UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D. C. 20460 OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES PC Codes: 029801, 029802, 029806, 128931, 128944, 129043 DP Barcode: 317696 August 31, 2005 MEMORANDUM Subject: EFED Reregistration Chapter For Dicamba/ Dicamba Salts To: Susan Lewis, Branch Chief Reregistration Branch 1 Special Review and Reregistration Division From: William Erickson, Biologist Ibrahim Abdel Saheb, Environmental Scientist Shannon Borges, Biologist Environmental Risk Branch 2, Environmental Fate and Effects Division Through: Thomas Bailey, Branch Chief, Environmental Risk Branch 2, Environmental Fate and Effects Division EFED has completed a screening level ecological risk assessment for the proposed reregistration of dicamba and its salts. Dicamba is a benzoic acid herbicide formulated for use in agricultural and residential settings. Its major use is weed control in corn, with other major use sites including wheat, barley, pastures, and lawn and turf. The risk assessment is based on toxicity and environmental fate studies submitted to support the registration of dicamba and its salts and on ecological modeling to estimate environmental concentrations. EFED's risk conclusions are summarized below.

° listed and non listed terrestrial plants are at risk from runoff and drift from all use sites ° risk exists to non vascular aquatic plants but is minimal for listed and non listed vascular aquatic plants ° acute risk exists to listed and non listed birds ° acute risk exists to small, listed mammals exposed to maximum residues from application to sugarcane ° chronic risk exists for listed and non listed mammals ° minimal risk is expected to listed and non listed vascular aquatic plants ° no adverse effects are expected for listed and non listed freshwater and estuarine fish and aquatic invertebrates The following data gaps have been identified ( see Appendix E for further details):

° seedling emergence and vegetative vigor studies ( 123 1a, b); dicamba acid, TEP ° seedling emergence and vegetative vigor studies ( 123 1a, b); dimethylamine salt, TEP ° seedling emergence and vegetative vigor studies ( 123 1a, b); diglycoamine salt, TEP ° seedling emergence and vegetative vigor studies ( 123 1a, b); isopropylamine salt, TEP ° seedling emergence and vegetative vigor studies ( 123 1a, b); sodium salt, TEP ° seedling emergence and vegetative vigor studies ( 123 1a, b); potassium salt, TEP Note: These seedling emergence and vegetative vigor tests can each be limited to the five most sensitive species determined in previous testing with the technical grade of dicamba acid ( MRID no. 42846301). Those species are soybean, onion, turnip, tomato, and lettuce.

EFED plans on conducting further refinements to this assessment after registrant comments have been received. These refinements include the following:

° An AgDrift analysis will be completed. ° An assessment of exposure and risk from granular formulations will be conducted. ° RQs for listed terrestrial plants will be recalculated. ° Available incident data will be more fully evaluated. ° ECOTOX literature references will be examined for relevant information. Environmental Fate and Ecological Risk Assessment for the Reregistration of Dicamba and Dicamba Sodium, Potassium, Diglycoamine, Dimethylamine and Isopropylamine Salts United States Environmental Protection Agency Office of Pesticide Programs Environmental Fate and Effects Division Ariel Rios Building 1200 Pennsylvania Ave., NW Mail Code 7507C Washington, DC 20460 Reviewed and Approved by:

Thomas Bailey, Branch Chief W. Erickson, Biologist I. Abdel Saheb, Agronomist S. Borges, Biologist Environmental Risk Branch 2 1 TABLE OF CONTENTS I. Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 A. Nature of Chemical Stressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 B. Potential Risks to Non target Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 C. Conclusions  Exposure Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 D. Conclusions  Effects Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 E. Uncertainties and Data Gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 II. PROBLEM FORMULATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 A. Stressor Source and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Source and Intensity: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2. Physical/ Chemical/ Fate and Transport Properties: . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3. Pesticide Type, Class, Mode of Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4. Overview of Pesticide Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 B. Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1. Ecological Effects: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2. Ecosystems at Risk: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 C. Assessment Endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 D. Conceptual Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 1. Risk Hypothesis: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2. Diagram: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 E. Analysis Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1. Preliminary Identification of Data Gaps and Methods: . . . . . . . . . . . . . . . . . . . . . . 32 2. Measures to Evaluate Risk Hypotheses and Conceptual Model . . . . . . . . . . . . . . . . 33 III. ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 A. Use Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 B. Exposure Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1. Environmental Fate and Transport Characterization . . . . . . . . . . . . . . . . . . . . . . . . 37 2. Measures of Aquatic Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3. Measures of Terrestrial Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 C. Ecological Effects Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 1. Aquatic Effects Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2. Terrestrial Effects Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 IV. RISK CHARACTERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 A. Risk Estimation  Integration of Exposure and Effects Data . . . . . . . . . . . . . . . . . . . . . 55 1. Non target Aquatic Animals and Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 2. Non target Terrestrial Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3. Non target Terrestrial and Semi aquatic Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 B. Risk Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 1. Risks to Aquatic Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 2. Risks to Terrestrial Organisms: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3. Review of Incident Data: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 4. Federally Listed Species Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5. Endocrine Disrupter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 2 TABLE OF CONTENTS ( cont.)

C. Description of Assumptions, Limitations, Uncertainties, Strengths and Data Gaps . . . . 78 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Appendix A: Environmental Fate Studies, Chemical Structures and Some Properties of Dicamba Salts and DCSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Appendix B: Aquatic Exposure Model Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Appendix C: Terrestrial Bird and Mammal Model Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Appendix D: TerrPlant and AgDrift Model and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Appendix E: Data Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Appendix F: Ecological Effects Summaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 3 I. EXECUTIVE SUMMARY A. Nature of Chemical Stressor Dicamba was first registered in the United States in 1967 and is widely used in agricultural, industrial and residential settings. Dicamba is used as an ingredient in agricultural and home use products, as a sole active ingredient and in conjunction with other active ingredients. Dicamba is a benzoic acid herbicide similar in structure and mode of action to phenoxy herbicides. Typical terrestrial application methods consist of ground and aerial spray to the leaves or to the soil. Dicamba controls annual, biennial and perennial broadleaf weeds in crops and grasslands, and it is used to control brush and bracken in pastures. In combination with a phenoxyalkanoic acid or other herbicide, dicamba is used in pastures, rangeland, and non crop areas such as fence rows and roadways to control weeds. Dicamba is absorbed by leaves and roots, and moves throughout the plant acting at multiple sites to disrupt hormone ( auxin) balance and protein synthesis, resulting in plant growth abnormalities. Dicamba is formulated primarily as a salt in an aqueous solution. Supported forms are; dicamba acid ( 29801), dicamba dimethylamine salt  DMA ( 29802), dicamba sodium salt ( 29806), dicamba diglycoamine salt  DGA ( 128931), dicamba isopropylamine salt ( 128944) and dicamba potassium salt ( 129043).

B. Potential Risks to Non target Organisms For this screening risk assessment, the potential exposure of dicamba and its salts to aquatic and terrestrial endpoints was modeled. The Tier II PRZM( 3.12)/ EXAMS( 2.98) models were used to estimate exposure concentrations for aquatic animals and plants in surface water. The potential levels of dicamba residues on various food items for birds and terrestrial mammals was modeled using the T REX 1.2.3. Likewise, the TerrPlant 1.0 model estimated exposure to nontarget plants. The risk assessment indicates risk to non target terrestrial plants and freshwater non vascular plants; acute sublethal risk to birds; chronic ( developmental/ reproductive) risk to mammals; and potential risks to listed species ( birds, small mammals, terrestrial and semi aquatic monocots and dicots) from dicamba use based on the maximum application rates of 2.8 lbs ae/ acre for sugarcane, 2.0 lbs ae/ acre for hay, pasture/ rangeland, soybean and turf, 1.0 lbs ae/ acre for wheat and 0.75 lbs ae/ acre for corn.

The results of this screening risk assessment indicate that dicamba applied at the maximum rates according to label directions as a liquid spray for ground or aerial applications will impact non target plants for some distance from the application site. Results of Tier I and II toxicity studies with monocots and dicots indicate that seed germination, seedling emergence, and vegetative vigor are impacted by exposure to dicamba. For the modeled scenarios at the label maximum application rates of 2.8, 2.0, 1.0 and 0.75 lbs ae/ acre, Acute Risk LOCs for non listed monocots and dicots located adjacent to treated areas, in semi aquatic areas, and as a result of spray drift were exceeded. Spray drift from coarse sprays would be expected to damage non target plants that are closer to the target site; whereas, finer sprays have the potential to travel greater distances. Exposure will depend on droplet size, wind speed, and other factors. Highly active herbicides, such as the growth regulators, present the greatest drift hazard because small amounts can cause severe problems. Even if only a small surface area of the plant is exposed to dicamba, or a seedling is exposed to dicamba as it breaks through the soil surface, there is a possibility that the plant may be severely damaged or die as a result. The resulting damage, even if only minor, may be sufficient to prevent the plant from competing successfully with other plants for resources and water. Currently, some labels for 4 the registered dicamba herbicides place restrictions on droplet size, wind speed or ambient temperatures during application. These specific requirements are intended to reduce the potential exposure of spray drift to susceptible non target plants.

The results of this screening risk assessment indicate that dicamba applied at the maximum rates according to label directions as a liquid spray for ground or aerial applications will impact freshwater non vascular plants. The non listed Acute Risk LOC for the non vascular aquatic plant ( blue green algae) was exceeded; consequently, direct effects to growth, development, and reproduction of aquatic non vascular plants inhabiting surface waters adjacent to a treated field may occur when exposed to dicamba as the result of the labeled use of the herbicide.

The results of this screening risk assessment indicate that dicamba applied at the maximum rates according to label directions as a liquid spray for ground or aerial applications will impact avian species. The Acute Use and Acute Restricted Use LOCs were exceeded for all weight classes of birds ( 20, 100, 1000 g) consuming short grasses, tall grasses and broadleaf forage/ small insects and for small birds ( 20 g) consuming fruit, pods, seeds, and large insects at the higher application rates ( 2.8 and 2.0 lbs ae/ acre) and maximum predicted residues. In addition, the Acute Use and Acute Restricted Use LOCs were exceeded for 20 and 100 g birds consuming short grasses, tall grasses and broadleaf forage/ small insects and for large birds ( 1000 g) consuming short grasses at the lower application rates ( 1.0 and 0.75 lbs ae/ acre) and maximum predicted residues. For mean predicted residues, the Acute Use and Acute Restricted Use LOCs were exceeded for small birds ( 20 and 100 g) consuming short grasses, tall grasses and broadleaf forage/ small insects and for large birds ( 1000 g) consuming short grasses at the higher application rates ( 2.8 and 2.0 lbs ae/ acre). In addition for mean predicted residues, the Acute Use and/ or Acute Restricted Use LOCs were exceeded for 20 g birds consuming short grasses, tall grasses and broadleaf forage/ small insects and for100 g birds consuming short grasses at the lower application rates ( 1.0 and 0.75 lbs ae/ acre). Consequently, there may be a concern for potential indirect effects to listed species dependent upon birds for food, pollination or seed dispersal, or habitat. Consequently, based on these results, birds may be subject to sublethal effects and indirect effects on foraging behavior when acutely exposed to dicamba as a result of the labeled use of the herbicide.

Assuming maximum residue levels at the maximum application rates of 2.8, 2.0, 1.0 and 0.75 lbs ae/ acre, Chronic Risk LOCs were exceeded for mammals consuming short grass, tall grass and broadleaf forage/ small insects. There were no exceedances of Chronic Risk LOC for mammals consuming fruit, seeds, pods and large insects. The risk assessment and calculated RQs assume 100% of the diet is relegated to single food types foraged only from treated fields. These assumptions may overestimate risk, especially considering that contaminated food items might be avoided for more preferred items and diets would likely be more variable over longer periods of time. Other exposure routes are possible for animals residing in or moving through treated areas. 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 5 developmental/ reproductive effects and direct effects on foraging behavior when chronically exposed to dicamba as a result of the labeled use of the herbicide.

Exposure to dicamba results in direct effects to plant species that could result in indirect effects at the higher levels of organization ( i. e. population, trophic level, community, ecosystem). The guideline terrestrial plant studies indicate direct adverse effects to seedling emergence and vegetative vigor, as well as non lethal effects including brown leaf tips, necrosis, chlorosis, stem tumors, leaf curl, and decrease in size. In terrestrial and shallowwater 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 dicamba, 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). In addition, allochthonous input from riparian vegetation is not only a significant component of the food supply for aquatic herbivores and detritivores but also provides habitat ( i. e. leaf packs, materials for casebuilding for invertebrates).

The screening risk assessment for listed species indicates potential risk to the following taxonomic groups for the dicamba use scenarios as specified below:

° small birds ( 20g) feeding on short grasses, tall grasses, broadleaf forage/ small insects, and fruit/ pods/ seeds/ large insects at all application rates ° small birds ( 100 g) feeding on short grasses, tall grasses, and broadleaf forage/ small insects at 0.75 and 1.0 lbs ae/ acre ° small birds ( 100 g) feeding on short grasses, tall grasses, broadleaf forage/ small insects, and fruit/ pods/ seeds/ large insects at 2.8 and 2.0 lbs ae/ acre ° large birds ( 1000 g) feeding on short grasses, tall grasses, and broadleaf forage/ small insects at all application rates ° small ( 15 g) mammals feeding on short grasses at 2.8 lbs ae/ acre ° non target terrestrial plants  monocots and dicots adjacent to treated areas and in semiaquatic areas at all application rates ( all uses modeled) by ground and aerial spray application.

Although exceedances occurred with comparisons of RQs calculated from mean Kenaga EECs to listed species LOCs, screening level risk assessments rely on maximum residues. Mean Kenaga EECs may be considered more closely in future refined risk assessments.

Since the Listed Species LOCs for birds, small mammals, and terrestrial monocots and dicots are exceeded for the use of dicamba, the LOCATES was run for all taxonomic groups. For terrestrial monocots and dicots, both the Acute Risk LOCs for non listed species and the Listed Species LOCs were exceeded; consequently a potential concern arises for species with both narrow ( i. e., species that are obligates or have very specific habitat or feeding requirements) and general dependencies ( i. e., cover type requirements). Information from LOCATES indicates that for the corn, wheat, sugarcane and pasture/ grazing uses, several potentially affected species of birds, mammals, reptiles and plants appear to be co located with pesticide use areas. Consequently, there may be a concern for potential indirect effects to 6 listed species dependent upon birds that consume feed items ( short and tall grasses; broadleaf plants; small and/ or large insects; and fruits, seeds, and pods) contaminated with dicamba residues; such as predatory birds and mammals. In addition, there may be a potential concern for indirect effects related to plants that require birds and/ or mammals for pollination or seed dispersal and for animals that use burrows for shelter or breeding habitat.

This screening risk assessment indicates that there are no acute risks to fish, aquatic invertebrates, aquatic vascular plants and mammals at maximum application rates of 2.8, 2.0, 1.0 and 0.75 lbs ae/ acre. In addition, there are no chronic risks to birds at the maximum application rates. Consequently, fish, aquatic invertebrates and aquatic vascular plants inhabiting surface waters adjacent to a dicamba treated field would not be at risk for adverse acute effects on reproduction, growth and survival when exposed to residues in surface runoff and spray drift as a result of ground and/ or aerial spray application. Likewise, acute risks to mammals and chronic risks to birds consuming food types containing dicamba residues are not expected from the labeled uses of the herbicide. EFED currently does not quantify risks to terrestrial non target insects.

C. Conclusions  Exposure Characterization EFED established a strategy for bridging the environmental fate data requirements for the dicamba sodium and potassium salts, dimethylamine salt ( DMA), isopropylamine salt and diglycoamine salt ( DGA) to the dicamba acid. Bridging data were submitted indicating that the dicamba salts will be rapidly converted to the free acid of dicamba. A laboratory dissociation study showed that each dicamba salt ( tested at > 99% purity) completely dissociated to dicamba acid within 75 seconds in pure water. EFED determined that fate studies conducted with dicamba acid provide " surrogate data" for the dicamba salts. However, there is uncertainty regarding the fate of formulated typical end use products ( TEPs) containing the dicamba salts in the environment. The influence of inert ingredients and additives, in formulated TEPs, on the degradation potential are unknown.

Based on the physical and chemical properties as well as the laboratory fate studies, dicamba acid is very soluble ( 6100 mg/ L) and very mobile in laboratory soil studies thus it is expected to mobile in environmental settings. Aerobic soil metabolism is the main degradative process for dicamba acid. A single observed half life for dicamba acid was six days, with formation of the intermediate non persistent degradate 3,6 dichlorosalicylic acid ( DCSA). DCSA degraded at approximately the same rate as dicamba with the final metabolites being carbon dioxide and microbial biomass. Dicamba is stable to abiotic hydrolysis at all pH's and photodegrades slowly in water and on soil. Dicamba is more persistent under anaerobic soil: water systems in the laboratory, with a half life of 141 days. The major degradate under anaerobic conditions was DCSA, which was persistent, comprising > 60% of the applied after 365 days of anaerobic incubation. There are no acceptable data for the aerobic aquatic metabolism of dicamba; supplemental information indicates that dicamba degrades more rapidly in aquatic systems when sediment is present. Dicamba is not expected to bioaccumulate in aquatic organisms because it is an anion at environmental pHs ( pKa = 1.9).

Routes of exposure evaluated in this screening risk assessment focused on deposition, runoff and spray drift from ground and aerial spray applications of dicamba. The dicamba exposure characterization combined the environmental fate data with Tier II exposure models to estimate environmental exposure concentrations ( EECs). EECs for aquatic endpoints were 7 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. Likewise, EECs for birds and terrestrial mammals were estimated using the T REX 1.2.3 model and EECs for non target terrestrial plants are estimated by the TerrPlant 1.0 model. A review of ground water and surface water monitoring data indicate historical detections of dicamba at low concentrations (< 1.14 µ g/ L). Approximately, 100 incidents have been reported associated with dicamba usage. Incidents reported include impacts to terrestrial and aquatic non target plants and animals. The majority of reported incidents are damage to plants including a wide range of crops ( corn, sorghum, soybeans, sugar beets and wheat) as well as impacts to non crop plants. The specific impacts varied from browning and plant damage to mortality of all plants within the treated area. Aquatic impacts reported consist of three fish kill incidents associated with pasture and residential turf application.

D. Conclusions  Effects Characterization Spray drift and runoff to adjacent bodies of water are the most likely sources of dicamba and dicamba salts exposure to nontarget aquatic organisms. Available acute toxicity data indicate that dicamba acid appears to be slightly toxic to freshwater fishes ( rainbow trout and bluegill sunfish) and the sodium salt of dicamba is slightly toxic to daphnids. No toxicity studies have been conducted to determine potential chronic effects to fish and aquatic invertebrates. Toxicity studies with non vascular aquatic plants exposed to dicamba acid indicate that cell densities were significantly reduced in blue green algae. However, aquatic vascular plant species were not sensitive to dicamba acid. Data are currently unavailable to determine potential impacts to sediment dwelling benthic organisms and to riparian habitats.

Ground deposition and spray drift with resulting residues on foliage and on insects and seeds are the most likely sources of dicamba exposure to nontarget terrestrial birds and mammals, including listed species. In addition, uptake in plant roots could occur through ground spray application. Available acute toxicity data indicate that the s dicamba salts are practically nontoxic to bobwhite quail and mallard ducklings in the diet; however, oral gavage studies indicate that dicamba acid was moderately toxic to bobwhite quail and slightly toxic to mallard ducks. In chronic studies with dicamba acid, a reduction in hatchability was observed in mallard ducks. No treatment related mortality, signs of toxicity, or effects on reproduction were observed in bobwhite quail. Dicamba acid is classified as practically non toxic to small mammals on an acute oral basis. In a 2 generation rat reproduction study, maternal neurotoxicity was observed as well as decreased pup growth. Developmental studies with rabbits reported irregular ossification of internasal bones and maternal toxicity. Mortality, clinical signs of toxicity, body weight changes, and decreased food consumption, was also observed in rats. In addition, sublethal effects were reported in subchronic feeding studies. The reproductive and developmental effects observed in these studies may lead to a potential concern for impacts to populations of mammals consuming feed items contaminated with dicamba and to the predators that feed on them. Since, dicamba is classified as practically non toxic to bees on a contact exposure basis ( LD 50 > 90.65 µ g/ bee); the potential for dicamba to have adverse effects on pollinators and other beneficial insects is low. Therefore, the label does not need a warning for honey bees.

Terrestrial plant toxicity studies indicate that dicamba acid negatively impacts seed germination ( radicle length; soybean EC 25 = 0.036 lb ai/ A), seedling emergence ( shoot length; 8 soybean EC 25 = 0.0027 lb ai/ A), and vegetative vigor ( shoot length; soybean EC 25 = 0.0068 lb ai/ A ) in monocots and dicots. The most sensitive monocot tested was onion ( EC 25 = 0.071 lb ai/ A  seed germination; EC 25 = 0.0044 lb ai/ A  seedling emergence; and EC 25 = 0.1507 lb ai/ A  vegetative vigor). Non lethal effects included brown leaf tips, necrosis, decrease in size, leaf curling, chlorosis, and stem tumors. Consequently, 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.

E. Uncertainties and Data Gaps There are a number of areas of uncertainty in the terrestrial and the aquatic organism risk assessments that could potentially cause an underestimation of risk. First, this assessment accounts only for exposure of non target organisms to dicamba, but not to its degradates. The risks presented in this assessment could be underestimated if degradates also exhibit toxicity under the conditions of use proposed on the label. Data are not available concerning the fate and toxicity of the degradation products of dicamba. Second, the risk assessment only considers the most sensitive species tested and only considers a subset of possible use scenarios. For the aquatic organism risk assessment, there are uncertainties associated with the PRZM/ EXAMS model, input values, and scenarios including the use of surrogate scenarios, however these uncertainties cannot be quantified. The potential impacts of these uncertainties are outlined in the Aquatic Exposure and Risk Assessment and the Terrestrial Exposure and Risk Assessment sections of this document.

There is uncertainty in the environmental fate of the typical end use products ( TEPs) which contain the sodium, DMA or DGA salts. Dissociation rates, adsorption/ desorption rates and field dissipation information are needed for TEPs to determine the persistence and mobility of the salts and their associated inert ingredients found in the TEPs.

Additional uncertainty results from lack of information in components of this ecological risk assessment. For example, actual residue levels in foliage, insects, and seeds are not available to accurately predict risks to terrestrial organisms ( birds, mammals, pollinators) which may contact dicamba residues after application. Therefore, model estimates are used in risk quotient calculations. Additionally, little field information is not available to help characterize risks. An AgDrift analysis also will be completed in further refinements to the chapter.

II. PROBLEM FORMULATION The purpose of the ecological risk assessment ( ERA) is to assist the Agency in evaluating the actions needed, if any, to address ecological risks associated with the reregistration of the herbicide dicamba ( 3,6 Dichloro o anisic acid). Dicamba is formulated in aqueous solutions as a salt and has herbicidal activity against annual, biennial and perennial broadleaf weed species and other plants in terrestrial settings.

A. Stressor Source and Distribution 1. Source and Intensity: Dicamba is a benzoic acid herbicide similar in structure and mode of action to phenoxy herbicides. Typical terrestrial application methods consist of ground and aerial spray to the leaves or to the soil. Dicamba controls annual, biennial and perennial broadleaf weeds in grain crops and grasslands, and it is used to control brush and bracken in 9 pastures. In combination with a phenoxyalkanoic acid or other herbicide, dicamba is used in pastures, range land, and non crop areas such as fence rows and roadways to control weeds. Dicamba is absorbed by leaves and roots, and moves throughout the plant where it inhibits plant growth.

Dicamba comes in multiple formulations and is found in numerous end use products intended for use in a wide range of terrestrial use patterns. Aqueous formulations are registered and methods of application include controlled droplet applicator, high volume ground sprayer, low volume ground sprayer, hand held sprayer, aerial and ground broadcast, high volume spray ( dilute), low volume spray ( concentrate), and spot treatment. Timing of application includes dormant, early fall, early spring, fall, late spring ( postemergence), spring, and summer. Table II. a. presents a summary of dicamba use sites.

Dicamba is an ingredient in several agricultural and home use products, as a sole active ingredient and in conjunction with other active ingredients. Dicamba is formulated primarily as a salt in an aqueous solution. Supported forms are; dicamba acid ( 29801), dicamba dimethylamine salt  DMA ( 29802), dicamba sodium salt ( 29806), dicamba diglycoamine salt  DGA ( 128931), dicamba isopropylamine salt ( 128944) and dicamba potassium salt ( 129043). ( See appendix A for chemical structures and properties of the dicamba salts.) Copies of all registered dicamba labels may be found at; http:// oaspub. epa. gov/ pestlabl/ ppls. home 10 Table II. a. Overview of Dicamba Uses Representative Crops Use Grouping Dicamba Acid Sodium Salt Potassium Salt Diglycoamine Salt Dimethylamine Salt Isopropylamine Salt Terrestrial food crop Agricultural/ farm premises,

Asparagus Agricultural/ farm premises,

Asparagus Asparagus Agricultural/ farm premises, Asparagus,

Proso millet Agricultural/ farm premises, Asparagus,

Corn Terrestrial food and feed crop Agricultural crops/ soils,

Agricultural fallow/ idleland,

Barley, Corn ( unspecified),

Corn ( field) Corn ( pop),

Cotton, Proso Millet, Oats,

Small grains, Sorghum,,

Soybeans, Sugarcane, Wheat Agricultural crops/ soils,

Agricultural fallow/

idleland, Barley, Corn ( unspecified), Corn ( field)

Corn ( pop), Cotton, Proso Millet, Oats, Sorghum,

Sorghum, Soybeans,

Sugarcane, Wheat Agricultural fallow/ idleland, Barley,

Corn ( unspecified),

Corn, field, Corn ( pop),

Proso Millet, Oats,

Sorghum, Soybeans,

Sugarcane, Wheat Agricultural fallow/ idleland,

Barley, Corn ( unspecified), Corn ( field), Corn ( pop),

Cotton, Oats,

Sorghum, Soybeans,

Sugarcane, Triticale,

Wheat Agricultural crops/ soils, Agricultural fallow/ idleland,

Barley, Corn ( unspecified), Corn ( field), Corn ( pop),

Proso Millet, Oats,

Small grains,

Sorghum, Soybeans Sugarcane, Wheat Agricultural fallow/ idleland,

Barley, Oats,

Sorghum, Wheat Terrestrial feed crop Grass forage/ fodder/ hay,

Millet ( foxtail), Pastures,

Rangeland Grass forage/ fodder/ hay,

Grasses grown for seed,

Pastures, Rangeland Corn, Grass forage/ fodder/ hay Corn, Grass forage/ fodder/ hay,

Grasses grown for seed, Pastures,

Rangeland Barley, Corn, Grass forage/ fodder/ hay,

Grasses grown for seed, Proso Millet,

Oats, Pastures,

Rangeland, Rye,

Sorghum, Sudangrass,

Wheat Representative Crops Use Grouping Dicamba Acid Sodium Salt Potassium Salt Diglycoamine Salt Dimethylamine Salt Isopropylamine Salt 11 Terrestrial non food crop Airports/ landing fields,

Commercial/ industrial lawns,

Commercial/ institutional/ ind ustrial premises/ equipment ( outdoor), Golf course turf,

Industrial areas ( outdoor),

Nonagricultural rights of way/ fencerows/ hedg erows, Nonagricultural uncultivated areas/ soils,

Ornamental sod farm ( turf),

Recreation area lawns,

Recreational areas Grasses grown for seed,

Industrial areas ( outdoor),

Nonagricultural rights of way/ fencerows/ he dgerows, Ornamental lawns and turf Golf course turf,

Industrial areas ( outdoor), Nonagricultural rights of way/

fencerows/ hedgerows,

Nonagricultural uncultivated areas/ soils, Ornamental lawns and turf, Ornamental sod farm ( turf), Recreation area lawns, Recreational areas Agricultural fallow/ idleland Agricultural rights of way/

fencerows/ hedgerows,

Agricultural uncultivated areas,

Agricultural/ farm structures/ buildings and equipment,

Airports/ landing fields, Commercial/

industrial lawns,

Commercial/

institutional/ industrial premises/ equipment ( outdoor), Fencerows / hedgerows, Golf course turf, Grasses grown for seed,

Industrial areas ( outdoor), Nonagricultural outdoor buildings/

structures, Nonagricultural rights of way/ fencero ws/ hedgerows, Nonagricultural uncultivated areas/ soils, Ornamental lawns and turf, Ornamental sod farm ( turf),

Paths/ patios, Paved Representative Crops Use Grouping Dicamba Acid Sodium Salt Potassium Salt Diglycoamine Salt Dimethylamine Salt Isopropylamine Salt 12 Terrestrial non food and outdoor residential Nonagricultural rights of way/ fencerows/

hedgerows, Ornamental and/ or shade trees,

Ornamental lawns and turf,

Ornamental woody shrubs and vines, Urban areas Nonagricultural rights of way/ fencerows/

hedgerows , Ornamental lawns and turf Nonagricultural rights of way/

fencerows/ hedgerows, Ornamental lawns and turf Fencerows/ hedgerows Nonagricultural rights of way/

fencerows/ hedgerows, Ornamental lawns and turf, Urban areas Outdoor residential Household/ domestic dwellings outdoor premises,

Residential lawns Household/ domestic dwellings outdoor premises, Ornamental lawns and turf,

Residential lawns Aquatic non food industrial Drainage systems Drainage systems Forestry Forest trees ( all) Forest trees ( all) Forest plantings ( reforestation programs, tree farms,

tree plantations, etc.),

Forest trees ( all) 13 2. Physical/ Chemical/ Fate and Transport Properties: A summary of selected physical and chemical properties for dicamba acid are presented in Table II. b.

EFED established a strategy for bridging the environmental fate data requirements for the dicamba sodium and potassium salts, dimethylamine salt ( DMA), isopropylamine salt and diglycoamine salt ( DGA) to the dicamba acid. Bridging data were submitted indicating that the dicamba salts will be rapidly converted to the free acid of dicamba. A laboratory dissociation study showed that each dicamba salt ( tested at > 99% purity) completely dissociated to dicamba acid within 75 seconds in pure water ( MRID 43288001). EFED determined that fate studies conducted with dicamba acid provide " surrogate data" for the dicamba salts.

Dicamba acid is very soluble ( 6100 mg/ L) and very mobile in laboratory soil studies. In batch equilibrium experiments, dicamba acid was determined to be very mobile in loam, clay loam, silt loam, and sandy loam soils and a loam sediment, with Freundlich K d values of 0.16, 0.10, 0.53. 0.07 and 0.21, respectively. Corresponding K oc values were 7.27, 3.45, 21.1, 17.5 and 17.5, respectively.

Aerobic soil metabolism is the main degradative process for dicamba acid. A single observed half life for dicamba acid was six days, with formation of the intermediate non persistent degradate 3,6 dichlorosalicylic acid ( DCSA). DCSA degraded at approximately the same rate as dicamba with the final metabolites being carbon dioxide and microbial biomass. Aerobic degradation of dicamba is slower at lower temperatures and low soil moisture and rainfall. Dicamba is stable to abiotic hydrolysis at all pH's and photodegrades slowly in water and on soil. Dicamba is more persistent under anaerobic soil: water systems in the laboratory, with a half life of 141 days. The major degradate under anaerobic conditions was DCSA, which was persistent, comprising > 60% of the applied after 365 days of anaerobic incubation. No other anaerobic degradates were present at > 10% during the incubation. There are no acceptable data for the aerobic aquatic metabolism of dicamba; supplemental information indicates that dicamba degrades more rapidly in aquatic systems when sediment is present.

Provided retention times of dicamba in aerobic soils are sufficient and conditions are amenable to allow degradation, dicamba can be biodegraded thus reducing the potential to leach to groundwater. Biodegradation in aerobic soils is reduced at lower temperatures and dry conditions. If dicamba did reach anaerobic soil or anaerobic groundwater zones, it would be somewhat persistent ( due to its anaerobic half life of 141 days); any DCSA that reached groundwater would also be expected to persist.

Results from field dissipation studies conducted with the dimethylamine salt of dicamba, indicated that dicamba dissipated with reviewer calculated half lifes ranging from 4.4 to 19.8 days with DCSA was the major degradate. Both, dicamba and its primary degradate were found at low concentrations (< 20 ppb) in soil segments deeper than 10 cm. Supplementary data in other field dissipation studies indicate that the sodium and diglycoamine salts of 14 dicamba dissipated similar to the dimethylamine salt with half lifes ranging from 3 to 12.9 days.

Based on the vapor pressure of 3.4e 5 torr, when released in the atmosphere dicamba will exist in both the vapor phase as well as the adsorbed to particulate phase. Soil volatilization rates for potassium salt and DMA ranged from 2.91 to 4.97 x 10 4 µ g/ cm2/ hr when dicamba was applied at rate of 0.5 lb a. i./ A ( MRID 41966602). There are numerous label restrictions for ground and aerial spray applications. Spraying is not recommended if wind is gusty or in excess of 5 mph and moving in the direction of adjacent sensitive crops. Recommendations on spray systems for coarse spray application are included on the labels as well as directions for keeping the spray pressure at or below 20 psi and spray volume at or above 20 gpa. Finally, dicamba should not be applied adjacent to sensitive crops when temperature on the day of application is expected to exceed 85 ° C as drift is more likely to occur.

Dicamba is not expected to bioaccumulate in aquatic organisms because it is an anion at environmental pHs ( pKa = 1.9).

Figure II. a. Chemical Structure of 3,6 Dichloro o anisic acid ( Dicamba) ( CAS No. 1918 00 9) 15 TABLE II. b. Some Physical Chemical and Other Properties of Dicamba Acid.

CAS Name 3,6 dichloro 2 methoxybenzoic acid IUPAC Name 3,6 dichloro o anisic acid CAS No 1918 00 9 PC Code 029801 Empirical Formula C8H6Cl2O3 Molecular Weight 221.04 Common Name Dicamba Formulated Product Banex; Banlen; Banval; Banvel; Banvel 10G; Banvel 4E; Banvel 5G; Banvel CST; Banvel D; Banvel XG; dianat; Dicambe; Dicamba; Dicamba ; dicamba + 2,4 D; dicamba + atrazine; dicamba ( amine); Clarity; Marksman; MDBA; Mediben; Velsicol 58 CS 11; Velsicol compound '' R''

Pesticide Type Herbicide Chemical Family Benzoic acid Color/ Form Colorless crystals Odor Odorless Melting Point 114  116 ° C ( Kidd and James, 1991))

Flash Point 199 ° C ( Gosselin, 1984)

Relative Density 1.57 g/ ml at 25 ° C ( Spectrum Laboratories: Chemical Fact Sheet)

Water Solubility 6100 mg/ L SANDOZE Safety Data Sheet ( Nov, 1989) 8240 mg/ L at 25 ° C ( Toxicology and Regulatory Affairs Flemington, NJ) 6500 mg/ L at 25 ° C ( Kidd and James, 1991)

Solubility in other solvents Acetone 810 g/ L at 25 ° C Dichloromethane 260 g/ L at 25 ° C Dioxane 1.18 kg/ L at 25 ° C Ethanol 922 g/ L at 25 ° C Toluene 130 g/ L at 25 ° C Xylene 8 g/ L at 25 ° C ( Worthing 1987)

Vapor Pressure 3.41 E 05 torr ( 25 ° C) SANDOZE Safety Data Sheet ( Nov, 1989) 3.4 E 05 torr ( 25 ° C) ( Kidd and James, 1991))

Henry's Law Constant 1.79 E 08 ( ARS Pesticide Properties Database)

pKa 1.87 ( MRID 43288001)

Kd( Freundlich) Koc 0.07  0.53 mL/ g ( MRID 42774101) 3.45  21.1 mL/ g ( MRID 42774101)

3. Pesticide Type, Class, Mode of Action: Dicamba is a benzoic acid herbicide similar in structure and mode of action to phenoxy herbicides. Like the phenoxy herbicides, dicamba mimics auxins, a type of plant hormone and causes abnormal cell growth by affecting cell 16 division. Dicamba acts systematically in plants after it is absorbed through leaves and roots. It is easily transported throughout the plant and accumulates in new leaves.

4. Overview of Pesticide Usage: Dicamba was first registered in the United States in 1967 and is widely used in agricultural, industrial and residential settings. Dicamba controls annual, biennial and perennial broadleaf weeds in grain crops and grasslands, and it is used to control brush and bracken in pastures. In combination with a phenoxyalkanoic acid or other herbicide, dicamba is used in pastures, range land, and non crop areas such as fence rows and roadways to control weeds. Dicamba herbicide is available in aqueous formulations and is commonly mixed in tanks with other herbicides and/ or fertilizers before application. In aqueous forms, dicamba is applied as a pre and post emergent via aerial or ground spray for control of most annual, biennial and perennial broadleaf weeds in crops. Dicamba is used to control weeds and brush in pasture, rangeland and noncropland areas such as utility, highway right of ways and non irrigation ditchbanks including grazed or hayed areas. Dicamba is also used on residential turf and lawns as well as golf courses for control of weeds and other unwanted plants.

Dicamba is registered for use on a variety of crops as described in Table II. c. Figure II. b. presents an depiction of dicamba use on crops in the United States. Based on 1997 USGS data, the primary crop for dicamba use is corn (> 6.7 million lb ai). Pasture ( 1.5 million lb ai), wheat ( 807,000 lb ai), and fallowland ( nearly 800,000 lb ai) also are major use sites, followed by sorghum, barley, other hay, sugarcane, and sod. 17 TABLE II. c. Registered Uses of Dicamba Use Sites Product/ Registration Number Forms1 Max Application Rate ( Unit/ Area) Max Application Rate ( year)

Non Food/ Non Feed Uses Agricultural Fallow/ Idleland (

Noncrop Banvel/ 7969 131 Banvel SGF/ 7969 135 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Agricultural rights

ofway fencerows/ hedgerows ( Non crop) 2 Dicamba DMA Salt/ 42750 40 Banvel 845H/ 7969 140 Vanquish/ 100 884 Dimethylamine Salt,

Sodium Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A)

Agricultural Uncultivated Areas (

Noncrop Banvel SGF/ 7969 135 Dicamba DMA Salt/ 42750 40 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Agricultural/ Farm Structures/ Buildings and Equipment ( Non crop) Banvel/ 7969 131 Dicamba DMA Salt/ 42750 40 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Airports/ Landing Fields ( Non crop) Banvel/ 7969 131 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Commercial/ Industrial Lawns (

Noncrop Banvel/ 7969 131 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 1.0 ( lbs a. e./ A) 1.0 ( lbs a. e./ A) year Commercial/ Institutional/ Industrial Premises/ Equipment ( Non crop) Banvel/ 7969 131 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Drainage Systems ( Non crop) Banvel/ 7969 131 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt,

DGA 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Fencerows/ Hedgerows ( Non crop) Banvel/ 7969 131 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year TABLE II. c. Registered Uses of Dicamba Use Sites Product/ Registration Number Forms1 Max Application Rate ( Unit/ Area) Max Application Rate ( year)

18 Forest Plantings ( reforestation programs, tree farms, tree plantations)

( Non crop) Banvel/ 7969 131 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Forest Trees ( Non crop) Banvel/ 7969 131 Vanquish/ 100 884 Dimethylamine Salt,

DGA 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Golf Course Turf Banvel/ 7969 131 Vanquish/ 100 884 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

DGA 1.0 ( lbs a. i./ A) 1.0 ( lbs a. e./ A) year Household Domestic Dwellings (

Noncrop Banvel/ 7969 131 Banvel SGF/ 7969 135 Dimethylamine Salt 1.0 ( lbs a. e./ A) 1.0 ( lbs a. e./ A) year Industrial Areas ( Outdoor)

( Non crop) Banvel/ 7969 131 Vanquish/ 100 884 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt,

DGA 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Nonagricultural Outdoor Buildings/ Structures ( Non crop) Banvel/ 7969 131 Banvel SGF/ 7969 135 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Nonagricultural Rights

ofway Fencerows/ Hedgerows ( Non crop) Banvel/ 7969 131 Banvel 845H/ 7969 140 Vanquish/ 100 884 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt,

Sodium Salt, DGA 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Nonagricultural Uncultivated Area/ Soils ( Non crop) Banvel/ 7969 131 Banvel SGF/ 7969 135 Vanquish/ 100 884 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt,

DGA 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year TABLE II. c. Registered Uses of Dicamba Use Sites Product/ Registration Number Forms1 Max Application Rate ( Unit/ Area) Max Application Rate ( year)

19 Ornamental Lawns and Turf Banvel/ 7969 131 Banvel 845H/ 7969 140 Vanquish/ 100 884 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA 1.0 ( lbs a. i./ A) 1.0 ( lbs a. i../ A) year Ornamental Sod Farm Banvel/ 7969 131 Vanquish/ 100 884 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

DGA 1.0 ( lbs a. e./ A) 1.0 ( lbs a. e./ A) year Paths/ Patios ( Non crop) Banvel/ 7969 131 Banvel SGF/ 7969 135 Dimethylamine Salt 2.0 ( lbs a. e/ A) 2.0 ( lbs a. e./ A) year Paved Areas ( Private Roads/ Sidewalks ( Non crop) Banvel/ 7969 131 Banvel SGF/ 7969 135 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt 2.0 ( lbs a. e/ A) 2.0 ( lbs a. e./ A) year Recreation Area Lawns Banvel/ 7969 131 Vanquish/ 100 884 Dicamba DMA Salt/ 42750 40 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

DGA 1.0 ( lbs a. i./ A) 1.0 ( lbs a. i./ A) year Recreational Areas Banvel/ 7969 131 Vanquish/ 100 884 Dicamba DMA Salt/ 42750 40 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

DGA 1.0 ( lbs a. i./ A) 1.0 ( lbs a. i./ A) year Residential Lawns Banvel/ 7969 131 Banvel SGF/ 7969 135 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 1.0 ( lbs a. i./ A) 1.0 ( lbs a. i./ A) year Urban Areas ( Non crop) Banvel/ 7969 131 Banvel SGF/ 7969 135 Dicamba DMA Salt/ 42750 40 Dimethylamine Salt 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year TABLE II. c. Registered Uses of Dicamba Use Sites Product/ Registration Number Forms1 Max Application Rate ( Unit/ Area) Max Application Rate ( year)

20 Food/ Feed Uses Agricultural Crops/ Soils Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt 2.0 ( lbs a. e/ A) 2.0 ( lbs a. e./ A) year Agricultural Fallow/ Idleland Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 All 2.0 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Agricultural/ Farm Premises Banvel/ 7969 131 Banvel SGF/ 7969 135 Vanquish/ 100 884 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

DGA 1.0 ( lbs a. e./ A) 1.0 ( lbs a. e./ A) year Agricultural/ Farm Structures/ Buildings and Equipment Banvel/ 7969 131 Banvel SGF/ 7969 135 Dicamba DMA Salt/ 42750 40 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 1.0 ( lbs a. e./ A) 1.0 ( lbs a. e./ A) year Asparagus Banvel/ 7969 131 Banvel 845H/ 7969 140 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA 0.5 ( lbs a. e./ A) 0.5 ( lbs a. e./ A) year Barley Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA,

IPA 0.25 ( lbs a. e./ A) 0.38 ( lbs a. e./ A) year TABLE II. c. Registered Uses of Dicamba Use Sites Product/ Registration Number Forms1 Max Application Rate ( Unit/ Area) Max Application Rate ( year)

21 Corn ( field, pop, seed, silage) Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA,

Potassium Salt 0.5 ( lbs a. e./ A) 0.75 ( lbs a. e./ A) year Hay Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Vanquish/ 100 884 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA 2.03 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year Millet ( Proso) Banvel/ 7969 131 Banvel SGF/ 7969 135 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 0.125 ( lbs a. e/ A) 0.125 ( lbs a. e./ A) year Oats Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA 0.125 ( lbs a. e/ A) 1.0 ( lbs a. e./ A) year Pastures2 Banvel/ 7969 131 Banvel 845H/ 7969 140 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Vanquish/ 100 884 Dimethylamine Salt,

Sodium Salt, DGA 2.0 ( lbs a. e./ A)

7.7 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year 7.7 ( lbs a. e./ A)/ year Rangeland2 Banvel/ 7969 131 Banvel 845H/ 7969 140 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Vanquish/ 100 884 Dimethylamine Salt,

Sodium Salt, DGA 2.0 ( lbs a. e./ A)

7.7 ( lbs a. e./ A) 2.0 ( lbs a. e./ A) year 7.7 ( lbs a. e./ A)/ year Rye Banvel/ 7969 131 Banvel SGF/ 7969 135 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 0.5 ( lbs a. e./ A) 1.0 ( lbs a. e./ A) year TABLE II. c. Registered Uses of Dicamba Use Sites Product/ Registration Number Forms1 Max Application Rate ( Unit/ Area) Max Application Rate ( year)

22 Sorghum Banvel / 7969 131 Banvel 845H/ 7969 140 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 All 0.2748 ( lbs a. e./ A) 0.5 ( lbs a. e./ A) year Soybean Banvel/ 7969 131 Banvel SGF/ 7969 135 Dicamba SG/ 42750 43 Sodium Salt, DGA 2.0 ( lbs a. e./ A) year 2.0 ( lbs a. e./ A) year Sudangrass Banvel/ 7969 131 Banvel SGF/ 7969 135 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt 0.5 ( lbs a. e./ A) As listed for Hay. 1.0 ( lbs a. e./ A) year Sugarcane Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA 2.8 ( lbs a. e./ A) 2.8 ( lbs a. e./ A) year Wheat Banvel/ 7969 131 Banvel SGF/ 7969 135 Banvel 845H/ 7969 140 Dicamba SG/ 42750 43 Gharda Dimethylamine Salt of Dicamba/ 70907 11 Dimethylamine Salt,

Sodium Salt, DGA,

IPA 0.5 ( lbs a. e./ A ) 1.0 ( lbs a. e./ A) year 1There are 5 forms of dicamba used in this Master Label from the July 22, 2005 SRRD Use Profile: Dimethylamine Salt ( PC Code 29802), Sodium Salt ( PC Code 29806),

Diglycoamine [ DGA] ( PC Code 128931), Isopropylamine Salt [ IPA] ( PC Code 128944), and Potassium Salt ( PC Code 129043).

2 Rate based on label 100 884 3 Based on label 51036 289 and 7969 131 23 Figure II. b. Dicamba crop usage on an area weighted basis ( from USGS; http:// ca. water. usgs. gov/ pnsp/ pesticide_ use_ maps_ 1997/). 24 B. Receptors 1. Ecological Effects Each assessment endpoint requires one or more " measures of ecological effect," which are defined as changes in the attributes of an assessment endpoint itself or changes in a surrogate entity or attribute in response to pesticide exposure. Ecological measurement endpoints for the screening level risk assessment are based on a suite of registrant submitted toxicity studies.

Toxicity studies used in the risk assessment are usually performed on a limited number of organisms in the following broad groupings:

° Birds ( mallard duck and bobwhite quail) used as surrogate species for terrestrial phase amphibians and reptiles ° Mammals ( laboratory rat) ° Freshwater fish ( bluegill sunfish and rainbow trout) used as a surrogate for aquatic phase amphibians ° Freshwater invertebrates ( water flea  Daphnia magna) ° Estuarine/ marine fish ( sheepshead minnow) ° Estuarine/ marine invertebrates ( Eastern oyster and mysid shrimp) ° Terrestrial plants ( corn, onion, ryegrass, wheat, buckwheat, cucumber, soybean, sunflower, tomato, and turnip) ° Algae and aquatic plants ( algae, diatoms, and duckweed)

Within each of these very broad taxonomic groups, an acute and/ or chronic endpoint is selected from the available test data. A discussion of some toxicity data available for this risk assessment and the resulting measurement endpoints selected for each taxonomic group is included in Section III of this document. A summary of the assessment and measurement endpoints selected to characterize potential ecological risk associated with dicamba exposure is provided in Table II. d below. 25 Table II. d. Summary of Assessment and Measurement Endpoints Assessment Endpoint Measurement Endpoints 1. Abundance ( i. e., survival, reproduction, and growth) of individual birds 1a. Mallard duck acute oral LD50 1b. Bobwhite quail subacute dietary LD50 1c. Mallard duck chronic reproduction NOAEL 2. Abundance ( i. e., survival, reproduction, and growth) of individual mammal 2a. Laboratory rat acute oral LD50 2b. Laboratory rat chronic ( reproductive) NOAEC 3. Survival and reproduction of freshwater fish and invertebrates 3a. Rainbow trout acute LC50 3b. Freshwater fish chronic NOAEC ( weight & length) 3c. Water flea acute EC50 3d. Water flea chronic NOAEC ( offspring)

4. Survival and reproduction of estuarine/ marine fish and invertebrates 4a. Sheepshead minnow acute LC50 4b. Estuarine/ marine fish chronic NOAEC & LOAEC 4c. Eastern oyster acute EC50 4d. Estuarine/ marine invertebrate chronic NOAEC & LOAEC 5. Perpetuation of individuals and populations of non target terrestrial plants ( crops and non crop plant species) 5a. Monocot and dicot seedling emergence EC25 5b. Monocot and dicot vegetative vigor EC25 6. Survival of beneficial insects 6a. Honeybee acute contact LD50 7a. Algae and duckweed acute EC50 7b. Algae and duckweed NOAEC/ EC05 7a. Algae and duckweed EC50 and NOAEC/ EC05 It should be noted that the aquatic animal and acute avian toxicity studies provided by the registrants were performed with the dicamba salts ( dimethylamine salt, sodium salt, and potassium salt). Conversion from active ingredient to acid equivalent was completed in accordance with conversion factors found on the appropriate label and molecular weight differences. The LC 50 / LD 50 / EC 50 values from the toxicity tests with the dicamba salts were converted to the acid equivalent by multiplying the value times the conversion factors presented below. 26 Form Molecular Weight ae Conversion Factor dicamba acid 221.0

dimethylamine salt of dicamba 226.1 0.977 sodium salt of dicamba 243.0 0.909 potassium salt of dicamba 259.1 0.853 The emphasis of this preliminary screening risk assessment is to address risk to non target aquatic and terrestrial species that may be exposed to dicamba and its salts. The labeled uses of dicamba ( Table II. c.) could result in exposure to aquatic and terrestrial organisms inhabiting flowing, non flowing or transient freshwater waterbodies and wildlands ( forests, wetlands and ecotones, such as edge and riparian habitats).

a. Aquatic Effects Spray drift and surface runoff/ leaching to adjacent bodies of water are the most likely sources of dicamba exposure to nontarget aquatic organisms, including listed species. Available acute toxicity data indicates that the toxicity of dicamba varies with the salt forms tested. Study results show that the salt forms appeared to be practically non toxic to freshwater fishes ( LC 50 > 100 mg/ L); however, dicamba acid ( LC 50 = 28 mg a. e./ L; 88% a. i.) was slightly toxic to rainbow trout. Toxicity to bluegill was similar. The sodium salt of dicamba ( 26.5% a. i.) was slightly toxic to daphnids with an EC 50 of 34.6 mg a. e./ L. Dicamba acid and the other salts were not toxic to daphnids, with EC 50 ' s > 100 mg/ L. Results of acute aquatic toxicity studies with the potassium salt of dicamba are questionable due to the precipitation of the test material during testing. Toxicity test results with marine/ estuarine species indicate that dicamba acid is practically non toxic to fish ( 96 hr LC 50 > 180 mg a. i./ L  sheepshead minnow) and invertebrates ( 96 hr LC 50 > 100 mg a. i./ L  grass shrimp; 96 hr LC 50 > 180 mg a. i./ L  fiddler crab). No toxicity studies have been conducted to determine potential chronic effects to freshwater and marine/ estuarine fish and aquatic invertebrates. Toxicity studies with algae exposed to dicamba acid indicate that cell densities were significantly reduced in blue green algae at test concentrations as low as 0.061 mg a. i./ L. Aquatic vascular plant species were not as sensitive to dicamba acid with 14 day EC 50 values of > 3.25 mg a. i./ L, which is greater than the equivalency of the maximum application rate [ 2.9 mg a. i./ L ( 4 lb ai/ ac)]. However, duckweed frond chlorosis occurred at mean measured concentrations as low as 0.39 mg a. i./ L. Laboratory studies indicate that dicamba should not bioaccumulate in aquatic organisms; however, it may persist in sediments with an estimated half life of 141 days ( MRID 43245208). Data are currently unavailable to determine potential impacts to sedimentdwelling benthic organisms and to semi aquatic/ transitional habitats ( wetlands, riparian habitats). 27 b. Terrestrial Effects Ground deposition, spray drift, and wind erosion of soil particles with resulting residues on foliage and on insects and seeds are the most likely sources of dicamba exposure to nontarget terrestrial organisms, including listed species. In addition, uptake in plant roots and foliage would be expected to occur. Current data were not provided to determine the potential exposure to birds, mammals, and pollinators from residues on foliage, insects, and seeds. Available acute toxicity data indicate that the salt forms of dicamba are practically non toxic to bobwhite quail and mallard ducklings in the diet; however, oral gavage studies indicate that dicamba acid ( 86.9% a. i.) was moderately toxic ( LD 50 = 188 mg ai/ kg) to bobwhite quail and slightly toxic to mallard ducks ( NOEL could not be determined due to signs of toxicity at all test levels). In chronic studies with dicamba acid ( 86.9% a. i.), a reduction in hatchability was observed in mallard ducks at 1390 ppm a. e. ( NOEC = 695 ppm a. e.). No treatment related mortality, signs of toxicity, or effects on reproduction were observed in bobwhite quail. Dicamba acid is classified as practically non toxic to small mammals on an acute oral basis. A 13 week subchronic oral study in Charles River CD rats reported body weight changes and liver effects at 1000 mg a. i./ kg/ day. Developmental studies with New Zealand white rabbits reported irregular ossification of internasal bones at 300 mg a. i./ kg/ day ( dicamba acid, 90.5% a. i.) and maternal toxicity ( abortion and clinical signs of toxicity, including ataxia, rales, and decreased motor activity) was reported at 150 mg a. i./ kg/ day. Maternal toxicity; including mortality, clinical signs of toxicity, body weight changes, and decreased food consumption, was also observed in Charles River CD rats at 400 mg a. i./ kg/ day ( dicamba acid, 85.8% a. i.). In a 2 generation reproduction study with Sprague Dawley rats ( dicamba acid, 86.5% a. i.), maternal neurotoxicity was observed at doses of 419 mg a. i./ kg/ day in males and at 450 mg a. i./ kg/ day in females and developmental effects, decreased pup growth, were observed in rats at a dose of 136 mg a. i./ kg/ day. No toxicity studies have been conducted to determine the potential effect of residues to pollinators. An additional source of exposure to dicamba could be in puddled water on treated fields through preening and grooming, involving the oral ingestion of material from the feathers or fur.

Terrestrial plant toxicity studies indicate that dicamba acid negatively impacts seed germination ( radicle length; soybean EC 25 = 0.036 lb ai/ A), seedling emergence ( shoot length; soybean EC 25 = 0.0027 lb ai/ A), and vegetative vigor ( shoot length; soybean EC 25 = 0.0068 lb ai/ A ) in monocots and dicots. The most sensitive monocot tested was onion ( EC 25 = 0.071 lb ai/ A  seed germination; EC 25 = 0.0044 lb ai/ A  seedling emergence; and EC 25 = 0.1507 lb ai/ A  vegetative vigor). Consequently, 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.

Dicamba is readily absorbed through the foliage and roots of plants; consequently, it could be injurious to non target plant species by drift, runoff, or leaching to roots. Dicamba may accumulate in the soil with frequent or extensive use which may result in damage to trees, shrubs, or other ornamentals. Residuals of dicamba in soil have been shown to reduce 28 emergence in sugarbeet and cause petiole epinasty, severe stunting of seedlings, and trumpeting ( Dexter et al, 1994). Dicamba 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. Numerous cases of soybean injury are reported yearly from the use of dicamba on corn that results in the exposure of adjacent fields of soybean to dicamba through spray drift and volatilization ( Proost and Boerboom 2004; Hartzler 2003). Injury includes leaf malformations, terminal bud kill, and delayed maturity. Yield loss can occur if soybeans are exposed to dicamba after they bloom ( in the reproductive stage).

Since the dicamba salts rapidly dissociate to dicamba acid and it rapidly degrades under aerobic conditions, it would not be expected to persist in surface soils. Thus, risks from exposure to birds, small mammals, and soil invertebrates through dermal contact or ingestion of soils should be minimal.

2. Ecosystems at Risk 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 dicamba, this may have negative effects not only on the herbivores, but throughout the food chain. Also, depending on the severity of impacts to the plant communities [ i. e., forests, wetlands, ecotones ( edge and riparian habitats)], community assemblages and ecosystem stability may be altered ( i. e. reduced bird and mammal populations in edge habitats; reduced riparian vegetation resulting in increased light penetration and temperature in aquatic habitats; reductions in algal biomass). In addition, allochthonous input from riparian vegetation is not only a significant component of the food supply for aquatic herbivores and detritivores but also provides habitat ( i. e. leaf packs, materials for casebuilding for invertebrates).

C. Assessment Endpoints The portion of the problem formulation which is an explicit statement of the characteristic of the environment to be protected is encompassed in a delineation of endpoints. These endpoints can include a particular species, a functional group of species, a community, or an ecosystem. 29 The major endpoints related to aquatic environments at issue are: ( a). Direct effects to growth and reproduction of aquatic vascular and non vascular plants. ( b). Direct effects to fish and aquatic invertebrates in the water column via survival, reproduction, and growth. ( c). Direct effects to listed aquatic species via survival, reproduction, and growth.

The major endpoints related to terrestrial environments at issue are: ( a). Direct effects to growth and reproduction of non target plants. ( b). Direct effects to birds and mammals via survival, reproduction, and growth. ( c). Direct effects to listed terrestrial species via survival, reproduction, and growth.

D. Conceptual Model 1. Risk Hypothesis: Problem formulation focused on laboratory studies and chemical properties of dicamba acid and its salts which indicate that the herbicide is mobile, has the potential to leach to groundwater, be transported via runoff to surface water bodies, persists in subsurface soils and sediments, undergoes aerobic biodegradation in soils and water, and does not bioaccumulate in aquatic organisms.

The following risk hypotheses are defined:

Non target terrestrial plants are subject to plant growth abnormalities, lethality, and developmental/ reproductive effects when exposed to dicamba acid and its salts as a result of the labeled uses of the pesticide.

Aquatic non vascular and vascular plants inhabiting surface waters adjacent to a treated field are subject to adverse effects to growth and development when exposed to dicamba acid and its salts as a result of labeled uses of the pesticide.

Terrestrial animals, including herbivores and pollinators, are subject to adverse effects such as reproductive/ developmental effects in birds and mammals, and indirect effects on foraging behavior when exposed to dicamba acid and its salts as a result of the labeled use of the pesticide.

Aquatic invertebrates, including benthic organisms inhabiting the sediment and/ or pore water, and fish inhabiting surface waters adjacent to a treated field are subject to adverse effects on reproduction, growth, and survival when exposed to dicamba acid and its salts as a result of the labeled uses of the pesticide.

Indirect effects to community assemblages in forest, wetlands, edge and riparian habitats could occur as a result of adverse direct effects to non target plants from exposure to 30 dicamba acid and its salts; resulting in reduced food supply and habitat availability affecting species abundance and diversity.

2. Diagram: Based on an examination of the physical/ chemical properties of dicamba and its salts, the fate and disposition in the environment, and mode of application ( e. g., ground and aerial spray application); a conceptual model ( Figure II. c) was developed that represents the possible relationships between the stressor, ecological endpoints, and the measurement endpoints. 31 Figure II. c. Dicamba ERA conceptual model 32 E. Analysis Plan The analysis plan is the final step in Problem Formulation. The plan describes the three measures used to evaluate the risk hypotheses developed in the conceptual model for dicamba use. First, the measures of exposure are derived as estimated environmental concentrations ( EEC) based on model predictions and environmental fate data. This screening assessment will use more refined models to predict exposure. Second, the measures of effect characterize the assessment endpoints and are based on toxicity data that describe the effects of diamba on individuals, species, populations, and communities in aquatic and terrestrial ecosystems. 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). The analysis plan also identifies the data gaps and uncertainties for conducting the risk assessment and suggests recommendations for new data collection ( if needed).

1. Preliminary Identification of Data Gaps and Methods: Environmental fate data for dicamba acid is mostly complete. Fate data are available concerning the hydrolysis and photodegradation of dicamba in water, the biodegradation of dicamba in soil, and the mobility of dicamba acid in soil and water. There is uncertainty in the environmental fate of the typical end use products ( TEPs) which contain the sodium, DMA or DGA salts. Dissociation rates, adsorption/ desorption rates and field dissipation information are needed for TEPs to determine the persistence and mobility of the salts and their associated inert ingredients found in the TEPs. A submitted laboratory study with each salt of dicamba (> 99% purity) indicates rapid dissociation in pure water; however, information is needed on the environmental fate of the formulated TEPs which contain the dicamba salts and inert ingredients.

Due to the widespread use of dicamba in agricultural, industrial and residential settings as as well as the detection of dicamba in groundwater, prospective groundwater studies are needed to provide information on the potential for soil leaching and groundwater migration potential of dicamba in field conditions. A key aspect of the field studies should include the formulated TEPs.

Spray drift in conjunction with volatilization presents a potential risk to non target plants inhabiting forest and edge habitats adjacent to target fields and wetland and riparian habitats along streams and/ or ponds in close proximity to sprayed fields. There are numerous label restrictions for ground and aerial spray applications ( see SAN 845H and Banvel SGF labels). Spraying is not recommended if wind is gusty or in excess of 5 mph and moving in the direction of adjacent sensitive crops. Recommendations on spray systems for coarse spray application are included on the labels as well as directions for keeping the spray pressure at or below 20 psi and spray volume at or above 20 gpa. Finally, applications adjacent to sensitive crops are not advised when temperature on the day of application is expected to exceed 85 ° C as drift is more likely to occur. Submitted dicamba field dissipation studies indicate half lifes of 3 to19.8 days for sodium, DMA and DGA salts when applied to bareground plots. However, these field dissipation studies are inadequate since application rates were not verified, soil sample storage stability data were inadequate, pan evaporation data were not collected and precipitation/ irrigation was inadequate to fulfill test guidelines. 33 Toxicity studies are available to determine the potential acute effects to freshwater and marine/ estuarine fish and invertebrates and the potential effects to aquatic vascular and nonvascular aquatic plants. Data are currently unavailable to determine potential chronic effects to freshwater and marine/ estuarine fish and invertebrates and potential impacts to sedimentdwelling biota since lab studies indicate that dicamba may have the potential to persist in sediments.

Toxicity studies are available to determine the potential acute effects to birds, mammals and honey bees and the potential reproductive/ developmental effects to birds and mammals. 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, insects, seeds, and roots. Additional data may be needed to adequately determine the potential for residues on non target plants resulting from spray drift application.

For this screening risk assessment, the potential exposure of dicamba to aquatic benthic organisms in sediments ( aquatic invertebrates) and to terrestrial herbivores and pollinators in residues will be modeled. The Tier II PRZM/ EXAMS models will be used to estimate exposure in surface water. The potential levels of dicamba residues on various food items for birds and terrestrial animals will be modeled using the T REX 1.2.3. Likewise, TerrPlant 1.0 model will estimate exposure to nontarget terrestrial plants.

2. Measures to Evaluate Risk Hypotheses and Conceptual Model Measures of Exposure Based on the conceptual model presented above ( Fig. II. c.), the potential exposure pathways by which dicamba may inadvertently affect non target plant and animal populations in aquatic areas include: drift during aerial and ground application, particularly downwind drift, and runoff/ leaching of contaminated water from treated areas to untreated areas. In semi aquatic areas, the routes are: drift during aerial and ground application, particularly downwind drift; runoff events ( off site movement of contaminated water); and wind erosion of contaminated soil particles. Since dicamba is designed to kill weeds, there may be exposure to non target terrestrial plants adjacent to treated areas via drift and runoff from transitional sites or wetlands which may be dry during certain periods, or via wind blown treated soil particles from those pathways for aquatic species. As part of the aquatic assessment, EFED modeled exposure concentrations of dicamba to nontarget aquatic plants and invertebrates following labeled use information. For aerial and ground spray applications, dicamba surface water concentrations were estimated using the Tier II screening models PRZM and EXAMS employing the standard field pond scenario The potential exposure pathways for terrestrial plants and animals include deposition from ground and aerial spray applications, runoff/ leaching from treated areas, spray drift, and wind erosion of soil particles resulting in residues on non target organisms as well as residues on food items for non target organisms. As part of the terrestrial assessment, EFED modeled exposure concentrations of dicamba to nontarget terrestrial plants and animals following the ground and aerial spray application rates for terrestrial uses ( Table II. e). 34 Table II. e. Exposure Scenarios for Dicamba Risk Assessment Crop ( location) Application Ratea ( lbs ae/ A) Application number/ year Application Date Label Reference ( Registration Number Asparagus ( MI) 0.5 1 May 1, 20xx SAN 845H ( 7969 140)

Corn ( CA, IL, MS, NC ND, MS, PA, TX) 0.75 ( total of 2 applications) 2 April 15, 20xx May 15, 20xx SAN 845H ( 7969 140)

Pasture/ Rangeland ( CA, MN, PA, TX) 2.0 1 May 1, 20xx SAN 845H ( 7969 140)

Sorghum ( KA, TX) 0.5 ( total of 2 applications) 2 May 1, 20xx June 1, 20xx SAN SGFc ( 7969 135)

Soybean ( MS) 2.0 1 May 1, 20xx SAN SGFc ( 7969 135)

Sugarcane ( FL, LA) 2.8 1 April 15, 20xx SAN 845Hb ( 7969 140)

Turf ( PA, FL) 2.0 1 May 1, 20xx SAN SGFc ( 7969 135)

Wheat ( ND, OR, TX) 1.0 ( total of 2 applications) 2 May 1, 20xx June 1, 20xx SAN 845H ( 7969 140)

aApplication rates taken from Dicamba Use Profile ( SRRD July 22, 2005). bSAN845H herbicide contains 77.0% sodium salt of dicamba which is equivalent to 70.0% dicamba acid ( label dated March 24, 2004). CSAN SGF herbicide contains 23.15% dimethylamine salt of dicamba which is equivalent to 21.06% dicamba acid ( label dated March 8, 2004).

Specific uses chosen for modeling include asparagus, corn, pasture/ rangeland, sorghum, soybean, sugarcane, turf and wheat ( Table II. f.). Although these uses represent only a portion of the crops for which dicamba has a labeled use, crops with highest application rates and crops which have a large percentage of their total acreage treated with dicamba are among these uses. Some crops with large total acreage treated were also included as modeled scenarios. These crops were also chosen to represent a wide geographic area, thus encompassing a variety of environmental conditions. By encompassing crops with large percentages of acreage treated with dicamba and a large geographic area, some crops with lower maximum application rates were also covered by the set of scenarios. All application rates were adjusted to acid equivalents. Risks to aquatic organisms ( i. e. fish, invertebrates, and plants) and terrestrial organisms ( i. e. birds, mammals, and plants) are assessed based on modeled Estimated Environmental Concentrations ( EECs). EECs for dicamba uses on terrestrial sites were modeled using T REX ( Ver. 1.2.3) to estimate dicamba residues on 35 various food items which may be contacted or consumed by wildlife. Exposure concentrations for nontarget plants were evaluated for the use scenarios using the TerrPlant 1.0 model.

Table II. f. Surface Water Exposure Inputs for PRZM/ EXAMS for Dicamba acid.

Input variable ( Units) Input value & calculations Source Crop name See table II. e. See table II. e.

Application rate ( lb ai/ acre) See table II. e. See table II. e.

Interval between appl. ( d) N/ A N/ A Application efficiency 0.95 ( aerial); 0.99 ( ground) Input parameters guideline ( 2/ 28/ 2002).

Spray drift fraction 0.05 ( aerial); 0.01 ( ground) Input parameters guideline ( 2/ 28/ 2002).

DWRATE ( day 1) 0.038 ( 6 d x 3) MRID # 43245207; Input parameters guideline ( 2/ 28/ 2002).

DSRATE ( day 1) 0.038 MRID # 43245207; Input parameters guideline ( 2/ 28/ 2002).

Koc ( mL/ g) 13.4 ( average Koc) MRID# 42774101; Input parameters guideline ( 2/ 28/ 2002).

Henry's Law Const. ( atm. m3/ mole) 1.6X10 9 calculated KBACW ( h 1) 0.058 ( 6X2= 12 d) No data; aerobic soil metabolism half life rate X 0.5; Input parameters guideline ( 2/ 28/ 2002).

KBACS ( h 1) 0.0016 ( 141X3= 423 d) MRID# 43245208; Input parameters guideline ( 2/ 28/ 2002).

KDP ( h 1) 0.00076 ( 914.4) MRID# 42774102; Input parameters guideline ( 2/ 28/ 2002).

KBH, KNH, KAH ( h 1) stable MRID# 40547902; Input parameters guideline ( 2/ 28/ 2002).

KPS ( mL/ g) 13.4 ( average Koc) MRID# 42774101; Input parameters guideline ( 2/ 28/ 2002).

MWT ( g/ mole) 221 SANDOZ Safety Data Sheet ( Nov, 1989).

Solubility @ 25 0C ( mg/ L) 6100 SANDOZ Safety Data Sheet ( Nov, 1989).

Vapor pressure ( torr) 3.41X10 5 SANDOZ Safety Data Sheet ( Nov, 1989). 36 Monitoring data Monitoring data were not used to refine this Tier I preliminary risk assessment. However, monitoring data are available in the Pesticides in Ground Water Database [ Hoheisel et al. 1991] for dicamba ( 3,172 wells sampled) and 5 hydroxy dicamba ( 87 wells sampled). Out of the wells sampled, there were no reports of residues greater than the stated MCL ( 200 µ g/ L lifetime). However, the detection limits are unknown, and it is not known if wells were sampled in areas where dicamba was used. STORET contains records for dicamba analyses in samples from lakes, ocean, estuary, canal, or reservoir sites. The data have not been extensively evaluated; in addition, it is uncertain what the actual detection limits were for the samples and whether samples were taken from areas where dicamba was not in use.

NAWQA analyzed for dicamba in the 1993 2004 survey of groundwater wells and surface waters of agricultural, urban and mixed land use settings. A total of 4676 groundwater samples were collected; detections of dicamba were in six samples at 0.035 ppb. Dicamba was detected in 141 surface water samples ( total of samples collected were 5813 samples).

Surface and Groundwater monitoring data are limited spatially and temporally in dicamba use areas to extract useful information about expected dicamba concentration in drinking water in use areas. Thus; at this time EFED believes that at the absence of a representative monitoring data, the use of modeling results for surface and water would be more appropriate 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 dicamba prelimnary risk 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 I screening risk assessment modeling of estimated exposure concentrations combined with toxicity information from dicamba toxicity studies.

A. Use Characterization Dicamba was first registered in the United States in 1967 and is widely used in agricultural, industrial and residential settings. Dicamba herbicide is available in aqueous formulations and is commonly mixed in tanks with other herbicides and/ or fertilizers before application. In aqueous forms, dicamba is applied as a pre and post emergent via aerial or ground spray for control of most annual, biennial and perennial broadleaf weeds in crops. Dicamba is used to control weeds and brush in pasture, rangeland and noncropland areas such as utility, highway right of ways and non irrigation ditchbanks including grazed or hayed areas. Dicamba is also used on residential turf and lawns as well as golf courses for control of weeds and other unwanted plants. 37 B. Exposure Characterization The dicamba exposure characterization in this assessment combined the environmental fate data with Tier II exposure models to estimate environmental exposure concentrations ( EECs). Exposure models estimate EECs following the conceptual diagram of dicamba usage and potential exposure endpoints 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. The goal of Tier II modeling is to better define the range of EECs that can be reasonably expected under variable weather conditions. Likewise, EECs for birds and terrestrial mammals are estimated using the T REX 1.2.3 model and EECs for non target plants are estimated by the TerrPlant 1.0 model.

1. Environmental Fate and Transport Characterization EFED established a strategy for bridging the environmental fate data requirements for the dicamba sodium and potassium salts, dimethylamine salt ( DMA), isopropylamine salt and diglycoamine salt ( DGA) to the dicamba acid. Bridging data were submitted indicating that the dicamba salts will be rapidly converted to the free acid of dicamba. A laboratory dissociation study showed that each dicamba salt ( tested at > 99% purity) completely dissociated to dicamba acid within 75 seconds in pure water ( MRID 43288001). EFED determined that fate studies conducted with dicamba acid provide " surrogate data" for the dicamba salts. However, there is uncertainty regarding the fate of formulated technical end use products ( TEPs) containing the dicamba salts in the environment. The influence of inert ingredients, in formulated TEPs, on the degradation potential, soil adsorption/ desorption and migration of dicamba are unresolved. Furthermore, dicamba is often mixed in tanks before application with other herbicides and fertilizers which may influence the environmental fate of dicamba. This fate summary does not address inert ingredients or other herbicides available in mixtures with dicamba.

In hydrolysis studies, uniformly ring labeled [ 14C] dicamba ( 3,6 dichloro o anisic acid) did not degrade significantly in aqueous buffered solutions adjusted to pH 5, 7, and 9, and distilled water treated with dicamba at 10 ppm or 100 ppm and incubated in the dark at 25 or 35 /

C for 30 days. In the test solutions incubated at 25 /

C, parent dicamba was 92.36 98.03% of the applied radioactivity at 30 days post treatment. In the test solutions incubated at 35 /

C, parent dicamba was > 92.4% of the applied radioactivity, except for the pH 7 test solution treated at 100 ppm; parent dicamba was 82.46% at 29 days post treatment. Three unidentified degradates were each < 3.54% of the applied radioactivity in any of the test systems. The material balances were 83.36 103.21% ( MRID 40335501).

The aqueous photolysis of dicamba ( 3,6 dichloro o anisic acid) resulted in a half life of > 30 days. This study was conducted in a sterile aqueous buffer solution ( pH 7) that was irradiated for 30 days with a xenon arc lamp at 25 /

C; dicamba did not degrade in the dark control sample. The registrant calculated half life was 38.1 days under continuous irradiation at 1.38 times natural sunlight at noon in the spring at 40 /

N. The major identified degradate was carbon dioxide ( maximum of 15.26% of the applied radioactivity at 30 days). Numerous other degradates were present at < 7.72% each and were not identified ( MRID 42774102).

In soil photolysis studies, dicamba ( 3,6 dichloro o anisic acid) slowly photodegraded ( approximately 20%) on silt loam soil that was continuously irradiated with a xenon arc lamp 38 for 30 days at 25 /

C. Dicamba acid did not degrade in the dark control. The only identified degradate was carbon dioxide ( maximum of 3.07% of the applied at 30 days); although unidentified degradates were formed during the study, none were present at > 3.71% of the applied at any time ( MRID 42774103).

Aerobic soil metabolism was studied in a silt loam soil that was moistened to 75% of 0.33 bar, treated at 2.555 µ g/ g ( 3.2 µ g/ g dry weight) with dicamba acid, and incubated aerobically in the dark at approximately 23 ° C for 365 day. Dicamba acid was found to degrade with a halflife of 6 days. CO 2 and 3,6 dichlorosalicylic acid ( 3,6 DCSA) were the primary degradates identified, at maximum concentrations of 67.3 and 17.4% of the applied, respectively. Two minor degradates, 5 hydroxy dicamba ( 5 OH) and 3,6 dichloro 2,5 dihydorxybenzoic acid ( 2,5 DiOH), were also identified at maximum concentrations of 0.8 and 2.7% of the applied, respectively. Other nonvolatile degradates were isolated at up to 3.7% of the applied but were not identified ( MRID 43245207).

In anaerobic soil metabolism studies, dicamba acid degraded with a half life of 141 days in loam soil: pond water systems that were treated at 3.85 ppm and incubated in the dark for 12 months under anaerobic ( nitrogen gas) conditions at approximately 25 ° C. The major degradate identified in the soil: water systems was 3,6 dicholorsalicylic acid ( 3,6 DCSA) at a maximum of 61.6% of the applied. Two minor degradates, 5 hydroxy dicamba ( 5 OH dicamba) and 3,6 dichloro 2,5 dihydroxybenzoic acid ( 3,6 dichlorogentisic acid; 3,6 DCGA), were also identified ; maximum concentrations were 1.9 and 3.64% of the applied, respectively. Volatile [ 14C] residues were a maximum of 1.3% of the applied radioactivity at 12 months post treatment ( MRID 43245208).

The anaerobic aquatic degradation study of dicamba acid found a half life of 141 days in loam soil: pond water systems that were treated at 3.85 ppm and incubated in the dark for 12 months under anaerobic ( nitrogen gas) conditions at approximately 25 ° C. The major degradate identified in the soil: water systems was 3,6 dicholorsalicylic acid ( 3,6 DCSA) at a maximum of 61.6% of the applied. Two minor degradates, 5 hydroxy dicamba ( 5 OH dicamba) and 3,6 dichloro 2,5 dihydroxybenzoic acid ( 3,6 dichlorogentisic acid; 3,6 DCGA), were also identified ; maximum concentrations were 1.9 and 3.64% of the applied, respectively. Volatile [ 14C] residues were a maximum of 1.3% of the applied radioactivity at 12 months post treatment ( MRID 43245208).

The aerobic aquatic metabolism study of uniformly phenyl ring labeled [ 14C] dicamba acid, at a nominal application rate of 0.12 µ g/ mL, resulted in a registrant calculated half life of 20.2 days in aerobic flooded loam soil that was incubated in darkness at 25 ± 1 ° C for 62 days. Using non linear analysis, a slightly longer registrant calculated half life of 24.3 days was determined. In the total soil/ water system, the parent ( reviewer calculated) was 97.2 100% of the applied radioactivity at 0 3 days, decreased to 81.7% by 14 days and to 60.2% by 21 days, was 36.2% at 30 days, and was not detected by 51 days post treatment. The parent compound in the water phase was initially present at 91.9% ( 0.113 ppm) of the applied radioactivity at day 0, decreased to 54.6 75.6% by 14 21 days post treatment, and decreased to 22.4% ( 0.55ppm) by 41 days post treatment. In the soil ( Soil Extract 1), the parent compound was initially present at 7.05% ( 0.009ppm) of the applied radioactivity at day 1 ( methanol extract only), decreased to 6.10% ( 0.008ppm) by 1 day post treatment, then increase to a maximum of 8.54% ( 0.011ppm) by 3 days post treatment, and decreased to 39 3.66% ( 0.005ppm) by day 41 post treatment. The minor degradate 3,6 DCSA was initially observed in the water phase at 6.50% ( 0.008ppm) of the applies activity at 14 days post treatment, increased to a maximum of 8.55% ( 0.011ppm) by 30 days, and decreased to 0.813% ( 0.001ppm, based on a single replicate) by day 62. In the " Soil Extract 1" ( methanol), 3,6 DCSA was present at 1.63% ( 0.002ppm) at 30 days post treatment and < 0.001% at 62 days post treatment only. In the " Soil Extract 2" ( acidified methanol: water), the major degradate 3,6 DCSA was present at 3.26% ( 0.004ppm) at day 14 post treatment, increased to 26.0% ( 0.032ppm) by day 41, and decreased to 4.88% ( 0.001ppm) by day 62. The distribution of [ 14C] residues between the soil and water fractions was not reported, but the majority of the residues were observed in the water phase throughout the study. [ 14C] Residues in the water phase were 92.4% ( 0.114ppm) of the applied radioactivity at day 0 and decreased to 2.04% ( 0.003ppm) by 62 days post treatment. In the soil extracts, total [ 14C] residues were 7.05% ( 0.009ppm) of the applied radioactivity at day 0, increased to 43.9% ( 0.054ppm) by 41 days , and were 22.0% ( 0.027ppm) at 62 days post treatment. Nonextractable [ 14C] residues comprised 14.65% ( 0.18ppm) of the applied at 62 days post treatment. Evolved 14CO 2 accounted for 1.63% ( 0.002ppm) of the applied radioactivity at 14 days post treatment and was 53.6% ( 0.066ppm) at 62 days post treatment ( MRID 43758509).

An aqueous dissociation study was conducted to provide bridging data for dicamba salts. As determined by a UV spectrophotometric method, dicamba salts reached essentially 100% dissociation within 75 seconds of the time of mixing with pure water. The observed dissociation half lives in pure water, 0.1 N NaOH ( pH 13), and 0.1 N HCl ( pH 1) for all of the salts were less than 10 seconds, establishing a value 6.9 x 10 2 sec 1 as the lower limit for the dissociation fate constant for each of the salts. These data, combined with the fact that dicamba is a moderately strong acid ( pK a = 1.87) predict that when these dicamba salts are release into the environment dissociation will be rapid ( MRID 43288001).

The adsorption/ desorption of unaged phenyl ring labeled [ 14C] dicamba was studied in loam, clay loam, silt loam, and sandy loam soils, and loam sediment. Based on batch equilibrium experiments, dicamba acid was determined to be very mobile in loam, clay loam, silt loam, and sandy loam soils and a loam sediment, with Freundlich K ads values of 0.16, 0.10, 0.53. 0.07 and 0.21, respectively. Corresponding K oc values were 7.27, 3.45, 21.1, 17.5 and 17.5, respectively ( MRID 42774101).

Adsorption/ desorption in soil information from an acceptable aerobic soil metabolism study ( MRID 43245207) indicates that 3,6 DCSA ( 3,6 Dichlorosalicylic acid) is the only degradate formed at greater that 10% of the applied. Based on batch equilibrium experiments 3,6 DCSA was determined to be mobile in sandy loam ( Freundlich K ads value of 2.51; Ko c 628) and clay loam ( K ads 7.03; Koc 242) soils. DCSA was determined to be of low mobility in silt loam and loam soils and in loam sediment; Freundlich K ads values were 20.29, 31.50, and 35.16, respectively; corresponding K oc values were 812, 1432, and 2930, respectively ( MRID 43095301).

Laboratory Volatility studies were conducted with the potassium salt of dicamba and the dimethylamine salt of dicamba and formulated with adjuvant. Dicamba ( as the potassium salt) volatilized from moist silty clay soil that was treated at a nominal field rate of 0.5 lb ai/ A ( 1.511 mg ai/ jar) with a soluble concentrate formulation fortified with [ 14C] dicamba ( radiochemical purity > 98%). Volatility rates ranged from 2.98 to 4.97 x 104 : g/ cm2/ hr; this 40 corresponded to air concentrations of 12.6 21.0, : g/ m3. Samples were incubated for up to 96 hours on a 16 hour photoperiod under continuous air flow ( 0.1 L/ min) at 30 C and 60% relative humidity. Recovery of the applied radioactivity was 96.5%. Dicamba ( as the dimethylamine salt formulated with the adjuvant Atplus 411f) volatilized from moist silty clay soil that was treated at a nominal field rate of 0.5 lb ai/ A ( 1.511 mg ai/ jar) with soluble concentrate formulations fortified with [ 14C] dicamba ( radiochemical purity > 98%). Volatility rates ranged from 2.91 to 4.95 x l0 4 : g/ cm2/ hr; this corresponded to air concentrations of 12.4 21.0, : g/ m3. Samples were incubated for up to 96 hours on a 16 hour photoperiod under continuous air flow ( 0.1 L/ min) at 30 ° C and 60% relative humidity. Recovery of the applied radioactivity was 70.6 88.8% ( MRID 41966602).

Field dissipation studies of dicamba salts were conducted in several locations across the US in the early 1990' s ( see table below). Dicamba salt forms were applied to bareground plots according to labeled rates and soils were sampled for loss of parent compound and the presence of degradates over time. The major dicamba degradate in soil samples was DCSA. These studies are supplemental as Subdivision N guidelines were not fulfilled in that application rates were not verified in the field, soil sample storage stability was not verified, measurements of pan evaporation were not collected during the studies and rainfall/ irrigation amounts did not fulfill guideline requirements.

MRID No. Dicamba Test Substance Application Rate Study Location and Soil Type Half life ( days)

43361506 SAN 845 H ( Na salt) SAN 821 H ( DGA salt) 1.0 lb ae/ A 1.0 lb ae/ A LA, silt loam soil LA, silt loam soil 3.2 3.0 43361507 Clarity and SAN 821 H ( DGA salt) 1.0 lb ae/ A NC, loam sand soil 3.29 43651405 SAN 1214 H ( DMA salt) 2.0 lb ae/ A LA, silt loam soil 9 43651407 Clarity and SAN 821 H ( DGA salt) 2.0 lb ae/ A IN, loam soil 12.9 43651408 Banvel SGF SAN845 H ( Na salt) 2.0 lb ae/ A 2.0 lb ae/ A NC, loam sand soil NC, loam sand soil 9 9 42754101 42883202 Banvel 4.0 ( DMA salt) 1.0 lb ae/ A CA, sandy loam soil 19.8 42754102 Banvel 4.0 ( DMA salt) 1.0 lb ae/ A IN, loam soil 4.4 The octanol/ water partition coefficients for 3,6 dichloro salicylic acid ( DCSA) at two concentrations ( nominally 4.96 x 104 M and 5.67 x 10 5 M) in buffered aqueous solutions at pHs 5, 7, and 9 ranged from 0.06 to 0.58 and averaged 0.29. Because of the low K ow , DCSA is not expected to bioaccumulate in aquatic organisms ( MRID 41966601). 41 2. Measures of Aquatic Exposure Aquatic Exposure Modeling Aquatic EECs for the ecological exposure to dicamba were estimated using PRZM 3.12/ EXAMS 2.98 employing the standard field pond scenario. 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. PRZMEXAMS 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 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 in a specific state is intended to represent a high end 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 peak EEC values for single and multiple applications, if necessary. Chronic risk assessments for aquatic invertebrates and fish are performed using the average 21 day and 60 day EECs, respectively.

Tables II. e and II. f. present the input parameters used in the Tier II PRZM/ EXAMS modeling for ecological assessment of dicamba and DCSA for surface water sources. To simulate field application of dicamba, multiple scenarios were selected representing different dicamba usage areas based on geography and weather ( see Fig. IIa). PRZM/ EXAMS scenarios were modeled to estimate dicamba EECs in surface water based on label information for dicamba application to asparagus, corn, pasture/ rangeland, sorghum, soybean, sugarcane, turf and wheat ( Table II. d.). The modeled surface water EECs for the these scenarios are presented in Table III. a. For a given crop, only the highest EECs are presented in these tables; however; results from all modeled scenarios are provided in Appendix B. For each PRZM/ EXAMS scenario, an aerial and ground spray application was evaluated following dicamba registered uses. The PRZM/ EXAMS input and output files from the aquatic ecological exposure assessment are presented in Appendix B.

Monitoring and Field Data Monitoring data were not used to refine this Tier I preliminary risk assessment. However, monitoring data are available in the Pesticides in Ground Water Database [ Hoheisel et al. 1991] for dicamba ( 3,172 wells sampled) and 5 hydroxy dicamba ( 87 wells sampled). Out of the wells sampled, there were no reports of residues greater than the stated MCL ( 200 µ g/ L lifetime). However, the detection limits are unknown, and it is not known if wells were sampled in areas where dicamba was used. STORET contains records for dicamba analyses in samples from lakes, ocean, estuary, canal, or reservoir sites. The data have not been extensively evaluated; in addition, it is uncertain what the actual detection limits were for the samples and whether samples were taken from areas where dicamba was not in use. The US Geological Survey National Water Quality Assessment program ( NAWQA) is not currently analyzing for dicamba in their samples, and they do not have analytical methods for this chemical in place. 42 NAWQA analyzed for dicamba in the 1991 2001 survey of groundwater wells and surface waters of agricultural, urban and mixed land use settings. Dicamba was only detected (> 0.11 µ g/ L) in groundwater and surface waters of agricultural settings. Frequency of detection was 0.41% in groundwater ( total of 1218 samples) and 0.26% in surface waters ( total of 1233 samples) with detected values less than 1.14 µ g/ L.

Table III. a. Estimated Environmental Concentrations ( µ g ae/ L) of Dicamba Acid in Surface Water ( PRZM EXAMS) from All Uses for Ecological Assessmenta Simulation Scenario Concentration ( µ g ae/ L)

Crop and Location Application rate 1 in 10 year Peak 21 Day Average 60 Day Average Asparagus ( MI) 0.5 lbs ae/ acre  1 application 0.82b 1.73c 0.66b 1.42c 0.42b 0.93c Corn ( TX) 0.75 lbs ae/ acre  2 applications with 30 day interval 21.53b 21.51c 13.86b 13.82c 6.58b 6.58c Pasture ( TX) 2.0 lbs ae/ acre  1 application 84.89b 83.96c 49.78b 49.20c 22.99b 28.09c Sorghum ( TX) 0.50 lbs ae/ acre 2 applications with 30 day interval 8.79b 8.99c 4.92b 5.04c 2.57b 2.71c Soybean ( MS) 2.0 lbs ae/ acre  1 application 33.29b 36.07c 20.22b 21.94c 9.77b 10.66c Sugarcane ( FL) 2.8 lbs ae/ acre  1 application 170a 166b 91.61a 89.23b 41.03a 40.41c Turf ( PA) 2.0 lbs ae/ acre  1 application 3.88b 8.05c 3.06b 6.49c 1.98b 4.18c Wheat ( TX) 1.0 lbs ae/ acre  2 applications with 30 day interval 18.74b 19.09c 10.43b 10.59c 5.33b 5.66c a Surface water EECs for all crop scenarios identified in Table II. d. are presented in Appendix B. Only the highest EECs for each crop scenario are presented in Table III. b.. b Ground spray application modeled using PRZM 3.12/ EXAMS 2.98. c Aerial spray application modeled using PRZM 3.12/ EXAMS 2.98.

3. Measures of Terrestrial Exposure Terrestrial Exposure Modeling For birds and mammals, dicamba 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. 1.2.3) model predicts maximum and mean EECs resulting from the single and multiple applications of dicamba. Acute and Chronic RQs are calculated using these EECs and appropriate toxicity data.

Maximum and mean EECs calculated by T REX are presented in table III. b, based on application scenarios represented by labels for sugarcane, pasture, soybean, corn, and wheat. These models were performed using the form of dicamba ( dicamba sodium salt) that is contained in the formulation that is applied at the highest rates. More comprehensive 43 modeling based on labels for other forms of dicamba may be performed in later refinements of this assessment. For terrestrial modeling, EECs are presented for single applications only, since they were calculated to be slightly higher than EECs for multiple applications. Using only these rates to calculate RQs did not alter the overall conclusion of risk that would be calculated using multiple rates.

Table III. b. Maximum and Mean Estimated Environmental Concentrations ( EECs) of Dicamba Acid on Food Items for Terrestrial Species ( from T REX)

Simulation Scenario Concentration ( ppm)

Application rate ( lbs ae/ A) a No. of Applications Short Grass Tall Grass Broadleaf plants/ Small insects Fruits/ Pods/ Seed s/ Large Insects Maximum EECs 2.8 1 672.00 308.00 378.00 42.00 2.0 1 480.00 220.00 270.00 30.00 1.0 1 240.00 110.00 135.00 15.00 0.75 1 180.00 82.50 101.25 11.25 Mean EECs 2.8 1 238.00 100.80 126.00 19.60 2 1 170.00 72.00 90.00 14.00 1.0 1 85.00 36.00 45.00 7.00 0.75 1 63.75 27.00 33.75 5.25 aApplication rates are associated with crops as follows: 2.8 lbs ae/ A for sugarcane, 2.0 lbs ae/ A for pasture and soybeans, 1.0 lbs ae/ A for wheat, 0.75 lbs ae/ A for corn Effects on non target terrestrial plants are most likely to occur as a result of spray drift from aerial and ground spray applications of liquid formulations. Spray drift is an important factor in characterizing the risk of dicamba to non target plants. The TerrPlant ( Ver. 1.0) model predicts EECs for terrestrial plants located adjacent to the treated field. Dicamba applied according to label directions as a liquid spray for ground or aerial spray applications may impact non target plants for some distance from the application site depending on droplet size, wind speed, and other factors. Several of the dicamba product labels specify a required or recommended droplet size for spray applications as well as advisories limiting application in certain weather conditions. Dicamba applied as a fine or medium spray, during windy conditions or when temperatures are above 85 ° C has the potential to damage off target plants. Coarse sprays may also damage non target plants through drift, but generally closer to the treated field.

C. Ecological Effects Characterization 1. Aquatic Effects Characterization Freshwater Fish, Acute 44 Fish toxicity studies for two freshwater species using the TGAI are required to establish the acute toxicity of dicamba acid and its salts to fish. The preferred test species are rainbow trout ( a coldwater fish) and bluegill sunfish ( a warmwater fish). A compilation of the acute studies from EFED databases are presented in Table III. c. and an analysis of the available data indicates that the dicamba salts are practically non toxic to fish. Results of the studies with the potassium salt are questionable due to precipitation of the test substance during testing. It appears that dicamba acid is slightly more toxic to fish than the dicamba salts with rainbow trout LC 50 of 28 mg ae/ L and bluegill LC 50 > 50 mg ae/ L. The guideline requirement ( 72 1) for acute freshwater fish toxicity is fulfilled; EFED will use the worst case value ( LC 50 28 mg ae/ L; MRID 40098001) for evaluating acute toxic exposure to freshwater fish.

TABLE III. c. Freshwater Fish Acute Toxicity for Dicamba Acid and Dicamba Salts.

Species % ai 96 hour LC50 ( mg ai/ L) 96 hour LC50 ( mg ae/ L) Toxicity Category MRID No. Author/ Year Study Classification Dicamba acid Rainbow trout ( Oncorhynchus mykiss) 86.8 135.4 135.4 Practically non toxic 0041272 NA, 1977 Acceptable Rainbow trout ( Oncorhynchus mykiss) 10 153 153 Practically non toxic 00036915 NA/ 1974 Supplemental Rainbow trout ( Oncorhynchus mykiss) 88 28 28 Slightly toxic 40098001 NA, 1986 Acceptable Bluegill sunfish ( Lepomis macrochirus) 86.8 135.3 135.3 Practically non toxic 0034703 NA, 1977 Acceptable Bluegill sunfish ( Lepomis macrochirus) 88 > 50 > 50 Slightly toxic 40098001 NA, 1986 Supplemental Dimethylamine salt of dicamba Rainbow trout ( Oncorhynchus mykiss) 48.3 1000 977 Practically non toxic 263000 Griffen & Thompson 1981 Acceptable Rainbow trout ( Oncorhynchus mykiss) 11.5 1000 977 Practically non toxic 46184 Thompson et al. 1980 Supplemental Bluegill sunfish ( Lepomis macrochirus) 48.2 1000 977 Practically non toxic 22530 Sleight 1971 Supplemental Bluegill sunfish ( Lepomis macrochirus) 11.5 1000 977 Practically non toxic 46183 Thompson et al. 1980 Supplemental Sodium salt of dicamba Rainbow trout ( Oncorhynchus mykiss) 22 558 507.2 Practically non toxic 00029623 Bentley 1974 Supplemental Bluegill sunfish ( Lepomis macrochirus 22 706 642 Practically non toxic 00022539 Bentley 1974 Supplemental Potassium salt of dicamba TABLE III. c. Freshwater Fish Acute Toxicity for Dicamba Acid and Dicamba Salts.

Species % ai 96 hour LC50 ( mg ai/ L) 96 hour LC50 ( mg ae/ L) Toxicity Category MRID No. Author/ Year Study Classification 45 Bluegill sunfish ( Lepomis macrochirus 38 230 196 Practically non toxic 258983 McAllister et al. 1985 Supplemental Diglycoamine salt of dicamba Rainbow trout ( Oncorhynchus mykiss) 40.15 > 400 > 270.8 Practically non toxic ACC263863 NA, 1986 Acceptable Bluegill sunfish ( Lepomis macrochirus 40.15 > 400 > 270.8 Practically non toxic ACC263863 NA, 1986 Acceptable * Conversion from active ingredient to acid equivalents was completed in accordance with conversion factors found on the label and molecular weight differences. The LC50 values from the toxicity tests were converted to acid equivalents by multiplying the value times factors as provided in Section II. B.

Freshwater Invertebrates, Acute A freshwater aquatic invertebrate toxicity test using the TGAI is required to establish the toxicity of dicamba acid and its salts to aquatic invertebrates. The preferred test species is Daphnia magna. A compilation of the acute studies from EFED databases are presented in Table III. d. and an analysis of the available data indicates that the sodium salt of dicamba is the most toxic form to daphnids with an acute 48 hour EC 50 value of 34.6 mg ae/ L ( NOEL = 16.4 mg ae/ L; MRID 00233292). EFED will use this value for evaluating acute toxic exposure to freshwater invertebrates. Dicamba acid and the other dicamba salts were practically non toxic to daphnids with 48 hour EC 50 values ranging from > 100  1563 mg ae/ L. The guideline requirement ( 72 2) for acute freshwater invertebrate toxicity is fulfilled. 46 TABLE III. d. Freshwater Invertebrate Acute Toxicity for Dicamba Acid and Dicamba Salts.

Species % ai 48 hour EC50 ( mg aiL) 48 hour EC50 ( mg ae/ L) Toxicity category MRID No. Author/ Year Study Classification Dicamba acid Waterflea ( Daphnia magna) 86.8 110.7 110.7 Practically non toxic 00521262 NA, 1977 Acceptable Waterflea ( Daphnia magna) 88 > 100 > 100 Practically non toxic 40094602 NA, 1980 Supplemental Sowbug ( Asellus brevicauda) 88 > 100 > 100 Practically non toxic 40098001 NA, 1986 Supplemental Scud ( Gammarus fascia) 88 > 100 > 100 Practically non toxic 40098001 NA, 1986 Supplemental Dimethylamine salt of dicamba Waterflea ( Daphnia magna) 48.2 1600 1563 Practically non toxic 00028283 Thompson & Forbis, 1979 Supplemental Sodium salt of dicamba Waterflea ( Daphnia magna) 26.5 38.1 34.6 Slightly toxic 00233292 Vilkas, 1977 Acceptable Potassium salt of dicamba Waterflea ( Daphnia magna) 38 750 639.8 Practically non toxic 258983 Forbis et al., 1985 Supplemental Diglycoamine salt of dicamba Waterflea ( Daphnia magna) 40.15 > 400 > 270.8 Practically non toxic ACC263863 NA, 1986 Supplemental * Conversion from active ingredient to acid equivalents was completed in accordance with conversion factors found on the label and molecular weight differences. The LC50 values from the toxicity tests were converted to acid equivalents by multiplying the value times factors as provided in Section II. B.

Freshwater Fish and Invertebrate, Chronic No data available. Studies were not required.

Estuarine/ Marine Fish, Acute Acute toxicity testing with estuarine/ marine fish using the TGAI is required for dicamba acid and its salts because the end use product may be expected to reach this environment due to its potential use on crops with significant acreage in coastal counties. An acute flow through toxicity study was performed with the sheepshead minnow. The data submitted showed that dicamba acid is practically non toxic to estuarine/ marine fish on an acute basis, with an LC 50 of > 180 mg ae/ L. The guideline ( 72 3a) is fulfilled ( MRID 0025390). 47 Table III. e Estuarine/ Marine Fish Acute Toxicity for Dicamba Acid.

Species/ Static % ai 96 hour LC50 ( mg ae/ L) Toxicity Category MRID No. Author/ Year Study Classification Sheepshead minnow ( Crassostrea virginianus) 86.8 > 180 Practically non toxic 0025390 NA , 1977 Acceptable Estuarine and Marine Invertebrates, Acute Acute toxicity testing with estuarine/ marine invertebrates using the TGAI is required for dicamba acid and its salts because the end use product may be expected to reach this environment due to its potential use on crops with significant acreage in coastal counties. The preferred test species are mysid shrimp and eastern oyster. Data from Acceptable studies with the grass shrimp and fiddler crab indicate that dicamba acid is practically non toxic to marine invertebrates with 96 hr EC 50 ' s of > 132 and > 173 mg ae/ L, respectively. Supplemental studies with the glass shrimp and eastern oyster indicate these species were more sensitive; however, the studies did not meet guideline requirements and Acceptable studies with freshwater invertebrates will be used to assess risk to aquatic invertebrates. The data requirements ( 72 3b) are fulfilled ( MRID # 0034702; MRID 0034704).

Table III. f Estuarine/ Marine Invertebrate Acute Toxicity for Dicamba Acid.

Species/ Flow through % ai. 96 hour EC50 ( mg ae/ L) Toxicity Category MRID No. Author/ Year Study Classification Grass shrimp ( Palaemonetes pu) 86.2 > 132 Practically nontoxic 0034702 NA, 1977 Acceptable Fiddler crab ( Uca pugilator) 86.8 > 173 Practically nontoxic 0034704 NA, 1977 Acceptable Glass shrimp ( Palaemonetes ka) 88 > 56 Slightly toxic 40098001 NA, 1986 Supplemental Eastern oyster ( Crassostrea virginica) 87 > 1.0 Moderately toxic 40228401 NA, 1986 Supplemental Estuarine and Marine Fish and Invertebrates, Chronic No data available. Studies were not required.

Aquatic Plants Several aquatic plant toxicity studies using the TGAI are required to establish the toxicity of dicamba acid to non target aquatic plants. The recommendation is for testing of five species: freshwater duckweed ( Lemna gibba), green alga ( Selenastrum capricornutum), blue green algae ( Anabaena flos aquae), marine diatom ( Skeletonema costatum), and a freshwater diatom. The EC 50 for the freshwater vascular plant ( duckweed) is > 3.25 mg ae/ L, based on reduced frond production. Sublethal effects observed in the duckweed included slight chlorosis and curled fronds. Dicamba acid appears to be more toxic to non vascular aquatic plants with the lowest EC 50 for blue green algae of 0.061 mg ae/ L ( NOEC 0.005 mg ae/ L), based on reduced cell density. EFED will use this value for evaluating toxic exposure to 48 aquatic plants. Studies submitted for the algal species indicate that the blue green algae is more sensitive to dicamba acid than the green algae ( EC 50 > 3.7 mg ae/ L). The marine diatom was more sensitive to dicamba acid than the freshwater diatom causing reductions in cell density at test levels as low as 0.033 mg ae/ L. Other toxic symptoms observed in the algal/ diatom studies included cell bloating, fragmentation, and thin walls. The guideline requirements ( 122 2 and 123 2) are fulfilled ( MRID 42774107; MRID 42774108; MRID 42774109; MRID 42774110; and MRID 42774111) for the five required species.

TABLE III. g. Non target Aquatic Plant Toxicity for Dicamba Acid.

Species [ Study Type] % ai EC50/ NOEC ( mg ae/ L) Endpoints Affected MRID No. Author, Year Study Classification Duckweed ( Lemna gibba) [ Tier II] 89.5 > 3.25/ 0.20 Frond production 42774111 Hoberg, 1993 Acceptable Green Algae ( Selenastrum capricornutum) [ Tier I] 89.5 > 3.7/ 3.7 Cell density 42774107 Hoberg, 1993 Acceptable Blue green Algae ( Anabaena flos aquae) [ Tier II] 89.5 0.061/ 0.005 Cell density 42774109 Hoberg, 1993 Acceptable Diatom ( Navicula pelliculosa) [ Tier II] 89.5 2.3/ 0.50 Cell density 42774108 Hoberg, 1993 Acceptable Diatom ( Skeletonema costatum) [ Tier II] 89.5 0.493/ 0.011 Cell density 42774110 Hoberg, 1993 Acceptable 2. Terrestrial Effects Characterization Birds, Acute and Subacute An oral toxicity study using the technical grade of the active ingredient ( TGAI) is required to establish the acute oral toxicity of dicamba acid and its salts to terrestrial birds. The preferred guideline test species is either mallard duck ( a waterfowl) or bobwhite quail ( an upland gamebird). The data that were submitted indicate that dicamba acid is categorized as moderately toxic to avian species with a 14 day oral LD 50 for bobwhite quail of 188 mg ae/ kg ( NOEL = 13.6 mg ae/ kg). Observed effects included reduction in body weight gain, loss of coordination, loss of righting reflex, lower limb weakness/ rigidity, reduced reaction to external stimuli, wing droop, ruffled appearance, lethargy, shallow and rapid respiration, depression, and coma. The guideline requirement ( 71 1) for acute oral avian toxicity is fulfilled; EFED will use the worst case value ( LD 50 188 mg ae/ kg; MRID 42774105) for evaluating acute oral exposure to terrestrial birds. 49 TABLE III. h. Avian Acute Oral Toxicity for Dicamba Acid and Dicamba Salts.

Species % ai LD50 ( mg ai/ kg) LD50 ( mg ae/ kg) Toxicity Category MRID No. Author, Year Study Classification Dicamba acid Northern bobwhite quail ( Colinus virginianus) 86.9 188 188 Moderately toxic 42774105 Campbell et al., 1993 Acceptable Mallard duck ( Anas platyrhynchos) 86.9 1373 1373 Slightly toxic 42774106 NA, 1993 Acceptable Dimethylamine salt of dicamba Mallard duck ( Anas platyrhynchos) 48.2 > 2510 > 2452 Practically non toxic 00073275 Fink et al., 1979 Supplemental Mallard duck ( Anas platyrhynchos) 11.5 > 2510 > 2452 Practically non toxic 00046180 Fink et al., 1980 Supplemental Potassium salt of dicamba Northern bobwhite quail ( Colinus virginianus) 38 724 618 Moderately toxic 261466 Beavers, 1986 Supplemental Diglycoamine salt of dicamba Northern bobwhite quail ( Colinus virginianus) 40 387 262 Moderately toxic ACC263863 NA, 1986 Acceptable * Conversion from active ingredient to acid equivalents was completed in accordance with conversion factors found on the label and molecular weight differences. The LC50 values from the toxicity tests were converted to acid equivalents by multiplying the value times factors as provided in Section II. B.

Two dietary studies using the TGAI are required to establish the subacute toxicity of dicamba acid and its salts to birds. The preferred test species are mallard duck and bobwhite quail. Acceptable data submitted for dicama acid indicate that the 8 day acute dietary LC 50 for both species was > 10,000 mg ae/ kg; therefore, dicamba acid is categorized as practically non toxic to avian species on a subacute dietary basis. Data available from studies with the dicamba salts reported LC 50 values ranging from > 1522 to > 9090 mg ae/ kg. The guideline ( 71 2) is fulfilled ( MRID 00025391; MRID TOUDIC07).

TABLE III. i. Avian Subacute Dietary Studies for Dicamba Acid and Dicamba Salts.

Species % ai LC50 ( mg ai/ kg) LC50 ( mg ae/ kg) Toxicity Category MRID No. Author, Year Study Classification Dicamba acid Northern bobwhite quail ( Colinus virginianus) 86.6 > 10,000 > 10,000 Practically non toxic 00025391 NA, 1977 Acceptable Northern bobwhite quail ( Colinus virginianus) 10 > 10,000 > 10,000 Practically non toxic 00023690 NA, 1974 Supplemental Mallard duck ( Anas platyrhynchos) 86.6 > 10,000 > 10,000 Practically non toxic TOUDIC07 NA, 1977 Acceptable TABLE III. i. Avian Subacute Dietary Studies for Dicamba Acid and Dicamba Salts.

Species % ai LC50 ( mg ai/ kg) LC50 ( mg ae/ kg) Toxicity Category MRID No. Author, Year Study Classification 50 Mallard duck ( Anas platyrhynchos) 86.6 2009 2009 Practically non toxic 00025392 NA, 1977 Supplemental Mallard duck ( Anas platyrhynchos) 10 > 10,000 > 10,000 Practically non toxic 00025317 NA, 1974 Supplemental Dimethylamine salt of dicamba Northern bobwhite quail ( Colinus virginianus) 48.2 > 4640 > 4533 Practically non toxic 00034693 Fink & Reno, 1974 Supplemental Northern bobwhite quail ( Colinus virginianus) 11.5 > 5620 > 5490 Practically non toxic 00046182 Fink et al., 1980 Supplemental Mallard duck ( Anas platyrhynchos) 48.2 > 4640 > 4533 Practically non toxic 00022527 Fink & Reno, 1974 Supplemental Mallard duck ( Anas platyrhynchos) 11.5 > 5620 > 5490 Practically non toxic 00046181 Fink et al., 1980 Supplemental Sodium salt of dicamba Northern bobwhite quail ( Colinus virginianus) 26.5 > 10,000 > 9090 Practically non toxic 00233292 Fink, 1977 Acceptable Northern bobwhite quail ( Colinus virginianus) 22 > 10,000 > 9090 Practically non toxic 00025328 Fink, 1975 Supplemental Mallard duck ( Anas platyrhynchos) 22 > 10,000 > 9090 Practically non toxic 00030102 Fink, 1975 Supplemental Potassium salt of dicamba Northern bobwhite quail ( Colinus virginianus) 38 > 5620 > 4794 Practically non toxic 00261465 Beavers, 1985 Supplemental Mallard duck ( Anas platyrhynchos) 38 > 5620 > 4794 Practically non toxic 00261466 Beavers, 1985 Supplemental Diglycoamine salt of dicamba Northern bobwhite quail ( Colinus virginianus) 40 > 2248 > 1522 Slightly toxic ACC263863 NA, 1986 Acceptable Mallard duck ( Anas platyrhynchos) 40 > 2248 > 1522 Slightly toxic ACC263863 NA, 1986 Acceptable * Conversion from active ingredient to acid equivalents was completed in accordance with conversion factors found on the label and molecular weight differences. The LC50 values from the toxicity tests were converted to acid equivalents by multiplying the value times factors as provided in Section II. B.

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 51 bobwhite quail. The mallard study reported a reduction in hatchability at 1390 ppm ae ( NOEC = 695 ppm ae); however, no evidence of adverse reproductive effects was observed in bobwhite quail at concentrations of 1,390 ppm ae. The guideline ( 71 4) is fulfilled; EFED will use the worst case value ( NOEC 695 ppm ae; MRID 43814003) for evaluating chronic exposure to terrestrial birds.

Table III. j. Avian Reproduction for Dicamba Acid.

Species % ai NOEC/ LOEC ( ppm ai) NOEC/ LOEC ( ppm ae) LOEC Endpoints MRID No. Author, Year Study Classification Northern bobwhite quail ( Colinus virginianus) 86.9 1600/ 1390/ No treatmentrelated toxicity 43814004 Beavers et al., 1994 Acceptable Mallard duck ( Anas platyrhynchos) 86.9 800/ 1600 695/ 1390 Reduction in hatchability 43814003 Beavers et al., 1994 Acceptable * Conversion from active ingredient to acid equivalents was completed in accordance with conversion factors found on the label and molecular weight differences. The LC50 values from the toxicity tests were converted to acid equivalents by multiplying the value times factors as provided in Section II. B.

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 dicamba acid is categorized as practically non toxic to small mammals on an acute oral basis ( LD 50 value 2,740 mg ai/ kg/ day). The guideline 81 1 is fulfilled ( MRID 00078444).

TABLE III. k. Mammalian Acute Toxicity for Dicamba acid.

Species % Purity Test Type Toxicity Affected Endpoints MRID No. Study author Classification Rat ( Rattus norvegicus) Tech Acute oral LD50 = 2,740 mg/ kg/ day Mortality 00078444 NA Acceptable Mammals, Subchronic and Developmental/ Reproductive In a 2 generation reproduction study with Sprague Dawley rats, systemic neurotoxicity was observed at doses of 419 mg a. i./ kg/ day in males and at 450 mg a. i./ kg/ day in females and developmental effects ( decreased pup growth) were observed in rats at a dose of 136 mg a. i./ kg/ day. Developmental studies with New Zealand white rabbits reported irregular 52 ossification of internasal bones at 300 mg a. i./ kg/ day and maternal toxicity ( abortion and clinical signs of toxicity, including ataxia, rales, and decreased motor activity) was reported at 150 mg a. i./ kg/ day. Maternal toxicity; including mortality, clinical signs of toxicity, body weight changes, and decreased food consumption, was also observed in Charles River CD rats at 400 mg a. i./ kg/ day. In addition, sublethal effects in subchronic feeding studies ( 13 weeks) with Charles River CD rats included body weight changes and liver effects at 1000 mg a. i./ kg/ day. The guidelines 82 1, 83 3 and 83 4 are fulfilled ( MRID 00128093, MRID 00084024, MRID 42429401, and MRID 43137101); EFED will use the worst case value ( NOAEL 45 mg ai/ kg/ day, MRID 43137101) for evaluating chronic exposure to terrestrial mammals.

TABLE III. l. Mammalian Subchronic and Developmental/ Reproductive Toxicity for Dicamba acid.