( Phase III 3/ 07/ 06) Environmental Fate and Ecological Risk Assessment for the Reregistration of MCPB and MCPB Sodium for Use on Peas Marie Janson, Environmental Scientist Alex Clem, Environmental Scientist Reviewed and Approved by: Ed Odenkirchen, SeniorScientist Kevin Costello, Acting Branch Chief Environmental Risk Branch I United States Environmental Protection Agency Office of Pesticide Programs Environmental Fate and Effects Division Environmental Risk Branch I Ariel Rios Building 1200 Pennsylvania Ave., NW Mail Code 7507C Washington, DC 20460 ( Phase III 3/ 07/ 06) i TABLE OF CONTENTS LIST OF TABLES..................................................................................................................... iii LIST OF FIGURES ................................................................................................................... iv I. EXECUTIVE SUMMARY................................................................................................... 1 A. Nature of Chemical Stressor ............................................................................................ 1 B. Potential Risks to Non target Organisms.......................................................................... 2 C. Conclusions  Exposure Characterization......................................................................... 6 D. Conclusions  Effects Characterization............................................................................. 6 E. Uncertainties and Data Gaps............................................................................................ 7 II. PROBLEM FORMULATION ............................................................................................ 10 A. Stressor Source and Distribution.................................................................................... 10 1. Source and Intensity................................................................................................. 10 2. Physical/ Chemical/ Fate and Transport Properties ..................................................... 10 3. Pesticide Type, Class, Mode of Action..................................................................... 14 4. Overview of Pesticide Usage.................................................................................... 15 B. Receptors ...................................................................................................................... 15 1. Aquatic Effects ........................................................................................................ 15 2. Terrestrial Effects ................................................................................................... 15 3. Ecosystems at Risk .................................................................................................. 16 C. Assessment Endpoints ................................................................................................... 16 D. Conceptual Model ......................................................................................................... 16 1. Risk Hypothesis ....................................................................................................... 16 2. Diagram................................................................................................................... 18 E. Analysis Plan ................................................................................................................. 19 1. Preliminary Identification of Data Gaps and Methods ............................................... 20 2. Measures to Evaluate Risk Hypotheses and Conceptual Model ................................ 21 III. ANALYSIS......................................................................................................................... 22 A. Use Characterization...................................................................................................... 22 B. Exposure Characterization............................................................................................. 23 1. Environmental Fate and Transport Study Summaries................................................ 23 2. Measures of Aquatic Exposure................................................................................. 25 3. Measures of Terrestrial Exposure............................................................................. 27 C. Ecological Effects Characterization................................................................................ 28 1. Aquatic Effects Characterization.............................................................................. 28 2. Terrestrial Effects Characterization .......................................................................... 33 IV. RISK CHARACTERIZATION........................................................................................... 40 A. Risk Estimation  Integration of Exposure and Effects Data ........................................... 40 1. Non target Aquatic Animals and Plants .................................................................... 40 2. Non target Terrestrial Animals and Plants ................................................................ 42 ( Phase III 3/ 07/ 06) ii TABLE OF CONTENTS ( CONT.)

B. Risk Description ...................................................................................................... 47 1. Risks to Aquatic Organisms ..................................................................................... 47 2. Risks to Terrestrial Organisms ................................................................................. 47 3. Review of Incident Data .......................................................................................... 51 4. Federally Threatened and Endangered ( Listed) Species Concerns ............................. 51 C. Description of Assumptions, Limitations, Uncertainties, Strengths and Data Gaps ............... 58 APPENDIX A: Environmental Fate Studies .............................................................................. 59 APPENDIX B: Aquatic Exposure Model Results ...................................................................... 69 APPENDIX C: Terrestrial Bird and Mammal Model Results ..................................................... 85 APPENDIX D: TerrPlant and AgDrift Model and Results ......................................................... 92 APPENDIX E: Ecological Effects Data..................................................................................... 98 APPENDIX F: Data Requirements.......................................................................................... 104 APPENDIX G: Environmental Fate Bibliography.................................................................... 108 APPENDIX H: Ecotoxicity Bibliography ................................................................................ 110 ( Phase III 3/ 07/ 06) iii APPENDIX I: Locates Endangered Species .................................................................................................................... 114 APPENDIX J: MCPA/ MCPB Calculations Acute to Chronic Ratio Aquatic Organisms........ 137 ( Phase III 3/ 07/ 06) iv TABLE OF CONTENTS ( CONT.)

LIST OF TABLES I. a. Summary of Environmental Risk Conclusions for Aquatic Organisms and Plants for label use application rate ( 1.5 ae). .................................................................................. 3 I. b. Summary of Environmental Risk Conclusions for Terrestrial Organisms and Plants for label use application rate ( 1.5 ae) ................................................................................... 4 I. c. Environmental Fate Data Requirements ............................................................................... 7 I. d. Ecological Toxicity Data Requirements............................................................................... 8 II. a. Some Physical Chemical and Other Properties of MCPB................................................... 13 II. b. Some Physical Chemical and Other Properties of MCPB Sodium...................................... 14 II. c. Use of MCPB and MCPB Sodium on Peas........................................................................ 15 II. d. Risk Presumptions for Terrestrial Animals ( birds and wild mammals) ................................ 19 II. e. Risk Presumptions for Aquatic Animals............................................................................. 19 II. f. Risk Presumptions for Terrestrial and Semi Aquatic Plants ............................................... 19 II. g. Risk Presumptions for Aquatic Plants ............................................................................... 20 III. a. PRZM/ EXAMS Input Parameters for MCPB.................................................................... 26 III. b. Estimated Environmental Concentrations ( µ g ae/ L) of MCPB + Metabolites in Surface Water( PRZM EXAMS) from All Uses for Ecological Assessment. 27 III. c. Estimated Environmental Concentrations ( ppm ae) of MCPB Acid on Terrestrial Food Items from Use on Peas.................................................................................................... 27 III. d. Summary of Endpoints for MCPB Acute and Chronic Aquatic Toxicity Studies for RQ Evaluation ..................................................................................................................... 30 III. e. Freshwater Fish Acute Toxicity for MCPB Sodium.......................................................... 31 III. f. Freshwater Invertebrate Acute Toxicity for MCPB Sodium. ............................................. 31 III. g. Non target Aquatic Plant Toxicity for MCPB Sodium. .................................................... 33 III. h. Avian Acute Oral Toxicity for MCPB Sodium. ................................................................ 34 III. i. Avian Acute Dietary Studies for MCPB Sodium.............................................................. 34 III. j. Mammalian Acute Toxicity for MCPB............................................................................. 35 III. k. Mammalian Chronic and Developmental/ Reproductive Toxicity for MCPB ..................... 36 III. l. Non target Insects  Acute Contact. ................................................................................ 37 III. m. Terrestrial Non target Plant Toxicity. .............................................................................. 39 IV. a. Summarized Acute Aquatic Organism Risk Quotients for MCPB Acid ............................ 40 IV. b. Summarized Acute Aquatic Plant Risk Quotients for MCPB Acid .................................. 41 IV. c. Summary of endpoints for MCPB acute terrestrial toxicity studies ................................... 42 IV. d. Avian Acute Risk Quotient Summary ............................................................................. 43 IV. e. Mammalian Acute Risk Quotient Summary ..................................................................... 44 IV. f. Mammalian Chronic Risk Quotient Summary .................................................................. 45 IVg. Summarized Terrestrial Plant Risk Quotients................................................................... 46 IV. h. Distance of Disposition of MCPB Equivalent to Rates Tested in Vegetative Vigor Study.................................................................................................... 50 IV. i. Summarized Data from LOCATES .................................................................................. 58 Data Requirement Tables for MCPB .............................................................................. 103 ( Phase III 3/ 07/ 06) v TABLE OF CONTENTS ( CONT.)

LIST OF FIGURES Figure II. a. Chemical structures of MCPB and MCPB sodium.................................................. 13 Figure II. b. Conceptual Model.................................................................................................. 18 ( Phase III 3/ 07/ 06)      1    147 I. EXECUTIVE SUMMARY A. Nature of Chemical Stressor Use, Application Rate, Mode of Action MCPB [ 4( 2 methyl 4 chlorophenoxy) butyric acid] is an acidic phenoxy herbicide that is currently registered only for use on peas ( field, canned, and dried) to control or suppress Canada thistle and certain other broadleaf weeds. It is applied when the peas are tolerant to the herbicide, which is from the time of shoot emergence until about three leaf nodes before flowering ( typically 6 to 12 nodes).

MCPB is formulated as its sodium salt ( sometimes designated as MCPB sodium), which can be applied once annually through direct aerial or ground spray. The maximum application rate for the salt is 1.6 lbs/ acre ( 1.79 kg/ ha); or, in terms of acid equivalents ( ae), this rate converts to 1.5 lbs/ acre ( 1.68 kg/ ha) of MCPB acid.

Information from the published literature ( Dexter et al. 1994, Heimann and Neman 1997) concerning the mode of action of phenoxy herbicides indicates that they are systemic growth regulating hormones that act at multiple sites in a plant to disrupt hormone ( auxin) balance and protein synthesis. The result is plant growth abnormalities. Uptake of phenoxy herbicides is said to be primarily through the foliage, but root and seed uptake are also said to occur.

Environmental Fate Summary Based on laboratory studies and physicochemical properties, MCPB is not volatile, not persistent, and not likely to bioconcentrate. Its acidic/ anionic nature, physicochemical properties, and relatively low sorption to soil ( average soil sorption coefficient of 0.85 mL/ g), indicate that MCPB is prone to leach and runoff. Field dissipation studies are not available.

In addition to MCPB, two by products of its aerobic soil metabolism, although minor (< 10%) in concentration, are also of potential concern because of their chemical structural similarity to parent. These are: ( 1) MCPA [( 4 chloro 2 methylphenoxy) acetic acid], which is another registered herbicide of the phenoxy class, and ( 2) the closely related CHPA hexose conjugate [( 4 chloro 2 methylphenoxy) 2   glucopyranoside acetic acid]. Chemical structures of these compounds are in Appendix A. In the single aerobic soil metabolism study available, these two compounds were each detected at average maxima of approximately 6 7% of applied radioactivity during the first 3 to 15 days of incubation, with both decreasing to less than 2% by the end of a 120 day study. The only major identified transformation product was carbon dioxide.

The MCPA metabolite, as previously documented in its USEPA Reregistration Eligibility Document ( dated September 30, 2004) and evidenced in fate studies of MCPB, is similar to MCPB in all available characteristics. Although we do not have such information for the CHPA hexose conjugate, based on its chemical structure, it is reasonable to assume that it also shares the same general chemical profile. As it so happens, because of their relatively minor presence and lack of persistence, whether we included or excluded these two metabolites had little influence on the overall risk assessment. Their inclusion makes ( Phase III 3/ 07/ 06)      2    147 negligible difference in terrestrial exposure and in acute aquatic exposure. Excluding the two metabolites from the longest ( 60 day) chronic aquatic exposure assessment results in a decrease in aquatic concentration of only approximately 10%, an amount well within the variation in natural processes and experimental error. Nevertheless, we included both metabolites in combination with parent MCPB as total toxic residues with a combined or overall half life of 26 days, and assumed toxicities and environmental fate properties equivalent to parent.

MCPB was essentially stable to hydrolysis ( extrapolated half life greater than 500 days based on a study lasting only 30 days), but photolyzed in laboratory water under optimal light exposure conditions with half lives of approximately 2 to 3 days. Phototransformation products included 4 ( 4 hydroxy o tolyloxy) butyric acid; 2,4 dihyroxyphenyl formate; ocresol benzoic acid; and 2 hydroxyphenyl formate. Specific study information is not available concerning the fate of these products, and we have not included any potential effects of aqueous photolysis products in the risk assessment. However, based on their chemical structure, these are not expected to be persistent. Furthermore, should there be any concerns for toxicity, we can conclude that, either singly or in summation, these products would be in aquatic concentrations below the maximum concentrations estimated for parent. Additional exposure refinements could be pursued, if warranted by any toxicological concerns.

B. Potential Risks to Non target Organisms The risk assessment indicates the potential acute risks to non target terrestrial plants, birds, and mammals. Also, this risk assessment indicates potential chronic ( developmental/ reproductive) risk to mammals, and potential risks to endangered species from MCPB usage on peas. Tables Ia and Table Ib summarize risks and uncertainties for aquatic and terrestrial organisms and plants. No estuarine marine fish or invertebrate data were submitted. Because peas may be planted near estuarine marine environments this data would be of significant value for the evaluation of estuarine marine organisms. Potential chronic risks for aquatic organisms cannot be evaluated due to lack of submitted data. Consequently, it is not possible to discount possible risks to these organisms until further data is submitted.

Table I. a. Summary of Environmental Risk Conclusions for Aquatic Organisms and Plants for label use application rate ( 1.5ae/ A) ( Phase III 3/ 07/ 06)      3    147 Assessment Endpoint Summarized Risk Characterization and Important Uncertainties Acute Risk to Freshwater Fish No exceedences occurred for acute freshwater fish , acute restricted use or endangered species LOCs for ground or aerial spray applications.

Chronic Risk to Freshwater Fish No chronic freshwater fish toxicity data were submitted for the TGAI. Therefore, it is not possible to discount possible chronic risks to freshwater fish until further data is submitted.

Acute Risk to Freshwater Invertebrates No exceedences occurred for acute freshwater invertebrates , acute restricted use or endangered species LOCs for ground or aerial spray applications.

Chronic Risk to Freshwater Invertebrates No chronic freshwater invertebrate toxicity data were submitted for the TGAI. Therefore, it is not possible to discount possible chronic risks freshwater invertebrates until further data is submitted.

Acute Risk to Estuarine/ Marine Fish No acute estuarine/ marine fish toxicity data were submitted for the TGAI. Therefore, it is not possible to discount possible acute and endangered species risks estuarine/ marine fish until further data is submitted.

Chronic Risk to Estuarine/ Marine Fish No chronic estuarine/ marine fish toxicity data were submitted for the TGAI. Therefore, it is not possible to discount possible chronic risks estuarine/ marine fish until further data is submitted.

Acute Risk to Estuarine/ Marine Invertebrates No acute estuarine/ marine invertebrate data was submitted for the TGAI. Therefore, it is not possible to discount possible acute and endangered species risks estuarine/ marine invertebrates until further data is submitted.

Chronic Risk to Estuarine/ Marine Invertebrates No chronic estuarine/ marine invertebrate toxicity data was submitted for the TGAI. Therefore, it is not possible to discount possible chronic risks estuarine/ marine fish until further data is submitted.

Risk to Aquatic Vascular Plants No exceedences occurred for acute non endangered aquatic vascular plants. Endangered vascular plants can not be assessed due to non discreet NOEC value.

Risk to Aquatic Non vascular Plants No exceedences occurred for acute non endangered aquatic non vascular plants. ( Phase III 3/ 07/ 06)      4    147 Table I. b. Summary of Environmental Risk Conclusions for Terrestrial Organisms and Plants for label use application rate ( 1.5ae/ A)

Assessment Endpoint Summarized Risk Characterization and Important Uncertainties Acute Risk to Birds Acute risk, acute restricted use and endangered species LOCs were exceeded for 20 g and 100g birds. Acute restricted use and endangered species LOCs were exceeded for 1000g birds.

Chronic Risk to Birds No chronic bird toxicity data were submitted for MCPB. However, the chronic bird study from MCPA was substituted for MCPB. No exceedences occurred for chronic risk to birds.

Acute Risk to Mammals No exceedences occurred for acute or acute restricted use mammal LOCs.. Endangered species LOCs were exceeded for 15g and 35g mammals Chronic Risk to Mammals Chronic risk LOCs were exceeded in all weight classes( 15g, 35g, and 1000g) of mammals Terrestrial Plants Acute non endangered and acute endangered species LOCs are exceeded for monocots and dicots from both aerial and ground applications.

Non target Insects Based on acute contact toxicity studies on honeybees, MCPB is classified as non toxic to these receptors.

The results of this risk assessment indicate that MCPB applied at the maximum application rate according to label directions, as a liquid spray for ground or aerial applications, will impact nontarget plants for some distance from the application site. At the label application rate of 1.5 lbs ae/ acre, model estimated RQs exceeded acute risk LOCs for non target monocots and dicots located in dryland and semi aquatic areas adjacent to treated areas, both as a result of combined runoff and spray drift, and from spray drift alone. .

Risk quotients for birds exceed the acute risk LOC from consumption of short grass ( all avian weight classes), broadleaf forage/ small insects ( 20 g and 100 g birds) and tall grass ( 20 g birds) feed items. Because these acute lethality risks were calculated based on a laboratory method of dosing and not actual feeding habits in the field, they represent a conservative estimation of risk The laboratory method is a gavage dose which represents a very short term high intensity exposure, whereas dietary exposure may be of a more prolonged nature. The dietary approach assumes that animals in the field are consuming food at a rate similar to that of confined laboratory animals. The strength of this assumption is uncertain, because energy content in food items differs between the field and in the laboratory, as do the energy requirements of wild and captive animals. However, because acute effects were observed in both studies, including the dietary study at doses > 569 ppm ae, acute risks to avian species using the treated fields or inhabiting adjacent edge or riparian communities could result from the labeled use of MCPB.

Assuming maximum and mean residue levels at the maximum application rate, chronic risk LOCs were exceeded in all weight classes ( 15 g, 35 g, and 1000g) of mammals for consumption of short grass, tall grass and broadleaf forage/ small insects. Assuming maximum residue levels at the maximum application rate, chronic risk LOCs were exceeded in 15 g and 35g mammals for consumption of fruit and large insects. However, because the chronic LOCs are exceeded for multiple food categories, potential exposure may still be high enough to warrant concern. Based ( Phase III 3/ 07/ 06)      5    147 on effects seen in the chronic mammalian toxicity studies, MCPB may be classified as a potential endocrine disruptor. When the appropriate screening and/ or testing protocols being considered under the Agency's Endocrine Disruptor Screening Program have been developed, MCPB may be subjected to additional screening and/ or testing to better characterize effects related to endocrine disruption.

The preliminary risk assessment for endangered species indicates that MCPB exceeds the endangered species LOCs for the single application per year for peas grown with an application rate of 1.5 lbs ae/ acre for the following taxonomic groups:

· small 20g, medium 100g and large 1000 g birds feeding on short grass, tall grass, and broadleaf forage/ small insects; small birds feeding on fruits pods seeds, and large insects · small 15g and medium 35g mammals feeding on short grass; small mammals ( 15 g) feeding on broadleaf forage/ small insects.

· non target terrestrial plants  monocots and dicots adjacent to treated areas and semi aquatic.

Information from LOCATES indicates that several species of birds, mammals and plants are potentially affected by use of MCPB on peas.

Exposure to MCPB results in direct effects to plant species that could result in effects at the higher levels of organization ( i. e. population, trophic level, community, ecosystem). Consequently, there may be a concern for potential indirect effects to listed species dependent upon birds that consume feed items contaminated with MCPB residues, such as predatory birds and mammals. The guideline terrestrial plant studies indicate direct adverse effects to seedling emergence as well as non lethal effects including brown leaf tips, necrosis, chlorosis, stem tumors, leaf curl, and decrease in size. In the guideline aquatic vascular plant studies, concentrations as low as 0.16 mg ae/ L resulted in chlorosis, curling, and decreased root formation in the plant. In terrestrial and shallow water aquatic communities, plants are the primary producers upon which the succeeding trophic levels depend. If the available plant material is impacted due to the effects of MCPB, this may have negative effects not only on the herbivores, but throughout the food chain. Also, depending on the severity of impacts to the plant communities ( edge and riparian vegetation), community assemblages and ecosystem stability may be altered ( i. e. reduced bird populations in edge habitats; reduced riparian vegetation resulting in increased light penetration and temperature in aquatic habitats). Furthermore, reduction of upstream riparian vegetation that would otherwise supply downstream habitats could result not only in a loss of a significant component of food for aquatic herbivores and detritivores, but also of habitat ( i. e. leaf packs, materials for case building for invertebrates). This assessment of risk to aquatic receptors provides toxicity data on freshwater systems only due to lack of submitted estuarine/ marine toxicity data.

The risk assessment indicates that there are no acute risks to fish, fresh water aquatic invertebrates, algae or mammals. There were no exceedances of the aquatic Acute Risk, Acute Restricted Use, and Endangered Species LOCs for freshwater fish and aquatic invertebrates. There were also no exceedances of the non endangered Acute Risk LOC for aquatic algae and vascular plants. ( Phase III 3/ 07/ 06)      6    147 Consequently, freshwater fish, freshwater invertebrates, algae and vascular plants inhabiting surface waters adjacent to an MCPB treated field would not be at risk for adverse acute effects to growth and survival when exposed to residues in surface runoff and spray drift as a result of ground and/ or aerial spray application. Acute Risk LOCs were not exceeded for mammals consuming short grass, tall grass, broadleaf forage and small insects, fruit and large insects, or seeds and pods with maximum or mean residue levels. EFED currently does not quantify risks to terrestrial non target insects.

C. Conclusions  Exposure Characterization Routes of exposure evaluated in this risk assessment focused on deposition, runoff and spray drift from ground and aerial spray applications of MCPB for peas. Based on the physical and chemical properties as well as the laboratory fate studies, MCPB will predominately exist in the ionic or salt form at ambient environmental pHs. In addition, the only registered formulation for field application is the MCPB sodium salt. MCPB salt is highly soluble ( 200,000 mg/ L) in water and mobile in aqueous environmental systems. MCPB degrades rapidly via photolysis ( half life of 2.6 days) and is readily biodegraded in aerobic and anaerobic soils; thus long term persistence in soils is not likely. The low octanol water partition coefficient ( 1.33) indicates that MCPB would have a low tendency to bioaccumulate. In addition, based on its tendency not to persist in the environment and the single application per year, long term persistence in the environment is not likely. No information is available on aquatic biodegradation of MCPB.

A review of ground water and surface water monitoring data indicated no detection of MCPB and there were no reported incidents from MCPB usage.

D. Conclusions  Effects Characterization Available acute toxicity data indicate that MCPB sodium is moderately toxic to rainbow trout and slightly toxic to bluegill sunfish and daphnids. No toxicity studies have been conducted to determine potential chronic effects to fish and aquatic invertebrates. Laboratory studies indicate that MCPB is toxic to algae and aquatic vascular plant species, based on observed adverse effects on growth and development.

Available acute toxicity data indicate that MCPB sodium is practically non toxic to bobwhite quail and mallard ducks in the diet. However, an oral gavage study with bobwhite quail indicates that MCPB sodium was moderately toxic. MCPB is classified as practically non toxic to small mammals on an acute oral basis. However, a 13 week chronic oral study in dogs reported reproductive effects, including testicular and prostate atrophy and curtailment of spermatogenic activity. In developmental studies with rats and rabbits, maternal toxicity was observed at doses ranging from 20  100 mg/ kg/ day ( NOAEL rabbit = 5 mg ai/ kg/ day; 4.55 mg ae/ kg/ day) and developmental effects were observed in rats at a dose of 100 mg/ kg/ day. An acute contact study indicates that MCPB sodium is relatively non toxic to honey bees. No toxicity studies have been conducted to determine the effect of residues to pollinators. An MCPA chronic bird study was substituted for MCPB which resulted in a NOAEC of 1000 mg/ kg diet.

Terrestrial plant toxicity studies indicate that MCPB sodium negatively impacts seedling emergence and vegetative vigor in monocots and dicots. Non lethal effects included brown leaf ( Phase III 3/ 07/ 06)      7    147 tips, necrosis, decrease in size, leaf curling, chlorosis, and stem tumors. Consequently, exposure to MCPB presents a potential risk to non target plants inhabiting edge habitats adjacent to target fields and riparian vegetation along streams and/ or ponds in close proximity to sprayed fields.

E. Uncertainties and Data Gaps There are a few areas of uncertainty in the terrestrial and the aquatic organism risk assessments that could potentially cause an underestimation of risk. First, MCPB chronic toxicity data for aquatic organisms are not available. MCPB acute toxicity data for estuarine marine fish and invertebrates are not available; thus the potential risk to estuarine marine fish and estuarine marine invertebrates cannot be precluded. Because the potential for risk to these taxa cannot be evaluated, this risk assessment should be considered incomplete.

Additional uncertainty results from the lack of information and/ or data in several components of this ecological risk assessment. For instance, this assessment accounts only for exposure of nontarget organisms to MCPB, but not to its degradates. Data are not available concerning the fate and toxicity of the photolytic degradation products of MCPB. MCPA is a product of anaerobic biodegradation in soil and this assessment provides available toxicity data for MCPA that indicates that the toxicity of MCPA acid is very similar to that of MCPB ( Reregistration Eligibility Decision for MCPA, 2004).

Tables I. c. and I. d. summarize data gaps and environmental fate and ecological toxicity data requirements submitted respectively.

TABLE I. c. of Environmental Fate Data Requirements Guideline # Data Requirement MRID # Study Classification Is more data needed?

161 1 Hydrolysis 42574301 Acceptable no 161 2 Photodegradation in Water 42574302 Acceptable no 161 3 Photodegradation on Soil 43829901 Invalid no 161 4 Photodegradation in Air N/ A no 162 1 Aerobic Soil Metabolism 43247601 Acceptable no 162 2 Anaerobic Soil Metabolism 43015501 Acceptable no 162 3 Anaerobic Aquatic Metabolism No study submitted no 162 4 Aerobic Aquatic Metabolism No study submitted ( not at this time)

163 1 Leaching Adsorption/ Desorption 42693701 43466401 Acceptable no 163 2 Laboratory Volatility N/ A 163 3 Field Volatility N/ A 164 1 Terrestrial Field Dissipation No study submitted yes 164 2 Aquatic Field Dissipation N/ A 164 3 Forestry Dissipation N/ A ( Phase III 3/ 07/ 06)      8    147 TABLE I. c. of Environmental Fate Data Requirements Guideline # Data Requirement MRID # Study Classification Is more data needed?

165 4 Accumulation in Fish N/ A 165 5 Accumulation aquatic nontarget N/ A 166 1 Ground Water small prospective N/ A 166 2 Groundwater  small retrospective N/ A 201 1 Droplet Size Spectrum N/ A 202 1 Drift Field Evaluation N/ A TABLE I. d. of Ecological Toxicity Data Requirements Guideline # Data Requirement MRID # Classification Is more data needed?

71 1 Avian acute oral LD50 ( bobwhite quail) 42560801 Acceptable No 71 2 Avian acute dietary LC50 ( bobwhite quail) ( mallard duck) 42560802 42560803 Acceptable Acceptable No 71 4 Avian reproduction ( bobwhite quail) ( mallard duck) 43505201 MCPA Acceptable No 72 1 Freshwater fish acute LC500 ( rainbow trout) ( bluegill sunfish) 42532608 42532601 Acceptable Acceptable No 72 2 Freshwater invertebrate acute EC50 ( daphnia) 42532602 Acceptable No 72 3a Estuarine/ marine fish acute LC50 ( sheepshead minnow) N/ A Yes 72 3b Estuarine/ marine invertebrate acute EC50 ( eastern oyster) N/ A Yes 72 4a Estuarine marine fish early life stage N/ A reserved 72 4a Freshwater fish early life stage ( fathead minnow) N/ A Yes 72 4b Freshwater invertebrate life cycle ( daphnia) N/ A Yes 72 4d Estuarine/ marine life cycle ( mysid) N/ A reserved 72 5 Freshwater fish full life cycle N/ A reserved 72 7 Aquatic Field Study N/ A No 81 1 Acute mammalian oral LD50 ( rat) 144801 Acceptable No ( Phase III 3/ 07/ 06)      9    147 82 1( a) 82 1( b) Mammalian chronic ( dog) ( rat)

116345 116344 Acceptable minimum Acceptable  minimum No 83 3 Mammalian Developmental ( rat) ( rabbit) 40865401 40865402 Acceptable Acceptable No 83 4 MCPB Mammalian Reproduction N/ A Yes 83 4 MPCA Mammalian Reproduction 40041701 Acceptable No 123 1( a) Seedling Emergence  Tier II 42560804 Acceptable No 122 1( b) Vegetative Vigor  Tier I 42560804 Acceptable No 123 1( b) Vegetative Vigor  Tier II 42560804 Acceptable No 122 2 Aquatic plant algae ( green algae) ( blue green algae) ( diatom) ( marine diatom) 42532605 42532603 42532609 42532606 Acceptable Acceptable Acceptable Acceptable No 123 2 Aquatic plant acute EC50 ( duckweed) 42532604 Acceptable No 141 1 Acute honey bee contact LD50 42532607 Acceptable No 141 2 Honey Bee Residue on Foliage N/ A Yes 141 5 Honey Bee Field Testing for Pollinator N/ A Yes ( Phase III 3/ 07/ 06)      10    147 II. PROBLEM FORMULATION The purpose of the ecological risk assessment ( ERA) is to evaluate and address ecological risks associated with the reregistration of the herbicide MCPB [ 4( 2 methyl 4 chlorophenoxy) butyric acid] for use on peas; including field, canned and dried peas. The current registration allows nationwide use on peas to control Canada thistle and other broadleaf weeds.

A. Stressor Source and Distribution 1. Source and Intensity: MCPB is a phenoxy herbicide that is currently registered for use on peas ( field, canned, and dried) to control or suppress Canada thistle and certain other broadleaf weeds. It is formulated only as its sodium salt ( MCPB sodium). It is applied once annually through direct aerial ( fine medium and coarse spray) or ground spray application at a maximum rate of 1.6 lbs ai/ acre ( 1.5 pounds acid equivalent per acre). Exposure to MCPB can occur by ground deposition, indirect spray drift, and surface water runoff.

2. Physical/ Chemical/ Fate and Transport Properties: A summary of selected physical and chemical properties for MCPB and MCPB sodium are presented below in Tables II. a and b, respectively. Section III. B. 1 and Appendix A have more detail on specific environmental fate studies.

Only laboratory environmental fate studies are available for MCPB. Field dissipation studies are not available. No study data ( laboratory or field) are available for biodegradation in water ( aerobic or anaerobic aquatic metabolism). In the absence of aquatic biodegradation data, for simulation modeling purposes EFED substitutes soil metabolism data with adjustment factors to allow for natural substrate variation.

As can be seen from Tables IIa and IIb, MCPB is an acidic compound ( pKa values of 4.6 and 4.8). ( This acid strength is comparable to that for acetic acid, which is the essential component present at a concentration of 5% in vinegar.) Because of its acidity, MCPB will exist predominately in the ionic ( anionic) or salt form at typical environmental pHs. The calculated degree of ionization corresponding to MCPB's acid strength is greater than 99% at pH 7, and ranges from approximately 70% to 99.99+% from pH 5 to 9, respectively. In all formulations registered for field application, MCPB is added as its sodium salt, which has a solubility in water of approximately 200,000 mg/ L ( 200 g/ L).

The relatively low Henry's Law Constant and vapor pressure for MCPB and collateral evidence showing its absence in traps for volatile organic compounds in various laboratory studies indicate that it is non volatile.

Based on laboratory studies, MCPB biodegrades in soil. In the only soil tested for aerobic metabolism, MCPB had a half life of approximately 18 days. The major identified transformation product was carbon dioxide. Two by products of aerobic soil metabolism, ( Phase III 3/ 07/ 06)      11    147 although minor (< 10%) in concentration, are also of potential concern because of their chemical structural similarity to parent. These are: ( 1) MCPA [( 4 chloro 2 methylphenoxy) acetic acid], which is another registered herbicide of the phenoxy class, and ( 2) the closely related CHPA hexose conjugate [( 4 chloro 2 methylphenoxy) 2   glucopyranoside acetic acid]. Chemical structures of these compounds are in Appendix A. In the single aerobic soil metabolism study available, these two compounds were each detected at average maxima of approximately 6 7% of applied radioactivity during the first 3 to 15 days of incubation, with both decreasing to less than 2% by the end of a 120 day study.

The MCPA metabolite, as previously documented in its USEPA Reregistration Eligibility Document ( dated September 30, 2004) and evidenced in fate studies of MCPB, is similar to MCPB in all available characteristics. Although we do not have such information for the CHPA hexose conjugate, based on its chemical structure, it is reasonable to assume that it also shares the same general chemical profile. As it so happens, because of their relatively minor presence and lack of persistence, whether we included or excluded these two metabolites had little influence on the overall risk assessment. Their inclusion makes negligible difference in terrestrial exposure and in acute aquatic exposure. Excluding the two metabolites from the longest ( 60 day) chronic aquatic exposure assessment results in a decrease in aquatic concentration of only approximately 10%, an amount well within the variation in natural processes and experimental error. Nevertheless, we included both metabolites in combination with parent MCPB as total toxic residues with a combined or overall half life of 26 days, and assumed toxicities and environmental fate properties equivalent to parent. ( For modeling purposes, in order to allow for natural variation in the microbiological activity of soils, EFED uses three times a single soil value as a reasonable upper confidence bound for an average halflife which in this case is approximately 78 days).

In the only soil tested for anaerobic metabolism, MCPB had a system half life of approximately 11 days. ( Again, for modeling purposes, in order to allow for natural variation in microbiological activity of soils, EFED uses three times a single soil value as a reasonable upper confidence bound for an average half life, which in this case is approximately 34 days.) The major transformation product in the aerobic phase of this anaerobic soil metabolism study was again MCPA [( 4 chloro 2 methylphenoxy) acetic acid]. Within experimental error, this product did not appear to form during the anaerobic phase.

MCPB was essentially stable to hydrolysis ( extrapolated half life greater than 500 days based on a study lasting only 30 days), but photolyzed in laboratory water under optimal light exposure conditions with half lives of approximately 2 to 3 days. [ When input directly into current EFED aquatic models, these photolysis half lives translate into effective half lives approximately 124 times longer ( 250 to 400 days) based on scenario water depths, clarity, and other factors.] Phototransformation products included 4 ( 4 hydroxy o tolyloxy) butyric acid; 2,4 dihyroxyphenyl formate; o cresol; benzoic acid; and 2 hydroxyphenyl formate. Specific study information is not available concerning the fate of these products, and we have not included any potential effects of aqueous photolysis products in the risk assessment. However, based on their chemical structure, these are not expected to be persistent. Furthermore, should there be any concerns for toxicity, we can conclude that, either singly or in summation, these products would be in aquatic concentrations below the maximum concentrations estimated for parent. Additional exposure refinements could be pursued, if warranted by any toxicological ( Phase III 3/ 07/ 06)      12    147 concerns.

Adsorption/ desorption ( batch equilibrium) of MCPB in four soils and one sediment indicate that MCPB is mobile. Mean adsorption coefficients ( Kads) measured for each of the soils were 1.69, 0.26, 0.65, and 0.78 mL/ g ( median of 0.72, average of 0.85 mL/ g); respective textures of these soils were sandy clay loam, sand, sandy loam, and clay loam. The sediment was a sandy loam ( pH of 5.95 and 2.85% organic carbon) for which the mean Kads was 10.58 mL/ g. Adsorption coefficients normalized for organic carbon ( K oc ) were 129.57, 47.91, 85.54, 31.27, and 371.17 mL/ g organic carbon for the sandy clay loam, sand, sandy loam, and clay loam soils and sandy loam sediment, respectively ( average K oc for the five values of 130 mL/ g organic carbon, median of 86 mL/ g organic carbon). The study was not consistent with guidelines in that the soils used in the study were not the same as those used in the aerobic soil metabolism studies.

Based on its acid nature and consistent correlations among relatively high solubility, relatively low octanol to water partitioning ratio ( 1.33 at pH 7), and relatively low sorption to soil, MCPB would be prone to leach to ground water and runoff to surface water. Judging from these factors and its lack of persistence in soil, bioconcentration of MCPB is not expected. Figure II. a. Chemical structures of MCPB and MCPB sodium MCPB MCPB Sodium ( Phase III 3/ 07/ 06)      13    147 TABLE II. a. Some Physical Chemical and Other Properties of MCPB.

CAS Name 4( 2 methyl 4 chlorophenoxy) butyric acid IUPAC Name 4 ( 4 chloro o tolyloxy) butyric acid CAS No 94 81 5 PC Code 019201 Empirical Formula C11H13ClO3 Molecular Weight 228.6 Common Name MCPB Formulated Product Thristrol Pesticide Type Herbicide Chemical Family Phenoxy Color/ Form Brown flakes; white crystalline solid ( purified technical  99.5% pure)

Odor Slightly phenolic Melting Point 101.5  103.0 ° C Flash Point Not flammable Relative Density 1.26 g/ ml ( at 20 ° C)

Water Solubility ( at 20 ° C) 60.4 mg/ L ( purified technical substance in purified water) 29.9 mg/ L at pH 4 3.83 mg/ L at pH 7 > 250 g/ L at pH 10 ( Podall 2002)

Solubility in other solvents n Heptane 0.414 g/ L at 20 ° C; Xylene 37.6 g/ L at 20 ° C dichloromethane 69.9 g/ L at 20 ° C; Methanol > 250 g/ L at 20 ° C n Octanol 71.6g/ L at 20 ° C; Acetone > 250 g/ L at 20 ° C Ethyl acetate 144 g/ L at 20 ° C ( Podall 2002)

Vapor Pressure 4.0 x10 7 torr ( for purified technical at 25 ° C) ( Podall 2002)

Henry's Law Constant 3.42 x 10 9 atm x m3/ mol; estimated at 25 ° C ( Howard and Meylan, 1997)

pKa 4.6 at 20 ° C ( Podall 2002)

log Pow 1.33 ( at pH 7 and 20 ° C) 3.45 ( at pH 4 and 20 ° C)  0.21 ( at pH 10 and 20 ° C) ( Podall 2002)

Redraw to be configuration shown for MCPB; move Na to end of carboxyl group; show Na with positive charge and COO with negative charge. ( Phase III 3/ 07/ 06)      14    147 TABLE II. b. Some Physical Chemical and Other Properties of MCPB Sodium.

CAS Name Sodium 4( 2 methyl 4 chlorophenoxy) butyrate IUPAC Name N/ A CAS No 6062 26 6 PC Code 019202 Empirical Formula C11H12ClNaO3 Molecular Weight 250.65677 Common Name MCPB sodium salt Formulated Product Thristrol Pesticide Type Herbicide Chemical Family Phenoxy Color/ Form Colorless liquid with phenolic odor Odor Slightly phenolic Melting Point N/ A Flash Point Not flammable Relative Density N/ A Water Solubility 200,000 mg/ L @ 25 ° C ( WSSA 1994)

Solubility in other solvents ( g/ L at 20 ° C) N/ A 3. Pesticide Type, Class, Mode of Action: MCPB is a phenoxy herbicide that is used for control of broadleaf weeds. Information from the published literature ( NDSU 1994, Heimann and Neman 1997) concerning the mode of action of phenoxy herbicides indicates that they are systemic growth regulating hormones that act at multiple sites in a plant to disrupt hormone ( auxin) balance and protein synthesis, resulting in plant growth abnormalities. Cell division is affected and can result in changes in cell size and shape and the cessation of tissue growth. Uptake of phenoxy herbicides is primarily through the foliage but root and seed uptake can also occur. It is then translocated to areas of new plant growth by the xylem and phloem..

Damage may include petiole twisting ( epinasty), fused petioles ( trumpeting), crinkling and cupping of leaf margins, thickening and flattening of stems ( fasciation), and proliferation and distortion of roots and flowering parts. Roots may lose the ability to take up soil nutrients and the xylem and phloem in stems may not be able to transport nutrients throughout the plant. The extent of damage is dependent upon the concentration and duration of exposure. Nontarget plants that do not receive a lethal dose may continue to grow normally beyond the affected parts unless tissue damage occurs while the plant is immature, thus retarding terminal growth. Phenoxy herbicides are also known to affect photosynthesis and root absorption. Examples of sensitive or susceptible plants include cotton, tomatoes, grapes, corn, soybeans, sugarbeets, sugarcane, and ornamentals. ( Phase III 3/ 07/ 06)      15    147 4. Overview of Pesticide Usage: MCPB sodium salt is currently registered for use on peas ( including field, canned, and dried), and no other agricultural crop. It is used postemergent primarily to suppress Canada thistle bud formation. MCPB is applied when the peas are tolerant to the herbicide, from shoot emergence until about three leaf nodes before flowering ( typically 6 to 12 nodes). Canada thistle reduces pea yields through competition and presents problems during harvesting. The buds are difficult to remove from the harvested crop resulting in loss of crop quality and profit to the grower. During the canning and/ or freeze processing of peas, the unopened Canada thistle buds contaminate the product. Other target pests include buttercup, mustard, lambsquarters, purslane, ragweed, smartweed, and pigweed. Table II. c. summarizes the application rates from the various product labels for all proposed applications.

TABLE II. c. Use of MCPB and MCPB Sodium on Peas.

Crop Product Appl. Rate ( lb ai/ A) Appl. Rate ( lb ae/ A) Max # Appl/ Yr Application Methods Peas Thistrol ® Herbicide 1.6 1.5 1 Spray/ ground and aerial Peas Sodium MCPB Solution 1.6 1.5 1 Spray/ ground and aerial There are two registered products: Thistrol ® Herbicide ( 71368 5) and Sodium MCPB Solution ( 71368 7). The registrants include A. H. Marks and Company Ltd., Nufarm BV and Nufarm, Inc. The product label for Thistrol ® lists the active ingredient ( 23.5%) as sodium salt of 4( 2 methyl 4 chlorophenoxy) butyric acid and 76.5% inert ingredients ( not provided).

B. Receptors 1. Aquatic Effects: The emphasis of the risk assessment is to address risk to non target aquatic species that may be exposed to residual MCPB and MCPB sodium. Spray drift and runoff to adjacent bodies of water are the most likely sources of MCPB and MCPB sodium exposure to nontarget aquatic organisms, including endangered and threatened species. Aquatic organisms downstream from application areas could also potentially be exposed.

2. Terrestrial Effects: Ground deposition and spray drift with resulting residues on animal feed items are the most likely sources of MCPB and MCPB sodium exposure to nontarget terrestrial organisms, including endangered and threatened species. Additional sources of exposure to MCPB sodium could be from water drunk from puddles in treated fields, ingested from feathers or fur through preening or grooming or from inhalation at the time of spraying. However, this screening assessment only estimates potential dietary exposure.

Spray drift and runoff from treated fields present a potential exposure route for non target plants in edge habitats adjacent to target fields and riparian vegetation along streams and/ or ponds in close proximity to sprayed fields.

3. Ecosystems at Risk: Because peas can be grown throughout the country, a variety of ecosystems may be exposed. The crop profile for Maryland peas indicates that peas are grown in estuarine watershed. Other crop profiles such as Delaware suggest that MCPB may be used in ( Phase III 3/ 07/ 06)      16    147 estuarine as well as freshwater environments. In terrestrial and shallow water aquatic communities, plants are the primary producers upon which the succeeding trophic levels depend. If the available plant material is impacted due to the effects of MCPB and MCPB sodium, this may have negative effects not only on the herbivores, but throughout the food chain. Also, depending on the severity of impacts to the plant communities ( i. e., edge habitats, algal biomass, riparian vegetation), community assemblages and ecosystem stability may be altered ( i. e. reduced bird populations in edge habitats; reduced riparian vegetation resulting in increased light penetration and temperature in aquatic habitats). Furthermore, reduction of upstream riparian vegetation that would otherwise supply downstream habitats could result not only in a loss of a significant component of food for aquatic herbivores and detritivores, but also of habitat ( i. e. leaf packs, materials for case building for invertebrates).

C. Assessment Endpoints The major assessment endpoints related to aquatic environments are:

( a). Direct effects to survival, reproduction and growth of fish and aquatic invertebrates in the water column via acute and/ or chronic toxicity. ( b). Direct effects to growth and development of algae and vascular plants via acute toxicity. ( c). Direct effects to endangered/ threatened aquatic species via acute and/ or chronic toxicity.

The major endpoints related to terrestrial environments at issue are:

( a). Direct effects to growth and development of non target plants. ( b). Direct effects on survival, growth and reproduction of birds, mammals, and by extension amphibians and reptiles via acute and/ or chronic toxicity.

D. Conceptual Model 1. Risk Hypothesis:

The Office of Pesticide Programs uses a screening risk hypothesis for its initial risk assessments.

The risk hypothesis is that the use of MCPB in accordance with the label results in adverse effects on survival and/ or fecundity of non target terrestrial and/ or aquatic animals; and that the use of MCPB according to the label results in adverse effects on survival, reproduction and/ or growth on aquatic, semi aquatic and terrestrial plants. 2. Diagram: Based on an examination of the physical/ chemical properties of MCPB and MCPB sodium, the fate and disposition in the environment, and mode of application ( e. g., ground and aerial spray application); a conceptual model ( Figure II. b) was developed that represents the possible relationships between the stressor, ecological endpoints, and the measurement endpoints. Risk to non target animals is also possible from dermal contact or inhalation, but because these are not considered in the risk assessment, they are not shown in the diagram below. ( Phase III 3/ 07/ 06)      17    147 Figure II . b. Conceptual Model Fig ( Phase III 3/ 07/ 06)      19    147 E. Analysis Plan This screening assessment uses a risk quotient ( ratio of exposure concentration to effects concentration) approach to evaluate the potential for adverse effects on non target terrestrial and aquatic animals. Calculated risk quotients are compared to predetermined levels of concern ( LOCs) to provide a preliminary indication of the potential for risk. Although risk, in the context intended here, is often defined as the likelihood and magnitude of adverse ecological effects, the risk quotient based approach does not provide a quantitative estimate of likelihood and/ or magnitude of an adverse effect. Such estimates may be possible through a more refined, probabilistic assessment.

Risk presumptions, along with the corresponding RQs, equations, and LOC s are summarized in Tables II d to II g. The exposure estimates in this screening assessment are derived using maximum label rates and minimum application intervals for each use.

Table II d. Risk presumptions for terrestrial animals ( birds and wild mammals).

Risk Presumption RQ LOC Acute EEC1/( LC50 or LD50/ ft2 or LD50/ day) 0.5 Acute Restricted Use EEC1/( LC50 or LD50/ ft2 or LD50/ day) ( or LD50 < 50 mg/ kg) 0.2 Acute Endangered Species EEC1/( LC50 or LD50/ ft2 or LD50/ day) 0.1 Chronic Risk EEC/ NOEC 1 1 abbreviation for Estimated Environmental Concentration ( ppm) on avian/ mammalian food items Table II e. Risk presumptions for aquatic animals.

Risk Presumption RQ LOC Acute EEC1/( LC50 or EC50) 0.5 Acute Restricted Use EEC/( LC50 or EC50) 0.1 Acute Endangered Species EEC/( LC50 or EC50) 0.05 Chronic Risk EEC/ NOEC 1 1EEC = ( ppm or ppb) in water Table II f. Risk presumptions for terrestrial and semi aquatic plants.

Risk Presumption RQ LOC Acute Risk EEC1/ EC25 1 Acute Endangered Species EEC/( EC05 or NOEC) 1 ( Phase III 3/ 07/ 06)      20    147 1 EEC = lbs ai/ A Table II g. Risk presumptions for aquatic plants.

Risk Presumption RQ LOC Acute High Risk EEC1/ EC50 1 Acute Endangered Species EEC/( EC05 or NOEC) 1 1 EEC = ( ppb/ ppm) in water Three measures are used to evaluate the risk hypotheses developed in the conceptual model for MCPB usage. First, the measures of exposure are derived as estimated environmental concentrations ( EECs) based on Prism Exam model predictions and environmental fate data. Second, the measures of effect characterize the assessment endpoints and are based on toxicity data that describe the effects of MCPB on individuals and species through terrestrial models such as; Trex ( version 1.1), Agdrift ( version 2.01) and Terrplant version 1.0). Third, the measures of ecosystem and receptor characteristics describe the attributes of the receptors and/ or ecosystems that may be affected by exposure to the stressor ( i. e. behavior and life history characteristics). This analysis plan also identifies the data gaps and uncertainties for conducting the risk assessment and suggests recommendations for new data collection.

1. Preliminary Identification of Data Gaps and Methods: Environmental fate data are available concerning the hydrolysis and photodegradation of MCPB in water, the biodegradation of MCPB in soil, and the mobility of MCPB in soil. However, information is not available concerning the fate of the aqueous phototransformation products. There are no acceptable study data on soil photolysis and aerobic or anaerobic aquatic biodegradation.

Toxicity studies are available to determine the potential acute effects to fish and aquatic invertebrates; however, no toxicity studies have been conducted to determine potential chronic effects to fish and aquatic invertebrates. The following chronic studies have not been submitted: early life cycle fish study, full life cycle fish study, and full life cycle aquatic invertebrate study. Therefore, chronic risk to these taxa cannot be evaluated and the risk assessment should be considered incomplete. Chronic risk to non endangered and listed aquatic animals cannot be dismissed.

Toxicity studies are available to determine the potential acute effects to birds, mammals and honey bees and the potential reproductive/ developmental effects to mammals. MCPB residues may affect the foraging behavior of herbivores ( birds, mammals) and of pollinators. However, data are not available to determine the potential exposure levels from residues in foliage, flowers and seeds. The only residue study ( MRID 44754101) available examined residues on peas at harvest. Therefore, the level of residues that occurred directly after application ( which would represent the highest concentration to which animals could be exposed) was not specified. No toxicity studies have been conducted ( Phase III 3/ 07/ 06)      21    147 to determine the effect of residues to pollinators. An MCPA chronic bird study was substituted for MCPB which resulted in a NOAEC of 1000 mg/ kg diet.

Spray drift presents a potential risk to non target plants inhabiting edge habitats adjacent to target fields and riparian vegetation along streams and/ or ponds in close proximity to sprayed fields. However, no effect levels in the vegetative vigor tests were not established for terrestrial plants. Also, the NOECs for aquatic plants were not determined. Therefore, the magnitude of spray drift that would cause effects to plants is not known.

Potential risk to estuarine/ marine species cannot be determined because studies were not submitted by the registrant.

2. Measures to Evaluate Risk Hypotheses and Conceptual Model Measures of Exposure Based on the conceptual model presented above, the potential exposure pathways for aquatic species include runoff/ leaching, spray drift, and residues in sediments. The potential exposure pathways for terrestrial species include ground deposition, runoff/ leaching and spray drift resulting in residues on non target plants. The exposure assessment for this risk assessment of MCPB will use Tier II models to provide a more realistic characterization that reflects actual labeled use. The Tier II PRZM/ EXAMS models will be used to predict EECs in surface water. This model provides peak concentrations in a variety of scenarios for ponds adjacent to treated areas, and can be used to vary the level of spray drift and surface runoff from a single large rain event. No transformation products were considered in the aquatic assessment as the environmental fate database was incomplete for degradates.

As part of the terrestrial assessment, EFED modeled exposure concentrations of MCPB to nontarget terrestrial plants and animals following the proposed application rates provided by the registrant. For terrestrial birds and mammals, estimates of initial levels of MCPB residues on various food items, which may be contacted or consumed by wildlife, were determined using the Kenega Fletcher nomogram followed by a first order decline model TREX 1.1. Exposure concentrations for nontarget plants were estimated using the TerrPlant 1.0 model. AgDrift 2.0.1 model provides further refinement of spray drift dispersion and deposition to terrestrial plants located in proximity to treated fields.

Measures of Effect Measures of effect are obtained from a suite of registrant submitted guideline studies conducted with a limited number of surrogate species. The test species are not intended to be representative of the most sensitive species, but rather were selected based on their ability to thrive under laboratory conditions. Consistent with EPA test guidelines, the registrant has provided ecological effect data. Acceptable guideline studies are available to assess the acute toxicity of MCPB sodium to aquatic fish and invertebrates, algae, ( Phase III 3/ 07/ 06)      22    147 aquatic vascular plants, birds, mammals, honey bees, and terrestrial plants, including monocots and dicots. Acceptable guideline studies are available to assess the subchronic and developmental effects to mammals.

Acute measures of effect are the concentrations that produce 50% mortality or growth reduction in the test organisms ( LC 50 s and EC 50 s, respectively). The measure of effect for terrestrial plants is the EC 25 . Chronic effects endpoints for listed and non listed plants are the highest test concentration where there is no observed adverse effect ( NOAECs) on survival and growth of terrestrial and aquatic plants.

III. ANALYSIS Analysis is a process that examines the two primary components of risk, exposure and effects, and their relationships between each other and site characteristics. The objective is to provide the ingredients necessary for determining or predicting ecological responses to pesticide uses under exposure conditions of interest. The products of analysis provide the basis for estimating and describing risks in risk characterization. The MCPB analysis consists of evaluating environmental fate data, modeling exposure concentrations and evaluating toxicity information to formulate potential risks to the defined endpoints shown in Figure II. b. The analysis is based on Tier II modeling of estimated exposure concentrations combined with toxicity information from MCPB toxicity studies.

A. Use Characterization MCPB ( 4( 2 methyl 4 chlorophenoxy) butyric acid ) is formulated as a sodium salt in aqueous solution. Methods of application include controlled droplet applicator, high volume ground sprayer, low volume ground sprayer, hand held sprayer, high volume spray ( dilute), low volume spray ( concentrate), aerial and ground broadcast, and spot treatment. Timing of application for the one registered use for peas is when shoots emerge until about three leaf nodes before flowering.

Supported formulations of MCPB are Thistrol ® Herbicide ( 71368 5) and Sodium MCPB Solution ( 71368 7). Copies of all labels may be found at http:// www. cdpr. ca. gov/ docs/ epa/ m2. htm.

The labels for MCPB do not contain specific requirements to minimize spray drift; only a broad statement is included to avoid spray drift to prevent injury to susceptible crops. The exception is the state of Florida, which has promulgated a rule ( Organo Auxin Herbicide Rule) that stipulates that buffer zones up to a half mile wide be observed when spraying phenoxy herbicides. The width of the required buffer zone is dependent on the wind speed and direction, and whether aerial or ground spray equipment is used. This has the potential to reduce the exposure susceptible non target plants to spray drift.

MCPB can be used on green and dry peas. The USDA crop profiles suggest that as a result, MCPB may be used throughout the country. For instance, USDA crop profiles indicate dry and green peas are grown in the following states: Delaware, Idaho ( green peas); Idaho, Montana, Washington ( dry peas) and Maryland, Minnesota, New York, Oregon and Wisconsin ( peas). ( Phase III 3/ 07/ 06)      23    147 The USGS also indicates MCPB usage on peas in Illinios, Michigan, Pennsylvania, New Jersey and Maine.

Because peas can be grown throughout the country, a variety of ecosystems may be exposed. The crop profile for Maryland peas indicates that peas are grown in estuarine watersheds which include Dorchester and Caroline counties. Other crop profiles such as Delaware suggest that MCPB may be used in estuarine as well as freshwater environments. USDA crop profiles and USGS 1992 use map can be accessed through the following websites. http:// pestdata. ncsu. edu/ cropprofiles/ cropprofiles. cfm http:// ca. water. usgs. gov/ pnsp/ use92/ mcpb. html.

B. Exposure Characterization The MCPB exposure characterization in this assessment combines the environmental fate data with Tier II exposure models to estimate environmental exposure concentrations ( EECs). Exposure models estimate EECs following the conceptual diagram of MCPB usage and potential exposure shown in Figure II. b. EECs for aquatic endpoints are developed using the Tier II surface water models PRZM/ EXAMS. These models are more comprehensive and determine EECs based on geographic areas nationwide and product use sites in close proximity to water bodies. EECs for birds and terrestrial mammals are estimated using the T REX 1.1 model, and EECs for non target plants are estimated by the TerrPlant 1.0 model.

1. Environmental Fate and Transport Study Summaries: Laboratory environmental fate data indicate that MCPB is likely to be mobile, but not persistent in the environment. Adsorption/ desorption studies of MCPB and a low octanol water partition coefficient indicate MCPB to be mobile in soil and soil: water systems. However, soil half lives indicate that MCPB would be relatively short lived and not likely to persist for extended periods in soils. Under aerobic soil conditions, the overall half life was 27 days and the major transformation product was volatilized 14CO 2. The half life for the anaerobic biodegradation of [ 14C] MCPB in sandy loam soil was 7.8 days and the major transformation product was ( 4 chloro 2 methylphenoxy) acetic acid ( MCPA).

Based on the physical and chemical properties, MCPB will exist predominately in the ionic or salt form at ambient environmental pHs. Based on simple chemical equilibrium calculation for MCPB ( a monobasic acid with a pKa of approximately 4.6), the degree of ionization of MCPB at pH 7 is 99.6%, and ranges from approximately 70% to 99.99+% at pHs 5 and 9, respectively. The only registered formulation for field application is the sodium salt.

The hydrolysis of [ phenyl U 14C] labeled ( 4( 2 methyl 4 chlorophenoxy) butyric acid ( MCPB) was studied in the dark at 25 ± 1 ° C in sterile aqueous 0.1 M buffer solutions adjusted to pH 5 ( acetate), pH 7 ( phosphate) and pH 9 ( borate) for 30 days in this acceptable study. The concentration of [ 14C] MCPB decreased from 94.4% at day 0 to 91.5% of the applied at study termination in the pH 5 solution, from 95.8% to 91.9% at pH 7, and from ( Phase III 3/ 07/ 06)      24    147 95.7% to 93.2% of the applied at pH 9. No major transformation product was detected in any of the solutions. Because less than 4% of MCPB hydrolyzed at any pH tested during a 30 day period, MCPB is essentially stable to hydrolysis for environmental fate purposes ( that is, half lives are indeterminately long during a 30 day test period). Gross extrapolation indicates half lives to be greater than 500 days ( MRID 42574301). The aqueous phototransformation of [ phenyl U 14C] labeled ( 4( 2 methyl 4 chlorophenoxy)

butyric acid( MCPB) was studied at 25 ± 1 ° C in sterile aqueous acetate, phosphate and borate buffer solutions at pH 5, 7 and 9, respectively. Irradiation was for 30 days ( 12 hours light/ 12 hours dark) with a filtered xenon arc lamp light source. The concentrations of [ 14C] MCPB decreased from 94.4% at day 0 to 0.2% of the applied at day 30 in the pH 5 solution, from 95.9% to < 0.1% at pH 7, and from 95.7% to < 0.1% at pH 9. Five transformation products were isolated at > 10% of the applied: 4 ( 4 hydroxy o tolyloxy) butyric acid; 2,4 dihyroxyphenyl formate; o cresol; benzoic acid; and 2 hydroxyphenyl formate. The half lives of MCPB in the irradiated pH 5, 7 and 9 buffer solutions measured in this acceptable study were 2.2, 2.6 and 2.4 days, respectively. Because the wavelengths and intensity of the filtered xenon arc lamp used in the laboratory experiment were equivalent to sunlight and there was no degradation in the dark control, no adjustments to the half lives are necessary ( MRID 42574302).

The adsorption/ desorption characteristics of phenyl ring labeled [ 14C] MCPB ( 4( 2 methyl 4 chlorophenoxy) butyric acid dissolved in methanol were studied in sterile sandy clay loam soil [ pH 6.09, organic carbon  1.3%] from France, and the following three soils and one sediment from England: sand soil [ pH  7.93, organic carbon  0.53%], sandy loam soil [ pH  6.08, organic carbon  0.76%], clay loam soil [ pH  7.6, organic carbon  2.49%], and sandy loam aquatic sediment [ pH  5.95, organic carbon  2.85%] in a batch equilibrium experiment. The mean adsorption Kads values calculated from this acceptable study were 1.69, 0.26, 0.65, 0.78, and 10.58 mL/ g for the sandy clay loam, sand, sandy loam, and clay loam soils and sandy loam sediment, respectively. Adsorption Koc values were 129.57, 47.91, 85.54, 31.27, and 371.17 mL/ g for the sandy clay loam, sand, sandy loam, and clay loam soils and sandy loam sediment, respectively. At the end of the desorption, 64.0%, 32.18%, 60.22%, 60.59%, and 24.63% of the adsorbed amount was desorbed in the sandy clay loam, sand, sandy loam, and clay loam soils and sandy loam sediment, respectively ( MRID 42693701).

The aerobic soil metabolism of [ phenyl U 14C] labeled ( 4( 2 methyl 4 chlorophenoxy) butyric acid ( MCPB) was studied in sandy loam soil ( pH in water 5.38, organic carbon 2.3%) from the United Kingdom for 120 days under aerobic conditions in darkness at 22 ± 1 ° C and soil moisture of 75% of 1/ 3 bar. The major transformation product of [ 14C] MCPB was volatilized 14CO2 which increased to a maximum 64.9 ± 0.6% of the applied at 65 days and was 54.5 61.8% at 90 120 days; no organic volatiles were detected. The overall aerobic half life in this acceptable study was 27.0 days ( r2 = 0.774, 0 120 days) with an initial half life of 9.1 days ( r2 = 0.952, 0 29 days) and a secondary half life of 79 days ( r2 = 0.659, 29 120 days). Two minor transformation products identified in soil extracts were the hexose conjugate of ( 4 chloro 2 methylphenoxy) 2   glucopyranoside acetic acid minor ( CHPA) and ( 4 chloro 2 methylphenoxy) acetic acid ( MCPA), which were detected at maximums of 9.5% ( 8 days) and 7.2% ( 15 days) of the applied radioactivity, respectively, with both decreasing to   2.1% by 120 days. Five additional unidentified [ 14C] compounds were each   5.3% of the applied at any sampling interval. ( Phase III 3/ 07/ 06)      25    147 The registrant proposed a biotransformation pathway for the degradation of MCPB in aerobic soil indicating degradation of MCPB to ( 4 chloro 2 methylphenoxy) acetic acid ( MCPA), which degrades to ( 4 chloro 2 methylphenoxy) 2   glucopyranoside acetic acid minor ( CHPA) and conjugates with hexose; and significant production of CO2. ( MRID 43247601).

The anaerobic soil metabolism of [ phenyl U 14C] labeled ( 4( 2 methyl 4 chlorophenoxy) butyric acid ( MCPB) was studied in sandy loam soil ( pH in water 7.7, organic carbon 0.3%) incubated for 62 days under anaerobic conditions ( flooding plus nitrogen atmosphere) in darkness at 25 ± 1 ° C following 4 days of aerobic incubation. Anaerobic half life values of [ 14C] MCPB in the water, soil and entire system using least squares linear regression analysis, based on first order kinetics, of [ 14C] MCPB recovered in each sample were 18.9, 7.8 and 11.4 days, respectively. The major transformation product of [ 14C] MCPB was ( 4 chloro 2 methylphenoxy) acetic acid ( MCPA) detected at maximums of 34.8% in the soil at 4 days just prior to flooding, 33.4% in the water after 14 days of anaerobic incubation, and 46.9% in the total soil: water system after 29 days. After 62 days of anaerobic incubation, [ 14C] MCPA was 6.6 ± 2.1% of the applied in the soil, 27.8 ± 4.8% in the water and 34.3 ± 2.7% in the entire soil: water system ( MRID 43015501). This study was classified as " acceptable".

Valid terrestrial field dissipation and soil photolysis studies are not available.

2. Measures of Aquatic Exposure Aquatic Exposure Modeling Aquatic exposure concentrations for MCPB in the standard field pond were estimated using the PRZM 3.12 and EXAMS 2.98 models in tandem. PRZM/ EXAMS is a Tier II screening model designed to estimate pesticide concentrations found in water at the edge of a treated field. As such, it provides high end values of the pesticide concentrations that might be found in ecologically sensitive environments following pesticide application.

PRZM/ EXAMS is a multi year runoff model that also accounts for spray drift from single and multiple applications. In the ecological exposure assessment, PRZM/ EXAMS simulates a 10 hectare ( ha) field immediately adjacent to a 1 ha pond, 2 meters deep with no outlet. The geographic location of the field is specific to the crop being simulated using site specific information on the soils, weather, cropping, and management factors associated with the scenario. The crop/ location scenario is intended to represent a highend vulnerable site on which the crop is normally grown. Based on historical rainfall patterns, the pond receives multiple runoff events during the years simulated.

Acute risk assessments are performed using 1 in 10 year peak EEC values for single applications of MCPB. Chronic risk assessments for aquatic invertebrates and fish are performed using the average 21 day and 60 day EECs, respectively.

Table III. a. presents the input parameters used in the Tier II PRZM/ EXAMS modeling for ecological assessment of MCPB for surface water sources. To simulate field application of MCPB to peas, two scenarios were selected representing different MCPB usage areas based on geography and weather. A California lettuce and an Oregon snap ( Phase III 3/ 07/ 06)      26    147 bean scenario were chosen as representative of the agricultural practices and areas in which peas are grown. The EECs for the two scenarios are presented in Table III. b. The Oregon scenario represents the typical use of MCPB application to peas, and the California scenario represents a reasonable upper bound estimate. Results for the two cases are similar. We also investigated several other possible scenarios ( approximately six others), and found all EECs to be rather tightly grouped in a range from approximately 15 to 40 µ g ae/ L. The PRZM/ EXAMS input and output files from the California and Oregon aquatic ecological exposure assessments are presented in Appendix B.

TABLE III. a. PRZM/ EXAMS Input Parameters for MCPB.

Model Parameter Value Comments Source Application Rate per Event 1.68 kg ae/ acre ( 1.5 lbs ae/ acre) application to peas by ground and aerial spray application Label Number of Applications per Crop Season 1 application per year; assumes one planting season per year Label Spray Application Efficiencies ground aerial 0.99 0.95 EFED Guidance, 2002 Spray Drift Fraction ground aerial 0.01 0.05 EFED Guidance, 2002 Aerobic Soil Metabolism t ½ 78 days 1 estimated upper 90 th percentile MRID 43247601 Anaerobic Soil Metabolism t ½ 34 days 2 estimated upper 90 th percentile MRID 43015501 Aerobic Aquatic Degradation t ½ 156 days 3 estimated ( 2x aerobic soil metabolism half life) EFED Guidance, 2002 Anaerobic Aquatic Degradation t ½ 68 days 4 estimated ( 2x anaerobic soil metabolism half life) EFED Guidance, 2002 Aqueous Photolysis t ½ 2.6 days pH 7 MRID 42574302 Hydrolysis t ½ stable MRID 42574301 Kd/ Koc 0.85 mL/ g 5 Average Kd MRID 42693701 Molecular Weight 228.6 Chemical Formula Water Solubility 600 mg/ L 10 x solubility Product Chemistry Vapor Pressure 4.0E 7 torr Product Chemistry Henry's Law Constant ( estimated at 25 ° C) 3.42 x 10 9 atmm3 mol ( Howard and Meylan, 1997) ( Phase III 3/ 07/ 06)      27    147 1 Upper 90th Percentile based on three times the single value for the combined/ total aerobic soil metabolism half life of 26 days for MCPB, MCPA, and CHPA/ CHPA hexose conjugate. 2 Upper 90th Percentile based on three times the single anaerobic soil metabolism half life of 11.4 days. 3 2x aerobic soil metabolism half life ( EFED Modeling Input Parameter Guidance, 2002). 4 2x anaerobic soil metabolism half life ( EFED Modeling Input Parameter Guidance, 2002). 5 From adsorption/ desorption data including Kd values of 1.69, 0.26, 0.65, and 0.78 mL/ g from MRID 42693701.

TABLE III. b. Estimated Environmental Concentrations ( µ g ae/ L) of MCPB + Metabolites ( MCPA and CHPA/ CHPA hexose) in Surface Water ( PRZM EXAMS) from All Uses for Ecological Assessment.

Simulation Scenario Concentration ( µ g ae/ L)

Crop and Location Application rate 1 in 10 year Peak 21 Day Max. 60 Day Max.

Lettuce ( CA) ( Surrogate for Peas) 1 .5 lbs ae/ acre ( 1.68 kg ae/ ha) ground spray aerial spray 40.4 43.2 39.0 41.7 36.4 38.9 Snap Beans ( OR) ( Surrogate for Peas) 1 .5 lbs ae/ acre ( 1.68 kg ae/ ha) ground spray aerial spray 29.5 33.1 29.0 32.5 28.1 31.5 The following surrogate scenarios are among those available in PRZM/ EXAMS to simulate peas grown in different regions of the US: California lettuce scenario represents a reasonable upper bound estimate for areas in which peas are or may be grown. Oregon snap bean scenario represents a typical use scenario for areas in which peas are grown. Input and output for PRZM3.12/ EXAMS2.98 modeling is in Appendix B.

Aquatic Exposure Monitoring and Field Data Surface water and groundwater monitoring data were not available for evaluation in this risk assessment.

3. Measures of Terrestrial Exposure Terrestrial Exposure Modeling For birds and mammals, MCPB concentrations on food items, based on data from Hoerger and Kenaga ( 1972) and Fletcher et al. ( 1994), are predicted using a first order residue decline method. EFEDs T REX ( Ver. 1.1) model predicts maximum and mean EECs resulting from the single application of MCPB. Acute and Chronic RQs are calculated using these EECs and appropriate toxicity data.

TABLE III. c. Estimated Environmental Concentrations ( ppm ae) of MCPB Acid on Terrestrial Food Items from Use on Peas.

Simulation Scenario Concentration ( ppm ae)

Crop Food item Maximum Mean Peas Short Grass Tall Grass Broadleaf Plants/ Small Insects 360 165 202.5 127.5 54 67.5 ( Phase III 3/ 07/ 06)      28    147 TABLE III. c. Estimated Environmental Concentrations ( ppm ae) of MCPB Acid on Terrestrial Food Items from Use on Peas.

Simulation Scenario Concentration ( ppm ae)

Crop Food item Maximum Mean Fruits/ Pods/ Seeds/ Large Insects 22.5 10.5 Effects on non target terrestrial plants are most likely to occur as a result of spray drift from aerial and ground applications of the liquid formulation. Spray drift is an important factor in characterizing the risk of MCPB to non target plants. The TerrPlant ( Ver. 1.0) model predicts EECs for terrestrial plants located adjacent to the treated field. MCPB applied according to label directions as a liquid spray for ground or aerial applications may impact non target plants for some distance from the application site depending on droplet size, wind speed, and other factors. The MCPB product label does not specify a required or recommended droplet size for spray applications. MCPB applied as a fine or medium spray has the potential to damage off target plants. In addition to the TerrPlant modeling of EECs, refinement of spray drift from treated fields was assessed with the AgDrift ( Ver. 2.0.1) model. The AgDrift model provides estimates of drift dispersion and deposition as the result of ground and aerial spray droplet and nozzle size, wind speed and distance from the treated field.

Residue Studies No residues of MCPB or its primary degradate, MCPA, were detected on peas and pods at harvest after broadcast treatment of Thistrol ( 1.5 lbs. ae/ acre) in eight field trials conducted in 1999 ( MRID 44754101). Succulent peas and pods were sampled 29 34 days after treatment with MCPB ( 1.5 lbs. ae/ acre) and dried peas were sampled 42 64 days after MCPB treatment and analyzed for residues. The maximum residue to which animals could be exposed would occur directly after application. The decline of residues from this maximum level was therefore not measured. To assess the potential risk to birds and terrestrial animals from exposure to residues immediately following application to pea plants, EFED modeled exposure concentrations using TRex ( ver. 1.1). These modeled residue concentrations on pea plants provide the avian and terrestrial mammal EECs for risk calculations. Since the foliar dissipation half life could not be determined from the residue study, a default value of 35 days was used.

C. Ecological Effects Characterization 1. Aquatic Effects Characterization The following tables present measures of effect both in terms of active ingredient and acid equivalents. Conversion from active ingredient to acid equivalents was made in accordance with molecular weight differences. One gram mole of MCPB acid has a mass of 228.67 grams and one gram mole of MCPB sodium salt has a mass of 250.66 grams; therefore, one unit of the salt would be equivalent to 0.912 units of the acid. Hence, the LC50 values from the toxicity tests with MCPB sodium were converted to acid equivalents by multiplying the values by 0.91. ( Phase III 3/ 07/ 06)      29    147 TABLE III. d. Summary of endpoints for MCPB acute and chronic aquatic toxicity studies for RQ evaluation Endpoint Environment/ Species Toxicity Value Used in Risk Assessment MRID# Comment Freshwater Rainbow Trout ( TGAI) 96 hr LC50 = 3.9 mg ae/ L 4253260 8 Acceptable Acute Toxicity to Fish Estuarine/ mari ne No data ( TGAI) No data NA No studies were submitted Freshwater No data ( TGAI) No data NA No studies were submitted Chronic Toxicity to Fish Estuarine/ mari ne No data No data NA No studies were submitted Freshwater Daphnia magna ( TGAI) 48 hr EC50 = 50.0 mg ae/ L 4253260 2 Acceptable Acute Toxicity to Invertebrates Estuarine/ mari ne No data ( TGAI) No data NA No studies were submitted Freshwater No data ( TGAI) No data NA No studies were submitted Chronic Toxicity to Invertebrates Estuarine/ mari No data NA No studies were submitted ( Phase III 3/ 07/ 06)      30    147 Endpoint Environment/ Species Toxicity Value Used in Risk Assessment MRID# Comment ne No data Toxicity to Aquatic Plants Vascular Duckweed ( TGAI) NonVascular Green Algae ( TGAI) EC50 = 0.21 mg ae/ L NOEC = <. 01mg ae/ L* EC50 = 0.38 mg ae/ L NOEC = <. 31mg ae/ L* 4.25e+ 15 Based on frond production Based on reduced cell density * NOEC can not be determined due to non discreet toxicity value therefore definitive endangered species RQs can not be calculated. EC05 was not available.

Freshwater Fish, Acute Fish toxicity studies for two freshwater species using the TGAI are required to establish the acute toxicity of MCPB to fish. The preferred test species are rainbow trout ( a coldwater fish) and bluegill sunfish ( a warmwater fish). The acute studies that were submitted that tested the parent compound showed that MCPB sodium is moderately toxic to the more sensitive coldwater rainbow trout ( LC 50 3.9 mg ae/ L) and slightly toxic to the warmwater bluegill ( LC 50 12.7 mg ae/ L). EFED will use ( LC 50 3.9 mg ae/ L) for evaluating acute risk to freshwater fish. The guideline ( 72 1) is fulfilled ( MRID 42532608; MRID 42532601).

TABLE III. e. Freshwater Fish Acute Toxicity for MCPB Sodium.

Species 96 hour LC50 ( mg ai/ L) ( nominal) 96 hour LC50 ( mg ae/ L) ( nominal) Toxicity Category MRID No. Author/ Year Study Classification Bluegill sunfish ( Lepomis macrochirus) 14 12.7 Slightly toxic 42532601 Bettencourt, 1992 Acceptable Rainbow trout ( Oncorhynchus mykiss) 4.3 3.9 Moderately toxic 42532608 Bettencourt, 1992 Acceptable Studies performed by the registrant for the anaerobic soil degradate MCPA indicate that it is less toxic to fish ( LC 50 values ranging from > 68  > 79 mg ae/ L).

Freshwater Invertebrates, Acute ( Phase III 3/ 07/ 06)      31    147 A freshwater aquatic invertebrate toxicity test using the TGAI is required to establish the toxicity of MCPB to aquatic invertebrates. The preferred test species is Daphnia magna. The data that were submitted that tested the parent compound showed that MCPB sodium is slightly toxic to Daphnia magna with an acute 48 hour EC 50 value of 50 mg ae/ L. EFED will use this value for evaluating acute risk to freshwater invertebrates. The guideline requirement ( 72 2) for acute invertebrate toxicity is fulfilled ( MRID 42532602).

TABLE III. f. Freshwater Invertebrate Acute Toxicity for MCPB Sodium.

Species 48 hour EC50 ( mg ai/ L) 48 hour EC50 ( mg ae/ L) Toxicity category MRID No. Author/ Year Study Classificatio n Waterflea ( Daphnia magna) 55 50 Slightly toxic 42532602 Putt, 1992 Acceptable A study performed by the registrant for MCPA indicates that the degradate is practically non toxic to aquatic invertebrates with an EC 50 of > 184 mg ae/ L.

Freshwater Fish, Chronic A freshwater fish early life stage test and life cycle fish test using the TGAI were not submitted by the registrant. Therefore, the guidelines ( 72 4a; 72 5) were not fulfilled.

Freshwater Invertebrate, Chronic A freshwater aquatic invertebrate life cycle test using the TGAI was not submitted by the registrant. The preferred test is a 21 day life cycle study with Daphnia magna. The guideline ( 72 4b) was not fulfilled.

Freshwater Field Studies Aquatic field studies were not submitted.

Estuarine/ Marine Fish and Invertebrate, Acute and Chronic Estuarine/ marine studies were not submitted by the registrant. Therefore, the following guidelines were not fulfilled: ( 72 3a for acute fish  sheepshead minnow; 72 3b for acute invertebrate  eastern oyster; 72 4d for mysid life cycle).

Aquatic Plants Several aquatic plant toxicity studies using the TGAI were submitted to establish the toxicity of MCPB to non target aquatic plants. The recommendation is for testing of five species: freshwater green alga ( Selenastrum capricornutum), duckweed ( Lemna gibba), marine diatom ( Skeletonema costatum), blue green algae ( Anabaena flos aquae), and a freshwater diatom. The EC 50 for the freshwater vascular plant ( duckweed) is 0.21 mg ( Phase III 3/ 07/ 06)      32    147 ae/ L, based on reduced frond production; and the lowest EC 50 for freshwater nonvascular plants is 0.38 mg ae/ L, based on reduced cell density in the green algae study. Studies submitted for the algal species indicate that the green algae is more sensitive to MCPB sodium than the blue green algae causing reductions in cell density at the lowest level tested ( 0.31 mg ae/ L). The freshwater diatom was more sensitive to MCPB sodium than the marine diatom causing reductions in cell density at test levels as low as 0.12 mg ae/ L. The aquatic vascular plant, duckweed was the most sensitive of the five aquatic species tested. Concentrations as low as 0.15 mg ae/ L resulted in chlorosis, curling, and decreased root formation in the plant. In addition, frond biomass was significantly reduced at 0.42 mg ae/ L. The guideline requirements ( 122 2 and 123 2) are fulfilled; MRID 42532603; MRID 42532604; MRID 42532605; MRID 42532606; and MRID 42532609) for the five required species.

TABLE III. g. Non target Aquatic Plant Toxicity for MCPB Sodium.( ai)/ MCPB acid ( ae)

Species [ Study Type] EC50/ NOEC ( mg ai/ L) EC50/ NOEC ( mg ae/ L) Endpoints Affected MRID No. Author, Year Study Classification Duckweed ( Lemna gibba) [ Tier I] 0.23/< 0.011 1.7/ 0.17 0.21/< 0.01*

1.55/ 0.15 Frond production Frond biomass 42532604 Hoberg, 1992 Acceptable Green Algae ( Selenastrum capricornutum) [ Tier I] 0.42/< 0.34 0.38/< 0.31* Cell density 42532605 Hoberg, 1992 Acceptable Blue green Algae ( Anabaena flosaquae [ Tier I] > 2.1/ 2.1 > 1.9/ 1.9 Cell density 42532603 Hoberg, 1992 Acceptable Diatom ( Navicula pelliculosa) [ Tier I & II] 0.71/ 0.048 0.65/ 0.044 Cell density 42532609 Hoberg, 1992 Acceptable Diatom ( Skeletonema costatum) [ Tier I & II] 1.5/< 0.11 1.36/ 0.10 Cell density 42532606 Hoberg, 1992 Acceptable * Can not determine a NOEC due to a non discreet toxicity value. Endangered species risk quotient can not be calculated without a NOEC.

Aquatic plant studies with the anaerobic soil degradate MCPA acid indicate that the toxicity is very similar to MCPB with the EC 50 for the freshwater vascular plant ( duckweed) of 0.17 mg ae/ L ( MRID 43126501) and the lowest EC 50 for the freshwater non vascular plant ( diatom) of 0.63 mg ae/ L ( MRID 43083202).

2. Terrestrial Effects Characterization The following tables present measures of effect both in terms of active ingredient and acid equivalents. Conversion from active ingredient to acid equivalents was made in accordance with molecular weight differences. One gram mole of MCPB acid has a mass of 228.67 grams and one gram mole of MCPB sodium salt has a mass of 250.66 grams; therefore, one unit of the salt would be equivalent to 0.912 units of the acid. ( Phase III 3/ 07/ 06)      33    147 Hence, the LC50 values from the toxicity tests with MCPB sodium were converted to acid equivalents by multiplying the values by 0.91.

Birds, Acute An oral toxicity study using the technical grade of the active ingredient ( TGAI) is required to establish the acute toxicity of MCPB to birds. The preferred guideline test species is either mallard duck ( a waterfowl) or bobwhite quail ( an upland gamebird). The data that were submitted report that the 14 day oral LD 50 is 257 mg ae/ kg. The NOEL was not determined due to abnormal effects at the lowest level tested. Observed effects including lethargy, dyspnea, loss of righting reflex and diarrhea. Gross necropsy showed white areas/ film on the heart, liver, gizzard, gallbladder, crop or intestines. Based on these results, MCPB is categorized as moderately toxic to avian species on an acute oral basis; the guideline ( 71 1) is fulfilled ( MRID 42560801).

TABLE III. h. Avian Acute Oral Gavage Toxicity for MCPB Sodium. ( ai)/ MCPB Acid ( ae)

Species LD50 ( mg LD50 ( mg Toxicity Category MRID No. Author, Year Study Classification Northern bobwhite quail ( Colinus virginianus) 282 257 Moderately toxic 42560801 Pederson and Helsten, 1992 Acceptable Two dietary studies using the TGAI are required to establish the acute toxicity of MCPB to birds. The preferred test species are mallard duck and bobwhite quail. The data that were submitted show that the 8 day acute dietary LC 50 for both species was > 4,550 ppm ae; therefore, MCPB sodium is categorized as practically non toxic to avian species on an acute dietary basis. The 8 day NOELs for each species based on sublethal effects ( reduced body weight gain) were 1138 ppm ae. In addition, gross necropsy revealed white spots on the liver of one bird and a dark red spot on the liver of another bird. The guideline ( 71 2) is fulfilled ( MRID 42560802; MRID 42560803).

TABLE III. i. Avian Acute Dietary Studies for MCPB Sodium ( ai)/ MCPB Acid ( ae)

Species 8 Day LC50 ( ppm ai) 8 Day LC50 ( ppm ae) Toxicity Category MRID No. Author, Year Study Classification Northern bobwhite quail ( Colinus virginianus) > 5,000 > 4,550 Practically non toxic 42560802 Pederson and Helsten, 1992 Acceptable Mallard duck ( Anas platyrhynchos) > 5,000 > 4,550 Practically non toxic 42560803 Pederson and Helsten, 1992 Acceptable Avian toxicity studies performed to determine the toxicity of the anaerobic soil degradate MCPA indicate similar results to MCPB sodium ( oral LD 50 221 to 377 mg ae/ kg bw in bobwhite quail; acute dietary LC 50 > 4,680 mg ae/ kg diet for both bobwhite quail and mallard duck). ( Phase III 3/ 07/ 06)      34    147 Birds, Chronic Avian reproduction studies using the TGAI are usually required for pesticide registration because birds may be subject to repeated or continuous exposure to the pesticide, especially preceding or during the breeding season. The preferred test species are mallard duck and bobwhite quail. No chronic bird studies were submitted for MCPB. EFED considered MCPA as a substitute for MCPB for chronic risk to birds, because the LD50 for bobwhite quail suggests that the acute potency of MCPB lies within the range of toxicity for acid equivalent MCPA. Also, rapid dissociation of MCPB to MCPA is expected to occur in the bird gut due to the chemical properties of MCPB. The chronic bird study for MCPA with bobwhite quail has a NOAEC of 1000 mg/ kg diet ( MRID # 435052 01) . No further studies are required for chronic risk to birds for MCPB at this time.

Mammals, Acute Wild mammal testing is required on a case by case basis, depending on the results of lower tier laboratory mammalian studies, intended use pattern and pertinent environmental fate characteristics. In most cases, rat or mouse toxicity values obtained from the Agency's Health Effects Division ( HED) substitute for wild mammal testing. These toxicity values are reported below.

The results indicate that MCPB is categorized as slightly toxic to practically non toxic to small mammals on an acute oral basis ( LD 50 values range from 912  7,400 mg ai/ kg/ day). The guideline 81 1 is fulfilled ( MRID 116340; MRID 144801).

TABLE III. j. Mammalian Acute Toxicity for MCPB.

Species % Purity Test Type Toxicity Affected Endpoints MRID No. Study author Classification Rat ( Rattus norvegicus) Tech Acute oral LD50 = 3100 5800mg ai/ kg/ day ( males) LD50 = 3800 74 00mg ai/ kg/ day ( females) Mortality 144801 Kynoch, 1985 Acceptable Rat ( Rattus norvegicus) Tech Acute oral LD50 = 912 2700 mg ai/ kg/ day ( males) LD50 = 969 2981 mg ai/ kg/ day ( females) Mortality 116340 Holsing, 1969 Acceptable Mammals, Subchronic and Developmental/ Reproductive Three subchronic feeding studies were performed with MCPB. In the two dog studies, reproductive effects, including testicular and prostate atrophy and curtailment of spermatogenic activity, were observed. In the acceptable dog study ( MRID 42883603), the LOAEL was 44 mg ai/ kg/ day based on reduced testes weights and physiological changes in clinical chemistry. The NOAEL was 25 mg ai/ kg/ day. Clinical chemistry changes in these studies ( increase in creatinine and urea nitrogen) were also related to MCPB exposure. In the rat study, the decreased food consumption and body weight gains were attributed to the lack of palatability of MCPB in the feed. Because no microscopic effects were observed in the rat study, the other effects were considered not to be toxicologically significant. The guidelines 82 1a and 82 1b are fulfilled ( MRID 42883602; MRID 42883603). ( Phase III 3/ 07/ 06)      35    147 In developmental toxicity studies with rats and rabbits, maternal toxicity was observed at doses ranging from 20  100 mg/ kg/ day. In the rat study, the maternal toxicity observed at 100 mg ai/ kg/ day included decreased body weights and body weight gains during gestation. In the rabbit study, maternal toxicity observed at 20 mg ai/ kg/ day included maternal deaths, clinical signs of toxicity, decrease in body weight gain during treatment, and change in color of liver and kidneys.

Developmental effects were observed in rats at a dose of 100 mg ai/ kg/ day, including decreased mean body weights/ litter for males and females, increases in unossified or poorly ossified sites and increases in several other skeletal variations. No malformations or variations were observed in the rabbit fetuses at the highest dose tested, 20 mg ai/ kg/ day. EFED will use the NOAEL for maternal toxicity of 5 mg ai/ kg/ day from the rabbit study for evaluating the developmental toxicity of MCPB acid to mammals. The guideline 83 3 is fulfilled ( MRID 40865401; MRID 40865402).

Maternal toxicity and developmental effects were also observed in a 2 generation reproduction study with rats exposed to the degradate MCPA ( MRID 40041701). The NOAEL for maternal toxicity was 7.5 mg ai/ kg/ day and the LOAEL was 22.5 mg ai/ kg/ day based on increased absolute and relative ovary weights. No maternal mortality was observed with exposure to MCPA. The LOAEL for offspring toxicity was 22.5 mg ai/ kg/ day based on decreased pup weight gain during lactation; the NOAEL was 7.5 mg ai/ kg/ day. No LOAEL was established for developmental toxicity.

TABLE III. k. Mammalian Chronic and Developmental/ Reproductive Toxicity for MCPB.

Species % Purity Test Type Toxicity ai Affected Endpoints MRID No. Study author Classification Dog NA Subchronic feeding  13 weeks NOEL = 480 ppm LOEL = 1600 ppm Reproduction1 116345 Rhodia, 1970 Supplemental Dog 91.1 Subchronic feeding  13 weeks NOEL = 25 mg ai/ kg/ day LOEL = 44 mg ai/ kg/ day Reproduction2 42883603 Dalgard, 1993 Acceptableminimum Rat 91.1 Subchronic feeding  13 weeks NOEL = 158 mg ai/ kg/ day No effects 42883602; 42883601 Trutter, 1993 Acceptableminimum Rat 97.6 Development al NOAEL/ LOAEL = 25/ 100 mg ai/ kg/ day NOAEL/ LOAEL= 25/ 100 mg ai/ kg/ day Maternal tox3 Developmental 40865402 Tyl, 1988 Acceptable Rabbit 97.6 Development al NOAEL/ LOAEL = 5/ 20 mg ai/ kg/ day NOAEL = 20 mg ai/ kg/ day Maternal tox4 Developmental 40865401 Tyl & Neeper Bradley, 1988 Acceptable Rat ( MCPA) 94.8% Reproduction NOAEL/ LOAEL = 7.5/ 22.5 mg ai/ kg/ day NOAEL/ LOAEL = 7.5/ 22.5 mg ai/ kg/ day NOAEL = 22.5 mg ai/ kg/ day Maternal tox5 Offspring tox Developmental 40041701 MacKenzie, 1986 Acceptable ( Phase III 3/ 07/ 06)      36    147 1 Testicular and prostate atrophy; curtailment of spermatogenic activity.

2 Reduced testes weights; physiological changes in clinical chemistry.

3 Maternal toxicity  Decreased body weight and body weight gain during gestation. Developmental toxicity  Decreased mean body weights/ litter; increases in unossified or poorly ossified sites; skeletal variations.

4 Maternal toxicity  Death, clinical signs of toxicity, decrease in body weight gain, change in color of liver and kidneys. Developmental toxicity  No malformations or variations were observed in the fetuses. 5Maternal toxicity  Increased absolute and relative ovary weights Offspring toxicity  Decreased pup weight gain during lactation. Developmental toxicity  No malformations were observed in the fetuses.

Insects, Acute Contact A honey bee acute contact study using the TGAI is required for MCPB because its foliar application treatment use will result in honey bee exposure. The acute contact LD 50 , using the honey bee, Apis mellifera, is an acute contact, single dose laboratory study designed to estimate the quantity of toxicant required to cause 50% mortality in a test population of bees. The acute contact LD 50 for MCPB sodium is > 23 µ g ae/ bee and it is, therefore, classified as practically non toxic to bees on a contact exposure basis. The guideline ( 141 1) is fulfilled ( MRID 42532607). No acute contact studies were available for the degradate MCPA.

TABLE III. l. Non target Insects  Acute Contact for MCPB Sodium ( ai)/ MCPB Acid ( ae)

Species LD50 ( µ g ai/ bee) LD50 ( µ g ae/ bee) Toxicity Category MRID No. Author/ Year Study Classification Honey Bee ( Apis mellifera) > 25 > 23 Relatively non toxic 42532607 Maggi, 1992 Acceptable Insects, Residual Contact A honey bee toxicity of residues on foliage study is required on an end use product for any pesticide intended for outdoor application when the proposed use pattern indicates that honey bees may be exposed to the pesticide and when the formulation contains one or more active ingredients having an acute contact honey bee LD 50 which falls in the moderately toxic or highly toxic range. The purpose of this guideline study is to develop data on the residual toxicity to honey bees. Bee mortality determinations are made from bees exposed to treated foliage harvested at various time periods after treatment. No residue toxicity study was submitted by the registrant; however, the acute contact honey bee LD 50 falls in the relatively non toxic range.

Terrestrial Plants Terrestrial Tier II studies are required for any pesticide showing a negative response equal to or greater than 25% in Tier I studies. Tier I and II terrestrial plant toxicity studies were conducted to establish the toxicity of MCPB to non target terrestrial plants. The recommendations for seedling emergence and vegetative vigor studies are for testing of ( 1) six species of at least four dicotyledonous families, one species of which is soybean ( Glycine max) and the second of which is a root crop, and ( 2) four species of at least two monocotyledonous families, one of which is corn ( Zea mays). The guidelines ( 122 1a; 122 1b; 123 1a; 123 1b) are fulfilled ( MRID 42560804). The guideline study met ( Phase III 3/ 07/ 06)      37    147 the requirements for Tier II seedling emergence testing for all ten required species; for Tier II vegetative vigor testing for cabbage, cucumber, lettuce, onion, ryegrass, radish, soybean, and tomato; and for Tier I vegetative vigor testing for corn and oat. Tier II vegetative vigor testing was not required for corn and oat because results from Tier I testing showed that < 25% detrimental effects were observed from the maximum label rate.

These studies indicate that the most sensitive monocot species in seedling emergence tests was the onion with the lowest EC 25 of 0.02 lb ae/ A based on shoot length. This value represents 0.093% of the maximum application rate for MCPB sodium. The most sensitive dicot species tested was cabbage with an EC 25 of 0.016 lb ae/ A in the seedling emergence study based on shoot length. The most sensitive monocot in the vegetative vigor test was also onion, with an EC25 of 0.016 lb ae/ A based on shoot weight. The most sensitive dicot species tested was tomato with an extrapolated EC 25 of 0.0017 lb ae/ A in the seedling emergence study based on shoot weight.

The observed non lethal effects included brown leaf tips in cabbage, corn, onion, ryegrass, radish, and soybean; necrosis in corn, radish, onion, and soybean; chlorosis in onion, cucumber, and lettuce; stem tumors in soybean and tomato; leaf curl in tomato, and decreased size in cabbage, cucumber, lettuce, onion, and ryegrass.

There is significant uncertainty in the vegetative vigor EC 25 values for dicots, because they were extrapolated below the lowest dose tested in the study. Furthermore, the NOEC values reported in the original study were reported as being higher than the EC 25 values. Further extrapolation of the data needs to be done to derive EC 05 values from the dose response curves for the vegetative vigor study. The uncertainty in these EC 05 values will be high; new data with lower application rates which bracket observed EC 25 and EC 05 levels would improve the assessment of potential risks to nonendangered and endangered/ listed terrestrial plants.

Results of Tier II toxicity tests with the soil degradate MCPA indicate that it also adversely affects seedling emergence and vegetative vigor in monocots and dicots. As with MCPB, onion was the most sensitive monocot tested with the lowest EC 25 of 0.028 lb ae/ A in the seedling emergence test. The most sensitive dicot species tested was cabbage with an EC 25 of 0.008 lb ae/ A in the seedling emergence study. The most sensitive dicot in the vegetative vigor test were the lettuce and turnip with an EC 25 of 0.013 lb ae/ A ( MRID 43083205).

Terrestrial Field Studies The requirement for terrestrial field studies was waived. TABLE III. m. Terrestrial Non target Plant Toxicity.*

Seedling Emergence Vegetative Vigor Shoot length Root weight Shoot length Shoot weight Species EC25/ NOEC ( lb ai/ A) EC25/ NOEC ( lb ae/ A) EC25/

NOEC ( lb ai/ A) EC25/

NOEC ( lb ae/ A) EC25/ NOEC ( lb ai/ A) EC25/ NOEC ( lb ae/ A) EC25/ NOEC ( lb ai/ A) EC25/ NOEC ( lb ae/ A)

Monocots Corn 0.23/ 0.19 0.21/ 0.17

Oat 0.12/ 0.093 0.11/ 0.08

Onion 0.021/ 0.012 0.02/ 0.01         0.018/< 0.088 0.016/< 0.08 Ryegrass 0.48/** 0.44/**      / 1.3  / 1.18

Dicots Cabbage 0.017/ 0.012 0.016/ 0.01  / 0.088  / 0.080 0.24/ 0.21/ 0.0079/ 0.0072/

Cucumber 0.10/ 0.093 0.091/ 0.085     0.53/ 0.34 0.48/ 0.31

Lettuce 0.059/** 0.054/** 0.027/   0.025/  0.055/  0.050/ 0.017/** 0.015/**

Radish 0.045/** 0.041/**     0.22/ 0.043 0.20/ 0.039

Soybean 0.13/ 0.048 0.12/ 0.044 0.14/ 0.13/ 0.45/  0.41/  0.072/** 0.066/**

Tomato 0.17/ 0.093 0.15/ 0.085    0.45/  0.41/  0.0017/** 0.0015/**

* MRID 42560804, Study author: K. Christensen, 1992, 38.9% active ingredient.

* NOEC reported in study higher than EC25. Further statistical analysis needed to establish EC05 for endangered species assessment. 39 ( Phase III 3/ 07/ 06)      40    147 IV. RISK CHARACTERIZATION Risk characterization provides the final step in the risk assessment process. In this step, exposure and effects characterization are integrated to provide an estimate of risk relative to established levels of concern ( LOCs). The results are then interpreted for the risk manager through a risk description and synthesized into an overall conclusion.

A. Risk Estimation  Integration of Exposure and Effects Data 1. Non target Aquatic Animals and Plants Estimated environmental concentrations ( EECs) from ground and aerial spray scenarios were calculated using the PRZM 3.12/ EXAMS 2.98 Oregon snap bean scenario and California lettuce scenario. As described in the exposure characterization, the input parameters were adjusted to account for degradates MCPA and CHPA hexose, which accounted for a maximum of 6  7% of MCPB in the aerobic soil metabolism study. Since MCPA has been shown to be less toxic to aquatic organisms than parent MCPB, and the toxicity of CHPA hexose is not known, the inclusion of these residues in the aquatic exposure modeling may be a conservative assumption.

Fish and Invertebrates For ground and aerial spray scenarios using the PRZM 3.12/ EXAMS 2.98 Oregon snap bean scenario and California lettuce scenario, the aquatic Acute Risk, Acute Restricted Use, and Endangered Species LOCs were not exceeded for freshwater fish and invertebrates with the assumption of the maximum estimated concentration of MCPB acid in the water body under consideration. Table IV. a. has summarized the risk quotients for freshwater fish and invertebrates with Oregon and California PRZM 3.12/ EXAMS 2.98 scenarios.

TABLE IV. a. Summarized Acute Aquatic Organism Risk Quotients for MCPB Acida, b, c, d Application/ Scenario Freshwat er Fish Freshwater Invertebrates Peas ( ground spray application) Oregon < 0.01 < 0.01 Peas ( aerial spray application) Oregon < 0.01 < 0.01 Peas ( ground spray application) California 0.01 <. 0.01 Peas ( aerial spray application) California 0.01 < 0.01 a Detailed calculations of PRZM 3.12/ EXAMS 2.98 modeling for peas grown in Oregon and California are provided in Appendix B.

b Acute toxicity thresholds ( LC50 or EC50) were 3.9 and 50 mg ae/ L for freshwater fish and freshwater invertebrates, respectively.

C EECs for Oregon bean Scenario were 29.7 and 33.4 µ g/ L for ground spray and aerial spray, respectively. DEECs for California lettuce Scenario were 40.6 and 43.4 µ g/ L for ground spray and aerial spray, respectively. ( Phase III 3/ 07/ 06)      41    147 Chronic risk to freshwater and estuarine marine fish and invertebrates cannot be assessed because chronic toxicity data have not been submitted.

Aquatic Plants For MCPB acid runoff/ drift, there were no exceedances of the non endangered Acute Risk LOC for the pea scenarios that were modeled ( Table IV. b.). However, the LOCs for endangered freshwater vascular plants could not be assessed due to a non discreet NOEC value.

TABLE IV. b. Summarized Acute Aquatic Plant Risk Quotients for MCPB Acid Non endangered Application/ Scenario Endangere d freshwater vascular Freshwater vascular Freshwater non vascular Peas ( ground spray application) Oregon N/ A 0.14 0.08 Peas ( aerial spray application) Oregon N/ A 0.16 0.09 Peas ( ground spray application) California N/ A 0.19 0.10 Peas ( aerial spray application) California N/ A 0.21 0.11 2. Non target Terrestrial Animals and Plants The following Table IV. c. summarizes the endpoints used in this assessment for RQ evaluation for non target terrestrial animals and plants:

TABLE IV. c. Summary of endpoints for MCPB acute terrestrial toxicity studies for RQ evaluationa Species toxicity value used in risk assessment in ae MRID#

bird ( oral gavage dose), LD 50 , mg ae/ kg bw 257 42560801 mammal, LD 50 , mg ae/ kg bw 832 116340 honey bee, LD 50 , µ g ae/ bee 23 42532607 ( Phase III 3/ 07/ 06)      42    147 terrestrial monocots emergence, EC 25 , lbs ae/ ac 0.02 42560804 terrestrial dicots emergence, EC 25 , lbs ae/ ac 0.016 42560804 terrestrial monocots vegetative vigor, EC 25 , lbs ae/ ac 0.018 42560804 terrestrial dicots vegetative vigor, EC 25 , lbs ae/ ac 0.0017 42560804 a Details for each study are presented in earlier sections of this document and in Appendix F.

Birds Acute avian RQs were calculated using the oral gavage study with bobwhite quail, which resulted in a 14 day LD 50 of 257 mg ae/ kg bw ( MRID 42560801). Assuming the maximum application rate ( 1.5 lbs ae/ acre) and maximum predicted residue levels, acute risk, acute restricted use and endangered species LOCs were exceeded for 20 g and 100g birds. Acute restricted use and endangered species LOCs were exceeded for 1000g birds.

As shown in Table IV. d., the acute LOC is exceeded for 20 g and 100 g birds for short grass and broadleaf forage and small insect feed items. The acute LOC is also exceeded for 20 g birds for tall grass feed, and nearly so for 100 g birds. The endangered species LOC is exceeded for all weight classes for short grass, broadleaf forage and small insects, and tall grass feed items. The endangered species LOC is also exceeded for 20 g birds consuming fruits, pods, seeds, and large insects. The endangered species LOC is exceeded for short grass even if mean residues are considered.

RQs were not calculated based on the acute dietary studies because no mortalities occurred at the highest concentration tested ( LC 50 > 4550 mg ae/ kg diet). In addition, the data evaluation records noted inconsistencies in the reporting of the measured concentrations of the chemical in the diet. Because of the lack of mortality in the acute dietary study, there is some uncertainty in the overall finding of potential acute risk to birds.

TABLE IV. d. Avian Acute Risk Quotient Summary a, b, c, d 1.5 lbs ae/ acre Acute RQd Food type Weight class ( g) predicted maximum residues predicted mean residues short grass 20 2.26*** 0.80*** ( Phase III 3/ 07/ 06)      43    147 100 1.01*** 0.36**

1000 0.32** 0.11*

20 1.03*** 0.34**

100 0.46** 0.15*

tall grass 1000 0.15* 0.05 20 1.27*** 0.42**

100 0.57*** 0.19*

broadleaf forage, small insects 1000 0.18* 0.06 20 0.14* 0.07 100 0.06 0.03 fruit, pods, seeds, large insects 1000 0.02 0.01 RQ values are dose base calculations * indicates an exceedance of Endangered Species Level of Concern ( LOC); RQ > 0.10. ** indicates an exceedance of Acute Restricted Use LOC; RQ > 0.20. *** indicates an exceedance of Acute Risk LOC; RQ > 0.50.

Mammals To evaluate the acute risk to mammals, RQs were calculated using the minimum LD 50 obtained from the acute oral studies ( 832 mg ae/ kg bwt, MRID 116340) at the maximum labeled rate of 1.5 lbs ae/ acre. To evaluate the chronic ( developmental/ reproductive) risk to mammals, RQs were calculated using the NOAEL for maternal toxicity obtained from the rabbit developmental toxicity study with MCPB acid equivalent ( NOAEL= 4.56 mg ae/ kg/ day, MRID 40865401). The exposure model T REX is set up to calculate RQs for the laboratory rat, which is the typical surrogate species for environmental risk assessments. Because the toxicity study for rabbit was used in this case, the toxicity values for the rabbit study were adjusted for a 3000 g rabbit in T REX model. The RQs are detailed in Tables IV. e. and IV. f. and they are summarized in Appendix F.

Assuming maximum residue levels at the maximum single application rate ( 1.5 lbs ae/ acre), the Acute Endangered Species Risk LOC was exceeded for small mammals ( 15 g and 35g) consuming short grass ( RQ = 0.19 and 0.16, respectively) and for small mammals ( 15 g) consuming broadleaf forage and small insects ( RQ = 0.11). Acute and acute restricted use LOCs were not exceeded. There were no exceedences of the risk LOCs by mammals consuming foods at the predicted mean MCPB residue levels.

TABLE IV. e. Mammalian Acute Risk Quotient Summary 1.5 lbs ae/ acre Food type Weight class ( g) Predicted maximum residues Predicted mean residues ( Phase III 3/ 07/ 06)      44    147 15 0.19* 0.07 35 0.16* 0.06 short grass 1000 0.08 0.03 15 0.09 0.03 35 0.07 0.02 tall grass 1000 0.04 0.01 15 0.11* 0.04 35 0.09 0.03 broadleaf forage, small insects 1000 0.05 0.02 15 0.01 0.01 35 0.01 < 0.01 fruit, large insects 1000 0.01 < 0.01 15 < 0.01 < 0.01 35 < 0.01 < 0.01 seeds, pods 1000 < 0.01 < 0.01 * indicates an exceedance of Endangered Species Level of Concern ( LOC); RQ > 0.10.

Assuming maximum and mean residue levels at the maximum application rate, Chronic Risk LOCs were exceeded in all weight classes ( 15 g, 35 g, and 1000g) of mammals for consumption of short grass, tall grass and broadleaf forage/ small insects. Assuming maximum residue levels at the maximum application rate, Chronic Risk LOCs were exceeded in 15 g and 35g mammals for consumption of fruit and large insects.

TABLE IV. f. Mammalian Chronic Risk Quotient Summary 1.5 lbs ae/ acre Food type Weight class ( g) Predicted maximum residues Predicted mean residues 15 19.94* 6.44*

35 17.12* 5.53*

short grass 1000 9.00* 2.91*

15 9.14* 2.73*

35 7.85* 2.34*

tall grass 1000 4.12* 1.23*

broadleaf forage, small i 15 11.22* 3.41* ( Phase III 3/ 07/ 06)      45    147 35 9.63* 2.93*

1000 5.06* 1.54*

15 1.25* 0.53 35 1.07* 0.46 fruit, large insects 1000 0.56 0.24 15 0.47 0.12 35 0.24 0.1 seeds, pods 1000 0.11 0.08 * indicates an exceedance of Chronic LOC, RQ > 1.0.

Terrestrial Non Target Insects EFED currently does not quantify risks to terrestrial non target insects; therefore, risk quotients are not calculated for these organisms. Risks are qualitatively discussed in the Terrestrial Organism Risk Characterization section of this document.

3. Non target Terrestrial Plants in Dryland and Semi aquatic Areas: An analysis of the results indicates exceedance of the Acute Risk LOC for non endangered monocots and dicots in dryland and semi aquatic areas located adjacent to treated areas, both as a result of combined runoff and spray drift, and from spray drift alone. ( Table IV. g). The Endangered Species LOC was exceeded for monocots and dicots located adjacent to treated areas and in semi aquatic areas and for dicots as a result of spray drift. The most sensitive seedling emergence EC 25 values were 0.02 and 0.016 lb ae/ acre for monocots and dicots, respectively. These values are used to calculate risk quotients for exposure from combined runoff and spray drift to adjacent fields.

Risk to terrestrial plants from spray drift alone is evaluated by comparing the estimated exposure from drift to the most sensitive EC 25 calculated from vegetative vigor laboratory tests. Among monocot species tested, only onion showed sensitivity to MCPB in the vegetative vigor test, with an EC 25 of 0.016 a. e/ acre, based on reductions in shoot weight. Based on this value, the acute LOC for monocots is exceeded. A NOEC could not be established in this study, but the exceedence of the LOC for nonendangered plants indicates that risk to endangered and listed monocots is also a concern. The fact that effects ( and therefore risk) were indicated for only one of four monocots tested suggests that only a subset of non target monocots may be at risk. The fact that monocots are not broadly sensitive is consistent with the fact that MCPA is an herbicide used to control broadleaf weeds.

Reduction in shoot weight was the most sensitive endpoint for the four most sensitive dicots tested in the vegetative vigor study. However, the magnitude of the EC 25 values is uncertain because they were extrapolated below the lowest dose tested in the study. For instance, although the calculated EC 25 for MCPB on tomato is 0.0015 lb ae/ acre, the lowest application rate tested in this study was 0.08 lb ai/ acre. Similarly, the EC 25 of ( Phase III 3/ 07/ 06)      46    147 0.015 for lettuce was extrapolated below the lowest application rate of 0.039. Based on these EC 25 values, however, the RQs exceed the level of concern.

Because RQs based on the EC 25 values exceed the acute LOC, and exposure can be expected which would cause greater than a 25% effect, risk to endangered plants is also a concern. However, risk quotients with which to evaluate risk from spray drift to endangered plants were not calculated because the NOEC values in the vegetative vigor study for the dicots were reported as being higher than the EC 25 values. A NOEC could not be determined for onion, the only monocot tested which was sensitive to MCPB. Therefore, a RQ could not be derived for comparison to the endangered species LOC.

Further extrapolation of the data needs to be done to derive EC 05 values from the dose response curves for the vegetative vigor study. The uncertainty in these EC 05 values will be high; new data with lower application rates which bracket observed EC 25 and EC 05 levels would improve the assessment of potential risks to nonendangered and endangered/ listed terrestrial plants.

Detailed calculations for plant risk quotients are presented in Appendix F.

TABLE IV. g. Summarized Terrestrial Plant Risk Quotients Acute Non endangered RQs Acute Endangered RQs Scenari o Adjacent to treated sites Semiaquatic areas Drift Adjacent to treated sites Semiaquatic areas Drift Ground spray application ( 1.5 lbs ae/ acre)

Monocot 4.50*** 38.25*** 0.94 9.00* 76.50*

Dicot 5.63*** 47.81*** 2.08*** 9.00* 76.50*

Aerial spray application ( 1.5 lbs ae/ acre)

Monocot 6.00*** 26.25*** 4.69*** 12.00* 52.50*

Dicot 7.50*** 32.81*** 10.42*** 12.00* 52.50*

* indicates an exceedance of the Endangered Species Level of Concern ( LOC). *** indicates an exceedance of the Acute Risk LOC.

B. Risk Description 1. Risks to Aquatic Organisms: In the conceptual model, spray drift and runoff to adjacent bodies of water were predicted as the most likely sources of MCPB and MCPB sodium exposure to nontarget aquatic organisms.

Fish and Invertebrates Based on acute risk quotients below the levels of concern, freshwater fish and invertebrates inhabiting surface waters adjacent to MCPB treated fields do not appear to ( Phase III 3/ 07/ 06)      47    147 be at risk for adverse acute effects on growth and survival. Toxicity studies are not available to determine the potential chronic effects to fish and invertebrates and acute risks to estuarine marine fish and estuarine marine invertebrates. Therefore, a complete risk assessment cannot be done for fish and invertebrates, and it is not possible to certify that MCPB use is   not likely to adversely affect  listed fish and invertebrates.

Aquatic Plants Toxicity studies with aquatic plant species indicate that exposure to MCPB results in significantly adverse effects to growth and development. The EC 50 for the freshwater vascular plant ( duckweed) is 0.21 mg ae/ L, based on reduced frond production; and the lowest EC 50 for the freshwater non vascular plant ( green algae) is 0.38 mg ae/ L, based on reduced cell density. Concentrations as low as 0.13 mg ae/ L resulted in chlorosis, curling, and decreased root formation in the aquatic vascular plant, duckweed. In addition, frond biomass was significantly reduced at 0.42 mg ae/ L.

For MCPB acid runoff/ drift, there were no exceedances of the non endangered Acute Risk LOC for the pea scenarios that were modeled ( Table IV. b.). However, it is not possible to calculate risk quotients to compare to the endangered species LOC, since a definitive NOEC was not determined for duckweed and green algae.

2. Risks to Terrestrial Organisms: In the conceptual model, ground deposition and spray drift with resulting residues on foliage, on flowers and seeds, and soil invertebrates were predicted as the most likely sources of MCPB and MCPB sodium exposure to nontarget terrestrial organisms. An additional predicted source of exposure to MCPB sodium was in puddled water on treated fields through preening and grooming, involving the oral ingestion of material from the feathers or fur.

Risks to terrestrial organisms ( i. e. birds, mammals, and plants) were assessed based on modeled Estimated Environmental Concentrations ( EECs) and available toxicity data. As part of the terrestrial assessment, EFED modeled exposure concentrations of MCPB to nontarget terrestrial plants and animals following the proposed application rates provided by the registrant. For terrestrial birds and mammals, estimates of initial levels of MCPB residues on various food items, which may be contacted or consumed by wildlife, were determined using the Kenega Fletcher nomogram followed by a first order decline model TREX 1.1. Likewise, the TerrPlant 1.0 model estimated exposure to nontarget plants and the AgDrift 2.0.1 model provided further refinement of spray drift dispersion and deposition to terrestrial plants located in proximity to treated fields.

Birds MCPB is categorized as moderately toxic to avian species on an acute oral basis ( 14 day LD 50 257 mg ae/ kg); but is practically non toxic to avian species on an acute dietary basis ( 8 day LD 50 > 4,550 ppm ae). In the oral study, the bobwhite quail exhibited sublethal effects; including reduced body weight gain ( dietary exposure), lethargy, dyspnea, loss of righting reflex and diarrhea. Gross necropsy of birds in both the oral gavage and dietary studies showed white areas/ film on ( Phase III 3/ 07/ 06)      48    147 the heart, liver ( dietary exposure), gizzard, gallbladder, crop or intestines. The 8 day NOELs for each species in the dietary study, based on sublethal effects ( reduced body weight gain), were 1138 ppm ae.

Based on these acute toxicity data, there is a large differential in the acute lethality when MCPB is administered as a single gavage or when mixed in the feed. However, there are limitations to both the dose based and dietary based method of calculating risk quotients. The dose based approach assumes that the uptake and absorption kinetics of a gavage toxicity study approximate the absorption associated with uptake from a dietary matrix. Toxic response is a function of duration and intensity of exposure and the importance of absorption kinetics across the gut and enzymatic activation/ deactivation of a toxicant may be important and are likely to be variable across chemicals and species.

For many compounds a gavage dose represents a very short term high intensity exposure, whereas dietary exposure may be of a more prolonged nature. The dietary approach assumes that animals in the field are consuming food at a rate similar to that of confined laboratory animals. The strength of this assumption is uncertain, because energy content in food items differs between the field and in the laboratory, as do the energy requirements of wild and captive animals.

In any case, because sublethal effects were observed in both studies, including the dietary study at doses > 569 ppm ae, sublethal risks to avian species using the treated fields or inhabiting adjacent edge or riparian communities could result from the labeled use of MCPB.

Avian reproduction studies using the TGAI are usually required for pesticide registration because birds may be subject to repeated or continuous exposure to the pesticide, especially preceding or during the breeding season. The preferred test species are mallard duck and bobwhite quail. No chronic bird studies were submitted for MCPB. EFED considered MCPA as a substitute for MCPB for chronic risk to birds, because the LD50 for bobwhite quail suggests that the acute potency of MCPB lies within the range of toxicity for acid equivalent MCPA. Also, rapid dissociation of MCPB to MCPA is expected to occur in the bird gut due to the chemical properties of MCPB. The chronic bird study for MCPA with bobwhite quail has a NOAEC of 1000 mg/ kg diet ( MRID # 435052 01) . No further studies are required for chronic risk to birds for MCPB at this time.

Mammals MCPB is classified as slightly toxic to practically non toxic to small mammals on an acute oral basis ( LD 50 values range from 912  7,400 mg ai/ kg/ day). ( Phase III 3/ 07/ 06)      49    147 Reproductive effects were observed in dogs at 44 mg ai/ kg/ day based on reduced testes weights and physiological changes in clinical chemistry. In developmental studies with rats and rabbits, maternal toxicity was observed at doses ranging from 20  100 mg ai/ kg/ day. In the rat study, the maternal toxicity observed at 100 mg ai/ kg/ day included decreased body weights and body weight gains during gestation. In the rabbit study, maternal toxicity observed at 20 mg ai/ kg/ day included maternal deaths, clinical signs of toxicity, decrease in body weight gain during treatment, and change in color of liver and kidneys. The maternal toxicity NOAEL for this study was 5 mg ai/ kg/ day. Developmental effects were observed in rats at a dose of 100 mg/ kg/ day, including decreased mean body weights/ litter for males and females, increases in unossified or poorly ossified sites and increases in several other skeletal variations.

The risk assessment and calculated RQs assume 100% of the diet is relegated to single food types foraged only from treated fields. However, because the Chronic LOCs are exceeded for multiple food categories, potential exposure may still be high enough to warrant concern. Other exposure routes are possible for animals residing in or moving through treated areas. Ingestion of contaminated soils, dermal contact, and inhalation are not considered in this screening assessment, and represent potential routes of exposure. Consumption of drinking water would appear to be inconsequential if water concentrations were equivalent to the concentrations from PRZM/ EXAMS; however, concentrations in puddled water sources on treated fields may be higher than concentrations in modeled ponds. Preening and grooming exposures, involving the oral ingestion of material from the feathers or fur remains an unquantified, but potentially important, exposure route. Consequently; based on these results, mammals may be subject to developmental/ reproductive effects and direct effects on foraging behavior when chronically exposed to MCPB as a result of the labeled use of the herbicide.