Children 1-2 years old            0.001523            19                  0.000111            22
----------------------------------------------------------------------------------------------------------------
Children 3-5 years old            0.001312            16                  0.000103            21
----------------------------------------------------------------------------------------------------------------
Children 6-12 years old           0.000911            11                  0.000069            14
----------------------------------------------------------------------------------------------------------------
Youth 13-19 years old             0.000967            12                  0.000048            10
----------------------------------------------------------------------------------------------------------------
Adults 20-49 years old            0.001475            18                  0.000057            11
----------------------------------------------------------------------------------------------------------------
Adults 50+ years old              0.000929            12                  0.000051            10
----------------------------------------------------------------------------------------------------------------
Females 13-49 years old           0.001000            13                  0.000050            10
----------------------------------------------------------------------------------------------------------------

    2. Drinking water models--a. NRDC's claims. NRDC argues that the
DDVP tolerances are unsafe because EPA has inadequate data on DDVP
levels in drinking water. (Ref. 1 at 40). NRDC notes that EPA has
limited groundwater monitoring data and no surface water monitoring
data for DDVP, naled, and trichlorfon. In the absence of DDVP

water monitoring data, NRDC claims EPA cannot find the DDVP tolerances
to be safe. Further, NRDC claims that the surface water exposure model
used by EPA in the preliminary risk assessment (PRA), GENEEC, has not
been properly validated, and that ``EPA has failed to demonstrate that
the surrogate data [in the model] are properly matched to DDVP and that
the model's assumptions and parameters are justified.'' (Id. at 54).
NRDC makes similar claims regarding the matching of surrogate
groundwater data to DDVP through the operation of the SCI-GROW ground
water model. (Id. at 55). According to NRDC, ``if the SCI-GROW model
employed surrogate data [on DDVP], it cannot be assumed to be reliable
unless full disclosure of its construction and inputs is made and this
information demonstrates its reliability.'' (Id.).
    In its comments on the DDVP IRED, NRDC raised similar issues. (Ref.
13 at 9). Citing a number of alleged uncertainties pertaining to the
SCI-GROW model, NRDC argues that because ``[n]one of these
uncertainties is quantitatively bounded ... the Agency has not or
cannot determine with reasonable certainty that the risks from
groundwater contamination by DDVP will not harm people.'' (Id.).
Additionally, NRDC claims the assessment for groundwater is incomplete,
because EPA has not aggregated DDVP in groundwater resulting from uses
of DDVP, naled, and trichlorfon. (Id.).
    Finally, in its petition, NRDC asserts that EPA's conclusion that
DDVP will not be persistent in surface waters is mere speculation.
(Ref. 1 at 44).
    b. Amvac's comments. Amvac disputes NRDC's criticism of EPA's
drinking water models stating ``NRDC appears to not understand the
underlying assumption and highly conservative nature of these models.''
(Ref. 14 at 63). Further, Amvac argues that, because of the highly
conservative nature of the models, the targeted monitoring data NRDC
calls for would show that DDVP exposure in drinking water is lower than
projected. (Id. at 70-71). Amvac further notes that targeted monitoring
data has limited applicability and would be unlikely ``to be
representative of potential exposure on a wider geographical scale.''
(Id. at 71).
    c. EPA's response. NRDC's general claims regarding EPA's drinking
water models are addressed for the most part in a prior EPA order
denying NRDC objections to use of these models in making a safety
finding for a pesticide tolerance. (69 FR 30042, 30058-30065 (May 24,
2006). In that order, EPA explained in detail as to each of the models:
(1) the basic principles on which the model is based; (2) the data
underlying the models; (3) the numerous conservatisms built in to each
of the models; (4) the extensive independent peer review used in the
development of the models; and (5) the external and internal testing of
the accuracy of the models. After this extensive analysis, EPA
concluded the models ``are based on reliable data and have produced
estimates that EPA can reliably conclude will not underestimate
exposure to pesticides in drinking water.'' (Id. at 30065). Not only
does this order provide a detailed description of the models and data
underlying the models but it referenced the many SAP reviews and Agency
policy documents that further explained the models. Additionally, it
should be noted that detailed information concerning the models is
available on EPA's website. EPA has recently updated this information
to insure that the website provides not only the ability to run the
models but also a description of the how the models work and the
underlying codes included in the structure of the model. (Ref. 57)
    NRDC's more specific allegations are also without merit. First, EPA
took the characteristics of DDVP, naled, and trichlorfon into account
in modeling DDVP levels in drinking water. Specific information
concerning these pesticides' mobility and persistence was combined with
information pertaining to application amounts in use of PRZM-EXAMS to
model surface water DDVP levels and SCI-GROW to model groundwater DDVP
levels. In addition, information on soil properties, cropping
characteristics, and weather appropriate to use of these pesticides was
incorporated in the PRZM-EXAMS model run. (Ref. 58). Second, EPA has
adequately addressed uncertainties in the PRZM-EXAMS model through peer
review and validation. NRDC claims that EPA has not quantified the
uncertainties in the SCI-GROW model and thus cannot rely on it;
however, NRDC's listing of uncertainties (e.g., small drinking water
reservoir, runoff prone soils) applies to considerations relative to
the surface water model PRZM-EXAMS not SCI-GROW. These apparent
criticisms of the PRZM-EXAMS model are without merit. As noted above,
while EPA has not specifically quantified each individual uncertainty
associated with the model, the overall model has been extensively peer-
reviewed and validated, and has proved very conservative in practice.
Third, EPA's estimation of surface water DDVP levels is not flawed for
failure to combine exposures from DDVP, naled, and trichlorfon. The
highest estimated surface water DDVP levels are from the naled use on
brassica and the trichlorfon use on turf ((33 parts per billion
(``ppb'') and 60 ppb, respectively, for acute exposure and 1.83 ppb and
1.56 ppb, respectively, for chronic exposure). These estimates are
based on the conservative assumption that 87 percent of the area of the
watershed is cropped to either brassica or turf and all of the brassica
or turf is treated with naled or trichlorfon, respectively. The figure
of 87 percent is based on the fact that ``87 percent cropped was the
largest cropped area in any 8-digit hydrologic unit in the continental
United States.'' (69 FR 30042, 30060 (May 26, 2004)). Thus, there is no
reason to combine these estimates. A watershed may be 87 percent turf
or 87 percent brassica but not both. Moreover, the available data
indicate that both trichlorfon and naled are used relatively
infrequently on turf and brassica, respectively; thus, the water level
estimate is overstated to begin with. (Refs. 56 and 59). In theory, the
DDVP use producing the highest estimated surface water levels (wide
area treatment for mosquitoes) could overlap somewhat with these uses
but not only is estimated water concentration from the DDVP use
insignificant compared to the levels used to assess acute and chronic
drinking water exposure (10X and 20X lower, respectively) but relevant
survey data show no report of DDVP for this use. (Ref. 60).
    EPA has chosen to rely on modeling estimates of DDVP in drinking
water because the drinking water modeling data it has were not
necessarily collected in areas of DDVP, naled, or trichlorfon usage and
there is inadequate data on drinking water from shallow, groundwater
wells. Nonetheless, the sampling data give some indication of the
conservativeness of the modeling estimates. USDA's Pesticide Data
Program (``PDP'') collected finished drinking water samples from
California and New York in 2001 (214 samples) and from California,
Colorado, Kansas, New York, and Texas in 2002 and 2003 (371 and 699
samples, respectively). In 2004, PDP sampled raw and finished water
from 171 community water systems from Michigan, North Carolina, Ohio,
Oregon, Pennsylvania, and Washington (234 samples). Although the
samples were analyzed for DDVP, no detectable residues of DDVP were
found in any sample. The limits of detection for these

monitoring data were between 0.4 and 22.5 parts per trillion (ppt). By
comparison, the estimates from EPA's drinking water models that EPA is
using in the DDVP risk assessment are 60 ppb for acute risk and 1.83
ppb for chronic risk. (Ref. 11). In parts per trillion, these values
would be 60,000 ppt and 1,830 ppt.
    As to NRDC's claims that EPA is simply speculating in stating that
DDVP is unlikely to persist in surface water, NRDC is mistaken. The
conclusion that DDVP will not be persistent in surface water is based
on the physical and chemical properties of DDVP and the results of the
suite of environmental fate and transport studies on the compound. As
EPA noted in the DDVP IRED, ``dichlorvos should not be persistent in
any surface waters due to its susceptibility to rapid hydrolysis and
volatilization.'' (Ref. 11 at 152).
    2. Dietary exposure models--a. NRDC's claims. NRDC contends that
the Dietary Exposure Model (DEEM) cannot be used to demonstrate the
safety of the DDVP tolerances because ``[t]he model is secret in that
the codes, internal structure and assumptions have not been made
available to the public for scrutiny and comment.'' (Ref 1 at 44).
Additionally, NRDC argues that the model cannot be relied upon because
it has never been validated. (Id.).
    b. Amvac's comments. Amvac notes that EPA has used DEEM for many
years and claims that the DEEM ``software and its use have received
many peer reviews ....'' (Ref. 14 at 57). Further, Amvac asserts that
``[t]his model and the other models that EPA uses to assess dietary
risk (i.e., LifelineTM and CARES) have all been made available to the
public and their computer codes are available for public review and
comment.'' (Id. at 57-58).
    c. EPA's response. DEEM and its successor, DEEM-FCID, are not
secret models. As explained in Unit III.B.3.b.i.(B)., these dietary
assessment models use relatively simple formulas to combine consumption
information with residue levels in food to estimate exposure and risk.
In 2000, the company that developed DEEM made a detailed explanation of
the model public so that the model could be reviewed by the FIFRA SAP.
(Ref. 7). That explanatory paper documented the data included in DEEM
and the algorithms DEEM uses to manipulate that data to estimate
exposure and risk. In addition to the algorithms, the paper contained a
full delineation of underlying computer segment codes that comprise the
DEEM program. In response to the SAP's concern that the DEEM paper did
not make public the ``recipes'' used to translate the CSFII consumption
data back to the precursor agricultural commodities (e.g. translating
pizza into tomatoes, wheat, cheese, etc.), EPA contracted to have a new
set of translations produced that would not be subject to proprietary
restrictions. Those new translations have been completed and
incorporated into DEEM-FCID, DEEM's successor, and are fully available
to the public. (Ref.61).
    Thus, NRDC is wrong in its assertion that DEEM is a ``secret''
model. The fundamental logic of this model is available to the public
(including both the algorithms and computer codes) and data on food
recipes is available on DEEM's successor DEEM-FCID, the model used to
run EPA's latest dietary risk assessment for DDVP. NRDC's concerns
regarding validation are misplaced as well in that DEEM and DEEM-FCID
have been reviewed by the SAP and produce similar results to other
publicly-available dietary exposure models. (See, e.g., 70 FR 77363
(December 30, 2005); 70 FR 40202 (July 13, 2005)). Accordingly, NRDC's
request that the DDVP tolerances be revoked because of reliance on DEEM
is denied.
    3. Percent crop treated data--a. NRDC's claims. NRDC asserts that
EPA has used percent crop treated data in calculating aggregate
exposure for DDVP without making the findings required by section
408(b)(2)(F). (Ref. 1 at 39). That section imposes certain conditions
upon EPA's use of percent crop treated data when assessing chronic
dietary risk. Among the specified conditions are the requirements that
EPA find (1) ``the data are reliable and provide a valid basis to show
what percentage of the food derived from such crop is likely to contain
such pesticide chemical residue;'' (2) ``the exposure estimate does not
understate exposure for any significant subpopulation group;'' and (3)
``if data are available on pesticide use and consumption of food in a
particular area, the population in such area is not dietarily exposed
to residues above those estimated by [EPA].'' (21 U.S.C.
346a(b)(2)(F)). Finally, if EPA does rely on percent crop treated data
EPA must provide for the periodic reevaluation of the estimate of
anticipated dietary exposure. (Id.). NRDC claims that EPA, having
failed to make the foregoing findings cannot rely on percent crop
treated in making a safety finding for the DDVP tolerances.
    b. Amvac's comments. Amvac asserts that adequate data are available
on percent crop treated referring to an EPA memorandum (Hummel, 2000).
(Ref. 14 at 47-48). According to Amvac, ``[t]hat memorandum describes
the source of the data and states that the upper end of the range was
assumed for acute dietary exposure analysis and that the typical or
average was used for the chronic dietary exposure analysis, as is
typical EPA practice.'' (Id.).
    c. EPA's response. EPA conducted a comprehensive evaluation of the
usage of DDVP, naled, and trichlorfon for the DDVP IRED. That
evaluation was described in the memorandum cited by Amvac and the
memorandum was included in the docket and on EPA's website page for
DDVP. In response to NRDC's petition EPA has updated its analysis of
percent crop treated information. Specifically, in its revised analysis
EPA used percent crop treated data in estimating exposure from use of:
(1) DDVP on livestock; (2) trichlorfon on turf; (3) DDVP and naled as a
mosquito (wide area) treatment; and (4) naled on agricultural crops.
    Based on the findings below, EPA concludes that its consideration
of usage or percent crop treated data to estimate percent crop treated
conforms to the requirements in section 408(b)(2)(F).
    i. Reliable data. The primary source of data for estimating the
percent of a commodity treated with a pesticide is the United States
Department of Agriculture's National Agricultural Statistics Service
(``NASS''). NASS collects data on a wide variety of agricultural topics
including pesticide usage. NASS uses the Agricultural Resources
Management Survey (``ARMS'') as well as other surveys to collect data
on pesticide usage and other agricultural topics. These surveys are
designed to produce statistically representative estimates of pesticide
usage on targeted crops in the surveyed States using a
probabilistically-based sampling procedure. (See http://www.usda.gov/nass/nassinfo/surveyprograms/index.htm
 and https://arms.ers.usda.gov/

GlobalDocumentation.htm ).
    ARMS is a multi-phase, multi-frame, stratified, probability-
weighted sampling design. There are three phases to the annual survey:
a screening phase to update data and help target sampling for phases
two and three; a second phase that collects information on agricultural
practices and chemical usage; and a third phase that collects costs and
financial information. ARMS consists of two ``frames'' collecting farms
and ranches. The main frame is the ``list frame'' that is intended to
contain the names and addresses of all farms and ranches in the
continental United States along with the acreage of the farms/ranches
and the crops grown or livestock raised. The list frame is compiled
based on the Census of Agriculture as well as numerous other

surveys and governmental and non-governmental sources. The list frame
is back-stopped by the ``area frame'' which is constructed from
satellite images of the continental United States broken down into
segments based upon degree and type of cultivation. Both frames are
divided into different strata such as crop type. Due to the complexity
of the sample design, ARMS uses a weighting system to adjust data
gathered in reports from sampling of the frames.
    Data is gathered by a statistically-designed sampling of the list
and area frames. The sampling is done on a state basis with the focus
for any particular crop on the major production states. Generally,
samples are conducted in states representing 90 percent or better of
the production acreage. Reports are usually prepared based on face-to-
face interviews with the identified growers. Surveys for field crops
are conducted annually with the crops varying each year. (See http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1560
)

Surveys for fruits and surveys for vegetables are conducted in
alternating years with fruits surveyed in odd years and vegetables in
even years. (See http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1567 and http://

usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1572).
There is some variation in the crops sampled in each survey. NASS data
on pesticide use on livestock are published periodically by USDA (1999
(summary of 1997 livestock and general farm survey), 2000 (summary of
1999 swine and swine facilities survey), 2001 (summary of 2000 sheep
and sheep facilities survey), 2002 (summary of 2001 dairy cattle and
dairy cattle facilities survey), and 2006 (summary of 2005 swine and
swine facilities survey), see http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1569
).

    To estimate percent crop treated for pre-harvest pesticide uses,
EPA has created a database containing NASS data from the years 1999-
2005. Also included in this database is data from a private service,
Doane Marketing Research, Inc., now known as dmrkynetec. This database
was used for making the majority of the percent crop treated estimates
for the DDVP assessment, namely, the estimates pertaining to the use of
naled as an agricultural pesticide. The 2007 estimates show that naled
is generally used on a very small percentage of crop acreage. This is
consistent with the estimates made for the 2000 dietary risk
assessment. Most estimates from the two assessments were similar with a
few crops showing declining use over time and one crop (strawberries)
showing increased use. (Refs. 62 at 27-30; 56 at 29).
    Dmrkynetec is a market research company. Originally, it focused on
providing market and tracking data to agribusiness but has expanded its
services to a wide range of industry sectors. In the agriculture area,
dmrkynetec gathers information by survey research on, among other
things, crop acres grown, pesticide active ingredients used, total
acres treated with pesticides, pesticide application rates and timing,
number of pesticide applications, and pesticide prices. For over 30
years, EPA has purchased dmrkynetec's proprietary database, which
provides pesticide usage information for over 50 crops. As part of
EPA's contract with dmrkynetec, EPA requires both a quality management
plan and a quality assurance project plan to insure that dmrkynetec's
survey practices and data compilation are well-designed and reliably
executed. Data from dmrkynetec is relied upon not only by EPA but by
other Federal agencies and private industry. (Ref.63).
    For one commodity, poultry, for which sufficient NASS and
dmrkynetec data were not available, EPA followed a different approach
in estimating percent crop treated. EPA interviewed agricultural
extension agents and professors in agricultural colleges in major
poultry-producing states and reviewed crop profiles compiled by USDA
and other literature from the extension services to obtain rough
estimates of usage. Because this information was not based on
statistically-designed surveys, EPA used it in a very conservative
manner to estimate worst case percent crop treated estimates.
Information gathered on broilers indicated that, DDVP was rarely, if
ever used in broiler production in most of the major producing states.
The one exception is Georgia, the largest broiler producing state,
where approximately 1/3 of the broiler flock is treated with a product
containing DDVP. As to layers (egg producers), DDVP is also not used in
significant amounts in most of the major producing states. However, an
expert in California (fourth in egg production among states) indicated
that a product containing DDVP was used on approximately 75 percent of
the state's layers. As a very conservative estimate, EPA assumed that
75 percent of the broilers and layers nationwide are treated with DDVP.
(Ref. 64).
    Estimates of the percent of crops that receive incidental treatment
with naled or DDVP as a result of these pesticides' usage as a wide
area treatment for the control of mosquitoes was based on a combination
of data from NASS and Kline and Company, Inc., a private market
research firm. Data from NASS' Census of Agriculture was used to
determine the total farm acreage in the United States. Data from Kline
provided information on the poundage of naled and dichlorvos used for
mosquito treatment. This information was combined in a very
conservative fashion with the data on total crop acreage in the United
States. EPA calculated what percentage of the total crop acreage could
have been treated with the naled and DDVP used for mosquito control and
assumed that every crop in the United States was treated to that extent
(3 percent). Although some treatment of agricultural crops will occur
from the mosquito usage, a significant part, if not most, of the
treatment area will be in wetlands, forest, urban and suburban land,
and other non-crop areas. Even where agriculture land is treated, such
treatment may occur when no crop is present or, even if a crop is
present, at such a time that all residues would be expected to degrade
prior to harvest. Estimates of percent crop treated for turf uses was
also based on data from Kline. This information was not used to
quantitatively estimate exposure but simply to qualitatively
characterize the conservativeness of the drinking water concentration
estimates from turf usage produced by EPA's drinking water model.
    NASS's Census of Agriculture is as the name would suggest a
complete count of United States farms and ranches. Additionally, the
Census collects information on land use and ownership, agricultural
practices, and farm income and costs. The Census is conducted every 5
years by law and involves individual contact with all farmers and
ranchers in the United States. (See http://www.agcensus.usda.gov ).

    Kline, like dmrkynetec, conducts market research through surveys on
a wide range of products. EPA has been purchasing data on non-
agricultural pesticide usage from Kline for over 20 years. As with the
dmrkynetec contract, EPA has required both a quality management plan
and a quality assurance project plan to insure that Kline's survey
practices and data compilation are well-designed and reliably executed.
Data from Kline is relied upon not only by EPA but by other federal
agencies and private industry. (Ref. 63).

    EPA concludes these data sources provided reliable data for the
percent crop treated estimates that were used by EPA.
    ii. Significant subpopulation group. EPA considered DDVP exposure
to the general population as well as 32 subpopulation groups based on
regional location, ethnicity, and age. Reliance on the estimates of
percent crop treated discussed above will not underestimate exposure
for any of these population subgroups.
    iii. Data on pesticide use and consumption. EPA takes information
on regional consumption patterns into account in estimating exposure to
significant subpopulation groups. EPA's information on percent crop
treated is primarily national in scope and does not indicate that
regional groups have greater exposures to DDVP than estimated by EPA.
    iv. Periodic evaluation. The statute provides that EPA shall
periodically reevaluate the estimate of anticipated dietary exposure.
This is a prospective requirement. Although it may do so sooner, EPA
expects that the exposure estimates will be reevaluated periodically
through the registration review process. (21 U.S.C. 346a(b)(2)(F); Ref.
65).
    To evaluate the sensitivity of dietary risk assessment to EPA's
percent crop treated findings, EPA conducted an alternate dietary
assessment assuming 100 percent crop treated for all commodities. (Ref.
56). As Table 2 shows, even using this very conservative assumption,
dietary exposure is well below the RfD/PAD for DDVP.

                     Table 2.--Dietary (Food and Water) Exposure and Risk for DDVP Incorporating 100 Percent CT for All Commodities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                               Acute Dietary(99.9 Percentile)                            Chronic Dietary
                                                     ---------------------------------------------------------------------------------------------------
                 Population Subgroup                  Dietary Exposure (mg/kg/                          Dietary Exposure (mg/kg/
                                                                day)                    % aPAD                    day)                    % cPAD
--------------------------------------------------------------------------------------------------------------------------------------------------------
General U.S. Population                                              0.002274                       28                 0.000112                       22
--------------------------------------------------------------------------------------------------------------------------------------------------------
All Infants (< 1 year old)                                            0.004152                       52                 0.000154                       31
--------------------------------------------------------------------------------------------------------------------------------------------------------
Children 1-2 years old                                               0.004663                       58                 0.000252                       50
--------------------------------------------------------------------------------------------------------------------------------------------------------
Children 3-5 years old                                               0.003533                       44                 0.000214  .......................
--------------------------------------------------------------------------------------------------------------------------------------------------------
Children 6-12 years old                                              0.002677                       33                 0.000138                       28
--------------------------------------------------------------------------------------------------------------------------------------------------------
Youth 13-19 years old                                                0.001660                       21                 0.000092                       18
--------------------------------------------------------------------------------------------------------------------------------------------------------
Adults 20-49 years old                                               0.001850                       23                 0.000102                       20
--------------------------------------------------------------------------------------------------------------------------------------------------------
Adults 50+ years old                                                 0.001437                       18                 0.000088                       18
--------------------------------------------------------------------------------------------------------------------------------------------------------
Females 13-49 years old                                              0.001603                       20                 0.000097                       19
--------------------------------------------------------------------------------------------------------------------------------------------------------

    4. Anticipated residues-- a. NRDC's claims. NRDC asserts that
because EPA relied upon anticipated residue data, EPA must issue a data
call-in to demonstrate that actual residues are not higher than the
anticipated residues relied upon by the Agency. (21 U.S.C.
346a(b)(2)(E)(ii)).
    b. EPA's response. This is a prospective requirement. To the extent
that NRDC is claiming that EPA must revoke all DDVP tolerances because
the FFDCA provides that EPA must require the registrant to submit data
in the next 5 years pursuant to section 408(f), that claim is rejected.
    5. Trichlorfon and naled--a. NRDC's claims. Based solely upon EPA's
statement in the prelimanry risk assessment that ``[n]on-detectable
Dichlorvos residues in livestock commodities are expected as a result
of Trichlorfon use[,]'' NRDC speculates that the method for detecting
DDVP in beef may not be sensitive enough to detect toxicologically
significant residues. (Ref. 1 at 40). Based on this speculation, NRDC
claims that the DDVP tolerances do not comply with the requirement in
section 408(b)(3) that ``a tolerance ... shall not be established at
... a level lower than the limit of detection of the method for
detecting and measuring the pesticide chemical residue ... .'' (21
U.S.C. 346a(b)(3)(B)). Further, NRDC claims that EPA has not explained
its conclusion that residues from trichlorfon use are estimated not to
increase residues from the use of DDVP. (Ref. 1 at 51). In addition,
NRDC contends that the Agency's analysis of DDVP residues from the use
of naled (which also degrades into DDVP) for mosquito control is
inadequate.
    b. EPA's response-- i. Trichlorfon. Trichlorfon degrades in plants
and livestock and one of the products (metabolites) that forms is
dichlorvos. Trichlorfon livestock feeding studies did not detect
residues of dichlorvos using a level of detection (``LOD'') of 0.05
ppm. The trichlorfon RED concluded that dichlorvos was not a
significant residue in the cattle based on the feeding study and a
metabolism study. The metabolism study found DDVP in subcutaneous fat
at 4 percent of the total radioactive residue (TRR), and less than 1
percent of the TRR in loin muscle (0.006 ppm). (Ref. 66). Subcutaneous
fat is not used for human consumption, and often has residues higher
than that in fat more distal from the site of application. Thus, it is
highly unlikely that livestock will contain residues of dichlorvos from
the use of trichlorfon. In any event, the residue monitoring data on
DDVP includes DDVP as a degradate of trichlorfon and thus any DDVP in
beef from use of trichlorfon would be captured by the monitoring data.
    The Agency has substantial data showing that residues of dichlorvos
as a result of trichlorfon use will be non-detectable in beef. USDA-
FSIS has sampled for trichlorfon and dichlorvos in the past. Although
there is no U.S. registration for trichlorfon on cattle, there are
tolerances so that foreign cattle can be treated and imported to the
United States. From 1993 through 1997, FSIS monitored over 12,000
samples of beef. (Ref. 67). No residues of dichlorvos

or trichlorfon were detected at a LOD of 0.2 ppm. However, detectable
residues of other organophosphates were found.
    In addition, monitoring data from PDP were available for milk at
the time the last anticipated residues were determined for the 2000
IRED, and were used in the dietary exposure assessment for the IRED.
One detectable residue was reported at 0.003 ppm out of 1,881 samples,
with an LOD of 0.001 - 0.002 ppm (avg. 0.0014 ppm). (Ref. 62 at 12).
Since that time, PDP collected over 300 samples of beef fat, liver, and
muscle from 2001 to 2002 and found no detectable dichlorvos at a LOD of
1.0 ppb; over 300 samples of pork in 2005 and found no detectable
dichlorvos residues at an LOD of 0.9 ppb in fat; and LOD of 0.45 ppb in
pork muscle; and over 600 samples of poultry commodities in 2000-2001
with no detectable residues of dichlorvos at an LOD of 6.3 ppb. PDP
also analyzed over 100 samples of heavy cream, and found no detectable
residues of dichlorvos at a LOD of 1-2 ppb. Finally, no detects of DDVP
were found 1,485 samples of milk analyzed in 2004-2005, at an LOD of
0.06 ppb. (Refs. 56 at 13; and 68).
    NRDC is mistaken to claim that the detection method for DDVP in
meat is not adequately sensitive. Generally, the Agency accounts for
non-detectable residues by using [frac12] the LOD or LOQ in its
calculations. (Ref. 69). If this calculation shows a potential risk
problem, then the limits of detection must be lowered. In the case of
dichlorvos, no risks of concern were identified for livestock
commodities when they were assessed at [frac12] the LOD. In fact, total
dietary risk from DDVP in food is just a small fraction of the RfD.
Thus, the LODs are low enough to be below the level of risk concern and
to ensure detection of toxicologically significant metabolites.
    ii. Naled. DDVP exposure from use of naled to control mosquitoes
through wide area treatment is likely to be very low to non-existent
for two reasons: (1) The treatment rate is very low--0.25 lb ai naled/
Acre, compared to the usual application rate for field crops of 1.8 lb
ai naled/Acre; (2) residues from treatment degrade rapidly; and (3) the
usage rate indicates few crops will be impacted by the mosquito use.
Residue data from field trials showed most samples to be 0.03 ppm or
less. One DDVP residue from the wide area treatment with naled was as
high as 0.27 ppm, with the duplicate of this sample having a residue of
0.08 ppm (average residue 0.18 ppm DDVP). (Ref. 70). Additional data
show that residues of DDVP are formed 1-3 days after field treatment
with naled, and decline to non-detectable within 7 days of treatment
with naled. (Ref. 71). Further, PDP data showed no detectable levels of
DDVP in crops not registered to be treated with naled out of roughly
10,000 samples. (Ref. 56 at 19-20).
    Despite these data suggesting there will be little to no exposure
in the diet from use of naled to control mosquitoes, EPA took a very
conservative approach to estimating exposure from the naled mosquito
use in its revised risk assessment. (Ref. 56). First, EPA examined
usage data to determine a rough estimate of the acreage treated with
naled for mosquito control. (Ref. 72). EPA assumed that all acres
treated were cropped farmland and not wetlands, woodlands, urban or
suburban areas, or other non-cropped areas. This acreage was then
expressed as a percentage of the overall farm acreage in the United
States. That percentage (3 percent) was the value used in estimating
the percent crop treated for all crops grown in the United States. If
DDVP or naled is not registered for use on a crop, EPA assumed that
three percent of that crop was treated. If DDVP or naled are registered
on a crop and EPA has data on the percent of that crop treated as an
agricultural use with DDVP or naled, EPA summed the percentages from
the agricultural use and the mosquito use in estimating percent crop
treated. Finally, if DDVP or naled are registered on a crop and EPA
does not have data on the percent of that crop treated as an
agricultural use with DDVP or naled, EPA assumed 100 percent of the
crop was treated with DDVP or naled. In the latter circumstance, EPA
considered but rejected somehow incorporating the mosquito use as an
overlapping use because, for among other reasons, exposure from crops
was based not on data from field trials but from monitoring data.
    6. Translation of reside levels--a. NRDC's claims. NRDC contends
that EPA cannot make the safety finding for DDVP because EPA has
translated data from grain dust to soybean aspirated grain fractions
and data from cattle to swine based on speculation and not validated
data. Indeed, NRDC argues that every translation of data from one plant
or species to another is a major data gap that cannot be addressed
through worst case or default assumptions because plant or animal
metabolism can produce metabolites that are more toxic than the parent
compound.
    b. EPA's response. EPA's translation of other residue data to
soybean aspirated grain fractions is reasonable. EPA translated
magnitude of the residue data from wheat and corn aspirated grain
fractions to soybean aspirated grain fraction. Another name for
``aspirated grain fractions'' is ``grain dust.'' This is the dust that
is removed from the grain by the rubbing of the grains together during
storage. Residues in grain dust are generally surface residues and thus
grain crops that have otherwise similar residues tend to have similar
residue levels in grain dust. This is especially the case for DDVP
given that it is applied in equal amounts to all grains post-harvest.
Post-harvest application generally results in surface residues, and
there would be no reason to expect different levels of residues across
grains. For similar reasons, metabolism of the pesticide in the crop,
which can play a role in residue levels, is unlikely to be a factor
with DDVP grain dust residues because metabolism occurs primarily when
a plant incorporates a pesticide through uptake and not when the
pesticide is applied to the crop surface post-harvest. Thus, EPA's
analysis is not based upon mere speculation, but rather a reasoned
analysis of the similarity between commodities and how DDVP is used.
    EPA's treatment of potential residue levels in swine is also
reasonable. EPA requires radio-labeled metabolism studies in a few
plant and animal commodities to identify all potential metabolites.
(Ref. 73). Then magnitude of the residue studies are generally required
for each treated plant and animal commodity for the purpose of
selecting tolerance values and, in the absence of monitoring data,
assessing risk.
    EPA has all required animal metabolism studies for DDVP. EPA has
required an additional study on the magnitude of DDVP residues in
swine. These data are needed to verify that a proper tolerance value
has been identified for pork commodities. In the absence of those data,
EPA has relied on data on cattle and poultry products because it is
likely that the residues will be similar to those in cattle and poultry
commodities. These additional magnitude of the residue data are not
needed for risk assessment because EPA has monitoring data on swine
commodities. These data show no detectable residues.
    7. Food monitoring data--a. NRDC's claims. NRDC asserts that the
FDA and USDA monitoring programs are inadequate because the number of
samples examined in these programs is too small to be representative of
the total quantity of food potentially having DDVP residues. (Ref. 1 at
49, 61-62). In addition, NRDC claims that the monitoring data are old
and, therefore,

do not represent current use patterns. NRDC also asserts that the
consumption data are insufficient because they have a limited number of
individuals in the age group of infants less than one year old. NRDC
further notes that samples collected from the FDA Total Diet Study were
collected in supermarkets in only four cities per year and residues in
other locations may be different and very little monitoring data are
available for fumigated commodities, requiring extensive translation
from one fumigated commodity to another. Moreover, NRDC raises the
concern that some of the FDA data were generated with an analytical
methodology that is not capable of detecting ``early eluters'' such as
DDVP and EPA has not taken this fact into account. Finally, NRDC
contends that residues potentially present at roadside produce stands
or farmer's markets are not represented and, additionally, that EPA
failed to consider such consumers major identifiable subgroup of
consumers. NRDC therefore concludes that EPA does not have reliable
food monitoring data and argues that EPA should use the default
assumption of 100 percent crop treated for all foods which may be
treated with DDVP as well as the default assumption of tolerance level
DDVP residues in all treated commodities.
    In a related comment on the IRED, NRDC takes issue with EPA's
decision not to sum potential residues resulting from multiple
treatments of a food with DDVP at different stages of the food
production process. (Ref. 13 at 8). NRDC claims EPA's conclusion that
sufficient time would pass between such treatments that only the last
treatment needs to be considered in estimating exposure is arbitrary
and capricious.
    b. EPA's response. In general, EPA disagrees that the monitoring
data are unreliable. To the contrary, EPA believes that the monitoring
data provide for an appropriately conservative risk assessment.
    i. Adequacy of data - Age and number of samples and sample
location. Contrary to NRDC's characterization, FDA and USDA each
analyze thousands of samples per year. FDA analyzed several hundred
samples per year for DDVP, but now analyzes less than 100. USDA
analyzes most of their samples for DDVP, generally 350 to 700 samples
per commodity per year, although sometimes only about 175 samples per
commodity per year. FDA targets their monitoring toward commodities
which have historically had residue problems. USDA-PDP uses a more
random sampling plan, which is statistically designed to be
representative of the U. S. food supply.
    In response to NRDC's concerns regarding the age of the monitoring
samples, EPA has updated its dietary risk assessment based almost
exclusively on USDA PDP data from the years 2000 to 2005. In the
updated assessment, FDA monitoring data was used for only one
commodity, berries (not including strawberries). The updated assessment
confirms what the earlier assessment found: DDVP residues are rarely
found in food commodities. Not including strawberries, PDP data showed
only 20 samples with detectable residues of DDVP out of more than
43,000 samples from 34 commodities which could potentially bear DDVP
residues. Even focusing on foods covered by registered agricultural
uses for DDVP or naled, there were only 20 samples with DDVP residues
out of approximately 33,000 samples (not including strawberries). In
the PDP data, strawberries were the only commodity with more than a
marginal number of detections - with 104 samples showing DDVP out of
1,986 samples. (Ref. 56 at 19-20).
    ii. Infant consumption. NRDC objects to EPA's reliance on an
alleged lack of infant consumption data. In response, EPA notes that
there is no more comprehensive a consumption survey in the United
States than the CSFII surveys. Moreover, the revised dietary assessment
relies upon more recent and updated CSFII data. Specifically, the FQPA
required additional sampling of infant and children for information on
their consumption has been completed. The results of the additional
sampling were incorporated into DEEM and DEEM-FCID. These surveys are
available to the public. (Ref. 6).
    iii. Fumigant monitoring data. EPA believes it has adequate data on
the fumigant use of DDVP. EPA has data from residue studies conducted
in warehouses with packaged and bagged commodities for the following
foods: flour, cocoa beans, coffee, dry beans, walnuts, and soybeans.
(Ref. 74). These studies were conducted by fumigating pallets
containing these commodities at a maximum rate and then sampling both
the outside layer and interior of the foods on the pallet. These data
were translated to other packaged and bagged commodities based on
starch and moisture content. Although translating these data to other
commodities creates some uncertainty as to the residue estimate, this
uncertainty is more than offset by other factors. First, the studies
used maximum treatment rates and sampled the commodities 6 hours after
treatment. Not only does this approach overstate residues that would
occur from lower treatment rates but it does not take into account the
rapid disappearance of DDVP that occurs due to its volatile nature.
Second, EPA assumed 100 percent of bagged and packaged commodities were
treated.
    iv. Early eluter. Because DDVP is an early eluter (i.e., DDVP will
avoid detection unless samples are analyzed under low temperature
chromatographic conditions), fewer samples are analyzed by FDA for DDVP
than are typically analyzed by the Luke multiresidue method. In its
prior dietary DDVP assessment EPA relied heavily on FDA monitoring but
only used monitoring that used early eluter conditions which are known
to detect DDVP. This issue has limited relevance given EPA's revised
dietary risk assessment which relies almost entirely on PDP monitoring
data which uses analytical methods which are known to detect DDVP.
    v. Farmers' markets and roadside produce stands. In an order
responding to NRDC objections to tolerances for different pesticides,
EPA has addressed NRDC's claims regarding pesticide exposure to persons
who purchase food at roadside stands or farmers' markets. (70 FR
46733). As EPA explained there, whether EPA relies on data from crop
field trials or monitoring data in estimating pesticide exposure, given
the sampling methods in field trials and food monitoring, residue
levels identified from these sources are unlikely to understate residue
levels at farm stands.
    EPA also rejects NRDC's challenge to EPA's decision not to sum
residues from treatments of a commodity at different stages of the
production process. Multiple treatments are a possibility for
commodities such as grains which may be treated as a bulk commodity and
later as a bagged and packaged commodity. EPA has estimated DDVP
exposure based on the treatment of bagged and packaged commodities.
EPA's decision was based on a number of inter-related considerations.
First, there are data showing that DDVP is a volatile compound that
rapidly degrades. Second, general monitoring data consistently show
very low to non-existent residues in food with the exception of one
commodity (strawberries) that are marketed very promptly. Third, EPA
has assumed that 100 percent of all bagged and packaged foods are
treated with DDVP and EPA's estimate of residue values in these
commodities is based on a conservative value from sampling of bagged
and packaged commodities 6 hours after treatment. Finally, the latest
data from FDA's Total Diet Study, a study measuring pesticide residues
and other

contaminants in food as consumed, has shown zero detections of DDVP in
the time period from the survey conducted in 1991 up until the latest
survey in 2003. (Ref. 75). The Total Diet Study examines 280 foods,
including many bagged and packaged foods, that are collected from
different regions in the United States. DDVP is one of many pesticides
analyzed for in the study.
    8. Cooking factors--a. NRDC's claims. NRDC takes issue with the
Agency's practice of using cooking factors to reduce estimates of
residues for particular commodities as well as the Agency's practice of
translating these factors to other commodities based upon similarity of
cooking time and temperature. In particular, NRDC asserts that in the
absence of empirical data demonstrating that each commodity will be
affected identically by cooking, EPA cannot use cooking factors in its
assessment of DDVP residues. In addition, NRDC contends that ``EPA
apparently failed to take into account vastly different cooking
practices for different commodities, including consumption of some
commodities raw.'' (Ref. 1 at 50). As such, NRDC asserts that EPA
should not assume cooking will result in any reduction in observed
residue levels.
    b. EPA's response. EPA's use of cooking factors is reasonable.
Amvac submitted a cooking study which examined residue decline due to
cooking in the following commodities: cocoa beans, dry pinto beans,
tomato juice, coffee beans, hamburger meat, eggs, and raw whole milk.
(Ref. 76 at 34-37). The study showed that DDVP residue reduction was
time and temperature dependent with dramatic reductions occurring when
items were cooked at high temperatures for more than a few minutes. For
example, eggs cooked for 3 minutes at greater than 100 degrees C
resulted in a residue decline of 38 percent, hamburger cooked at a
similar temperature for six minutes showed a 70 percent decline in DDVP
residues, and cocoa beans cooked for 10 minutes at 135 degrees C
resulted in a residue decline of 99.7 percent. Residue decline factors
(i.e., cooking factors) were translated from tested items only to
similar commodities which are cooked in a similar manner. For example,
data on dry pinto beans was translated to other dried beans and peas
and to boiled peanuts; data on hamburger was translated to other meats;
and data on tomato juice was translated to celery juice. EPA believes
these cooking times and temperatures are reasonable, conservative
estimates. Although certain of these commodities may occasionally be
cooked for shorter times or at lower temperatures, EPA expects those
instances to be infrequent. Moreover, given the conservative
assumptions on cooking times any variations are very unlikely to be
``vastly different.'' As to consumption of some of these foods
uncooked, NRDC's concern about use of cooking factors is unwarranted
because EPA's consumption database differentiates between amounts of
foods consumed cooked and uncooked and only applies cooking factors as
to the former. Further, EPA concludes that its choice of translation
commodities is also reasonable given the similarity between the cooking
methods for the tested commodity and the translated commodity and the
strong relationship shown in the data between cooking time and
temperature and residue decline.
    In any event, EPA disagrees that it cannot rely on cooking data
unless it has data on all varieties of cooking practices within the
United States and its cooking data take that full range of cooking
practices into account. Implicit in this argument, is the view that EPA
must adopt a cooking factor that reflects the shortest possible cooking
time, no matter how infrequently such practice is used. Section 408,
however, does not take such an extreme approach to assessing exposure.
Rather, section 408, directs EPA to focus on major, identifiable
subgroups of consumers not worst case scenarios or maximally-exposed
individuals. EPA believes that use of reasonable, conservative exposure
assumptions are consistent with this statutory mandate.
    Additionally, it is important for EPA to adapt the assumptions
underlying any exposure assessment to the complexity of the assessment.
For simple assessments - a single pesticide to which a human is exposed
by a single route (e.g., oral) from a single source (e.g., apples) - a
more conservative approach to assumptions such as cooking factors may
be necessary to assure high end exposures are captured because high end
exposure may be defined by consumption of a single food. This is not
the case with complex assessments like for DDVP that involve multiple
pesticides, multiple routes of exposure, and multiple sources of
exposure within routes. In evaluating exposure to DDVP in food alone,
EPA's exposure assessment takes into account residues in hundreds of
food commodities. If EPA were to assume worst case residue values for
each of these commodities (worst case pesticide usage, worst case
potential residues on the raw crop, worst case processing values, worst
case cooking factors, etc.) and then combine that information with the
assumption of worst case consumption for each commodity, the exposure
assessment would not reflect reality. Just as no one person, and
certainly no major subgroup of consumers, is a worst-case consumer of
every commodity, no one person, or major subgroup of consumers, is
likely to be consumers of every commodity at its worst-case residue
amount. To make such assumptions when multiple commodities are involved
compounds multiple conservatisms and would produce an assessment that
overstates exposure probably by several orders of magnitude. For this
reason, EPA's exposure assessment guidance advises using a mixture of
high end and central tendency assumptions to produce a high end
exposure assessment. (Ref. 77). Accordingly, EPA's use of conservative,
but not worst case, cooking factors in the DDVP exposure assessment is
reasonable.
    9. Missing data--a. NRDC's claims. NRDC claims that various data
are missing: storage stability data for meat, milk, poultry, and egg
residue studies; crop field trials on tomatoes; and tomato processing
studies. (Ref. 1 at 43).
    b. EPA's response. The tomato use has been canceled so no data are
needed on tomatoes. Although the IRED stated that data are needed on
storage stability, that statement was in error. (Ref. 11 at 189). In
fact, storage stability requirements have been met. The IRED noted that
storage stability data were needed in connection with some of the
residue data used in the 1987 Registration Standard for DDVP.
Subsequent to 1987, the registrant submitted new residue data on the
commodities in question and that residue data met the requirements for
storage stability data. (See, e.g., Ref. 74 at 10).
    10. Uncertainties in estimating residues in foods--a. NRDC's
claims. NRDC argues that EPA has identified uncertainties in its
dietary assessment but fails to take these uncertainties into account.
Uncertainties cited by NRDC include lack of data on residue values in
foods sold at farm stands, use of cooking data, the limited sampling
sites in the FDA Total Diet Study, the reliance on residue trial
instead of monitoring data for warehouse uses of DDVP, the extensive
translation between commodities in estimating residues from DDVP
warehouse uses, and the reliance on field trial data for some
commodities. (Refs. 1 at 52; and 13 at 8-9).
    b. EPA's response. EPA does take into account any uncertainties in
its food exposure analysis in determining whether it has estimated risk
in a manner that is protective of the general

population and all major identifiable consumer subgroups. For DDVP
there were a number of factors that might have led to an
underestimation of exposure levels but these factors are dwarfed by
considerations indicating that EPA has overestimated exposure. Each of
the factors highlighted by NRDC as well as others are discussed below:
    i. Food from farm stands. As discussed above, EPA does not believe
that farm stands are likely to sell food containing a significantly
different residue profile than found in PDP monitoring data. This
factor introduces little to no uncertainty concerning the possibility
of underestimation of residues into EPA's analysis.
    ii. Use of cooking factors. As discussed above, EPA used cooking
factors in a conservative fashion in estimating exposure. For several
reasons, EPA believes its use of cooking factors did not fully take
into account the degree of reduction of DDVP residues that occurs with
cooking. First, cooking factors were only applied to a relatively small
number of commodities that may contain DDVP residues. Cooking of other
commodities containing DDVP residues (e.g., grains and vegetables) will
undoubtedly decrease residues in those commodities substantially.
Second, the manner in which EPA translated the residue reduction data
will tend to exaggerate residue levels in many commodities. For
example, data on the residue reduction that occurs from cooking
hamburger for six minutes was translated to all cooked meats. Given
that most meats are cooked substantially longer than six minutes, this
use of the cooking data will understate exposure. This factor will
overestimate exposure to DDVP.
    iii. FDA Total Diet Study. In the updated risk assessment the FDA
Total Diet Study data was not relied upon to quantitatively estimate
residues in food. This factor has no bearing on the DDVP exposure
assessment.
    iv. Residues from warehouse use. EPA did do extensive translation
of data between commodities for the warehouse use. There was a
reasonable basis for these translations; nonetheless, some uncertainty
attends any such translation. However, EPA's estimation of exposure
from the warehouse use will clearly overstate DDVP exposure for two
reasons. First, EPA is not relying on monitoring data from warehouses
but data from residue trials in the warehouse. Invariably, residue
trials result in findings of higher residue values than monitoring data
because residue trials involve prompt sampling after treatment whereas
monitoring can occur days or weeks later. Thus, residue trials do not
take into account the normal degradation that occurs over time. With
DDVP, this decline in residues is likely to be exaggerated given the
data showing both DDVP's volatility and rapid degradation. Monitoring
data that is available on other commodities confirms the rapid decline
of residues. Second, EPA assumed that all food in warehouses is treated
with DDVP. This is a very conservative estimate. Accordingly, this
factor will tend to significantly overstate exposure to DDVP.
    v. Reliance on field trial data. For many commodities that may be
legally treated with naled, EPA relied upon field trial data or assumed
tolerance level residues rather than monitoring data. For the reasons
noted immediately above, this assumption will significantly overstate
residues on those commodities.
    vi. Percent crop treated. For many commodities that may be legally
treated with DDVP or naled (other than in warehouses), EPA assumed that
100 percent of the commodity is treated. Again, this is a very
conservative estimate and will significantly overstate DDVP exposure
from those commodities.
    vii. Default processing factors. For several processed commodities,
EPA relied on default processing factors in estimating DDVP residues in
the processed food. EPA's default processing factors project worst case
levels of pesticides in processed food. (70 FR at 46733-46734). Thus,
use of default processing factors instead of specific processing data
for DDVP will overestimate residues in food.
    Considering all of this information, EPA's conclusion is that its
assessment of exposure to DDVP from food will not under-estimate but
rather over-estimate, and in all likelihood substantially over-
estimate, DDVP exposure.
    In any event, EPA's latest dietary assessment shows that, by a
large margin, the biggest driver in the DDVP dietary risk assessment
are DDVP residues in water not food. (Ref. 56). To the extent food is a
driver, that food is food with residue estimates from its treatment as
a bagged and packaged food. As explained above, estimates of residues
in bagged and packaged foods are likely to be a significant
overestimate due to the assumption of 100 percent treatment and use of
magnitude of the residue study rather than actual monitoring data.

C. Residential Exposure

    1. Aggregating Exposures. The safety standard in FFDCA section 408
for tolerances requires that there be a reasonable certainty of no harm
from ``aggregate exposure to the pesticide chemical residue, including
all dietary exposures and all other exposure for which there is
reliable information.'' (21 U.S.C. 346a(b)(2)(A)(ii)). Further, EPA in
evaluating the safety of tolerances is directed to ``consider ...
available information concerning the aggregate exposures of consumers
... to the pesticide chemical residue ... including dietary exposure
under [all] tolerance[s] ... in effect for the pesticide chemical
residue and exposure from other non-occupational sources.'' (21 U.S.C.
346a(b)(2)(D)(vi)).
    Unit VII.B. discusses EPA's assessment of aggregate dietary
exposure to DDVP from residues in food and water. That assessment
showed that these aggregate exposure levels were well below the acute
and chronic RfD/PADs. Although refined, these exposure estimates still
are likely to overstate exposure and risk. This is particularly
apparent when it is considered that the commodities that drove the risk
numbers were those commodities (drinking water and bagged and packaged
goods) for which the most conservative assumptions were made. (Ref.
56).
    Pesticide residues to which humans are exposed from residential
uses of pesticides must be considered as part of section 408's
aggregate exposure calculus. The concern, of course, is that pesticide
tolerances should not be established or left in effect if dietary
exposures, when combined with other sources of exposure, exceed safe
levels. As the analysis in Unit VII.D.2. shows, however, dietary
exposures are insignificant compared to residential exposures and thus
the safety determination turns on an evaluation of the exposure and
risk from the residential uses of DDVP.
    2. Revised residential exposure - pest strips. In light of the
numerous issues raised by NRDC concerning EPA's assessment of the risk
posed by DDVP pest strips, EPA has substantially revised its assessment
of exposure and risk from this use. EPA first discusses that revised
assessment before turning to NRDC's specific claims. The changes in the
assessment come in three areas: (1) analysis of exposure data and
exposure assumptions used; (2) the types of durational scenarios
assessed; and (3) the endpoint used for chronic exposure. (Ref. 78).
    Currently, there are four sizes of DDVP pest strips that are
registered. The largest strip (65-80 grams) may only be used in
unoccupied areas in and around the house (garage, attic, crawl space,

shed) where humans are present for no greater than four hours per day.
There are three smaller strips (16, 10.5, and 5.25 grams) that may be
used in the home in closets, wardrobes, or cupboards. The IRED
recommended, and Amvac has accepted, label restrictions for these
smaller strips which bars use in closets of rooms where infants or
children or sick or elderly people will be confined for an extended
period or generally in closets of rooms for which any person will be
present for extended periods. (Refs. 11 at 161; and 79 ). EPA's risk
assessments examined each of these pest strips.
    a. Exposure data and assumptions. In assessing exposure from pest
strips, EPA has relied on a study (Collins and DeVries) measuring air
concentrations in 15 houses treated with multiple large DDVP pest
strips hung directly in the living areas of the houses. (Id.). In its
prior assessment, EPA averaged air concentrations measured in the study
across houses. To insure its assessment is conservative, EPA, in its
most recent assessment, estimated risk based on the air concentrations
in the individual houses. (Id.). Additionally, for chronic risk
assessment, rather than project exposure from the 91 days of the
Collins and DeVries study over a period of 120 days (the period for
which a pest strip is generally designed to be effective), EPA used the
air concentration measured over the 91 days in the study. This approach
increases exposure estimates as the data show that DDVP air
concentrations are higher in the first weeks. Finally, rather than
calculate MOEs for different time periods in the home for strips used
in occupied portions of the home, EPA calculated MOEs assuming that
people are exposed in their homes 24 hours per day and spend 24 hours
per day in a room with a pest strip. For strips used in unoccupied
portions of the home, EPA assessed the risk based on 4 hours of
exposure per day.
    b. Durational scenarios. Previously, EPA focused only on chronic
exposure to DDVP from pest strips and compared that chronic exposure to
the chronic RfD/PAD. In its revised risk assessment, EPA assessed risks
for acute, short/intermediate-term, and chronic exposures. (Id.). The
acute assessment examined risk based on the air concentrations in the
15 houses in the Collins and DeVries studies for the first 24 hours
after the pest strip is installed. The short/intermediate-term
assessment examined risk based on the air concentrations for the first
two weeks after installation of a pest strip. Appropriate acute and
short/intermediate-term endpoints were used.
    c. Chronic endpoint. EPA's prior risk assessment used the benchmark
dose level of 10 percent (BMDL10) for RBC cholinesterase
from a chronic inhalation study in rats to assess chronic risk from
exposure to pest strips. EPA reexamined this choice in light of its
policy on the use of cholinesterase inhibition in risk assessments.
Consistent with that policy, EPA determined that it would be more
appropriate to use the BMDL20 for RBC cholinesterase from
that study in assessing chronic risk (but not for acute risk). That
decision was based on the consistent and large difference in doses
between indications of RBC cholinesterase inhibition at both the
BMDL10 and the BMDL20 and inhibition of brain
cholinesterase and clinical signs in numerous studies when exposure was
for 90 days or greater. (Id.).
    d. Revised risk assessments. EPA's revised assessment shows that
(1) for the large strips permitted only in unoccupied portions of a
home, the target MOE is exceeded (i.e., there is not a risk of concern)
for all homes for four hours of exposure for acute, short/intermediate-
term, and chronic scenarios (Table 3, Table 5, and Table 7); (2) for
the largest closet strip the target MOE is exceeded for all homes for
24 hours of exposure for the acute scenario (Table 4); (3) for the
largest closet strip the target MOE is exceeded for most homes for 24
hours of exposure for the short/intermediate-term and chronic scenarios
(Table 6 and Table 8); (4) for the smaller closet strip and the
cupboard strip the target MOE is all but met or exceeded for all homes
for acute, short/intermediate-term, and chronic scenarios (Table 9 and
Table 10); and (5) dietary exposure is insignificant compared to pest
strip exposure for all scenarios. (Id.). The MOEs for all of these
scenarios for the large pest strip and the large closet strip are
presented in the tables below.
    The acute risk assessments for large pest strips (Table 3) and
closet, wardrobe, and cupboard pest strips (Table 4) use a hazard value
of 0.800 mg/kg which is the BMDL10 for RBC cholinesterase
from a rat study. Exposure is based on Day 1 air concentrations in the
Collins and DeVries study. Four hours of exposure is assumed for the
large strip and 24 hours of exposure is assumed for the closet,
wardrobe, and cupboard strips. The MOE of concern is 30, as opposed to
100, because when exposure is expressed in units of air concentration
such as part per million (``ppm'') or milligrams/meter3
(``mg/m3'') (as it is in the Collins and Devries data), then
the pharmacokinetic component of the interspecies factor is decreased
from 10X to 3X to account for the different breathing rates between
species. (Id.).

  Table 3.--Acute Risk from Exposure to Large (65 g) Strips for 4 hours
------------------------------------------------------------------------
                                                    Day 1
          Collins and DeVries Home ID           Concentration     MOE
                                                   (mg/m3)
------------------------------------------------------------------------
6N                                                     0.11           45
------------------------------------------------------------------------
7W                                                     0.11           45
------------------------------------------------------------------------
2C                                                     0.08           61
------------------------------------------------------------------------
14W                                                    0.08           61
------------------------------------------------------------------------
10C                                                    0.07           70
------------------------------------------------------------------------
13W                                                    0.07           70
------------------------------------------------------------------------
5N                                                     0.05           98
------------------------------------------------------------------------
11C                                                    0.05           98
------------------------------------------------------------------------
12N                                                    0.05           98
------------------------------------------------------------------------
3C                                                     0.04          123
------------------------------------------------------------------------
15N                                                    0.04          123
------------------------------------------------------------------------
1W                                                     0.02          245
------------------------------------------------------------------------
4N                                                     0.02          245
------------------------------------------------------------------------
8W                                                     0.02          245
------------------------------------------------------------------------
9C                                                     0.01          490
------------------------------------------------------------------------

 Table 4.-- Acute Risk from Exposure to Large Closet (16 g) Pest Strips
                              for 24 hours
------------------------------------------------------------------------
                                                    Day 1
          Collins and DeVries Home ID           Concentration     MOE
                                                   (mg/m3)
------------------------------------------------------------------------
6N                                                    0.028           30
------------------------------------------------------------------------
7W                                                    0.028           30
------------------------------------------------------------------------
2C                                                    0.020           41
------------------------------------------------------------------------
14W                                                   0.020           41
------------------------------------------------------------------------
10C                                                   0.018           47
------------------------------------------------------------------------
13W                                                   0.018           47
------------------------------------------------------------------------
5N                                                    0.013           66
------------------------------------------------------------------------
11C                                                   0.013           66
------------------------------------------------------------------------
12N                                                   0.013           66
------------------------------------------------------------------------
3C                                                    0.010           82
------------------------------------------------------------------------
15N                                                   0.010           82
------------------------------------------------------------------------
1W                                                    0.005          165
------------------------------------------------------------------------

4N                                                    0.005          165
------------------------------------------------------------------------
8W                                                    0.005          165
------------------------------------------------------------------------
9C                                                    0.003          329
------------------------------------------------------------------------

    The smaller closet strip and cupboard strip will have higher MOEs.
Background dietary DDVP exposure when expressed in mg/m3 is
0.00026 and this value is insignificant compared to the air
concentration levels in higher concentration houses.
    The short/intermediate-term risk assessments for large pest strips
(Table 5) and for closet, wardrobe, and cupboard pest strips (Table 6)
use a hazard value of 0.1 mg/kg/day which is the LOAEL for the human
repeat dose oral study. Exposure is based on the average air
concentration of the first 2 weeks of exposure in the Collins and
DeVries study. Four hours of exposure is assumed for the large strip
and 24 hours of exposure is assumed for the closet, wardrobe, and
cupboard strips. The MOE of concern is 30 based on an intraspecies
safety factor of 10X and an additional safety factor of 3X for reliance
on a LOAEL.

  Table 5.--Short/Intermediate-term Risk from Exposure to Large (65 g)
                         Strips for 4 hours/day
------------------------------------------------------------------------
                                                    2-Week
                                                   Average
          Collins and DeVries Home ID           Concentration     MOE
                                                   (mg/m3)
------------------------------------------------------------------------
7W                                                    0.074           29
------------------------------------------------------------------------
2C                                                    0.073           29
------------------------------------------------------------------------
10C                                                   0.072           29
------------------------------------------------------------------------
6N                                                    0.066           32
------------------------------------------------------------------------
13W                                                   0.065           32
------------------------------------------------------------------------
14W                                                   0.059           36
------------------------------------------------------------------------
12N                                                   0.048           43
------------------------------------------------------------------------
11C                                                   0.038           55
------------------------------------------------------------------------
3C                                                    0.032           65
------------------------------------------------------------------------
5N                                                    0.030           69
------------------------------------------------------------------------
15N                                                   0.028           74
------------------------------------------------------------------------
8W                                                    0.019          109
------------------------------------------------------------------------
1W                                                    0.019          112
------------------------------------------------------------------------
4N                                                    0.017          126
------------------------------------------------------------------------
9C                                                    0.012          177
------------------------------------------------------------------------
------------------------------------------------------------------------

Table 6.--Short/Intermediate-term Risk from Exposure to Large Closet (16
                     g) Pest Strips for 24 hours/day
------------------------------------------------------------------------
                                                    2-Week
                                                   Average
          Collins and DeVries Home ID           Concentration     MOE
                                                   (mg/m3)
------------------------------------------------------------------------
7W                                                    0.018           19
------------------------------------------------------------------------
2C                                                    0.018           19
------------------------------------------------------------------------
10C                                                   0.018           20
------------------------------------------------------------------------
6N                                                    0.016           21
------------------------------------------------------------------------
13W                                                   0.016           22
------------------------------------------------------------------------
14W                                                   0.015           24
------------------------------------------------------------------------
12N                                                   0.012           29
------------------------------------------------------------------------
11C                                                   0.010           37
------------------------------------------------------------------------
3C                                                    0.008           43
------------------------------------------------------------------------
5N                                                    0.008           46
------------------------------------------------------------------------
15N                                                   0.007           50
------------------------------------------------------------------------
8W                                                    0.005           73
------------------------------------------------------------------------
1W                                                    0.005           75
------------------------------------------------------------------------
4N                                                    0.004           84
------------------------------------------------------------------------
9C                                                    0.003          118
------------------------------------------------------------------------

    The smaller closet strip and cupboard strip will have MOEs of 29 or
higher. Background dietary DDVP exposure when expressed in mg/
m3 is 0.00026 and this value is insignificant compared to
the air concentration levels in higher concentration houses.
    For the chronic risk assessments for large pest strips (Table 7)
and closet, wardrobe, and cupboard pest strips (Table 8, Table 9, and
Table 10), EPA calculated MOEs for a range of hazard values: the
BMDL10 and BMDL20 for RBC cholinesterase from a
2-year chronic rat study, BMDL10 for brain cholinesterase
from a 90-day rat study, and the NOAEL for clinical signs from a 7-day
rat study. Exposure is based on the average air concentration for the
91 days of the Collins and DeVries study. Four hours of exposure is
assumed for the large strip and 24 hours of exposure is assumed for the
closet, wardrobe, and cupboard strips. The MOE of concern is 30 for the
same reason as with the acute exposure assessment.

                                       Table 7.--Chronic Risk from Exposure to Large (65 g) Strips for 4 hours/day
--------------------------------------------------------------------------------------------------------------------------------------------------------
                        Study                                            Rat 2-Year Inhalation                     Rate 90 Day oral     Rate 7 Day oral
--------------------------------------------------------------------------------------------------------------------------------------------------------
                      POD Type                                        BMDL10                        BMDL20              BMDL10               LOAEL
--------------------------------------------------------------------------------------------------------------------------------------------------------
                     POD (mg/m3)                             0.078               0.41                0.196                0.4                 7.3
--------------------------------------------------------------------------------------------------------------------------------------------------------
             Home ID                  CD avg / 6              RBC                Brain                RBC                 RBC            Clincal signs
--------------------------------------------------------------------------------------------------------------------------------------------------------
10C                                         0.00607                  13                  67                  32                  66                1200
--------------------------------------------------------------------------------------------------------------------------------------------------------
2C                                          0.00575                  14                  70                  34                  70                1300
--------------------------------------------------------------------------------------------------------------------------------------------------------

13W                                         0.00483                  16                  84                  41                  83                1500
--------------------------------------------------------------------------------------------------------------------------------------------------------
7W                                          0.00337                  23                 120                  58                 119                2200
--------------------------------------------------------------------------------------------------------------------------------------------------------
12N                                         0.00330                  24                 123                  59                 121                2200
--------------------------------------------------------------------------------------------------------------------------------------------------------
14W                                         0.00330                  24                 123                  59                 121                2200
--------------------------------------------------------------------------------------------------------------------------------------------------------
6N                                          0.00212                  37                 191                  93                 189                3400
--------------------------------------------------------------------------------------------------------------------------------------------------------
3C                                          0.00212                  37                 191                  93                 189                3400
--------------------------------------------------------------------------------------------------------------------------------------------------------
11C                                         0.00207                  38                 196                  95                 194                3500
--------------------------------------------------------------------------------------------------------------------------------------------------------
15N                                         0.00192                  41                 211                 102                 208                3800
--------------------------------------------------------------------------------------------------------------------------------------------------------
8W                                          0.00161                  48                 251                 122                 248                4500
--------------------------------------------------------------------------------------------------------------------------------------------------------
1W                                          0.00137                  57                 295                 143                 291                5300
--------------------------------------------------------------------------------------------------------------------------------------------------------
9C                                          0.00127                  61                 318                 154                 314                5700
--------------------------------------------------------------------------------------------------------------------------------------------------------
5N                                          0.00109                  71                 370                 179                 366                6700
--------------------------------------------------------------------------------------------------------------------------------------------------------
4N                                          0.00099                  79                 409                 198                 404                7400
--------------------------------------------------------------------------------------------------------------------------------------------------------

               Table 8.--Chronic Risk from Exposure to Large (16 g) Closet Strips for 24 hours/day
----------------------------------------------------------------------------------------------------------------
                   Study                              Rat 2-Year Inhalation            Rate 90 Day   Rate 7 Day
-------------------------------------------------------------------------------------     oral          oral
                 POD Type                             BMDL10               BMDL20    ---------------------------
-------------------------------------------------------------------------------------    BMDL10*        LOAEL
                POD (mg/m3)                     0.078         0.41          0.196    ---------------------------
-------------------------------------------------------------------------------------      0.4           7.3
                                                                                ---------------------------
           Home ID             CD avg / 4        RBC          Brain          RBC                      Clinical
                                                                                RBC          signs
----------------------------------------------------------------------------------------------------------------
10C                               0.00910             9            45            22            44           780
----------------------------------------------------------------------------------------------------------------
2C                                0.00862             9            47            23            46           830
----------------------------------------------------------------------------------------------------------------
13W                               0.00725            11            56            27            55           980
----------------------------------------------------------------------------------------------------------------
7W                                0.00506            15            80            39            79          1400
----------------------------------------------------------------------------------------------------------------
12N                               0.00495            16            82            40            81          1400
----------------------------------------------------------------------------------------------------------------
14W                               0.00495            16            82            40            81          1400
----------------------------------------------------------------------------------------------------------------
6N                                0.00318            25           127            62           126          2100
----------------------------------------------------------------------------------------------------------------
3C                                0.00318            25           127            62           126          2200
----------------------------------------------------------------------------------------------------------------
11C                               0.00310            25           131            63           129          2300
----------------------------------------------------------------------------------------------------------------
15N                               0.00288            27           141            68           139          2500
----------------------------------------------------------------------------------------------------------------
8W                                0.00242            32           168            81           166          3000
----------------------------------------------------------------------------------------------------------------
1W                                0.00206            38           196            95           194          3400
----------------------------------------------------------------------------------------------------------------
9C                                0.00191            41           212           103           209          3800
----------------------------------------------------------------------------------------------------------------
5N                                0.00164            48           247           119           244          4100
----------------------------------------------------------------------------------------------------------------
4N                                0.00148            53           273           132           270          4700
----------------------------------------------------------------------------------------------------------------

              Table 9.--Chronic Risk from Exposure to Small Closet (10.5 g) Strips for 24 hours/day
----------------------------------------------------------------------------------------------------------------
                                 Study                                            Rat 2-Year Inhalation
----------------------------------------------------------------------------------------------------------------
                               POD Type                                           BMDL10               BMDL20
----------------------------------------------------------------------------------------------------------------
                              POD (mg/m3)                                   0.078         0.41          0.196
----------------------------------------------------------------------------------------------------------------
                         Home ID                           CD avg / 6        RBC          Brain          RBC
----------------------------------------------------------------------------------------------------------------
10C                                                           0.00607            13            67            32
----------------------------------------------------------------------------------------------------------------
2C                                                            0.00575            14            70            34
----------------------------------------------------------------------------------------------------------------
13W                                                           0.00483            16            84            41
----------------------------------------------------------------------------------------------------------------
7W                                                            0.00337            23           120            58
----------------------------------------------------------------------------------------------------------------
12N                                                           0.00330            24           123            59
----------------------------------------------------------------------------------------------------------------
14W                                                           0.00330            24           123            59
----------------------------------------------------------------------------------------------------------------
6N                                                            0.00212            37           191            93
----------------------------------------------------------------------------------------------------------------
3C                                                            0.00212            37           191            93
----------------------------------------------------------------------------------------------------------------
11C                                                           0.00207            38           196            95
----------------------------------------------------------------------------------------------------------------
15N                                                           0.00192            41           211           102
----------------------------------------------------------------------------------------------------------------
8W                                                            0.00161            48           251           122
----------------------------------------------------------------------------------------------------------------
1W                                                            0.00137            57           295           143
----------------------------------------------------------------------------------------------------------------
9C                                                            0.00127            61           318           154
----------------------------------------------------------------------------------------------------------------
5N                                                            0.00109            71           370           179
----------------------------------------------------------------------------------------------------------------
4N                                                            0.00099            79           409           198
----------------------------------------------------------------------------------------------------------------

               Table 10.--Chronic Risk from Exposure to Cupboard (5.25 g) Strips for 24 hours/day
----------------------------------------------------------------------------------------------------------------
                                 Study                                            Rat 2-Year Inhalation
----------------------------------------------------------------------------------------------------------------
                               POD Type                                           BMDL10               BMDL20
----------------------------------------------------------------------------------------------------------------
                              POD (mg/m3)                                   0.078         0.41          0.196
----------------------------------------------------------------------------------------------------------------
                         Home ID                           CD avg / 12       RBC          brain          RBC
----------------------------------------------------------------------------------------------------------------
10C                                                           0.00303            26           134            65
----------------------------------------------------------------------------------------------------------------
2C                                                            0.00287            27           141            68
----------------------------------------------------------------------------------------------------------------
13W                                                           0.00242            32           168            81
----------------------------------------------------------------------------------------------------------------
7W                                                            0.00169            46           240           116
----------------------------------------------------------------------------------------------------------------
12N                                                           0.00165            47           245           119
----------------------------------------------------------------------------------------------------------------
14W                                                           0.00165            47           245           119
----------------------------------------------------------------------------------------------------------------
6N                                                            0.00106            74           382           185
----------------------------------------------------------------------------------------------------------------
3C                                                            0.00106            74           382           185
----------------------------------------------------------------------------------------------------------------
11C                                                           0.00103            75           392           190
----------------------------------------------------------------------------------------------------------------
15N                                                           0.00096            81           422           204
----------------------------------------------------------------------------------------------------------------
8W                                                            0.00081            97           503           243
----------------------------------------------------------------------------------------------------------------
1W                                                            0.00069           113           589           285
----------------------------------------------------------------------------------------------------------------
9C                                                            0.00064           123           636           308
----------------------------------------------------------------------------------------------------------------

5N                                                            0.00055           143           740           358
----------------------------------------------------------------------------------------------------------------
4N                                                            0.00049           158           819           396
----------------------------------------------------------------------------------------------------------------

    Background dietary DDVP exposure when expressed in mg/m3
is 0.00026 and this value is insignificant compared to the air
concentration levels in higher concentration houses.
    Despite the fact that some homes from the Collins and DeVries study
do not have acceptable MOEs for the short/intermediate-term and chronic
scenarios for the large closet strip, EPA concludes that the pest
strips do not pose a risk of concern for the following reasons. First,
use of BMDL20 for RBC cholinesterase is a conservative
endpoint based on the DDVP database. As Table 7 indicates, target MOEs
are well exceeded for all homes for chronic risk if the
BMDL10 for brain cholinesterase or the NOAEL for clinical
signs are used as the Point of Departure. Second, for short/
intermediate-term risk, EPA has used the results of the human oral
study in a conservative fashion. The maximum inhibition of RBC
cholinesterase from the 0.1 mg/kg/day dose used in that study was 16
percent (group mean) after 18 days of exposure. As discussed above,
however, 20 percent inhibition is a more appropriate line of
demarcation for DDVP given, among other things, the wide margin between
RBC cholinesterase inhibition and clinical effects. If that approach is
followed the one dose from that study, then 0.1 mg/kg/day would be a
NOAEL not a LOAEL and the additional 3X safety factor would be
unnecessary. Without that 3X safety factor, the MOE of concern would
drop to 10. The conservativeness of the 3X safety factor is also
supported by the HSRB's conclusion that a dose lower than 0.1 mg/kg/day
would not be expected to show a significant inhibition response.
    Finally, EPA made numerous conservative assumptions regarding
interpretation of the Collins and DeVries data in using it to estimate
exposure, including that: (1) the large strips used in the Collins and
DeVries study emitted the same amount of DDVP as the largest strip
currently registered even though the current large strip (65 - 80
grams) is smaller than the strip used in the Collins and DeVries study
(100 grams); (2) placement of a strip in a closet is the same as
hanging it in the adjacent living area; (3) for closet, wardrobe, and
cupboard strips, exposure is 24 hours per day (despite label
restrictions barring use in rooms where people would be exposed for
extended periods); (4) during the 24 hours per day a person is in a
home that person is continually in a room with a pest strip; and (5)
strips are replaced every 90 days.
    3. Issues raised by NRDC concerning pest strips--a. NRDC's claims.
NRDC argues that EPA's exposure assessment for pest strips ``is based
on unsupported assumptions and inadequate data'' and therefore EPA
cannot conclude that aggregate exposure to DDVP is safe. NRDC's
specific allegations are described below.
    i. Reliance on an inadequate exposure study. NRDC notes that EPA
relied on a single study (Collins and DeVries) monitoring 15 homes in
one geographic area to estimate residential exposure to DDVP from pest
strips. NRDC claims this study is inadequate because (1) the number of
homes monitored is too small to be representative of the housing stock
in the United States; (2) the study was conducted in only one
geographic area and at one time of year and thus would not be
representative of weather conditions (including humidity and
temperature) in other regions of the United States; (3) sampling in the
homes was done in only one location and thus the study ``provides no
information about the movement of residues from room-to-room and []
exposure in other rooms in the homes;'' (4) homes were only treated
with three or four pest strips but homeowners with severe pest problems
may ``place pest strips in every room or most rooms in the house;'' and
(5) the study contained insufficient information to estimate exposure
levels for pest strips of different sizes. (Ref. 1 at 19, 58-59).
    ii. Unsupported assumption that users will not replace pest strips
more frequently than every 120 days. NRDC claims that EPA's assumption
that homeowners will not replace pest strips until the strip has been
in use for at least 120 days is unreasonable because the label does not
prohibit more frequent replacement and EPA has no empirical data to
support this assumption. (Id. at 59). NRDC argues that ``[i]n the
absence of reliable empirical data demonstrating that consumers do not
... replace the strips more often than is assumed by EPA, at a minimum,
the labels of these products should be amended to place restrictions on
use consistent with the assumptions made in the risk assessment.''
(Ref. 13 at 10).
    iii. Only considered average exposure over 120 days. NRDC argues
that EPA erred by averaging exposure levels over a 120-day period.
According to NRDC, EPA should have considered ``the higher, more
dangerous exposures that occur when a strip is first hung ....'' (Ref.
1 at 59). Instead, NRDC asserts, EPA ``should have presented the range
of risks displayed over time.'' (Id.).
    iv. Failure to consider exposure from use in unoccupied spaces.
NRDC claims that EPA has not taken into account that DDVP residues
could migrate from use of the full-size pest strips in attics, crawl
spaces, and garages to the main living areas of a home. (Ref. 13 at
10). NRDC notes that EPA has found that use of chlorpyrifos in crawl
spaces leads to residues in living areas. (Id.). NRDC further contends
that attics can be part of the air exchange for the living areas in a
house.
    v. Estimates of exposure durations in homes are too low. While NRDC
concedes that an estimate of 16 hours/day in a home would be a high end
estimate for most people, NRDC argues that this estimate ignores
``several significant population groups'' such as ``[p]eople who work
or stay at home, retired and elderly people, and pre-school children.''
(Id.). Further, NRDC asserts that EPA's low end estimate of 2 hours/day
in the home is ``absurd on its face.'' (Id.).
    vi. No consideration of incidental oral and dermal exposure. NRDC
claims that

EPA had insufficient data to conclude that incidental oral and dermal
exposure resulting from DDVP residues that settle on home surfaces
would be minimal. (Id. at 19.). According to NRDC, the only information
EPA relied upon was data on residues that settle on foodstuffs and such
data would not be representative of other home surfaces.
    vii. Failure to collect data on consumer use practices with pest
strips. Echoing comments from the SAP that ``better knowledge of real
world use practices would serve to improve residential exposure
analyses,'' NRDC argues that the failure of EPA to collect such data
``undermines the risk analysis for pest strips.'' (Ref. 1 at 62).
    viii. Failure to consider aggregation of pest strip exposure with
other residential exposures. NRDC claims that EPA does not support its
statement that pest strip exposures would not co-occur with high
dietary exposures. NRDC also argues that EPA should consider co-
occurrence of exposure between pest strips and other DDVP residential
products. (Ref. 13 at 12-13).
    b. Amvac's comments. Amvac contends that the Collins and DeVries
study is adequate for assessing exposure from pest strips citing
several other studies which it states contain similar results. (Ref. 14
at 45). Further, Amvac argues that ``the estimated time-weighted
average concentration used by EPA (0.015mg/m3) is higher
than found in many other studies.'' (Id.). Amvac also defends EPA's use
of a time-weighted average in estimating risk noting that ``EPA is
assessing chronic exposure and thus it is appropriate to average over
the entire period to compare to a chronic endpoint.'' (Id.). Finally,
Amvac argues that, if EPA assessed acute risk from pest strips, it
would be appropriate for EPA to use the highest concentration from the
Collins and DeVries study (0.11 mg/m3) but that this
exposure level does not show an acute risk concern. (Id.).
    c. EPA's response--adequacy of the Collins and DeVries Study. EPA
believes this study is sufficiently representative to estimate exposure
and EPA disagrees with each of NRDC's contentions. First, EPA does not
believe the study is inadequate due to being performed in a single
location on 15 houses during a single season of the year. As noted by
Amvac, there are a number of studies other than Collins and Devries
that test DDVP pest strips in houses. Specifically, data on DDVP air
concentrations from the use of pest strips are available for over 100
homes in the United States, United Kingdom, and France. (Ref. 80).
There was no major difference in the DDVP air concentration in the 100
houses and the DDVP air concentration in the study of the 15 houses
that were used for exposure estimates.
    Second, EPA does not view the study as flawed because it only
sampled DDVP concentrations in one location in each home. Importantly,
the sample location in each instance was in a room with a pest strip,
pest strips were used in other rooms of the house, and EPA assumed, for
its calculation of the MOE, that the air concentration for all areas of
a house is the same as at the sampled location. Thus, EPA has assessed
MOEs in an appropriately conservative fashion given the sampling
location in the Collins and DeVries study.
    Third, NRDC's suggestion that some homeowners may put a pest strip
in every room fails to take into account that (1) the label now bars
use of full-size pest strips except in infrequently-occupied spaces
(attics, crawl spaces, sheds, and garages); (2) in-home pest strips
must contain significantly less DDVP than full-size strips and are
limited to use in closets, wardrobes, and cupboards; and (3) EPA's risk
assessment assumes a person spends all of their time in a room with a
closet or cupboard that contains a pest strip. Relevantly, the largest
closet strip is only labeled as effective in a 200 cubic foot area.
Areas beyond that efficacious zone of treatment are likely to contain
significantly lower air concentrations.
    Fourth, the Collins and DeVries study does provide sufficient
information to estimate exposure from different size strips. The
Collins and Devries study used a pest strip that was larger than the
largest size available today and EPA made the conservative assumption
that the currently-registered large strip would have similar exposure
to the older, larger version and extrapolated exposure levels for
smaller strips proportionately based on that conservative assumption.
    Finally, to insure that EPA has the most accurate information
possible on exposure for pest strips, EPA plans to require as part of
the data call-in to be issued in connection with reregistration that an
additional study be conducted that measures DDVP air concentrations in
houses from use of pest strips.
    i. Replacement of strips. EPA's risk assessment has a built-in
margin of error in the event strips are replaced more frequently than
every 120 days because it is based on an average of the first 91 days
of exposure which was the period of time air concentrations were
measured in the Collins and DeVries study.
    ii. Use of time-weighted average exposure. EPA believes that use of
a time-weighted average of the DDVP concentration levels is appropriate
for chronic risk and does not understand NRDC to be contesting this
approach to assessing chronic risk. As to acute exposures that occur
during the first day after a strip is hung, EPA has now expanded its
risk assessment to address both this scenario and a short/intermediate-
term exposure scenario (exposure for the two weeks after a strip is
installed).
    iii. Exposure from use in unoccupied spaces. EPA believes it
unlikely that DDVP residues will migrate from attics, crawl spaces,
garages, and sheds to living areas within a house because it would be
unusual for these spaces to be connected to the air exchange for a
house. On the other hand, basements may be included in a home's air
exchange system and, for that reason, the large pest strips may not be
used in a basement. This is likely part of the explanation for the
result in the cited chlorpyrifos study. In that study, the chlorpyrifos
was injected into the foundation and migrated to the basement of the
house. From there, it is likely that chlorpyrifos moved to other rooms
in the house through air exchange. Further, the chlorpyrifos study
cited by NRDC has little relevance to pest strips given the vastly
different amounts of active ingredient involved. (Ref. 81). In the
chlorpyrifos study, approximately 100 gallons of a solution containing
1 percent of pesticide product (Dursban TC) was injected into basement
walls. According to the label, Dursban TC contains 4 pounds per gallon
of chlorpyrifos. Thus, that study used approximately 4 pounds of
chlorpyrifos. A large pest strip contains, at most, 80 grams of
pesticide product, of which 18.6 percent is DDVP. Accordingly, the pest
strip exposure in unoccupied areas would contain roughly 15 grams of
DDVP compared to approximately 1,800 grams of chlorpyrifos in the study
cited.
    iv. Exposure durations in homes. First, EPA believes it is unlikely
that a person would spend four hours per day, day in and day out for an
extended period in an attic, crawl space, garage, or shed. In any
event, the label forbids use of the large pest strips in such locations
should they be occupied that regularly. Second, as to the closet,
wardrobe, and cupboard strips, EPA has assumed 24 hours per day
exposure in calculating margins of exposure. Amvac has agreed to modify
labels on these products so that they bar use of these strips in
closets in rooms where infants or children, or sick or elderly people
are confined for extended periods. Additionally, the label prohibits
use of

the strip in any area of the house where people are present for
extended periods.
    v. Incidental oral and dermal exposure. NRDC is incorrect in its
assertion that EPA's risk assessment does not take into account
incidental oral and dermal exposure. Although dermal and incidental
oral exposure from contact with DDVP adsorbed on solid surfaces was not
assessed directly, the inhalation study used for assessing inhalation
risk includes dermal and oral exposure components because the study
involved continuous whole-body exposure resulting in adsorption of DDVP
vapors to the animal's fur and food. In other words, the inhalation
study is actually a total exposure study accounting for exposure by all
routes when DDVP is delivered as a vapor. Further, the pest strip use
is unlikely to leave significant DDVP residues on residential surfaces
leading to dermal or incidental oral exposures. DDVP is highly volatile
and degrades rapidly. Thus, even if a person repeatedly uses pest
strips in the home, significant long-term dermal exposure is unlikely.
The Collins and DeVries study showed very low concentrations of DDVP in
the air and almost all food sampled in the home had no detectable
residues. EPA reasonably concluded that any dermal exposures from
deposit of air residues on surfaces would be negligible compared to
residues inhaled directly.
    vi. Data on real world use practices. Data on ``real world'' use
practices of pest strips might make it possible for EPA to determine
the extent to which EPA is likely overestimating exposure. EPA believes
its conservative projection of exposure, given the clarity and
reasonableness of the label directions, as amended, preclude the need
to require additional data on use practices.
    vii. Aggregating pest strip exposure with other residential
exposures. In assessing aggregate risks, EPA believes it is unrealistic
to add high-end exposures from intermittent and unconnected pesticide
exposures which are likely to affect relatively small population
groups. Thus, in aggregating dietary exposures to pest strip exposures,
EPA has compared chronic (rather than acute) dietary exposure levels of
DDVP as a background exposure to the various pest strip durational
scenarios (acute, short/intermediate-term, chronic). It should also be
noted that the dietary exposure estimates for DDVP are driven by high-
end model estimates of residues in drinking water which is an
additional conservatism.
    For similar reasons, EPA does not believe it is realistic to add
high-end acute or short-term exposures for the residential use of
trichlorfon on turf and DDVP as a spot insect treatment by aerosol
spray. Although dietary exposure to DDVP, and possibly exposure from a
DDVP pest strip, may be appropriately aggregated as a background
exposure to the turf or spot treatment uses, assuming that the windows
for high-end acute exposures from the turf use and the spot treatment
overlap is overly conservative. In any event, however, even if
exposures from turf and spot treatment uses are aggregated with each
other and with background exposures from food and water and pest
strips, the aggregate exposure still does not show a risk of concern.
Aggregating the MOEs of 100 for both the turf and spot treatment uses,
(Ref. 11 at 160, 165), with MOEs for background exposure for dietary
(900) and pest strips (93) gives an aggregate short-term MOE of 31 for
the child who simultaneously experiences outdoor exposures from the
trichlorfon turf use with indoor exposures from DDVP spot treatments
and pest strips. The target MOE here is 30. This aggregation relies
upon average dietary exposure for the most highly exposed subgroup
which may have turf post-application exposures (children aged 1-2)
compared to the short-term oral Point of Departure and average pest
strip exposure over 91 days compared to the short-term inhalation Point
of Departure. (Refs. 11 at 138, 162; 56 at 18).

D. Risk Characterization

    1. 99.9th percentile--a. NRDC's claims. NRDC asserts that EPA has
failed to provide a rationale for using the 99.9th percentile in the
DDVP risk assessment for acute population effects. (Ref. 1 at 51). NRDC
further contends that some 300,000--0.1 percent of the U.S.
population--will not be considered because they ``fall below the level
of sensitivity of the calculation method.'' (Id.). NRDC therefore
argues that EPA cannot make its FFDCA safety finding.
    b. EPA's response. Contrary to NRDC's assertion, EPA has not
ignored 300,000 of the U.S. population in estimating acute DDVP risks
through reliance on the 99.9th exposure percentile in the DDVP risk
assessment. As EPA has repeatedly explained in the past - in science
policy documents and in responses to NRDC's objections to tolerances -
``the use of a particular percentile of exposure is a tool to estimate
exposures for the entire population and population subgroups and not a
means to eliminate protection for a certain segment of a subgroup.''
(69 FR 30070 and 70 FR 46733).
    In examining pesticide exposure, EPA does not have the capability
of measuring actual exposure to individuals across the population.
Rather, EPA uses data on factors bearing on exposure such as residue
levels in food and drinking water, food consumption patterns, and air
concentration levels and transferable surface residues to estimate
exposure to hypothetical individuals across major identifiable
subgroups in the population. These data on exposure factors can range
from highly conservative values (e.g., assumption that 100 percent of a
crop is treated with a pesticide) to highly realistic values (e.g.,
market basket monitoring data on pesticide residue levels). In
interpreting exposure estimates based on such factors, EPA makes
judgments regarding what exposure level (expressed as a percentile) is
protective of the relevant population subgroups taking into account the
relative conservativeness of the factors which are the basis of the
assessment.
    Generally, EPA uses the 95th percentile exposure as a starting
point for evaluating the safety of pesticide in circumstances where EPA
has employed very conservative assumptions on residue values and risk
assessment techniques. In EPA's judgment, the 95th percentile exposure,
when calculated using such conservative assumptions, will not
underestimate exposure for any major identifiable subgroups. However,
when EPA uses more realistic residue values and refined risk assessment
techniques, it starts its evaluation of safety at the 99.9th percentile
of exposure to be sure that it is protecting the entire population and
all major, identifiable subgroups. EPA uses the 99.9th percentile as
the starting point for refined assessments rather than the 100th
percentile because generally its exposure assumptions, even when
refined, contain residual conservatisms. Thus, whether EPA is relying
on the 95th percentile, the 99.9th percentile, or some other value, the
population exposure percentile is a means to an end and not a
designation of those people worthy of protection. As EPA noted in a
science policy document on this issue: ``just as when OPP uses the 95th
percentile with non-probabilistic exposure assessments OPP is not
suggesting that OPP is leaving 5 percent of the population unprotected,
OPP is not by choosing the 99.9th percentile for probabilistic exposure
assessments concluding that only 99.9 percent of the population
deserves protection.'' (Ref. 8 at 31). Perhaps the best evidence that
use of population percentiles is not identifying those worthy of
protection but simply a tool in estimating exposure

is that refined assessments using the 99.9th percentile invariably
estimate exposure to be lower for a pesticide than an unrefined
assessment for that same pesticide using the 95th percentile. (69 FR
30071). Yet, under NRDC's logic the use of the 95th percentile, by
itself, would signal that fewer people are being protected than if the
99.9th percentile was used, and thus an exposure estimate based on the
95th percentile should necessarily be lower than one based on the
99.9th percentile.
    2. Inappropriate use of 100% of the RfD/PAD as a ``Bright Line''
Rule--a. NRDC's claims. NRDC contends that EPA is unlawfully
disregarding significant risks by relying on a ``bright line rule''
that risks below 100 percent of the acute population adjusted does
(aPAD) are not of concern and risks above 100 percent are of concern.
(Ref. 1 at 51-52). Specifically, NRDC argues that (i) EPA treats the
100 percent threshold as a rule that has not been subject to notice and
comment rulemakings; (ii) use of a 100 percent threshold is arbitrary
and capricious; (iii) use of 100 percent threshold improperly excludes
acute risks unless they exceed 100 percent of the aPAD; and (iv) EPA
cannot reasonably explain how children aged 1 to 6, the sub-population
with the highest percentage exposure, will not be harmed.
    b. EPA's response. NRDC appears to be suggesting that EPA's
approach of comparing estimated DDVP exposure to an EPA-derived safe
dose for DDVP is unlawful because (1) EPA cannot adopt an analytical
approach of comparing exposure to the safe dose without a regulation
that permits such an approach; and (2) EPA has not adequately justified
that its chosen safe dose is actually safe. Such claims are baseless.
    In assessing risks posed by a pesticide, EPA first examines
toxicological studies with the pesticide and calculates a safe dose in
humans (RfD/PAD) based on the results of those studies and
incorporating appropriate safety factors. This analysis, based on well-
established risk assessment principles used both across the federal
government and internationally, is designed to establish a dose without
appreciable risk to humans. EPA then compares estimated aggregate
exposure to humans to the safe dose to make a determination on the
safety of the pesticide. EPA believes this type of case-by-case
assessment of the risk from exposure to a pesticide is precisely what
section 408 demands. Other than the statutory mandates in FFDCA section
408, EPA does not follow ``bright line'' rules in making safety
determinations but rather is guided by what the data show on a
particular pesticide. Of course, at the end of its pesticide-specific
analysis EPA must make a safety determination. EPA does not believe it
needs a rule saying so to conclude that, where it has confidence that
exposure is below the safe dose, a tolerance is safe. Further, there is
no merit to NRDC's bald claim that EPA's safe dose determination for
DDVP is arbitrary and capricious because EPA has failed to explain the
basis for its safe dose determination. EPA's safe dose determination is
supported and explained by extensive documentation including the IRED
and numerous EPA-produced data evaluation and other analytical
memoranda addressing DDVP as well as long-established and commonly-
employed risk assessment principles. (See, e.g., Ref. 11).
    3. FQPA Safety Factor--a. NRDC's claims. NRDC asserts that the
Agency has no basis upon which to apply anything lower than a 10X FQPA
safety factor in the DDVP risk assessment. According to NRDC, ``[t]he
admitted potential for pre- and post-natal toxicity from exposure to
DDVP, combined with incomplete data regarding toxicity and exposure to
infants and children, compel EPA to retain the default FQPA tenfold
safety factor for DDVP.'' (Ref. 1 at 15). As to pre- and post-natal
toxicity, NRDC called particular attention to a study in the open
literature (Mehl et al (1993), which reported brain effects in guinea
pig pups. (Id. at 15-16). As to missing data, NRDC placed particular
evidence on the absence of a DNT study. NRDC also criticizes EPA's
choice of an additional safety factor of 3X arguing that ``[t]he Agency
did not explain why it chose 3X as opposed to 4X or any other factor.''
(Id. at 14).
    b. EPA's response. As discussed above, under the FQPA, EPA
presumptively applies an additional tenfold margin of safety (i.e.,
safety factor) when assessing the risk of pesticide exposure to infants
and children to take into account potential pre-and post-natal toxicity
and completeness of the data with respect to exposure and toxicity to
infants and children. FQPA, however, authorizes the Agency to use a
different margin of safety for pesticide residues if, on the basis of
reliable data, such a margin will be safe for infants and children.
When EPA issued its preliminary risk assessment for DDVP, it employed
an FQPA safety factor of 3X because the Agency lacked an acceptable DNT