOAEC	97	mg ai/L	416728-06

Aquatic nonvascular plants EC50/NOAEC	4.6 / 0.63	µg ai/L	416801-02

Aquatic vascular plants EC50/NOAEC	0.48 / 0.21	µg ai/L	435385-03

(1) Details for each study are presented in earlier sections of this
document and in   REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H:
Ecological Effects Data Summaries ,

Fish and Aquatic Invertebrates

All available LC50 or EC50 values derived from acute toxicity tests on
freshwater and marine/estuarine fish and invertebrates are greater than
the highest test concentration measured in these studies (>38 to >150 mg
ai/L;   REF _Ref178452513 \h  Table 39 ).  Therefore, risks to these
taxa are described qualitatively.  Compared to these ‘indefinite’
toxicity values, the peak EEC derived from the PRZM/EXAMS scenario
yielding the highest exposure (31 µg/L) is three orders of magnitude
lower.  For bounding purposes, if one assumes that these indefinite LC50
or EC50 values represent the lower bound of actual (definitive) LC50 or
EC50 values from these tests, then the resulting acute RQs would be
approximately three orders of magnitude lower than the LOCs for
non-endangered aquatic animals.  For endangered fish and aquatic
invertebrates, the RQs would be approximately two orders of magnitude
lower than the LOC of 0.05.  Considering that no mortality was observed
at the highest test concentrations from these acute toxicity tests, the
actual RQ values clearly represent conservative estimates of acute risk
to these species.

The lowest available chronic NOAEC in aquatic invertebrates is 97 mg/L
(97,000 ug/L).  Compared to the highest 21-d EEC of 26 µg/L derived
from PRZM/EXAMS modeling, the chronic RQ for freshwater invertebrates
would also be several orders of magnitude lower than the LOC of 1.0.

For chronic toxicity to freshwater fish, no acceptable data were
available.  In the absence of chronic toxicity data, it is common to
apply an extrapolation factor (e.g., acute-chronic ratio or ACR) to
estimate chronic toxicity from acute toxicity test results.  However, a
valid ACR could not be determined from the sulfometuron methyl toxicity
database because a definitive LC50 or EC50 was not established for any
aquatic animals.  Considering data for another sulfonylurea herbicide
with a similar toxicity profile and the same mode of action
(flazasulfuron, PC code: 119011), an ACR of 7 can be calculated for
rainbow trout:

	Rainbow trout LC50 = 115.2 mg ai/L 		(MRID 46220967; Sousa 2003)

	Rainbow trout NOAEC = 17 mg ai/L		(MRID 46220970; Sousa, 2004)

	ACR = 115.2 / 17  =  7 (rounded)

Thus, applying an ACR of 7 to the LC50 of > 148 for freshwater fish
yields an estimated NOAEC of >21 mg/L for sulfometuron methyl.  Compared
to the maximum 60-d average EEC of 20 ug/L derived from the PRZM/EXAMS
modeling, the chronic RQ would be at least three orders of magnitude
lower than the LOC of 1.0.

Although chronic studies were not available for marine/estuarine fish
and invertebrates, there is no evidence to indicate marine or estuarine
animals are substantially more sensitive than freshwater animals such
that the risk profile would differ markedly from freshwater animals.
Furthermore, acute toxicity studies indicate that sulfometuron methyl is
not acutely toxic at (or near) toxicity limits for both freshwater and
saltwater fish and invertebrates.  Considering that the freshwater
chronic RQs for fish and invertebrates would be several orders of
magnitude lower than the LOCs, it appears highly unlikely that marine
and estuarine animals would be at risk from chronic exposures to
sulfometuron methyl as determined by PRZM/EXAMS modeling.

Acute and chronic risk to aquatic animals is further discussed in the
Risk Description (Section   REF _Ref178453261 \r \h  4.2 ),

Aquatic Plants

Risk quotients were derived using the peak EEC of 31 ug/L (determined
from the PRZM/EXAMS exposure scenario yielding the highest peak exposure
concentrations) and EC50 and NOAEC values for vascular and non-vascular
aquatic plants, respectively (  REF _Ref178157491 \h  \* MERGEFORMAT
Table 40 ).  For sulfometuron methyl, RQs exceeded the endangered and
non-endangered LOCs for both vascular and non-vascular aquatic plants
receiving pesticide runoff/drift, indicating a potential risk to these
species.

 tc "Table IVA-5.  Summarized Acute Aquatic Plant Risk Quotients for
Turf Uses " \f D

Table   SEQ Table \* ARABIC  40 .  Summary of Acute Aquatic Plant Risk
Quotients for Rights of Way Uses.

Scenario	Endangered	Non-endangered

	Vascular	Non-vascular	Vascular	Non-vascular

TX Rights of Way (max rate of 0.375 lbs ai/acre x 1 aerial application/
yr) (a,b)	148  (c)	49 (c)	65 (d)	6.7 (d)

(a) Based on a peak EEC of 31 ug/L derived from the TX rights of way
exposure scenario which yielded the highest EECs.  Details on scenarios
and PRZM-EXAMS modeling are provided in Section    REF _Ref178580641 \r
\h  \* MERGEFORMAT  <IP_ADDRESS>  and   REF _Ref179348297 \h  \* MERGEFORMAT
APPENDIX C:  Ecological Aquatic Exposure Modeling .

(b) For sulfometuron methyl, endangered plants toxicity threshold
(NOAEC) was 0.21µg ai/L for vascular and 0.63µg ai/L for non-vascular
plants; acute toxicity thresholds (EC50) used for non-endangered plants
were 0..48 and 4.6 µg ai/L for vascular and non-vascular plants,
respectively.

(c) indicates an exceedence of Endangered Species Level of Concern
(LOC); RQ > 1.0.

(d) indicates an exceedence of non-target (i.e., non-endangered) Species
Level of Concern (LOC); RQ > 1.0.

Non-target Terrestrial Animals  tc "2.         Non-target Terrestrial
Animals " \l 3

A summary of the toxicity values used to derive risk quotients for
terrestrial animals is provided in   REF _Ref178157575 \h  \*
MERGEFORMAT  Table 41  below.

Table   SEQ Table \* ARABIC  41 .  Endpoints Used for Estimating Risks
of Sulfometuron Methyl to Terrestrial Animals.

Organism Group (a)	Toxicity	MRID #

Bird LD50 (oral dose-based, mg ai/kg-bw)	>4,650	245375

Bird LC50  (dietary-based, mg ai/kg-diet)	>4,600	71414

Mammal LD50 (oral dose-based, mg ai/kg-bw)	>5,000	430892-01

Honeybee LD50, µg ai/bee	>100	416728-10

Mammal chronic NOAEL (dose-based, mg ai/kg-bw/day)	300(b)	78798 (c)

(a) Details for each study are presented in earlier sections of this
document and in   REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H:
Ecological Effects Data Summaries .

 (c) Highest dose tested.

(c) Accession number.

Birds, Acute Risks

The acute LC50/LD50s for birds are greater than the highest
concentration/dose tested in each study.  Therefore, while precise
estimates of RQs are not possible with indefinite (i.e., “greater
than”) LC50/LD50 values, a bounding analysis can be conducted to
provide a conservative, upper bound estimate of the RQs (  REF
_Ref178157712 \h  \* MERGEFORMAT  Table 42  and   REF _Ref178157714 \h
\* MERGEFORMAT  Table 43 ).

In this bounding analysis, calculated EECs for various food items from
the TREX terrestrial exposure model are compared to dose-base LD50
values (treated as definitive values) that have been adjusted for
different avian size classes.  The highest dose-based EEC (102 mg
ai/kg-bw/d) is approximately 1/25th the lowest adjusted dose-based LD50
(> 2414 mg ai/kg-bw) thus yielding an upper bound RQ of < 0.04.  This
upper bound RQ is less than the LOCs for acute risk (0.5), acute
restricted use (0.2) and acute endangered species (0.1) for terrestrial
animals.

Results from diet-based RQ calculations with birds are similar to those
described above for dose-based RQs (  REF _Ref178157714 \h  Table 43 ).
Specifically, the highest diet-based EEC (90 mg ai/kg-diet for short
grass) is approximately 1/50th the avian subacute dietary LC50 of  >4600
mg ai/kg-diet, thus yielding an upper bound RQ of <0.02.  This upper
bound RQ is less than the LOCs for acute risk (0.5), acute restricted
use (0.2) and acute endangered species (0.1) for terrestrial animals.
The potential for acute risk to birds is discussed further in the Risk
Description (Section   REF _Ref178453261 \r \h  4.2 ).

Table   SEQ Table \* ARABIC  42 .  Upper Bound Kenaga, Acute Avian
Dose-Based Risk Quotients (Bounding Analysis Only).

Size Class

(grams)	Adjusted

LD50

(mg ai/kg-bw)	Short Grass(1)

EEC	RQ(2)

20	> 2414	102.5	< 0.04

100	> 3074	58.5	< 0.02

1000	> 4342	26.2	< 0.01

(1) Calculations provided for short grass only because upper bound
dose-based EECs were higher than any other food item modeled.

(2) RQs derived using unadjusted LD50 of >4650 mg ai/kg-bw for mallard
and dose-based EECs (mg ai/kg-bw) calculated using TREX ver. 1.3.1 with
a single application at the maximum allowable label rate (0.375 lb
ai/acre/yr).  See Section   REF _Ref178578557 \r \h  \* MERGEFORMAT  3.2
 and “  REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H: Ecological
Effects Data Summaries ” for details on the model inputs, calculations
and output.

Table   SEQ Table \* ARABIC  43 . Upper Bound Kenaga, Subacute
Dietary-Based Risk Quotients (Bounding Analysis Only).

Dietary-based LC50

(mg ai/kg-diet)	Short Grass(1)

	EEC(2)	RQ

> 4600 	90.0	< 0.02

(1) Calculations provided for short grass only because upper bound
residues were higher than any other food item modeled.

(2) Diet-based EECs are expressed in units of mg ai/kg-diet and are
calculated using TREX ver. 1.3.1 based on a single application at the
maximum allowable label rate (0.375 lb ai/acre/yr).  See Section   REF
_Ref178578557 \r \h  \* MERGEFORMAT  3.2  and “  REF _Ref178405615 \h
\* MERGEFORMAT  APPENDIX H: Ecological Effects Data Summaries ” for
details on the model inputs, calculations and output.   Size class not
used for dietary risk quotients.

Birds, Chronic Risks

As described in Section 3.3, no acceptable chronic toxicity data were
available on the effects of sulfometuron methyl on birds.  Therefore,
chronic risks to avian fauna could not be characterized.  Uncertainty
associated with the lack of chronic toxicity data with avian fauna is
further described in the Risk Description section.

Mammals, Acute Risks

The unadjusted, acute LD50 for mammals is greater than the highest dose
tested in the study (> 5000 mg ai/kg for rat; MRID 430892-01).
Therefore, while a precise estimate of the mammalian acute RQ is not
possible with an indefinite (i.e., “greater than”) LD50 value, a
bounding analysis can be conducted to provide a conservative, upper
bound estimate of the acute, mammalian RQ (  REF _Ref178157883 \h  \*
MERGEFORMAT  Table 44 ).

In this bounding analysis, calculated EECs for various food items from
the TREX terrestrial exposure model are compared to dose-base LD50
values (treated as definitive values) that have been adjusted for
different mammalian size classes.  When the highest EECs (from the short
grass food item) are compared to the size-class adjusted LD50 values,
the largest upper bound RQ is < 0.02, which occurs for the 20g mammal
size class.  This upper bound RQ is less than the LOCs for acute risk
(0.5), acute restricted use (0.2) and acute endangered species (0.1) for
terrestrial animals.  The RQ calculations are detailed in “  REF
_Ref179708540 \h  APPENDIX F: T-REX Output ” and acute mammalian risks
are further described in the Risk Description (Section 4.2). “

Table   SEQ Table \* ARABIC  44 .   Upper Bound Kenaga, Acute Mammalian
Dose-Based  Risk Quotients (Bounding Analysis Only).

(1)

Size Class

(grams)	Adjusted

LD50	Short Grass(1)

EEC	RQ(2)

15	> 10989	85.8	< 0.01

35	> 8891	59.3	< 0.01

1000	> 3846	13.8	< 0.01

(1) Calculations provided for short grass only because upper bound
dose-based EECs were higher than any other food item modeled.

(2) RQs derived using unadjusted LD50 of >5000 mg ai/kg-bw and
dose-based EECs (mg ai/kg-bw) calculated using TREX ver. 1.3.1 with a
single application at the maximum allowable label rate (0.375 lb
ai/acre/yr).  See Section   REF _Ref178578557 \r \h  \* MERGEFORMAT  3.2
 and “  REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H: Ecological
Effects Data Summaries ” for details on the model inputs, calculations
and output.

Mammals, Chronic Risks

To evaluate the chronic risk to mammals, dose-based and dietary-based
RQs were calculated using the rabbit NOAEL of 300 mg ai/kg-bw/d from the
developmental toxicity study (Accession No. 78798).  The rabbit
developmental toxicity study was selected for assessing chronic risks to
mammals because an acceptable NOAEL was not available from the
2-generation chronic rat reproduction study (that study is considered
invalid by HED) or other small mammals (mouse).  Because TREX assumes
the test NOAEL corresponds to a 350g mammal (rat), calculation of
size-class adjusted NOAELs for the rabbit (which averaged 3.9 kg in the
study) first involved adjusting the rabbit NOAEL to a 350g mammal
adjusted NOAEL using the same equation as TREX.  This 350g,
size-adjusted NOAEL (549 mg ai/kg-bw/d) was then input to TREX for the
remainder of the chronic mammalian EEC and RQ.

Neither the chronic, dose-based risk quotients (  REF _Ref178157965 \h
Table 45 ) nor the dietary-based risk quotients (  REF _Ref178494277 \h
Table 46 ) exceed the chronic LOC for all weight classes (15 g, 35 g,
and 1000g) of mammals consuming short grass, tall grass, broadleaf
forage/small insects and seeds. Details of the RQ calculations are
provided in (See   REF _Ref179708540 \h  APPENDIX F: T-REX Output ).

Table   SEQ Table \* ARABIC  45 .  Upper Bound Kenaga, Chronic Mammalian
Dose-Based Risk Quotients.

Size Class

(grams)	Adjusted NOAEL(1)

(mg ai/kg-bw/d)	EECs and RQs

Short Grass	Tall Grass	Broadleaf Plants/

Small Insects	Fruits/Pods/

Seeds/

Large Insects	Granivore

EEC	RQ	EEC	RQ	EEC	RQ	EEC	RQ	EEC	RQ

15	1206.6	85.8	0.07	39.3	0.03	48.3	0.04	5.36	<0.01	1.19	<0.01

35	976.3	59.3	0.06	27.2	0.03	33.4	0.03	3.71	<0.01	0.82	<0.01

1000	422.3	13.8	0.03	6.3	0.01	7.7	0.02	0.86	<0.01	0.19	<0.01

(1) RQs derived for different size classes using unadjusted NOAEL of
>300 mg ai/kg-bw/d and dose-based EECs (mg ai/kg-bw/d) calculated using
TREX ver. 1.3.1 with a single application at the maximum allowable label
rate (0.375 lb ai/acre/yr).  See Section   REF _Ref178578557 \r \h  \*
MERGEFORMAT  3.2  and “  REF _Ref178405615 \h  \* MERGEFORMAT
APPENDIX H: Ecological Effects Data Summaries ” for details on the
model inputs, calculations and output.

Table   SEQ Table \* ARABIC  46 .  Upper Bound Kenaga, Chronic Mammalian
Dietary-Based Risk Quotients

NOAEC (ppm)	EECs and RQs

	Short Grass	Tall Grass	Broadleaf Plants/

Small Insects	Fruits/Pods/

Seeds/

Large Insects

	EEC	RQ	EEC	RQ	EEC	RQ	EEC	RQ

10980	90.00	0.01	41.25	<0.01	50.63	<0.01	5.63	<0.01

Dietary-based RQs derived by converting the rabbit NOAEL (>300 mg
ai/kg-bw/d) to a diet-based NOAEC and comparing with diet-based EECs (mg
ai/kg-diet) calculated using TREX ver. 1.3.1 at the single maximum
allowable label rate (0.375 lb ai/acre/yr).  See Section   REF
_Ref178494380 \r \h  \* MERGEFORMAT  3.2  and “  REF _Ref178405615 \h
\* MERGEFORMAT  APPENDIX H: Ecological Effects Data Summaries ” for
details on the model inputs, calculations and output.  Size class not
used for dietary risk quotients

Non-Target Terrestrial-phase Amphibians, Reptiles and Terrestrial
Invertebrates

In absence of taxa-specific data, EFED currently uses birds as
surrogates for terrestrial non-target terrestrial phase amphibians and
reptiles and fish for aquatic phase amphibians.  LOCs were not exceeded
for any of the surrogate species; therefore, potential risks to reptiles
and amphibians are also presumably lower than the Agency’s concern
level.

EFED does not currently estimate risk quotients for terrestrial
non-target invertebrates.  However, a label statement is required to
protect foraging honeybees when the LD50 is <11 µg/bee.  Based on the
acute contact toxicity study to honeybees, the LD50 for sulfometuron
methyl is >100 µg/bee.  This classifies sulfometuron methyl as
practically non-toxic to honeybees on an acute contact exposure basis.
For RQ derivation for endangered terrestrial invertebrates, the LD50 for
honeybees (>100 ug a.i./bee) is converted to units of μg ai/g (of bee)
by multiplying by 1 bee/0.128 g, thereby resulting in an LD50 of >780
μg ai/g.  This LD50 value is then compared to the EEC of 50.6 ug/g for
small insects/broadleaf plants (  REF _Ref177798194 \h  Table 17 ). The
resulting RQ (EEC/LD50) is <0.06, which is at or below the LOC for
endangered terrestrial invertebrates (0.05).  Therefore, the risk of
direct adverse effects to terrestrial invertebrates is considered low;
however, due to the potential risk identified to plants, the potential
for indirect effects to terrestrial invertebrates from sulfometuron
methyl use cannot be discounted.

Additional discussion of potential risks to these taxa is qualitatively
discussed in the Risk Description portion of this document (Section
REF _Ref178454248 \r \h  4.2 ).

Non-target Terrestrial Plants

A summary of the toxicity values used to derive risk quotients for
terrestrial plants is provided in   REF _Ref178454331 \h  Table 47
below.

Table   SEQ Table \* ARABIC  47 .  Summary of Selected Endpoints from
Terrestrial Plant Toxicity Studies of Sulfometuron Methyl

Organism Group	Toxicity

(Lbs A.I./Acre)	MRID #

Terrestrial monocots emergence, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre	EC25 = 1.9 x 10-4

EC05 = 4.3 x 10-5	435385-01

Terrestrial dicots emergence, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre	EC25 = 3.2 x 10-5

NOAEC = 2.9 x 10-5	435385-01

Terrestrial monocots vegetative vigor, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre	EC25 = 3.7 x 10-5

EC05 = 8.4 x 10-6	435385-01

Terrestrial dicots vegetative vigor, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre	EC25 = 1.8 x 10-5

EC05 = 9.9 x 10-7	435385-01

a Details for each study are presented in earlier sections of this
document and in “  REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H:
Ecological Effects Data Summaries ”.

Non-Endangered and Endangered Plant Risks

  REF _Ref178405382 \h  \* MERGEFORMAT  Table 48   SEQ CHAPTER \h \r 1
presents terrestrial plant RQs for sulfometuron methyl based on aerial
and ground spray applications.  These RQs were derived using TerrPlant
(ver 1.2.2) using a single application rate at the annual maximum of
0.375 lb ai/A.  TerrPlant is a Tier 1 model that estimates pesticide
aerial drift and runoff to dry and semi-aquatic adjacent areas.  Results
indicate that the LOCs are widely exceeded for non-endangered and
endangered monocots and dicots located in adjacent dry areas and in
semi-aquatic areas as the result of receiving a combination of runoff
and spray drift from ground and aerial applications. In addition, the
LOCs were exceeded for terrestrial plants receiving spray drift alone
from ground and aerial application. These risks will be discussed in
detail in the AgDrift spray drift analysis in the Risk Description
(Section   REF _Ref178453261 \r \h  4.2 ). However, TerrPlant modeling
results are based on the assumption of a single application, risk
quotients for non-target terrestrial plants may be underestimated. Bold
indicates an LOC exceedence in   REF _Ref178405382 \h  Table 48 .

Table   SEQ Table \* ARABIC  48 .  RQ Values For Plants In Dry And
Semi-Aquatic Areas Exposed To Sulfometuron Methyl Through Runoff And/Or
Spray Drift.

Plant Type	Application Method	Terrestrial Adjacent Areas	Semi-Aquatic
Adjacent Areas	Spray Drift

Non-endangered Plant RQs a,b,d

Monocot	 ground spray	118	1007	101

Dicot	 ground spray	703	5977	208

Monocot	Aerial	197	1086	507

Dicot	Aerial	1172	6445	1042

Endangered Plant RQs a,c,d

Monocot	ground spray	523	4448	446

Dicot	ground spray	776	6595	3788

Monocot	Aerial	872	4797	2232

Dicot	Aerial	1293	7112	18939

aDetailed calculations for RQs and TerrPlant (ver 1.2.2) input and
output are provided in “  REF _Ref179701993 \h  \* MERGEFORMAT
APPENDIX D:  Terrplant Spreadsheet .”

b Non-endangered toxicity thresholds (EC25) are 1.9 x 10-4 (seedling
emergence, monocot), 3.2 x 10-5 (seedling emergence, dicot),  3.7 x 10-5
(vegetative vigor, monocot), 1.8 x 10-5 (vegetative vigor, dicot) lb
ai/A.

c Endangered toxicity thresholds (NOAEC of EC05) are 4.3 x 10-5
(seedling emergence, monocot), 2.9 x 10-5 (seedling emergence, dicot),
8.4 x 10-6 (vegetative vigor, monocot), 9.9 x 10-7 (vegetative vigor,
dicot) lb ai/A.

d Bold RQ values exceed the Non-Endangered Species LOC and Endangered
Species LOC (RQ >1.0).

Use of Contaminated Irrigation Waters

The potential risk to plants when exposed to irrigation water
contaminated with sulfometuron methyl is presented in the form of RQs in
  REF _Ref178394370 \h  \* MERGEFORMAT  Table 49 . These RQs are derived
using EECs of 0.33 µg/L (ground water) and 31 µg/L (surface water).
The EEC for ground water was calculated using the Tier 1 SCIGROW model (
 REF _Ref178394075 \h  Table 16 ) while that for surface water was
calculated using PRZM/EXAMS for the scenario yielding the highest EECs (
 REF _Ref178044350 \h  Table 15 ).  For semi-aquatic and terrestrial
areas adjacent to irrigation fields, EECs in lb ai/acre were calculated
assuming 1% of the irrigation water drifts into adjacent wetlands. It
was further assumed that no runoff of irrigation water occurs. Toxicity
endpoints were taken from the vegetative vigor study because it was
assumed that non-target plants are exposed to sulfometuron methyl
directly through spray drift from irrigation water. Details of the
calculation of the irrigation EECs are provided in   REF _Ref179708808
\h  APPENDIX G:  Modeling of Terrestrial plant Exposure from
Contaminated irrigation Water ).

Based on this screening analysis, results suggest that sulfometuron
methyl levels in irrigation water from ground water sources would not
exceed non-target or endangered species LOCs (i.e, RQs < 1.0).  However,
RQs based on sulfometuron methyl in irrigation water derived from
surface water sources exceed the LOCs for both non-target and endangered
species (3.9 and 71, respectively), thus indicating a potential risk to
plants adjacent to areas irrigated with surface water sources.

Table   SEQ Table \* ARABIC  49 .  Risk Quotients for Non-target and
Endangered Plants, Resulting From Exposure to Sulfometuron Methyl in
Irrigation Water

Location	Ground water and Surface Water EEC: 1, 2

(lbs ai/A)	Risk Quotients:

Ground water (GW) and Surface Water (SW) Irrigation

Non-target plants3

(EEC/EC25)	Endangered plants3

(EEC/NOAEC)

Semi-aquatic and terrestrial areas adjacent to irrigated fields	Ground
water: 7.5 x 10-7

Surface water: 6.1 x 10-5

	GW:   0.04

SW:    3.9	GW:   0.76

SW:   71

1 Estimated EEC assumes 1 inch of irrigation water is applied to the
target field, 1% drift of irrigated water containing sulfometuron
methyl, and no runoff of irrigated water.  See Appendix G for details on
irrigation exposure calculations.

2 EECs based on sulfometuron methyl concentrations of 0.33 ug/L in
ground water and 31 ug/L in surface water

3 Based on non-target plant EC25 of 1.8 x 10-5 lb ai/A and endangered
plant NOAEC of 9.9 x 10-7 (MRID 435385-01) for the most sensitive
vegetative vigor endpoint.  Bold RQ indicates exceedence of LOC of 1.0
(i.e., RQ > 1)

RISK DESCRIPTION

Risk to Aquatic Animals and Plants

In the conceptual model, spray drift and surface runoff/leaching to
adjacent bodies of water were predicted as the most likely sources of
exposure of sulfometuron methyl to non-target aquatic animals and
plants.  Risks to aquatic organisms (i.e. fish, invertebrates, and
plants) were assessed based on modeled estimated environmental
concentrations (EECs) and available toxicity data.  Aquatic EECs for the
ecological exposure to sulfometuron methyl were estimated using
PRZM-EXAMS employing the standard ecological water body (Section   REF
_Ref178400427 \r \h  \* MERGEFORMAT  <IP_ADDRESS> ;   REF _Ref177972956 \h
\* MERGEFORMAT  Table 13 ).

The risk hypothesis stated that the use of sulfometuron methyl has the
potential to cause adverse effects to aquatic animals and plants.  This
assessment confirms this hypothesis.  Risks of direct effects to aquatic
vascular and nonvascular plants are above the Agency’s LOCs.  However,
the assessment refutes the risk hypothesis regarding direct effects to
aquatic animals, suggesting that direct effects to aquatic animals are
unlikely.  Although risk from direct toxicity to aquatic animals is not
indicated in this screening level assessment, the dependence of aquatic
animals on primary producers (plants) results in the potential for
indirect effects to aquatic animals.

Fish and Aquatic Invertebrates

The submitted acute toxicity data for aquatic species indicate that
sulfometuron methyl is practically non-toxic to fish and invertebrates
with LC50 and EC50 values >38 to >150 mg ai/L, respectively.  A
comparison of the PRZM/EXAMS peak EEC of sulfometuron methyl in surface
water of 31 ug/L to toxicity values for fish and invertebrates indicates
that these indefinite (i.e., ‘greater than) acute toxicity values are
three orders of magnitude above the highest peak EEC.  A bounding
analysis indicates that even if these indefinite LC50 and EC50 values
are interpreted as the lower bounds for acute toxicity (a conservative
assumption since no mortality occurred in these test concentrations),
the resulting acute RQs would still be at least two orders of magnitude
below the LOCs for non-endangered and endangered aquatic animals.  This
risk finding is consistent with those from other ecological risk
assessments with sulfonylurea herbicides (e.g., florasulam,
flazasulfuron).  While it was noted in the Analysis Section (  REF
_Ref178400557 \r \h  \* MERGEFORMAT  3.3 ) that uncertainty exists in
the actual exposure concentration derived from the estuarine/marine
acute toxicity tests, this uncertainty is not judged to be large enough
to impact the risk conclusions, given the large difference between EECs
and toxicity levels.

Therefore, it is concluded that acute risk to aquatic animals from
direct effects of sulfometuron methyl is expected to be minimal.

Similarly, chronic risk quotients are all less than the LOC of 1.0 for
the modeled uses.  For freshwater aquatic invertebrates and fish, the
PRZM/EXAMS 21-day EEC (26 ug/L) and 60-d EEC (20 ug/L) are also three
orders of magnitude below the chronic NOAEC of 97 mg/L and >21 mg/L,
respectively.  As noted in the Analysis Section (  REF _Ref178400557 \r
\h  \* MERGEFORMAT  3.3 ), the chronic NOAEC for fish had to be
estimated using an ACR of 7 derived from another chemical
(flazasulfuron) with a similar toxicity profile and mode of action.
Clearly, there is uncertainty associated with extrapolation of an ACR
across chemicals, as ACRs can vary by chemical, species, test designs,
and other factors.  In a recent analysis, Raimondo et al. (2007)
evaluated the variability in ACRs derived from multiple sources,
including EFED’s Pesticide Ecotoxicity database.  Raimondo et al.
(2007) report a 90th percentile ACR of 80 across all chemicals, which if
applied to the freshwater fish LC50 of > 148 mg/L, would yield an
estimated NOAEC of > 2 mg/L.  This value is still 100-fold higher than
the chronic 60-d EEC of 20 ug/L.  This 90th percentile ACR reflects
pesticides with modes of action that differ from sulfometuron methyl and
therefore may not reflect the 90th percentile ACR within the
sulfonylurea class of herbicides.  However, for the purposes of
evaluating uncertainty in acute-to-chronic toxicity extrapolations, it
is considered a reasonable approximation of a “high end” ACR.

The potential for chronic risks to fish was further evaluated by
comparing the 60-d (chronic) EEC for freshwater fish with available
chronic toxicity values (NOAECs) for other sulfonylurea herbicides (
REF _Ref184015257 \h  Figure 3 ).  Results indicate that chronic
toxicity of other sulfonylurea herbicides occurs at concentrations two
to three orders of magnitude greater than the chronic EEC of 0.020 mg/L.
 Therefore, based on the use of a conservative “high end” ACR and
comparison with toxicity information for other sulfonylurea herbicides,
the potential for chronic risk to aquatic animals from direct effects of
sulfometuron methyl appears unlikely.

Figure   SEQ Figure \* ARABIC  3 . Chronic Toxicity of Sulfonylurea
Herbicides to Freshwater Fish

Although no chronic studies in saltwater fish or invertebrates have been
submitted to the Agency, the acute studies do not indicate that
saltwater species are expected to be more sensitive than freshwater
species.  Given the low magnitude of the freshwater animal risk
quotients, submission of chronic studies in saltwater species would not
likely affect conclusions of this assessment.

An ECOTOX literature search found no acceptable or supplemental studies
on the acute toxicity of technical grade sulfometuron methyl to fish or
invertebrates.  Results from a supplemental study of microcrustaceans
using the formulated product, Oust, indicates that sulfometuron methyl
is practically nontoxic to these aquatic invertebrate crustaceans.
Therefore, toxicity findings of the formulated product (Oust®) are
consistent with those using the technical grade active ingredient with
Daphnia magna (MRID 435018-03).

Non-target Aquatic-phase Amphibians

EFED currently uses surrogate data (fish) to estimate potential risks to
non-target aquatic phase amphibians. Risks to fish species were
discussed above and do not indicate significant risk to these organisms.

One study of the effect of sulfometuron methyl on an aquatic-phase
amphibian was found was found that met OPP/ECOTOX screening criteria (
REF _Ref178401495 \h  \* MERGEFORMAT  Table 50 ).  In this study, Fort
et al. (1999) conducted three separate tests of sulfometuron methyl
exposure to the African clawed frog, Xenopus laevis: (1) a 4-day frog
embryo teratogenesis assay (FETAX) to evaluate embryo mortality/
malformations; (2) a 14-d test to evaluate effects on tail resorption,
and (3) a 30-d exposure to evaluate effects on limb development. Both
analytically impure (85% ai) and purified (99.5% ai) sulfometuron methyl
exposures were evaluated in the study, but due to the confounding
influence of impurities on sulfometuron methyl toxicity, results from
only the purified (99.5% ai) sulfometuron methyl are used here.

In the FETAX assay, 2 replicates of 20 mid-blastula frog embryos (stage
8) were exposed to 11 nominal test concentrations of sulfometuron methyl
ranging from 0.001 to 24.9 mg ai/L for 96-h.  Sulfometuron methyl stock
solutions were prepared using a DMSO carrier and verified analytically
(analytical results not reported).  Both a negative and solvent control
were included.  Test procedures generally conformed to ASTM
recommendations for the FETAX assay (ASTM, 1996).  Results indicate no
statistically significant effect of sulfometuron methyl on embryo
survival or percent malformations up to (and including) the highest test
concentration (24.9 mg ai/L).  Solvent controls were not significantly
different from negative controls.

Similar results were found in the 30-d study, whereby no statistically
significant effect of sulfometuron methyl exposure was found on limb
development (% malformations) up through 24.9 mg ai/L.  Results from the
14-d tail resorption study indicate a significant reduction in tail
resorption at 9.95 and 24.9 mg ai/L beginning at development stage 64
through 66 (test termination).  No significant reduction occurred at or
below 1 mg ai/L.

This study is classified as supplemental primarily because exposure
concentrations were not measured during the test.  Although the authors
report that sulfometuron methyl was ‘stable’ over the 24 to 96-h
renewal cycles used in the studies, no analytical chemistry results were
provided.  Furthermore, randomization of study organisms and replicates
was not indicated (an ASTM requirement).  Collection and testing of
embryos by separate clutches (an ASTM recommendation) was not apparent
in the study. Finally, the final concentrations of carrier solvent in
the various treatments was not reported (solvent concentrations were
only reported for the stock solutions).

Table   SEQ Table \* ARABIC  50 .  Toxicity of sulfometuron methyl to
the African clawed frog from a study by Fort et al.  (1999).

Species	Test Chemical	Exposure Duration	Endpoint (Effect)	Effect Level

(mg ai/L)	Study Classification	Ref.

Xenopus laevis		sulfometuron methyl (99.5% ai)	96-h	LC50 (% mortality)

NOAEC  (% malformations)	> 24.9

 24.9 (a)	Supplemental	Fort et al. (1999)

14-d	NOAEC (tail resorption)

LOAEC (tail resporption)	0.995

9.95

30-d	NOAEC (limb deformation)	24.9(a)

(a) Highest tested dose, LOAEL not achieved in study.

Although results from the Fort et al (1999) study are not being used
quantitatively in this risk assessment, they suggest that acute toxicity
to Xenopus larvae occurs at levels > 1000 times the maximum EEC of 31
ug/L derived from the PRZM/EXAMS model.  The lowest NOAEC from this
study (1.0 mg/L) is approximately 45 times higher than the maximum 21-d
EEC of 26 ug/L. Therefore, based on conclusions for fish discussed
previously and supplemental information from Fort et al (1999), risk to
aquatic phase amphibians is also expected to be lower than the
Agency’s concern level.

Aquatic Plants   tc "b.         Aquatic Plants  " \l 4

Toxicity studies indicate that sulfometuron methyl is classified as
highly toxic to aquatic plants, and the RQ values (65-148 for vascular
plants; 6.7-49 for nonvascular plants) indicates the potential risk to
aquatic vascular and nonvascular plants is above the Agency’s concern
level.   The freshwater vascular plant (duckweed) is the most sensitive
aquatic plant species (14-d EC50 and NOAEC are 0.48 and 0.21 μg/L,
respectively) followed by the green algae (EC50 is 4.6 µg ai/L and the
NOAEC is 0.63 ug ai/L).  Sulfometuron methyl was much less toxic to
diatoms (>370 and >410 mg/L), and potential risks to this taxonomic
group do not exceed the Agency’s concern level.

In the duckweed study described previously (MRID 435385-03), recovery
from the 14-d sulfometuron methyl exposures was assessed at the end of
the study by exposing organisms to untreated medium for an additional 14
days.  Effects were expressed as percent inhibition of frond counts and
biomass.  The results are as follows:

											14-d Recovery			14-d Recovery:

		14-d Exposure Conc.		Frond Count Inhibition		Biomass Inhibition

			1.045 ppb					41.1%				38.3%

			0.590 ppb					11.8%				10.8%

			0.323 ppb					0.6%				- 1.0%

Therefore, the study authors concluded that sulfometuron methyl was
phytotoxic to duckweed at concentrations of > 0.590 ppb and phytostatic
at 0.323 ppb.  These data suggest that the effects of sulfometuron
methyl to aquatic vascular plants may be reversible following 14-d
exposures at selected concentrations (0.323 ppb and below).  To evaluate
the potential for duckweed (and by extension, other vascular plants) to
recover from sulfometuron methyl exposures predicted using PRZM/EXAMS
modeling, the predicted long-term exposures to sulfometuron methyl
(e.g., 90-d average concentration) was compared to available toxicity
information. Results indicate that the 90-d average concentration (16
ug/L;   REF _Ref178044350 \h  \* MERGEFORMAT  Table 15 ) derived from
the exposure scenario yielding the highest exposure concentrations still
exceeds the 14-d EC50 (0.48 ug/L) by a factor of 33 and the 14-d
phytotoxic concentration (0.59 ppb) by a factor of 27.  Therefore, the
ability of duckweed and other vascular aquatic plants to recover from
predicted long-term exposure concentrations of sulfometuron methyl in
adjacent, static aquatic systems appears unlikely.  The sensitivity of
RQ estimates for aquatic vascular and nonvascular plants to different
assumptions regarding application rates and timing of application is
discussed later in Section   REF _Ref178582210 \r \h  4.3 .

Byl et al. (1994) conducted a laboratory study on the effect of
sulfometuron methyl on the aquatic vascular plant, Hydrilla
verticillata.  In this study, Byl et al. (1994) exposed plants to
aqueous solutions ranging from 0.001 to 1.0 mg/L sulfometuron methyl (as
Oust) in three replicate chambers per treatment for 5 days.  The % ai
was not reported nor is it clear whether nominal concentrations reflect
adjustment for % ai.  A significant decrease in combined shoot and root
length was observed at or above 0.01 mg/L (approximating 30% of the
controls).  Although not conclusive, results from Byl et al. suggest
that the combined root and shoot length response of Hydrilla is less
sensitive to 5-d exposure to the formulated product (Oust) compared to
the 14-d exposure to TGAI for duckweed (NOAEC = 0.21 ug ai/L), even if
nominal concentrations are adjusted downward to reflect the typical 75%
ai found in Oust.  However, the relative toxicity of TGAI and formulated
product can not be determined conclusively from comparison of these two
studies because study protocols differed substantially (e.g., exposure
duration, measurement endpoints).

Aquatic Toxicity of Sulfometuron Methyl Degradates

As discussed earlier in Section   REF _Ref184002208 \r \h  <IP_ADDRESS> , no
acceptable or supplemental studies were available on the toxicity of the
major sulfometuron methyl degradates to aquatic organisms.  To
characterize the potential toxicity of the major degradates of
sulfometuron methyl, predicted toxicity values were determined from
EPA’s ECOSAR model (v. 0.99h).  Note that these QSAR results should
not, by OPP policy, be used directly for risk management decisions. This
model is based on quantitative structure activity relationships (QSAR)
for chemical effects on fish, daphnids, and green algae.    REF
_Ref184002630 \h  Table 51  displays the results of the ECOSAR model
predictions for five major sulfometuron methyl degradates.

Table   SEQ Table \* ARABIC  51 .  ECOSAR-predicted toxicity values for
major degradates of sulfometuron methyl.

Degradate Name	ECOSAR Class	Organism	Toxicity Endpoint	Toxicity Value
(mg/L)

2-Hydroxy, 4,6-dimethyl pyrimidine	Phenols	Fish	96-h LC50

90-d Chronic Value	49

0.31

Daphnid	48-h LC50

21-d Chronic Value	13

5.3

Green Algae	96-h EC50	257

2-(Aminosulfonyl) benzoic acid	Neutral organic acids	Fish	96-h LC50

30-d Chronic Value	137,000*

12,600

Daphnid	48-h LC50

16-d EC50	128,000*

2,620

Green Algae	96-h EC50	70,676

Saccharin	Thiazolinone (iso-)	Fish	96-h LC50

Chronic Value**	1.9

0.14

Daphnid	48-h LC50

Chronic Value**	1.6

0.057

Green Algae	96-h EC50	0.41

2-(Aminosulfonyl) benzoic acid, methyl ester	Esters	Fish	96-h LC50

Chronic Value**	152

136

Daphnid	48-h LC50	2,350

Green Algae	96-h EC50

Chronic Value**	11.6

8.7

2-Pyrimidinamine, 4,6-dimethyl	Aromatic amines	Fish	96-h LC50

Chronic Value**	214

0.93

Daphnid	48-h LC50

Chronic Value**	1.6

0.042

Green Algae	Chronic Value**	12.9

 * predicted toxicity value may exceed compound’s aqueous solubility

** duration associated with the reported chronic value was not reported
by the ECOSAR program

The peak, 21-d, and 90-d EECs predicted for the parent chemical,
sulfometuron methyl are: 0.031, 0.026, and 0.016 mg/L, respectively (
REF _Ref178044350 \h  \* MERGEFORMAT  Table 15 )

Toxicity predictions from the ECOSAR model ranged widely across the five
degradates, likely due in part to the differences in chemical structure
and ECOSAR class used for the predictions (e.g., phenols, neutral
organic acids, thialozinone, esters and aromatic amines).

Predicted toxicity and risk characterization for 2-(aminosulfonyl)
benzoic acid

Of the five degradates evaluated, 2-(aminosulfonyl) benzoic acid was
predicted to be the least toxic, with toxicity predictions for all
aquatic species tested ranging from 2,600 to 137,000 mg/L.  Predicted
EECs were not modeled for the any of the degradates due to lack of
appropriate data on the environmental fate of these compounds.  However,
if one assumes the EECs for the degradates are similar that of the
parent compound (sulfometuron methyl), then the toxicity value for
2-(aminosulfonyl) benzoic acid appears at least 5 orders of magnitude
greater than the EEC for sulfometuron methyl.  While this assumption may
have uncertainty due to the potential differential environmental fate
characteristics of sulfometuron methyl and 2-(aminosulfonyl) benzoic
acid, it appears highly unlikely that such differences would span the 5
order of magnitude range between EECs and predicted toxicity values for
2-(aminosulfonyl) benzoic acid, thus suggesting that the potential
ecological risk to fish, daphnids and green algae associated with
2-(aminosulfonyl) benzoic acid would be highly unlikely.

Predicted toxicity and risk characterization for the other degradates

Effects on Fish. With the remaining four degradates (2-hydroxy,
4,6-dimethyl pyrimidine, saccharin, 2-(aminosulfonyl) benzoic acid,
methyl ester, and 2-pyrimidinamine, 4,6-dimethyl), the predicted acute
and chronic toxicity values for fish ranged from 1.9-214 mg/L and
0.14-136 mg/L, respectively (  REF _Ref184002630 \h  \* MERGEFORMAT
Table 51 ).  Except for saccharin, these predicted acute toxicity values
for fish were comparable to those observed for sulfometuron methyl (>150
mg ai/L). The predicted acute toxicity of saccharin to fish was at least
two orders of magnitude lower than that observed sulfometuron methyl.
However, when compared to the peak predicted EEC for sulfometuron methyl
(0.031 mg/L), the predicted acute toxicity of the degradates to fish is
still at least two orders of magnitude greater (1.9-214 mg/L).  The
lowest predicted chronic toxicity value for fish (0.14 mg/L for
saccharin) was about an order of magnitude greater than the predicted
90-d EEC for sulfometuron methyl (0.016 mg/L). Given the relatively long
degradation half lives used to predict EECs for sulfometuron methyl
(e.g., several months or longer,   REF _Ref177972956 \h  Table 13 ), it
also appears unlikely that these degradates would reach concentrations
that would exceed those of sulfometuron methyl by 1-2 orders of
magnitude (although it is possible that exposure on a molar basis to the
most persistent degradates could be somewhat higher than to parent).

Effects on daphnids. For daphnids, the acute and chronic toxicity values
predicted from ECOSAR ranged from 1.6-2,350 mg/L and 0.042-5.3 mg/L,
respectively, for the remaining four degradates: 2-hydroxy, 4,6-dimethyl
pyrimidine, saccharin, 2-(aminosulfonyl) benzoic acid, methyl ester, and
2-pyrimidinamine, 4,6-dimethyl (  REF _Ref184002630 \h  \* MERGEFORMAT
Table 51 ).   When compared to the peek EEC of 0.031 mg/L for
sulfometuron methyl, the ECOSAR-predicted acute toxicity of the
degradates was at least two orders of magnitude greater (1.6-2,350
mg/L).  However, for two degradates (saccharin and 2-pyrimidinamine,
4,6-dimethyl), the ECOSAR-predicted chronic toxicity (0.052 and 0.042
mg/L, respectively) are relatively close to the 21-d EEC of sulfometuron
methyl (0.026 mg/L).  Thus, if the EECs for these degradates are
comparable to the parent compound (sulfometuron methyl) and the toxicity
predictions from ECOSAR are accurate, chronic toxicity of these two
degradates to daphnia would be just a factor of two greater than the
degradate EECs.

Effects on green algae. For green algae, the ECOSAR-predicted acute and
chronic toxicity values for the degradates (0.41 - 257 mg/L; (  REF
_Ref184002630 \h  \* MERGEFORMAT  Table 51 ) are much greater than those
of sulfometuron methyl (0.0046 and 0.00063 for acute and chronic
toxicity, respectively.  This finding is expected given the mode of
action of the degradates likely differ from sulfometuron methyl, which
is specific to ALS inhibition in plants.   The most sensitive of these
toxicity values (0.41 mg/L for saccharin) is about an order of magnitude
greater than the peak EEC of 0.031 mg/L for sulfometuron methyl.  This
implies the potential risks from sulfometuron methyl to aquatic plants
(green algae) are much more of a concern compared to its degradates.
However, the phytotoxicity of saccharin may not be discounted entirely,
especially if there is an underestimation of saccharin toxicity by
ECOSAR and/or a higher level of exposure to saccharin due to (possibly)
greater environmental persistence.

Although the above comparisons are subject to considerable uncertainty
in both the toxicity estimates (ECOSAR) and EECs (assumed to be similar
to those for sulfometuron methyl), they do suggest that the toxicity of
the degradates is likely not a dominant concern, with the possible
exception of chronic toxicity to freshwater invertebrates (daphnia) and
acute toxicity to algae.

Risk to Terrestrial Animals

In the conceptual model, direct deposition, spray drift, root uptake,
sediment and water runoff water, wind erosion of soil particles, and
volatilization/inhalation are identified as the most likely exposure
routes for sulfometuron methyl exposure to non-target terrestrial
organisms.  Risks to terrestrial animals and plants (i.e. birds,
terrestrial-phase amphibians, reptiles, mammals, and plants) were
assessed based on modeled EECs and available toxicity data.  As part of
this screening terrestrial risk assessment, exposure concentrations of
sulfometuron methyl to non-target terrestrial plants and animals were
modeled according to maximum labeled application rates.  For terrestrial
birds, terrestrial-phase amphibians, reptiles and mammals, estimates of
upper bound levels of sulfometuron methyl residues on various food
items, which may be contacted or consumed by wildlife, were determined
using the Fletcher nomogram followed by a first order decline model TREX
1.3.1.  Likewise, the TerrPlant 1.2.2 model was used to estimate
exposure to non-target plants and the AgDRIFT 2.0.1 model provided
further refinement of spray drift dispersion and deposition to
terrestrial plants located in proximity to treated fields. Note that
AgDRIFT offers the ability to examine the variation in the amount of
spray drift with application practices and conditions whereas TerrPlant
does not (fixed values are used). Since spray drift is a dominant
contributor to off-site exposure to terrestrial animals, the AgDRIFT
predicted exposures, depending on the input assumptions, may be higher
than those estimated with TerrPlant.

The risk hypothesis stated that the use of sulfometuron methyl has the
potential to cause adverse effects to terrestrial animals and plants.
This risk hypothesis is confirmed for terrestrial plants, and also for
adverse effects to non-target terrestrial animals via indirect effects
resulting from potential effects to plants.  However, the assessment
refutes the risk hypothesis regarding direct effects to animals and
suggests that direct effects to terrestrial animals are unlikely.

Birds

Sulfometuron methyl is categorized as practically nontoxic to both
waterfowl (mallard duck) on an acute oral basis (LD50 >4,650 mg/kg-bw)
and practically nontoxic to both upland game birds and waterfowl by the
subacute dietary route (LC50 >5,620 mg/kg-diet and > 4,600 mg/kg-diet,
respectively). Since the LD50 and LC50 values are greater than the
highest dose tested in the studies, with no effects occurring at any
dose, a bounding analysis was conducted to evaluate potential effects
associated with acute oral and subacute dietary exposure to sulfometuron
methyl (Section   REF _Ref178404082 \r \h  \* MERGEFORMAT  4.1 ;   REF
_Ref178157712 \h  \* MERGEFORMAT  Table 42  and   REF _Ref178157714 \h
\* MERGEFORMAT  Table 43 ).  This bounding analysis compared size class
adjusted ‘indefinite’ LD50 values (i.e., ‘greater than’ values)
based on a bird’s weight to predicted doses on food residues (EEC
equivalent dose) following a single ground application of sulfometuron
methyl at 0.375 lb ai/A. Based on this analysis, predicted RQs were all
< 0.04 or lower, despite the conservative assumption that the
‘indefinite’ LC50 and LD50 values (at which no mortality was
observed in the test) represent definitive LC50 and LD50 values (where
50% mortality occurred).  Therefore, risk to birds from acute oral and
subacute dietary exposure to sulfometuron methyl is judged to be highly
unlikely.

No data were available on the effects of sulfometuron methyl to avian
fauna from chronic exposures. Therefore, risks to birds from chronic
exposure to sulfometuron methyl could not be directly quantified in this
risk assessment.  A qualitative assessment is conducted here based on
chronic avian toxicity data obtained for 12 studies from 9 other
sulfonylurea herbicides with the same mode of action (inhibition of
acetolactate synthase;   REF _Ref179612370 \h  Figure 4 ).  These data
were obtained from EFED’s Ecotoxicity database using a cross reference
with another EFED “Active Ingredient” database that links active
ingredients with mode of action.  Although these 12 sulfonylurea
herbicides likely do not represent the entire universe of sulfonylureas
with chronic avian toxicity data, they are considered to provide a
representative sample from which to qualitatively evaluate the
uncertainty associated with lack of chronic avian toxicity data for
sulfometuron methyl.

Figure   SEQ Figure \* ARABIC  4 . Chronic Avian Toxicity of
Sulfonylurea Herbicides

Results from   REF _Ref179612370 \h  Figure 4  indicate that out of the
12 chronic avian NOAECs examined for sulfonylurea herbicides, two
occurred below the peek EEC of 90 mg ai/kg-diet calculated for short
grass (  REF _Ref177798194 \h  Table 17 ).  These two NOAECs were 30 mg
ai/kg-diet for tribenuron methyl (MRID 43594201) and 28 mg ai/kg-diet
for prosulfuron (MRID 42949701). The LOAELs from these two studies (180
and 100 ppm, respectively) are above the 90 mg ai/kg-diet peek EEC.
Thus, out of the 9 sulfonylureas evaluated, the peak EEC would exceed
the LOC for 2 herbicides (or 12% of the chemicals).  This finding is
consistent with the generally low toxicity sulfonylurea herbicides
terrestrial animals. Thus, while considerable uncertainty exists in
extrapolating chronic NOAELs across chemicals even within the same mode
of action, these results suggest that chronic toxicity to avian fauna is
not likely to be a dominant concern in this risk assessment, although it
cannot be discounted entirely since LOCs would be exceeded for 2 of the
9 herbicides evaluated.

Mammals

As observed for avian fauna, sulfometuron methyl is classified as
practically nontoxic on an acute basis to mammals.  As described in
Section 4.1, a bounding analysis compared predicted EECs to indefinite
LD50 values (adjusted for different size classes) for the purposes of
estimating the upper bound of acute toxicity risk.  The highest EEC for
mammals is 85.8 mg/kg-bw for short grass consumed by a 15 g mammal.  The
adjusted LD50 for 15 g mammals would be 10,989 mg/kg bw.   There is an
approximately 120-fold difference between these two values.  Since the
acute RQs for all weight classes of mammals consuming all feed types are
< 0.01 and less than the Agency LOCs (  REF _Ref178157883 \h  \*
MERGEFORMAT  Table 44 ), acute risks from direct effects of sulfometuron
methyl on mammals is not expected from the modeled uses.

The chronic LOC for mammals was not exceeded for the modeled uses.
Predicted residues of sulfometuron methyl on different food types was
compared to size class adjusted NOAELs.  The highest RQ (0.07) occurred
for the 15g mammal (  REF _Ref178157965 \h  Table 45 ) which is below
the Agency’s LOC of 1.0 for chronic effects to terrestrial animals.
Therefore, chronic risks from direct effects of sulfometuron methyl on
mammals are not considered likely.

Non-target Terrestrial-phase Amphibians, Reptiles, and Beneficial
Insects

EFED currently uses data on surrogate species (birds) to assess
non-target terrestrial phase amphibians and reptiles and does not derive
risk quotients for terrestrial non-target insects. Based on the
evaluation of potential risks to birds as surrogates for reptiles,
potential risks to reptiles and terrestrial phase amphibians is also
considered lower than the Agency’s concern level.

As previously discussed, EFED does not currently estimate risk quotients
for terrestrial non-target invertebrates.  However, submitted
terrestrial insect toxicity data, based on tests with honeybees, suggest
that sulfometuron methyl is practically non-toxic to bees (LD50 of >100
µg/bee).  The mode of action of sulfometuron methyl suggests it is
likely not to be highly toxic to terrestrial invertebrates.  To the
extent that honey bees are representative of the sensitivity of insects
and other terrestrial invertebrates to sulfometuron methyl, potential
risk to terrestrial insects and invertebrates in treatment area is
expected to be minimal.

Risk to Terrestrial Plants

Tier 1 Modeling of Runoff and Spray Drift

Results presented in Section   REF _Ref178405021 \n \h  \* MERGEFORMAT
4.1  using the TerrPlant model indicate the modeled uses of sulfometuron
methyl result in exposures to non-endangered and endangered plants
adjacent to treated areas that exceed the Agency’s LOC of 1.0.  Both
monocots and dicots appear highly sensitive to sulfometuron methyl, with
dicots appearing to be the more sensitive group of plants.  At the
maximum aerial application rate of 0.375 lb ai/A, the maximum predicted
EEC resulting from combined drift and runoff to semi-aquatic areas (0.21
lb ai/A) exceeded terrestrial monocot and dicot EC25 values by
approximately 1000 and 6500 times, respectively (  REF _Ref178405382 \h
\* MERGEFORMAT  Table 48 ). For endangered monocots and dicots where a
more sensitive endpoint is used (NOAEC), the predicted EEC for combined
drift and runoff were 4800 and 7100 for monocots and dicots,
respectively.  For the spray drift analysis, predicted EECs were
compared to results from the vegetative vigor test, which resulted in
RQs of 500 and 1000 for non-endangered monocots and dicots respectively
(  REF _Ref178405382 \h  \* MERGEFORMAT  Table 48 ).  RQ values for
endangered monocots and dicots resulting from drift from aerial
application were 2200 and 19000 for monocots and dicots, respectively.

These high RQ values are generally consistent with results from other
sulfonylurea herbicide risk assessments both internal and external to
the Agency.  Furthermore, it is worth noting that the most sensitive
monocot and dicot from the seedling emergence and vegetative vigor test
is used to calculate risks to terrestrial plants.  However, examination
of the sensitivity of the other 9 test species indicates they too would
be at risk from adverse effects of sulfometuron methyl at the modeled
application rate.  Specifically, the range in EC25s between the least
and most sensitive plant from the seedling emergence study was about a
factor of 75, while that for the vegetative vigor study was a factor of
5 (MRID 435385-01). The RQ values for the most sensitive monocot and
dicot species are well above this margin.  This indicates the predicted
exceedence of the Agency’s LOC would also occur for the 9 other
terrestrial plants tested and are not simply a function of a single,
highly sensitive species.

Given these high RQ values for terrestrial plants, a more refined spray
drift analysis for exposures to non-target terrestrial plants in dry and
semi-aquatic areas is provided in Section   REF _Ref178407275 \r \h  \*
MERGEFORMAT  4.2.4 .   The potential risk to endangered monocots and
dicots will be discussed in greater detail in Section   REF
_Ref178496349 \r \h  <IP_ADDRESS> .

  SEQ CHAPTER \h \r 1 Field and Greenhouse Studies

Based on a search of EPA’s ECOTOX database, field and greenhouse
studies on the effects of sulfometuron methyl or its degradates were
reviewed.  Most of the field studies that passed the ECOTOX and OPP
screening criteria were concerned with the efficacy of sulfometuron
methyl control of target plants (weeds) and therefore are not considered
useful indicators of the effects of sulfometuron methyl on non-target
plant species (See   REF _Ref178405615 \h  \* MERGEFORMAT  APPENDIX H:
Ecological Effects Data Summaries ).  Those studies that contained
relevant information on the effects of sulfometuron methyl or its
degradates on non-target plants are summarized below.

In a greenhouse study, Busse et al. (2005) studied the effect of
sulfometuron methyl (applied as the formulated product Oust) on
ectomycorrhizal formation and seedling growth of three conifer species:
ponderosa pine (Pinus ponderosa), Douglas fir (Pseudotsuga menziesii),
and white fir (Abies concolor).  Conifer seedlings (5 replicates) were
grown in four different soil types and applied with sulfometuron methyl
at 0, 1X and 2X its application rate of 0.14 kg ai/ha (0.125 lb/A).
Sulfometuron methyl was applied to soil at the onset of lateral root
formation (approximately 45-55 d post planting) due to the high
sensitivity of seedlings to sulfometuron methyl applied prior to this
time period. Results indicate that ectomycorrhizal formation was not
inhibited for any conifer regardless of soil type or application rate
(1X or 2X).  For ponderosa pine, seedling dry weight and root growth
(number of root tips/plant) were significantly reduced relative to
controls at 0.125 and 0.250 lb ai/A in two of the four soil types.  For
Douglas fir and white fir, no significant reduction in seedling dry
weight occurred at any treatment level.  However, root growth was
reduced for Douglas fir at 0.125 lb ai/A for three of the four soil
types and at 0.25 lb ai/A for the forth soil type.  White fir appeared
least sensitive to sulfometuron methyl, with significant reductions in
root growth at 0.125 lb ai/A in one soil type and at 0.25 lb ai/A in a
second soil type.  The authors conclude that sulfometuron methyl does
not inhibit mycorrhizal formation at the specified application rates but
does inhibit plant growth of ponderosa pine and root growth of all three
species, depending on soil type and application rate. The lowest NOAEC
from this study is 1X the application rate or 0.125 lb ai/A, several
orders of magnitude above NOECs observed in the seedling emergence and
vegetative vigor guideline studies.

Boyle and Walters (2005) examined the effect of saccharin, a major
degradation product of sulfometuron methyl, on resistance of broad bean
(Vicia faba) to rust fungus.  Although not conceived as a degradate
study per se, these results nevertheless have some relevance to the
ecotoxicology of one of the sulfometuron methyl degradation products.
In this study, 200 ml of 0.3 mM saccharin was applied either as a soil
drench or to foliage of broad bean which were exposed to rust fungus
four times over a 14-d period.  Results indicate that saccharin did not
induce resistance to rust fungus nor did it significantly affect shoot
weight or leaf area.  However the authors report the number of leaflets
formed was significantly reduced relative to controls.

Neary et al. (1984) evaluated the effects of sulfometuron methyl (as the
formulated product Oust) on slash pine (Pinus elliottii) and loblolly
pine (Pinus taeda) seedlings inhabiting coastal plain flatlands.  In
this study, 60 trees of each species were exposed to sulfometuron methyl
via broadcast spray at 0.50 lb ai/A in a randomized factorial design
involving different plot locations, irrigation and fertilization levels.
 Although this study was designed primarily to investigate the efficacy
of different weed control methods, the authors reported three months
after treatment, application of sulfometuron methyl did not reduce
survival of slash or loblolly pine, suggesting an unbounded NOAEC of
0.50 lb ai/A (only dose tested).

Contaminated Irrigation Water

The potential risks to plants when exposed to irrigation water
contaminated with sulfometuron methyl were estimated for both ground
water and surface water irrigation sources (Section   REF _Ref178406112
\r \h  \* MERGEFORMAT  4.1.4 ).    The EEC for ground water (0.33 ug/L)
was calculated using the Tier 1 SCIGROW model (  REF _Ref178394075 \h
\* MERGEFORMAT  Table 16 ) while that for surface water (31 ug/L) was
calculated using PRZM/EXAMS from the scenario yielding the highest EECs
(  REF _Ref178044350 \h  \* MERGEFORMAT  Table 15 ).  Comparisons were
made to the most sensitive endpoint from vegetative vigor study assuming
that runoff of irrigation water does not occur.  Results suggest that
sulfometuron methyl levels in irrigation water from ground water sources
would not exceed non-endangered or endangered species LOCs (i.e, RQs <
1.0).  However, RQs based on sulfometuron methyl in irrigation water
derived from surface water sources exceed the LOCs for both
non-endangered and endangered species (3.9 and 71, respectively), thus
indicating a potential risk to plants adjacent to fields irrigated with
surface water sources.

Refined Spray Drift Analysis

As described in Section   REF _Ref178406298 \r \h  \* MERGEFORMAT
<IP_ADDRESS>  (Terrestrial Exposure Modeling), a more in-depth spray drift
exposure assessment utilizing Tier I and II AgDRIFT® (version 2.01) was
conducted to better characterize potential exposure of terrestrial
plants.  AgDRIFT® is a useful too for evaluating the potential of
buffer zones to protect sensitive habitats from undesired exposures.
Four different application scenarios were modeled reflecting typical and
reasonable worst case assumptions regarding potential exposure
conditions (labeled A through D in   REF _Ref178147274 \h  Table 20  and
  REF _Ref178147279 \h  Table 21 ).

Table   SEQ Table \* ARABIC  52 .  Risks to Terrestrial Plants from
Spray Drift According to Distance Downwind, Application Method, and
Drift Exposure Conditions

Distance Down Wind (Feet)	PERCENT OF APPLICATION RATE	eec (1)
non-endangered plants (2)	endangered plants(3)

	Percent	lb ai/A	RQ	RQ

[A] Ground Application (Low Boom)

0	102.0	0.3822	21233	386061

50	1.77	0.0066	367	6667

100	0.95	0.0036	200	3636

200	0.51	0.0019	106	1919

500	0.21	0.0008	44	808

750	0.13	0.0005	28	505

900	0.11	0.0004	22	404

[B] Ground Application (High Boom)

0	106.0	0.3956	21978	399596

50	5.00	0.0187	1039	18889

100	2.48	0.0093	517	9394

200	1.20	0.0045	250	4545

500	0.39	0.0015	83	1515

750	0.22	0.0008	44	808

900	0.17	0.0006	33	606

[C] Aerial (Following Many Label Recommendations)

0	50.00	0.1874	10411	189293

50	17.12	0.0642	3567	64848

100	9.79	0.0367	2039	37071

200	4.69	0.0176	978	17778

500	1.92	0.0072	400	7273

750	1.39	0.0052	289	5253

900	1.24	0.0046	256	4646

[D] Aerial (High-End Exposure Scenario)

0	77.35	0.2900	16111	292929

50	38.32	0.1437	7983	145152

100	25.11	0.0941	5228	95051

200	14.07	0.0527	2928	53232

500	5.40	0.0203	1128	20505

750	3.82	0.0143	794	14444

900	3.32	0.0125	694	12626

(1) Details of the refined spray drift modeling are provided in Section
 REF _Ref178494837 \r \h  \* MERGEFORMAT  <IP_ADDRESS> .

(2) Non-endangered plant RQs based on vegetative vigor EC25 for soybean
of 1.8 x 10-5 lb ai/A (MRID 435385-01)

(3)  Endangered plant RQs based on vegetative vigor EC05 for soybean of
9.9 x 10-7 lb ai/A (MRID 435385-01).

Results from the refined spray drift modeling indicate that RQs exceed
the Agency LOC of 1.0 for endangered and non-endangered terrestrial
plants based on all four exposure scenarios at the maximum distance
modeled (the model limit of 900 ft downwind of the treated field; see
REF _Ref178147274 \h  Table 20 ).  The highest initial RQ values
occurred with ground applications (high and low boom), although RQs
dropped substantially as the distance downwind increased.  At a downwind
distance of 900 ft, RQs dropped by approximately a factor of 1000 and
600 of the edge of field RQs (0 ft) for low boom and high boom ground
applications, respectively.  The 50 ft buffer resulted in the largest
proportional decline in EECs relative to edge of field estimates,
declining to 1.7% and 5.0 % of the initial EECs for low and high boom
ground applications, respectively.

Compared to ground applications, aerial applications resulted in lower
initial EECs at the edge of the field (downwind distance = 0), however,
the attenuation of EECs with distance downwind was not as great as that
observed with ground applications.  The EECs (and RQs) declined to 17%
and 38% 50 ft from the edge of field for the typical and high end
exposure scenarios, respectively.  At 900 ft downwind, RQs for
non-endangered plants are approximately 250 and 700 for the typical and
high end aerial application exposure scenarios, respectively.   For
endangered plants, RQs calculated at 900 ft downwind are approximately
4,600 and 12,600 for the typical and high end aerial application
exposure scenarios, respectively.

Pertinent to these modeling results are a number of recommendations (but
not requirements) on the product labels for sulfometuron methyl. The
labels suggest that “The most effective way to reduce drift potential
is to apply large droplets (>I50 - 200 microns)”; but there is no
specific mandate on the label.  Other suggestions on the label include:
that boom height less than 10 feet decreases the potential for spray
drift from helicopter or aircraft applications, For ground applications;
the applicator receives the following directions: “Setting the boom at
the lowest height that provides uniform coverage and reduces the
exposure of droplets to evaporation and wind.”  The label notes that
drift is minimized when the wind speed is between 3 and 10 mph.

Review of Incident Data

An analysis of the ecological incidents associated with a pesticide
application (or misapplication) is an important part of EPA’s
ecological risk assessment because such information can help establish
additional lines of evidence to the risk assessment conclusions.  A
search of EPA’s Ecological Incident Information System (EIIS) was
conducted in September, 2007 which revealed 35 incidents reports for
sulfometuron methyl with varying degrees of confidence in the causal
association.  Of these 35 incidents, one was classified as highly
probable, 20 were classified as probable and 14 were classified as
possible (“  REF _Ref184019372 \h  APPENDIX E: Adverse Ecological
Incidents Associated with Sulfometuron Methyl Use ”).  Only the
incidents classified as either highly probable or probable are discussed
further here.

Highly Probable Incidents.  The incident classified as highly probable
is worthy of discussion here because it is one of the few incidents
involving sulfonylurea herbicides where positive findings of pesticide
residues were reported.  In this case (Incident Report 1011666-001),
Oust herbicide (containing sulfometuron methyl) was applied by the
Bureau of Land Management (BLM) personnel to approximately 22,000 acres
of Idaho forest and grassland in the autumn of 2000 for weed control.
These areas were severely damaged or burned by wildfires that occurred
the previous year.  Following the aerial application of Oust at a rate
of 0.0625 lb ai/A, drought and windy conditions (up to 20-40 mph) caused
pesticide drift, presumably via erosion of dry treated soils.  Thousands
of acres were alleged to have been affected, including sugar beets,
small grains, garlic, potato, corn, and alfalfa.  Soil residues of
sulfometuron methyl measured on BLM land ranged from 0.079 to 0.82 ppb.
Documentation by the State of Idaho Dept. of Agriculture showed that in
one case, there was evidence to show that sulfometuron methyl was
present 13 miles from the application site.  Crop damage was estimated
to be in excess of $72 million.

Probable Incidents.  Of the 20 probable incidents involving sulfometuron
methyl, 5 involved accidental misuse and all but one of the remaining
involved registered uses.  Regarding the application method, the
majority of probable incidents involved ground application, although
about one third of the incident reports did not contain information on
the application method.  Relative to the type of application site, 7
involved railroad or road rights of way and 6 involved agriculture
sites.  In terms of route of exposure, pesticide drift (either alone or
in combination with runoff) was reported for 11 probable incidents,
while runoff (either alone or in combination with drift) was reported
for 9 probable incidents.  A total of 19 probable incidents reported for
sulfometuron methyl involved damage to terrestrial plants and only one
reported damages to aquatic plants and animals.

Although these sulfometuron methyl ecological incident reports do not
conclusively establish sulfometuron methyl as the cause of the reported
damages, in the aggregate they suggest that non-target terrestrial
plants in particular can be susceptible to both sulfometuron methyl
drift and runoff, which was found to be the pathway and receptor of
greatest concern in this risk assessment.  The also are consistent with
the risk assessment findings of no significant risk of direct toxicity
to aquatic and terrestrial animals.

Overall Ecological Risk Conclusions

The results of this screening risk assessment indicate that potential
risks from direct effects to aquatic and terrestrial animals from
exposure to sulfometuron methyl modeled at the maximum annual
application rate (0.375 lb ai/A) are below the Agency’s LOCs.
Therefore, risk from direct effects to aquatic and terrestrial animals
is considered unlikely.  Given the mode of action of sulfometuron methyl
(ALS inhibitor), the potential for direct effects to aquatic and
terrestrial plants is indicated by this screening level risk assessment.
 Based on a refined analysis of sulfometuron methyl spray drift, RQs for
terrestrial plants exceed the Agency’s LOC at 900 ft downwind from a
treated field in all four application scenarios evaluated.  While the
potential for direct effects to aquatic and terrestrial animals is
considered small, the potential exists for indirect effects on animals
due to impairment of aquatic and terrestrial plants.  Specifically,
direct effects to plant species could present an indirect risk at the
higher levels of organization (i.e. population, trophic level,
community, and ecosystem).  Field studies are not available to quantify
actual risk to plant and animal communities in forest/edge and
wetland/riparian habitats.  However, in terrestrial and shallow-water
aquatic communities, plants are the primary producers upon which the
succeeding trophic levels depend.  If the available plant material is
impacted due to the effects of sulfometuron methyl, this may have
negative effects not only on the herbivores, but throughout the food
chain.  Also, depending on the severity of impacts to the plant
communities [i.e., forests, wetlands, ecotones (edge and riparian
habitats)], community assemblages and ecosystem stability may be altered
(i.e. reduced bird populations in edge habitats; reduced riparian
vegetation resulting in increased light penetration and temperature in
aquatic habitats, loss of cover and food for fish).  In addition,
riparian vegetation, which is a significant component of the food supply
for aquatic herbivores and detritivores provides habitat (i.e. leaf
packs, materials for case-building for invertebrates) may also be
affected.

Endocrine Effects

EPA is required under the Federal Food, Drug, and Cosmetic Act (FFDCA),
as amended by the Food Quality Protection Act (FQPA), to develop a
screening program to determine whether certain substances (including all
pesticide active and other ingredients) “may have an effect in humans
that is similar to an effect produced by a naturally occurring estrogen,
or other such endocrine effects as the Administrator may designate.”
Following the recommendations of its Endocrine Disruptor Screening and
Testing Advisory Committee (EDSTAC), EPA determined that there was a
scientific basis for including, as part of the program, the androgen and
thyroid hormone systems, in addition to the estrogen hormone system.
EPA also adopted EDSTAC’s recommendation that the Program include
evaluations of potential effects in wildlife.  When the appropriate
screening and/or testing protocols being considered under the Agency’s
EDSP have been developed, sulfometuron methyl may be subjected to
additional screening and/or testing to better characterize effects
related to endocrine disruption.

Federally Threatened and Endangered (Listed) Species

Both acute endangered species and chronic risk LOCs are considered in
this screening-level risk assessment of pesticide risks to listed
species. Endangered species acute LOCs are a fraction of the
non-endangered species LOCs or, in the case of endangered plants, RQs
are derived using lower toxicity endpoints than non-endangered plants.
Therefore, concerns regarding listed species within a taxonomic group
are triggered in exposure situations where restricted use or acute risk
LOCs are triggered for the same taxonomic group. The risk assessment
also includes an evaluation of the potential probability of individual
effects for exposures that may occur at the established endangered
species LOC in both the risk characterization and the endangered species