## 24 September 2001

**RE-REGISTRATION ELIGIBILITY DOCUMENT**

**FOR SODIUM AND CALCIUM SALTS OF METHANEARSONIC ACID** 

**(MSMA/DSMA/CAMA)**

## TABLE OF CONTENTS Page

List of Tables 4 Ecological Risk Conclusions 5 1. Terrestrial Risk Conclusions 5 2. Aquatic Risk Conclusions 5 Environmental Fate and Drinking Water Conclusions 6 1. Environmental Fate Conclusions 6 2. Drinking Water Conclusions 7 Introduction 9 1. Usage 9 2. Background Environmental Concentrations 9 3. Arsenic Environmental Chemistry 10 4. General Toxicology 11 Risk Characterization 12 1. Terrestrial Risk 12 a. mammals and birds 12 b. terrestrial plants 14 c. summary of terrestrial risk 15 2. Aquatic Risk 15 a. summary of aquatic risk 16 3. Endangered Species 16 Environmental Fate Assessment: Perspective, Basis, and Summary 21 1. Perspective and Basis 21 2. Summary 24 3. Chemical Structures and Physicochemical Properties 25 4. Transformation 27 5. Metabolites 28 6. Bioconcentration 29 7. Transport/Mobility 29 Drinking Water Assessment 30 1. Groundwater Exposure Conclusions 31 2. Surface Water Exposure 32 3. Index Drinking Water Reservoir Simulation Results 35 4. Surface Water Exposure Conclusions 36

## Aquatic Exposure and Risk Assessment 37

1. Exposure Assessment 37 2. Hazard Assessment 38 a. freshwater animals 38 b. marine/estuarine animals 38 c. plants 38 3. Risk Assessment 39 a. animals 39 b. plants 39 Terrestrial Exposure and Risk Assessment 39 1. Exposure Assessment 39 a. food items 39 b. off-site plant 39 2. Hazard Assessment 40 a. birds 40 b. mammals 40 c. insects 41 d. non-target plants (Tier II) 41 3. Risk Assessment 41 a. birds 41 b. mammals 42 c. non-endangered plants 42 d. endangered species 42 Appendices Appendix 1. Toxicity, EEC, and risk quotient tables 44 Appendix 2. Definitions and explanations of terms and acronyms 62 Appendix 3. Formulas for off-site terrestrial plant exposure 64 Appendix 4. Estimating residues on terrestrial food items 65 Appendix 5. Cacodylic acid drinking water assessment 66 Appendix 6. Index reservoir drinking water concentrations 71 Appendix 7. GENEEC model/output tables for aquatic ecological assessment 76 Appendix 8. Data requirements tables 77 Appendix 9. References 83 Appendix 10. Arsenic concentrations in US ground waters, USGS map 86

## LIST OF TABLES

Table # Page #
1 Acute toxicities to mammals 45
2 EECs on terrestrial food items 46 3 Risk quotients for mammals 47
4 Risk quotients for avian species 48 5 Acute toxicities to avian species 49
6 EECs at off-site terrestrial environments 50
7 Risk quotients for non-endangered terrestrial plants 51 8 Risk quotients for endangered terrestrial plants 52 9 Acute toxicities to freshwater aquatic fish and invertebrates 53 10 Risk quotients for aquatic fish and invertebrates 54
11 Acute toxicities to estuarine/marine aquatic fish and invertebrates 55
12 Risk quotients for non-endangered aquatic plants 56 13 EECs in aquatic environment 57
14 Acute toxicities to aquatic plants 58 15 Acute toxicities to honey bees 59 16 Acute toxicities to non-target terrestrial plants (Tier II) 60 17 Chronic risk quotients for small mammals 61

## 5

**ENVIRONMENTAL RISK CONCLUSIONS** Disodium methanearsenate (DSMA), monosodium methanearsenate (MSMA), and calcium methanearsenate (CAMA) are used as contact herbicides on a wide variety of predominantly agricultural, but also non-agricultural sites. Approximately four times as much MSMA (4,333,000 lbs a.i. weighted avg) is applied annually in the United States as compared to DSMA (1,077,000 lbs a.i. weighted avg) with the predominant usage for both being on cotton (QUA case no. 2395, PC code nos. 13803 and 13802). Very little information was available relating to CAMA usage or application rates other than it is used for residential crabgrass control (QUA case no. 2395, PC code no. 13806). **Terrestrial Risk Conclusions** Acute risk exists within the terrestrial environment near the site of application, for a short period after application, due to the high use rates for these chemicals at certain sites. Toxicity classifications of the chemicals to birds and mammals range from moderately toxic to practically non-toxic, indicating that the inherent toxicity of these chemicals to animals is not great. However, the use rates are high enough to lead to exceedences of acute risk levels of concern (LOC). For example, MSMA is applied to orchards up to three times, each at a rate as high as 15.5 lbs a.i./A, leading to estimated environmental concentrations (EECs) on grasses that exceed the acute risk LOC by 12 times for mammalian herbivores. Use on cotton may result in EECs on grasses that exceed the acute risk by as much as 1.8 times for mammalian herbivores. Therefore, the potential risk of these chemicals in the terrestrial environment is related mostly to their high use rates. Chronic risk for these chemicals in the terrestrial environment is uncertain. Modeling predicts the residues to be present on food items for up to several months, but the persistence of the food items may not be long enough to present residues to organisms over that period of time. Chronic reproductive studies with methylarsenate, a component of all three herbicides, indicate that they are chronically toxic to mammals. As such, they may also be chronically toxic to avian species. Unfortunately, no chronic avian toxicity studies were submitted. Their submission is required. **Aquatic Risk Conclusions** There does not appear to be considerable acute risk to aquatic organisms. Acute toxicity studies revealed that the three herbicides are considered to be slightly toxic to practically non-toxic to aquatic organisms. Combining this with the modeled aquatic EECs revealed that no acute risk LOCs were exceeded. Chronic risk is uncertain. These herbicides are heavily applied in the environment meaning that their continuous low level release into the aquatic environment is possible, especially near sites of repeated applications. As such aquatic organisms would be chronically exposed to these chemicals. Unfortunately, no chronic aquatic toxicity studies were submitted. Their submission is required.

## 6

**ENVIRONMENTAL FATE AND DRINKING WATER CONCLUSIONS Environmental Fate Conclusions**  As explained in special context in the Environmental Fate Assessment Section in the main body of this document, formal data requirements for MSMA/DSMA/CAMA are satisfied at this time, exceptfor 1) submission and EPA laboratory validation of analytical chemical methods for detection and measurement in water

and soil and 2) field spray-drift and droplet-size spectral data for these herbicides. Results of the environmental fate assessment were used integrally to estimate exposures for the preceding ecological risk characterizations and conclusions. The environmental fate of arsenic compounds is complex, and entwined as part of a global biogeochemical cycle. Rather than attempt out-of-context and oversimplified conclusions here, the reader is directed to the Environmental Fate Assessment Section proper, which begins with a perspective and basis, followed by a “boxed” abstract of the assessment which then follows. However, the potential for long-term accumulation of arsenical residues at sites receiving repeated applications over many years bears repeating here. These arsenicals, in combination with their transformation products, including the pesticide cacodylic acid as well as other natural arsenic containing species with known toxicities, maintain the total, immutable arsenic environmental load. That is, arsenic from the pesticides is not lost, but redistributed and transformed (recycled) throughout the environment (plants, animals, air, soil, sediment, water) into other arsenic containing substances. It is also crucial not to confuse transformation with detoxification. Currently, the Agency has a limit of 43 parts per million (ppm) of total (unspeciated) arsenic in soil as the concentration beyond which remediation is necessary (for example, at Superfund sites impacted by various sources of arsenic and currently on The American University campus in Washington, DC, where World War I chemical warfare agents containing the poisonous gas lewisite (ClCHCHAsCl2) were tested and disposed). As an example of potential accumulation, let us take MSMA at a constant, annual application rate of one pound per acre (all actual MSMA rates are higher). Without redistribution of arsenic from soil which originally may have contained only a few parts per million of natural arsenic at the site of application, the regulatory total arsenic limit would be reached in approximately 190 years. At the maximum cotton use rate, the limit would be reached in around 30 years; at the maximum orchard use rate, in only 3 years. However, since we know that global redistribution, transformation, and recycling of arsenic in all possible environmental compartments occurs in the guise of different arsenical compounds such as those given in the environmental fate assessment, different maximum concentrations would be reached at indefinite future times. This would depend on local quasi-equilibrium conditions for arsenic chemistry and entwined environmental factors (biogeochemistry). Thus, although there is no doubt that local arsenic concentrations will be elevated, the degree of long-term or chronic exposure

## 7

and potential effects are largely unknown from the standpoint of our assessment. This uncertainty suggests the need for systematic, long-term field monitoring for potential buildup of total arsenic residues. **Drinking Water Conclusions for Humans** MSMA, DSMA, CAMA, and cacodylic acid are four of several arsenic containing pesticides which the Agency is considering for re-registration eligibility. Ultimately, in another action, the Office of Pesticide Programs (OPP) will assess the potential overall (aggregate, cumulative) drinking water exposure to these compounds and common transformation products. The Agency’s Office of Water (OW) is scheduled to issue a final regulation on the larger issue of “arsenic” in drinking water during the year 2001. We conclude from monitoring and modeling that surfacedrinking water concentrations originating from use of these salts of methanearsonic acid will impose an additive, localized burden on background concentrations of these and other chemical species of arsenic, including cacodylic acid. Ground water should notbe impacted incrementally. Based on our surface water assessment, application of arsenical pesticides will result in a superposition upon existing local, “non-pesticidal” (anthropogenic and natural) background concentrations of arsenic species in surface drinking water. In some locations, these incremental amounts caused by pesticidal application would be relatively small compared to some of the existing concentrations. In other locations where the background is low, the superposition could be relatively large. Provided repeated, long-term pesticidal applications at the higher labeled rates do not occur, it is most likely that local biogeochemistry of arsenic (redistribution, transformation, recycling) would moderate or prevent significant alteration in local, long-term arsenic equilibria. Therefore, provided local biogeochemistry is not overwhelmed by excessive application of arsenical pesticides (or arsenic compounds from other human activities), local, long-term average concentrations of available arsenic should remain relatively unaffected. Whatever the sources of arsenic, natural or otherwise, if there are toxicological concerns near the monitored, modeled, and/or regulatory limit concentrations, then, clearly, this invites broader scale, systematic environmental sampling and analysis for speciated arsenic, not just total arsenic, in order to determine statistically the associations, ranges of exposure, and possible effects. Adequate analytical methods for speciating arsenic are now readily available. The effects of water treatment on raw water concentrations are known, and should be considered for “public water systems” (as defined in 40 CFR 141.2). However, it also should be acknowledged that many users of surface drinking water do not drink from regulated public water systems. According to the USEPA Office of Drinking Water, which is currently engaged in new regulation for total arsenic in drinking water in public water systems, many larger water treatment facilities use sedimentation-

## 8

flocculation procedures that are capable of lowering total arsenic to 1 ppb (part per billion) or less. However, in smaller public water systems, the method is less effective, and can lower concentrations to only approximately 20-25 ppb. At the present time, public water systems only assure protection against excursions of total arsenic beyond the regulatory 50 ppb MCL (maximum contaminant level) (10 ppb if pending regulation is enacted). Furthermore, within the regulatory limit for total arsenic in drinking water are inorganic forms that are most often in higher concentrations and generally accepted to be far more toxic than the organic. Determining the kind (chemical speciation) and degree of acceptable arsenic exposure in drinking water involves many regulatory considerations (for example, cost/benefit) representing complex issues for EPA Program Offices. However, the Office of Drinking Water, after extensive project funding, protracted deliberations with expert panels, practical considerations, and public/stakeholder input, has set the regulatory limit for public water systems (which are notinclusive of all drinking water sources) at 50 ppb (10 ppb if current proposed regulation is enacted) for total arsenic (which includes organic and inorganic forms), even if that limit should happen to exceed the Office of Pesticide’s level of concern for arsenical pesticides or their by-products.

## 9

**INTRODUCTION** While some arsenicals are present naturally within the environment, continued heavy use of the arsenical herbicides could present a risk in use areas. Indeed, both inorganic and organic arsenicals have been shown to have deleterious toxic consequences within an organism, among which are those leading to cancer. Therefore, while the arsenicals may be naturally present, they mayoccur at concentrations which can lead to harm or death. **Usage** Monosodium methanearsenate (MSMA), disodium methanearsenate (DSMA), and calciummethanearsenate (CAMA) are contact herbicides used in a wide variety of agricultural and nonagricultural applications. The major application is cotton with over 93% of total usage. As a result, the southeastern US is the major area of use including Georgia, Arkansas, Mississippi, Louisiana, North Carolina, and Texas. Other uses for arsenicals include sugarcane, sod farms, corn, wheat, pasture and others too numerous to list. Orchards have the highest use rate, with as many as three applications annually, each at 15.5 lb a.i./acre (annual total of 46.5 lb/acre). All totaled, these other uses account for approximately 5% of the total national usage. With reference to cotton, MSMA and DSMA are generally applied to a field multiple times during a single growing season. MSMA is a pre/post-emergent herbicide applied before or sometime after cotton emergence. Prior to harvest, DSMA may be applied along with another arsenical not addressed in this risk assessment, cacodylic acid, to defoliate cotton. While applied as different product names initially, MSMA and DSMA end up as the same chemical in the environment, monomethylarsenate (MMA), also known as methanearsonic acid (MAA). Therefore, while the arsenical herbicides are different formulations and are applied separately, in essence, when they are applied in the field, MAA is applied each time leading to potential arsenical accumulation in the field. CAMA is a minor use contact herbicide applied to control crabgrass in residential areas. Its total usage accounts for less than 1% of total arsenical usage nationally. **Background Environmental Concentrations** Arsenic presence is widespread within the environment. The primary natural source of arsenic is from bedrock from which it is weathered, but it is also emitted from industrial processes and various agricultural practices. Total arsenic concentrations in air range from 0.01 

## : g/m 3

## to as high as 0.75 

## : g/m

3

## in smelter emissions. Surface and ground water total arsenic concentrations are generally quite low. Surface waters of a southeastern, cotton producing state can reach several parts per billion (ppb) arsenic according to EPA's BASINS and STORET databases, but are typically less than 3 ppb. High arsenic concentrations ranged between 10 and 50 ppb. For comparison, arsenic concentrations in raw water samples from Washington, DC area rivers were not above the lower detection limit of 2

## 10

ppb. However, water concentrations of arsenic can be quite high. For example, 86 of 2125 sampled water wells in Wisconsin had arsenic concentrations in excess of 50 ppb (Burke and Stoll 1999). The source of that arsenic was determined to be a sandstone aquifer over which the wells were drilled. Arsenic concentrations in ground water of the lower Madison river valley range from 16 to 176 ppb (Nimick 1998). The source of that arsenic was believed to be from the Madison river, which has arsenic concentrations up to 100 ppb. Soils and sediments will contain greater arsenic concentrations, typically in the range of 1 to 50 parts per million (ppm), but possibly greater than that in areas near bedrock outcrops and mine spoilings. More substantive discussion on the prevalence of arsenic in water and other environment compartments is reserved for the environmental fate and drinking water sections of this document. Arsenic can also be found in various food items. Arsenic concentrations of 1.6 to 2.4 

## : g/g (ppm) were found in cans of tuna (Higham and Tomkins 1993) while samples of fruits, vegetables, grains, fast foods, and dairy products had an average arsenic concentration of 2 

## : g/g dry weight (Nielson et al.1991). Even alcoholic beverages had arsenic concentrations ranging from 1.5 to 12.4 ppb (HercePagliai et al. 1999). Due to the widespread occurrence of arsenic, determination of arsenical risk through simple presence alone is difficult. **Arsenic Environmental Chemistry** Discerning arsenic risk in the environment would be furthered by understanding arsenic chemistry. Microbiota mediated adsorption/desorption processes take place between arsenic and both aluminum and iron oxide fractions in soils and sediments (Menzer and Nelson 1986). These processes control the fate of arsenic in the environment. Once sorbed to the clay fractions of soils, they may be transported to water bodies and deposited into sediments, the ultimate sink for arsenic. The statement of the sediment being the ultimate sink for arsenic is corroborated by Woolson (1975) who stated that the residence time of arsenic in air is around 9 days, but is millions of years in sediments. The chemistry of arsenic is very complex, and is the reason that detection of the arsenical herbicides would be difficult following their dissolution in water. Like many metals, once exposed to the environment, arsenic is oxidized to various forms, generally to trivalent arsenite (AsO 3 3-

## ) and pentavalent arsenate (AsO 4 3-

## ). These two species, commonly encountered in environmental soils,waters, and sediments, may be further transformed into methylated arsenic chemicals such as monomethylarsenate (MMA or MAA), di-methylarsenate (DMA also known as cacodylate), trimethylarsine oxide and the reduced, highly volatile mono-methylarsine, di-methylarsine, and trimethylarsine (Bright et al. 1996). These methylated arsenic species are all generated through biologicalprocesses. Once the methylated arsenic species are in the environment, they may just as easily be demethylated back to their inorganic forms (arsenite and arsenate) by soil bacteria (Gao and Burau 1997). Many mammalian species also successively methylate the oxidized, inorganic arsenic species to MMA and DMA (Hughes et al. 2000, Vahter 2000, Moore et al. 1997). MMA and DMA are both more readily excreted from the body relative to the inorganic species (Hughes et al. 2000).

## 11

Interestingly, the ability to methylate arsenic varies among species, and even among different age groups, genders, and communities within a species (Vahter 2000). This variability, resulting fromvarious factors including the ability to produce enzymes responsible for arsenic methylation (methyltransferases) and nutritional status, can alter individual susceptibility to the arsenic species. The preponderant commentary on arsenic environmental chemistry is given in the environmental fate section of this document. It is evident that arsenic can be found in the environment in many different forms, due to natural processes. Addition of the methylated arsenic species (i.e., DSMA, MSMA, CAMA) to the environment could lead to the temporary accumulation of inorganic arsenic species in the environment, and at the same time be difficult to discern from naturally occurring arsenic. Considering this, how could arsenic present a risk in the environment? Paracelsus once said, "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy." Excessively high concentrations of a chemical in an environment where such occurrence is abnormal could present a risk to that environment and its inhabitants. **General Toxicology** Despite the obvious widespread presence of arsenic and its multiple forms in the environment, considerable concern over its toxicity exists as incidents of cancer have been associated with arsenic exposure (Goering et al. 1999). The inorganic forms of arsenic are generally considered more potent direct toxins than the organic forms. Trivalent arsenite has a high affinity for protein sulfhydryl groups, but appears to be selective for closely spaced dithiols, which are common in DNA-binding proteins, transcription factors, and enzymes involved in the repair of damaged DNA (Vahter 2000). Pentavalent arsenate can replace phosphate and uncouple cellular respiration, thereby impairing cellular function (Vahter 2000). Also, one study found the relative, direct genotoxic potencies of arsenite and arsenate, when compared to MMA and DMA, differ by a few orders of magnitude (Moore et al. 1997). Active concentrations of those chemicals were 1-2 ug/L, 10-14 ug/L, 2,500-5,000 ug/L, and 10,000 ug/L, respectively. This indicates that the methylated arsenicals have a much lower affinities for the same substrates and are less potent direct toxins at equivalent concentrations. This is why some state the metabolic process leading to methylation of arsenic could be considered a detoxification process (Vahter 2000). In addition, methylation leads to quicker elimination of arsenic from the body (Hughes et al. 2000) leading it away from the site of action. Therefore, metabolic transformation of arsenic may mediate some of its risk. On the other hand, it appears that the organic arsenic species are also toxic in that they are inducers of oxidative stress (Schlenk et al. 1997, Yamanaka and Okada 1994, Kreppel et al. 1993). Oxidative stress is the condition, within cells, in which highly reactive chemicals become involved in oxidative/reductive reactions with cellular components, resulting in cellular component degradation. This degradation leads to mutagenicity (Bartsch and Nair 2000) and is a precursor to carcinogenicity (Bartsch and Nair 2000, Bostwick et al. 2000). However, unlike the direct action of the inorganic

## 12

arsenic species mentioned earlier, it is an indirect mode of action intiated by methylated arsenic species. According to one author, the methylated species are slightly more potent inducers of oxidative stress than are the inorganic species. For example, channel catfish ( Ictalurus punctatus) exposed to 1ppm of MSMA experienced twice the oxidative stress compared to catfish exposed to the same concentration of sodium arsenite (Schlenk et al. 1997). Another author states that the inorganic arsenic species is a more potent inducer of oxidative stress (Kreppel et al. 1993). Regardless of the relative potencies, while methylation can reduce the direct toxicity of arsenic, it can enhance the indirect toxicity yielding species that lead to oxidative stress. Furthermore, it demonstrates the potential toxicity of the methylated arsenic. In fact, di-methylarsinic acid (DMAA also known as cacodylic acid) orally administered to mice induced lung specific DNA damage attributed to reactive chemical species in lung tissues (Yamanaka and Okada 1994). Fortunately, methylation also appears to hasten elimination as the half-life for the methylated arsenic species in rats is less than 24h (Hughes et al. 2000). However, risk of the arsenicals would be increased with continued chronic exposure to levels exceeding normal background levels. **RISK CHARACTERIZATION Terrestrial**  Mammals and Birds What is known about potential risk from MSMA, DSMA, and CAMA is the hazard of the various formulations of each chemical to various laboratory organisms. The toxicity classifications range from moderately toxic to practically non-toxic (Tables 1 and 5). Of course, there is always the uncertainty of extrapolating chemical toxicity from laboratory animals to other species in the field. But there is also the uncertainty of trying to predict the complex environmental exposure scenarios. Even given this uncertainty, it might still be assumed that these chemicals are not considerably hazardous to terrestrial organisms. However, application rates of the three herbicides are great enough that acute risk LOCs are exceeded for both chemicals, provided adequate exposure occurs. Estimated environmental concentrations (EECs) on grasses following MSMA use in orchards exceed the mammalian herbivore acute LOC by 12 times. In fact, ten of the eleven arsenical uses presented in table 3 equal or exceed the mammalian acute risk LOC for herbivores, while seven of eleven uses exceed the acute avian LOC for herbivores (Table 4). The environmental fate of these chemicals is variable and not fully understood. These chemicals can enter into very stable chemical associations with clays, and as such, would likely be biologically unavailable. On the other hand, if the chemicals are bioavailable, both animals and microorganisms can transform them, altering the toxicity of the original chemical. In addition, the central structure of these herbicides is part of a complex suite of naturally occurring arsenic-based chemicals ubiquitous within the

## 13

environment, making exposure differentiation between herbicidal and naturally occurring arsenic-based chemicals difficult. Even though the identity of the actual toxic moiety in the environment is uncertain, heavy use of these herbicides does present an increased exposure risk of the arsenic-based chemicals to organisms near the application site. Given that exposure does take place, how long will residue levels on potential food items remain high enough to present a risk to animals that enter the field to feed? Application of DSMA on cotton does not result in acute risk LOC exceedence for any longer than a few days (Fig 1). On the other hand, MSMA residues on grasses, following application to cotton, would remain high enough to exceed the same mammalian acute risk LOC for up to 77 days (Fig. 2). The highest use, MSMA in orchards, presents the longest period of potentially hazardous exposure with residues on grasses exceeding the mammalian herbivore acute risk LOC for nearly 140 days (Fig 4). Therefore, there is the potential for extended exposure of organisms to arsenicals. Multiple applications of the same or a different arsenical would increase the time frame for animal exposure to potentially hazardous arsenical residue levels on food items. For example, MSMA is used as a pre/post-emergent herbicide on cotton, applied either before cotton emergence or at some point post emergence. Several months later, DSMA and/or cacodylic acid (another arsenical) is applied shortly before harvest to defoliate cotton. Under this scenario, applications of different arsenicals at the same site can occur during one growing season, a situation depicted in figure 3. MSMA residues on grasses and insects would potentially remain above the acute risk LOC for 80 and 40 days, respectively, from the first day of application in the spring. Several months later, the same site is exposed to DSMA. DSMA residues on grasses and insects result in decidedly lower RQs, but there is a period of a few days during which an acute risk LOC would be exceeded for mammalian herbivores. This scenario indicates potential chronic exposure and toxicity to organisms due to repeated applications. In reality, persistence on certain food items is not likely to be great. Considering that these chemicals are herbicides, grasses are likely to die, or at least the edible portion will be desiccated, to later be replaced by new, unexposed leaves. What is unknown is how long the exposed edible portion will be available for consumption. On the other hand, some plants have been shown to be resistant to MSMA toxicity increasing the potential exposure period. Feeding behavior could also influence exposure. If an organism prefers to consume living plant material, then risk is limited by the survival period of the plant. If the animal will consume dead plant material, then risk is not limited by plant survival and will be extended beyond the risk presented by living plants alone. Therefore, while herbicide residues on grasses may potentially be available for extended periods of time, the actual risk due to availability of exposed grasses is unknown. Risk to insectivorous organisms will be related to insect survival and mobility. Considering that insects are mobile, they may be at the application site during application and move off site after application presenting exposure to organisms off-site. But judging from the low acute toxicity of MSMA and

## 14

DSMA to honey bees, the insects may not immediately die from exposure to the chemicals and will be able to move off site presenting exposure to organisms off-site. On the other hand, arsenicals have been used as insecticides, indicating these chemicals have insecticidal activity. Even if insects do die shortly after exposure, their carcasses would be available for opportunistic foraging by insectivores. It is uncertain if an insectivore will consume a dead, motionless insect, or if some motion cue is necessary to trigger a feeding response in the animal. These aspects of insectivore exposure are unknown. Mammalian reproductive studies have been submitted for methanearsonate (MRID 431783-01). These tests with laboratory rats found that exposure to methanearsonate resulted in reduced fertility and reduced litter survival. Other chronic studies (MRID 416690-01) found that, following oral gavage, methanearsonate led to affects on body weight gain and food consumption as well as leading to development of parathyroid adenomas. This latter endpoint supports information presented in the introduction describing the relationship between arsenicals, oxidative stress, and carcinogenicity. Terrestrial Plants Low risk from DSMA exposure is presumed for non-endangered plants inhabiting upland areas adjacent to application sites (Table 6). Offsite loading of DSMA due to drift, and due to drift plus sheet run-off, presented exposure that would be less than the acute risk LOC (Table 7). Greater risk is presumed for non-endangered semi-aquatic plants, which inhabit lowland areas surrounding the application site, exposed to DSMA. Channelized runoff and drift result in predicted exposures that result in exceedences up to three times the acute risk LOC.Due to its apparently greater inherent toxicity, MSMA use presents a potentially greater risk to nonendangered terrestrial plants than does DSMA despite the similarity of exposure levels for MSMA and DSMA (Table 6). Predicted MSMA exposure resulted in acute risk LOC exceedences up to 8 times the LOC for upland terrestrial plants exposed to drift and sheet run-off adjacent to the application sites, and up to 75 times the LOC for semi-aquatic plants exposed to drift and channelized run-off (Table 7). These exceedences indicate a high level of risk for terrestrial and semi-aquatic plants. However, there is uncertainty in the prediction of terrestrial and semi-aquatic exposure levels. The assumptions for the exposure scenarios, presented in appendix 3, are subject to debate. For instance, 5% of the applied chemical is assumed to be in the channelized run-off for highly soluble chemicals (solubility >100ppm). Since arsenicals are highly soluble, this would be the percentage of the applied arsenicals assumed to be in runoff. However, given that these arsenicals can strongly bind to soils, and that these chemicals are applied to fields, it is uncertain what proportion of the arsenicals in the run-off are actually dissolved in water, hence biologically available, and what proportion is sorbed to soil particles suspended in water, and thereby less biologically available. The actual percentage of the applied chemicals in run-off could be significantly higher than 5% due to erosion of soils in humid areas that receive considerable rainfall, or less than 5% due to the lack of erosion in arid regions.

## 15

Summary of Terrestrial Risk MSMA appears to be inherently more toxic than DSMA as evidenced by lower acute toxicity values (greater toxicity) for a number of organisms (Tables 1, 5, and 16). This apparent toxicity difference is a significant area of uncertainty since the two chemicals are essentially the same. Both chemicals are sodium salts, one of methanearsonate (DSMA) and the other of protonated methanearsonate (MSMA). This area needs further investigation, especially since it leaves unanswered the question of what is the toxic moiety in the field. The overall risk of these herbicides in the terrestrial environment is uncertain. They are not highly toxic to mammals and birds as evidenced by the toxicity values, but the use rates yield EECs on food items that exceed acute risk LOCs for the majority of uses. Therefore, while short term risk is evident, long term risk is uncertain. Registrant submitted studies indicate these compounds are relatively long-lived (see fate assessment below), but peer reviewed literature indicates considerable variability. It is possible that they are more persistent in relatively sterile soils once adsorbed to the clay component, but in environmental soils, they may be degraded by soil microbiota. In addition, they may be eroded from the application site while adsorbed to soils, and deposited into sediments. From there, they may be further transformed by sediment microbiota, or, possibly absorbed by the roots of semi-aquatic plants. Considerable uncertainty exists for predicting long-term risk. Given the uncertainty of environmental persistence and potentially long-term exposure, chronic toxicity in the environment is a possibility. How long these chemicals may remain on potential food items is also unknown, as well as the time frame during which the food item would effectively present the chemicals to potential consumers. Avian chronic toxicity studies would be essential to fully understand the potential of risk to avian species, especially in light of the acute toxicity of arsenicals to birds and the demonstrated reproductive and chronic toxicity of methanearsenate to mammals. **Aquatic** Arsenical use appears to present minimal acute risk to organisms within the aquatic environment. Thetoxicity classifications for the tested arsenical formulations range from slightly toxic to practically nontoxic (Tables 9, 11, 14). Adjustment of some of the formulations for active ingredient purity changed the classification to moderately toxic, but there is uncertainty if such an adjustment would accurately reflect the true hazard of 100% active ingredient. Comparing the low hazard of these chemicals to the aquatic EECs for these chemicals (Table 13) resulted in the exceedence of no acute high risk LOCs for any aquatic plant or animal (Tables 10 and 12). Potential effects on benthic organisms is uncertain. Eroded or suspended soil settles to the bottom of a water body and presents arsenical exposure to benthic organisms. While sorption of chemicals reduces biological availability in water, ingestion of contaminated sediments and microbiological activity can

## 16

enhance exposure. No data regarding the potential acute toxicity of DSMA to estuarine/marine organisms was presented. These studies are necessary to evaluate the risk DSMA presents within the marine/estuarine environment. Also no chronic studies were submitted for any of the arsenical herbicides. While there appears to be low acute toxicity to many of the tested species, chronic toxicity may still be a concern at low exposure concentrations, especially in water bodies that repeatedly receive run-off from sites of arsenical application. Summary of Aquatic Risk Overall risk of arsenicals within the aquatic environment is uncertain. Data gaps remain. Acute toxicity along with EECs indicate low risk. Available data are insufficient to assess chronic risk to aquatic organisms. Like for terrestrial animals, the toxicity is not considerable, but the exposure level may present significant risk. In addition, with the heavy use rates and possible episodic (rain events) introduction of these chemicals into water bodies, chronic risk is a possibility. Data gaps regarding acute toxicity of DSMA in estuarine/marine environments, and chronic toxicity of these arsenicals need to be filled. **Endangered Species** The endangered species risk quotients exceed the Agency’s LOC for birds, mammals and terrestrial plants from exposure to DSMA and MSMA. The risk quotients also exceed the LOC for freshwater fish exposed to MSMA.

## 17 

# Risk Quotient Decrease due to DSMA Residue Dissipation



# 0.00 0.10 0.20 0.30 0.40 0.50 0.60

0 28 56 84 112 140 168

Avian Herbivores Avian Insectivores Mammalian Herbivores Mammalian Insectivores Figure 1. Risk quotient (EEC/LC50) decrease due to DSMA dissipation (35 day half-life) from food items (grasses and insects) following two applications (3.6 lbs a.i./A) on cotton, 14 days apart. The levels of concern(LOC) are 0.5 for acute risk, 0.2 for restricted use, and 0.1 endangered species.

## 18 

# Risk Quotient Decrease due to MSMA Dissipation



# 0.00 0.50 1.00 1.50 2.00

0 28 56 84 112 140 168

Avian Herbivores Avian Insectivores Mammalian Herbivores Mammalian Insectivores Figure 2. Risk quotient (EEC/LC50) decrease due to MSMA dissipation (35 day half-life) from food items (grasses and insects) following two applications (3 lbs a.i./A) on cotton, 14 days apart. The levels of concern(LOC) are 0.5 for acute risk, 0.2 for restricted use, and 0.1 endangered species. Note the greater degree of LOC exceedences for MSMA use on cotton compared to DSMA use on cotton.

## 19



# Risk Quotient Decrease due to MSMA and DSMA Dissipation



# 0.00 0.50 1.00 1.50 2.00

0 28 56 84 112 140 168 196 224 252 280

Avian Herbivores Avian Insectivores Mammalian Herbivores Mammalian Insectivores Figure 3. Risk quotient (EEC/LC50) decrease due to dissipation of MSMA and DSMA residues from potential food items (grasses and seeds) following application of first MSMA and then DSMA. This figure represents application of MSMA in cotton fields at the time of cotton emergence followed by DSMA application five months later to desicate the crop prior to cotton harvest. The levels of concern(LOC) are 0.5 for acute risk, 0.2 for restricted use, and 0.1 endangered species. Note the extended period of potentially hazardous exposure to organisms resulting from multiple arsenical applications on cotton fields.

## 20 Risk Quotient Decrease due to MSMA Dissipation in Orchards



## 0 2 4 6 8 10 12 14

0 28 56 84 112 140 168 Avian Herbivores Avian Insectivores Mammalian Herbivores Mammalian Insectivores Figure 4. Risk quotient (EEC/LC50) decrease due to MSMA residue dissipation from potential food items (grasses and insects) in orchards following three applications (15.5 lbs/A), 14 days apart. The levels of concern(LOC) are 0.5 for acute risk, 0.2 for restricted use, and 0.1 endangered species. Note the considerable LOC exceedences for this use, and the length of time over which the LOCs are exceeded.

## 21

**ENVIRONMENTAL FATE ASSESSMENT: PERSPECTIVE, BASIS, AND SUMMARY Perspective and Basis**  This fate assessment for the salts of methanearsonic acid, is intimately and inextricably linked with that previously completed for the Reregistration Eligibility Document (RED) for their close arsenical ally, cacodylic acid (and its sodium salt). Chemically speaking, all these arsenical species are better treated in a single document, but logistical and proprietary constraints precluded this. It was intended that the cacodylic acid RED be the more inclusive and comprehensive on the environmental chemistry and transport of this class of compounds, and most of that material is not repeated here. However, some of the general fate and most of the drinking water assessment conclusions expressed in the main text below are taken directly from that document, but, in effect, with a simple change of subject noun(s). The previous cacodylic acid RED (including an expanded environmental fate assessment in its Appendix 6) is indispensablefor arsenical chemical perspective, additional details, interpretation, and references to eclectic sources which may not be included here. However, for ready reference and reader convenience, we have extracted the drinking water assessment and citations from the more technical Appendix 6 of the Cacodylic acid RED, and copied it here as Appendix 5. Previous OPP/EFED reviews (for example, Edelstein, 1994) have correctly pointed out deficiencies and seeming inconsistencies in registrant generated data. In the context of this RED and the cacodylic acid RED, which attempt to show the many facets of arsenic chemistry through sources in addition to registrant generated data, the nature of the discrepancies is more understandable. In a formal sense, the Agency could “require” more research data and/or literature review from the registrant. However, based upon the available information and the manner in which we have used the information to conduct the present risk assessment, in a realistic regulatory sense, there would be little practical value added by additional submissions. While we have considered in detail the specific influences of MSMA/DSMA/CAMA in our drinking water assessment, the larger, general EPA issue of arsenic compounds from all sources in drinking water (which we touch on below) is reserved for another forum. Therefore, on this basis, we consider formal data requirements for MSMA/DSMA/CAMA satisfied at this time, exceptfor submission and EPA laboratory validation of analytical chemical methods for detection and measurement in water and soil and for field spray-drift and droplet-size spectral data for these herbicides. To establish proper context and some perspective, in addition to that given in the previous introductory section of this document, it is worth copying here nearly verbatim (beginning in the next paragraph in italics below) an excerpt from the cacodylic acid RED. The principal non-verbatim exceptions are the additions of “MSMA”, “DSMA”, and “CAMA” or their collective use; the addition of supplemental chemical information on the element arsenic; changes for agreement of subject and predicate or similar editorial changes; and updating the calendar. The fourth of the italicized paragraphs below emphasizes the fact that the conditions of standard FIFRA environmental fate study requirements, which are suited more for neutral organic substances, are generally unsuited for compounds such as these organo-

## 22

metalloids with multiple oxidation states and a biogeochemical history. The fourth paragraph also indicates the eclectic nature of the fate assessment. With the stated minor alterations (by the same, present author), here is the excerpt from the cacodylic acid RED: MSMA, DSMA, CAMA, and cacodylic acid are four of several arsenic containing pesticides which the Agency is, or soon will be, considering for reregistration eligibility. Ultimately, in another action, the Agency will assess the potential overall (aggregate, cumulative) drinking water exposure to these compounds and common transformation products. The EPA Office of Water (OW) is scheduled to issue a final regulation on the larger issue of “arsenic” in drinking water during the year 2001. Because of historical toxicological interest in arsenic compounds (the name arsenic has been practically synonymous with "poison" for thousands of years), there is a substantial body of published and unpublished scientific study on their chemistry and environmental fate. Modern literature clearly shows that the biogeochemical interactions of these compounds are complex, and still the subject of active research. However, it is not within the scope of this document to comprehensively review this fascinating area. This has been done to a large extent in the past by the EPA in 1988, the National Academy of Sciences (NAS, 1977), the U.S. Department of the Interior’s Fish and Wildlife Service (FWS, 1988), other agencies, individual scientists (e.g., ACS, 1975 Symposium), and very recently by the National Research Council (NRC, 1999; sponsored by EPA) and by the U.S. Geological Survey (USGS, see below). Although the focus here is on MSMA, DSMA, CAMA, and cacodylic acid, their place in the larger scheme should be understood at the outset. Essentially all the arsenic since the earth's formation is still present and virtually immutable (barring nuclear transmutation), with new amounts added daily as cosmic dust. Arsenic is everywhere in the form of many different organic and inorganic compounds. The uncombined element arsenic is a steel grey, very brittle, crystalline, semi-metallic (metalloid) solid., which tarnishes in air. Because of its reactivity, arsenic is found only occasionally as the free element in nature, but is usually found chemically combined in a number of minerals, in plants and animals, and in products of decay or metabolism. Soils, for example, commonly contain from 1- 50 parts per million (ppm) of total arsenic in various combined forms, averaging around 5 ppm. Sediments average somewhat higher. Many of the compounds of arsenic, including our subject chemicals, are synthetically manufactured (ultimately from some primary mineral source) and occur naturally and ubiquitously as well. All are subject to the same fate and transport processes, and are entwined inseparably as part of the global arsenic biogeochemical cycle. These compounds introduced locally through agriculture cannot be distinguished molecularly from that which is present in the natural background. Only unnaturally high localized concentrations would serve as a telltale. Likewise, other chemical forms of arsenic (organic or inorganic/mineral) resulting from the transformation of arsenic-containing pesticides or other arsenic sources which are either naturally present or introduced by human activities (e.g., fossil

## 23

or wood fuels; agricultural burning; waste incineration; spreading of sewage sludge; pharmaceuticals; poultry and swine manure; mining; smelting; congener contaminant in phosphate detergents and fertilizers; industrial production of semiconductors and glass) cannot, in general, be distinguished as originating exclusively from pesticidal application. There is certainly much more arsenic in all environmental compartments (air, soil, sediments, water, plants, animals) than could ever be attributed to pesticidal application of MSMA, DSMA, CAMA, cacodylic acid, and other arsenicals. Because of the established complexity, the environmental fate of the subject arsenicals and other arsenicals cannot be adequately captured by standard FIFRA, 1988, Guideline studies, which are designed primarily for aspects of xenobiotic organic compounds subjected to a very limited set of experimental conditions. Therefore, in addition to the registrant’s FIFRA studies performed under Good Laboratory Practices (GLP), the Agency relies substantially on the open scientific literature, including very recent publications (or some in press), for nuggets of information which directly impact the Office of Pesticide Programs (OPP) environmental fate and effects risk assessment. Even so, evidence is often highly variable or seemingly conflicting, indicating that processes, speciation, and environmental interactions (including effects of moisture, pH, and oxidation-reduction conditions) among the various organic and inorganic species of arsenic are in constant biogeochemical flux and still incompletely understood. Recent outbreaks of serious arsenic poisoning originating from drinking water wells in India and Bangladesh, as well as those long-established in Taiwan, have attracted the worldwide attention of newspapers and public health officials. Although these events are notassociated with use of MSMA, DSMA, CAMA, or cacodylic acid, they have had the collateral effect of stimulating renewed scientific interest in the environmental chemistry and fate of arsenicals (Nickson, et al., 1998; Masud, 2000; numerous others). In addition, as will be discussed under the drinking water exposure assessment section of this document, recently completed projects by the USGS and the pending regulation by the EPA Office of Water also attest to the interest in arsenicals in our environment. A better understanding of the many facets of the environmental chemistry and potential risks of environmental arsenic is evolving. (End of excerpt from cacodylic acid RED)

## 24

**Environmental Fate Summary for MSMA/DSMA/CAMA**

## 25

**ABSTRACT.**This environmental fate assessment is based on registrant submissions and published technical literature. The previous cacodylic acid RED serves as the primary, more comprehensive document on the nature of the environmental chemistry and transport of arsenical pesticides. The environmental fates of MSMA, DSMA, and CAMA, sodium salts of methanearsonic acid (MAA or MMA) are, for our purposes, virtually indistinguishable. Transformation is by aerobic and anaerobic microbial metabolism. Aerobic soil metabolism rates depend critically on ambient conditions such as soil moisture, pH,oxidation-reduction potential, and their complex interrelationships. Thus, the concept of simple first-order (“halflife”) degradation is simplistic. Direct abiotic transformation processes are ineffectual. Aerobic soil “half-lives” may range from a few weeks under favorable conditions to several years under dry conditions not conducive to agriculture. Registrant submitted field studies did not adequately account for dissipation. The Agency has selected eight months (240 days) as an effective aerobic soil metabolism “half-life”. The aerobic aquatic metabolism half-life is similar. The anaerobic (flooded) soil metabolism half-life appears to be measured in years. With the selected aerobic soil metabolism “half-life” of eight months, the amount of parent material remaining one year after an initial application would be approximately 35% of applied. The asymptotic first-order kinetics limit for build-up parent after several years of successive applications is approximately 50% of an annually applied amount. However, it is crucial not to confuse transformation with detoxification. Total arsenic, although redistributed, is immutable. Regulatory limits of total arsenic in soil may be reached in a few years in some cases. Metabolites of MSMA (see below) include the pesticide cacodylic acid as well as other arsenic species with known toxicities. Major metabolites occur inconstantly and in variable proportions for complex, unclear reasons. Principal identified metabolites are cacodylic acid (which could reach up to approximately 30-35% chemical equivalent units of parent material in the environment), arsenate, carbon dioxide, and the volatile compounds dimethylarsine and trimethylarsine. Arsenite was either not detected or not speciated, but would be subject to formation under conditions of its natural occurrence. In the biosphere, soils/sediments ultimately sequester the more thermodynamically stable mineral forms of arsenic; for example, sulfides. Volatilization of parent materials is not a significant route of dispersal. However, volatile arsenicals are part of the global arsenic cycle. Sorption to numerous diverse soils varied tremendously, but indicates intermediate to low mobility. Simple sorption coefficients (Kd) in over 20 soils ranged from 2.5 to 110 mL/g with with a median of around 30 mL/g. That there is no correlation with soil organic carbon is demonstrated by pseudo soil organic carbon sorption coefficients (Koc) widely ranging from approximately 400 to 50,000 mL/g of organic carbon. Sorption is correlated better with clay and iron and aluminum oxide content. If pursued, there would most likely be a strong correlation with pH, reflecting acid/base chemical speciation. Field studies provide some evidence supporting little likelihood of leaching. Bioconcentration is not indicated for parent compounds. Although many plant and animal species have selectively high bioconcentration factors for arsenic, these are for other complex organic forms of arsenic which are reported as practically nontoxic. Drinking Water for Humans: We conclude from monitoring and modeling that surfacedrinking water concentrations originating from use of these salts of methanearsonic acid will impose an additive, localized burden on natural background concentrations of these and other chemical species of arsenic, including cacodylic acid. Ground water should not be impacted incrementally. Any drinking water levels of concern should be coordinated with the pending regulatory plan of the EPA Office of Water for arsenic.

## 26 As O O

O 

### C H3 

### Na+ 

### Na+ As O H O

O 

### C H3 

### Na+ 

## MSMA, DSMA, and CAMA are salts of the dibasic weak acid methanearsonic acid (MAA) (also variously abbreviated in this document and in the published literature as MMA or MMAA for m onom ethylarsonic acid). Chemical structures and some of the physicochemical properties for MSMA and DSMA are given below. For comparison, the structure of cacodylic acid (sometimes abbreviated herein as CA or DMA for dimethylarsonic acid) and its sodium salt, which have two methyl groups instead one attached to the central arsenic atom, are also given. **Structures and Physicochemical Properties for MSMA, DSMA, and Cacodylic Acid**

**DSMA** Empirical Formula: CH3

## AsNa 2

## O 3 

## Molecular Weight: 183.92 CAS Registry No.: 144-21-8 PC Code: 013802 **MSMA** Empirical Formula: CH 4

## AsNaO 3 

## Molecular Weight: 161.94 CAS Registry No.: 2163-80-6 PC Code: 013803 M.P.: >300 C M.P.: 116-121 C Density: 1.04 g/mL Density: 1.65 g/mL V.P.: 1 x 10-7

## mm Hg V.P.: 7.5 x 10-7

## mm Hg log Pow < 1 log Pow < 1 Water Sol. 34 g/100mL Methanol Sol. 26 g/100mL Hexane Sol. 0.0025 g/100 mL Water Sol. 104 g/100mL Methanol Sol. 16 g/100mL Hexane Sol. 0.005 g/100 mL pKa1, 2 4.0, 9.0 (approx.) pKa1, 2 4.0, 9.0 (approx.)

## 27 **Cacodylic Acid Sodium Cacodylate**  O O || || CH 3–As–OH CH 3–As–O -Na + | | CH 3 CH 3 

## EPA PC Code: 012501 Chem. Abs. No.: 75-60-5 Other Names: dimethyl arsenic acid, hydroxydimethylarsine oxide Empirical Formula: C 2

## H 7

## AsO 2 

## Molecular Weight: 138.0 daltons pKa: 6.2 Once dispersed and diluted to trace concentrations by water and physical disturbance in environmental media (parts per million and below), the sodium ions become part of the background morass of natural metal cations (positive ions), while the methanearsonate anions (singly and doubly charged) tend to associate with hydrogen (hydronium) ions through the process of simple ionic hydrolysis. The process is analogous to the familiar hydrolysis of the basic carbonate ion to bicarbonate ion and carbonic acid (carbon dioxide in water). The three arsenic species are symbolized here as H 2

## MMA, HMMA 1- 

## , and MMA2- 

## . The degree of association depends on pH. Reported titration studies for MSMA and DSMA yield base strengths for the anions corresponding to pKa values for the acid MMA of approximately 4 and 9. Assuming these pKa values, at pH 5, 7, and 9, for example, the ratios of acid to respective anions H

2

## MMA / HMMA 1- 

## / MMA2-

## are approximately: pH 5 pH 7 pH 9 1 000 / 10 000 / 1 1 / 1 000 / 10 1 / 100 000 / 100 000 Hence, we are discussing the pH dependent equilibria and environmental fate of acid, anions, and possibly other unknown soil/sediment/solution associated complexes or precipitates. Thus, for our purposes, and based on the available data, the environmental fates of MSMA, DSMA, and CAMA are virtually indistinguishable. Therefore, fate data for MSMA serve as surrogate data for DSMA/CAMA and conversely. Although imprecise, we will continue to simply refer to the environmental collection of chemical species (acid, anions, other complexes) as if they were the pure, active starting material MSMA (equivalently DSMA/CAMA). Perhaps a more appropriate designation would be MMA, which connotes the acid nature of the underlying chemical structure, or HMMA 1-

## since it tends to dominate in the range of typical agricultural pHs. The important point is that in the environment chemical speciation is in dynamic flux, depending on variations in pH and intimate contact (affected by transport, mixing, diffusion, etc.), in accordance with principles of chemical equilibria and kinetics

.

## 28

**Transformation Is By Microbes** Environmental fate laboratory studies showed that MSMA (equivalently DSMA/CAMA) was essentially stable under all tested conditions, except microbial metabolism. That is, transformation did not occur appreciably under the influence of abiotic (sterile) chemical or photochemical processes in soil or water. Aerobic and anaerobic microbial processes were slow. Field studies which the registrant submitted did not adequately account for dissipation. The aerobic soil "half-life” which we have selected for modeling purposes is approximately eight months (240 days). This value derives from data from a one-year laboratory study (MRID 44767601) which the registrant submitted for one soil (approximately 35% of the dose remained after one year). This value is essentially the same as that which the reviewer estimated from two data points reported in a published seventy-day study of several arsenicals (Gao and Burau, 1997) after rough normalizations for soil moisture (suction) and concentration effects based on comparison with more complete results for cacodylic acid. However,based on these and other published results (confer cacodylic acid RED), the concept of simple firstorder kinetics (which uniquely gives rise to the “half-life” concept) is overly simplistic, with transformation rates punctuated dramatically by varying ambient conditions such as soil moisture, redox potential, pH, and temperature. We proffer that sensitivity to local, transitory conditions may be so exquisite that under suitable conditions degradation rates could suddenly be much faster or much slower. An aerobic aquatic metabolism study conducted for only 30 days yielded a rough extrapolated half-life similar to the eight months selected for aerobic soil. The anaerobic "half-life" appears to be measured in years (a recent study submission indicated an extrapolated “half-life” of roughly two years in an anaerobic aquatic metabolism study lasting one year). With the selected aerobic soil metabolism half-life of eight months, the amount of parentMSMA material remaining in soil (without offsite transport) one year after an initial application would be approximately 35% of applied. The asymptotic first-order kinetics limit for build-up in soil (without offsite transport) of parentafter several years of successive applications would be approximately 50% of an annually applied amount. It is crucial not to confuse transformation with detoxification. Metabolites of MSMA, to be discussed below, include the pesticide cacodylic acid as well as other arsenic species with known toxicities. In combination, all of these maintain the total, immutable arsenic load. Currently, the Agency has a limit of 43 parts per million of total arsenic in soil as the concentration beyond which remediation is necessary (for example, at Superfund sites impacted by various sources of arsenic and currently on The American University campus in Washington, DC, where World War I chemical warfare agents containing the poisonous gas lewisite (ClC HCHAsCl 2

## ) were tested and disposed). Thus, without redistribution of arsenic from soil which originally may have contained only a few parts per million of natural arsenic at the site of application, a constant annual rate of application of one pound per acre of MSMA (all actual rates are higher), the regulatory arsenic limit would be reached in approximately 190 years. At the maximum cotton use rate, the limit would be reached in around 30 years; at the maximum orchard use rate, in only 3 years. However, since we know that global redistribution, transformation, and recycling

## 29

of arsenic in all possible environmental compartments (plants, animals, air, soil, sediment, water) occurs in the guise of compounds such as those given in the metabolites section below, different maximum concentrations would be reached at indefinite future times, depending on local quasi-equilibrium conditions for arsenic chemistry and entwined environmental factors. Thus, although there is no doubt local arsenic concentrations will be elevated, the degree of long-term or chronic exposure and potential effects are largely unknown from the standpoint of this assessment. Furthermore, it must be remembered that total arsenic is only a crude measure of potential toxicity. Ideally and logically, toxicity should be based on the specific kinds and proportions of arsenic moieties. Whenever arsenic concentrations are elevated above local background, to speciate is common sense. **Metabolites** The major metabolites identified in published sources and registrant submissions are inconstant-- sometimes detected and sometimes not. They also occur in widely variable proportions. Reasons for this are unclear, but are most likely associated with exquisite sensitivity to the ambient conditions mentioned above, and as discussed in more detail in the cacodylic acid RED. Listed below with chemical formulas and names are the principal metabolites variously identified: cacodylic acid, arsenate, carbon dioxide, and volatile alkylarsines. Arsenite was not detected under aerobic soil conditions, or was otherwise not speciated, but would be subject to formation under conditions of its natural, local occurrence. According to the published literature, in biogeochemical time frames, sediment is the sink that sequesters the thermodynamically more stable, less soluble mineral forms of arsenic; for example, sulfides. In seawater, concentrations of total arsenic are typically in the range of 1 to 2 ug/L (ppb). Arsenic Species Commonly Found in Environmental Samples and Cited Above “Organic” Species “Inorganic” Species (CH 3 

## ) 2

## AsO(OH) cacodylic acid AsO 4 3- 

## arsenate (CH 3 

## ) 2

## AsH dimethylarsine AsO 3 3- 

## arsenite (CH 3 

## ) 3

## As trimethylarsine As2

## S 3 

## , As4 

## ,S 4 

## sulfides
With the selected "half-life" for MSMA (equivalently DSMA/CAMA) of approximately 240 days and that for cacodylic acid of approximately 100 days (value selected for the cacodylic acid RED), then the maximum amount of cacodylic acid would be reached approximately 220 days after pesticidal application (assuming first-order kinetics), and would be chemically equivalent to approximately 23% of the initial amount of parent. At the same time (220 days after application), parent compound would be at approximately 53% of original amounts. These values could be considered "typical", but widely variable, in accordance with widely variable environmental behavior. Depending on whether conservative focus is on parent material or cacodylic acid, legitimate adjustments to "half-lives" could be

## 30

made to alter relative proportions at various time intervals. However, based on the available data, it is not likely that cacodylic acid would ever reach much more than 30-35% of chemical equivalent units of parent compound in the environment. **Bioconcentration** Since MSMA did not bioconcentrate significantly in bluegill sunfish and both MSMA and DSMA have low octanol/water partitioning ratios (log Pow < 1), there is little potential for bioconcentration. Although the scientific literature (for example, ACS, 1975; NAS, 1977) shows that many plant and animal species (shrimp, for example) have selectively high bioconcentration factors for arsenic, these are for other complex organic forms of arsenic (such as organobetaines) which are reported as practically nontoxic. The published literature also shows the absence of biomagnification of arsenic. **Transport/Mobility** In Air.Based on physical properties tabulated above, volatilization of parent materials would not expected to be a significant route of dispersal. Consistent with this expectation, volatilization of parent was not reported in any lab study. However, as mentioned above, volatile arsines produced by metabolism are part of the global arsenic transformation and transport cycle. In Soil. Sorption to numerous diverse soils varied tremendously, but indicates intermediate to low mobility. In a study with five soils, simple sorption coefficients (Kd) ranged from 2.5 to 110 mL/g with a median of 40 mL/g. That there is no correlation with soil organic carbon is demonstrated by pseudo soil organic carbon sorption coefficients (Koc, in units of mL/g of organic carbon) ranging from a low of approximately 400, for a heavy clay with over 9% organic carbon, to 50,000 for a sandy clay with 0.22 organic carbon. A sand soil with less than 0.1% organic carbon had a pseudo Koc of 4,200. In a published study (Wauchope, 1975) with 16 Mississippi River flood plain soils at an experimentally fixed (artificial) pH of 5.6, Kds ranged from a reviewer calculated 17 to 95 mL/g, with a median value of 28 units. Again, there was poor correlation with organic carbon. No doubt, if pursued, there would be a correlation with natural pH which would reflect the chemical speciation discussed above and in more detail in the cacodylic acid RED. Thus, at higher pHs more typical of agricultural soils, the Kd values for the 16 soils would be expected to be significantly lower. In the 16 soils, sorption at fixed pH was better correlated with clay and iron and aluminum oxide content. By direct comparison with phosphate, the three arsenic chemical species cacodylate, arsenate, and MSMA (methylarsonate ) were more strongly sorbed than phosphate in the increasing order:

phosphate < cacodylate < arsenate ~methylarsonate. In this respect, the organic arsenicals (cacodylic acid and methylarsonate) behaved like the inorganic arsenate and phosphate.

## 31

The drinking water section of this document, which follows below, expands upon the subject of transport and monitoring for ground and surface water exposure. **DRINKING WATER ASSESSMENT** (The Cacodylic Acid RED document, especially its Appendix 6 Environmental Fate Assessment, is the primary source of information for this drinking water assessment. Its Appendix 6 has substantial additional details and cited references not included below. For convenience and ready reference, the drinking water portion of that Appendix 6 is included here as Appendix 5.) The drinking water exposure assessment was based primarily on 1) limited monitoring for MAA (analytical form of MSMA/DSMA/CAMA) and other speciated forms of arsenic, including the cacodylic acid metabolite and the inorganic arsenite and arsenate; 2) extensive monitoring for total (unspeciated)arsenic; and 3) submitted environmental fate studies and associated simulation modeling. Although monitoring data for individual chemical forms of arsenic were sparse, the available measured data were revealing. Surface water conclusions from these sources were compared with simulation model predictions. Monitoring sources included USGS (mostly ground water, but with some surface water), BASINS, STORET (surface water only), and published literature (surface and groundwater). Limited, but valuable, surface and groundwater data exist for speciated arsenic [MAA, cacodylic acid (abbreviated as CA or DMA), arsenite, and arsenate]. In most cases, however, monitoring was for total arsenic (unspeciated) in areas not targeted for MSMA, DSMA, or CAMA use. Thus, most monitoring data are useful for assessing total exposure to arsenic, but are generally not useful for estimating exposure to MSMA, DSMA, CAMA, or CA as such. Furthermore, in most cases, monitoring was in areas not specifically targeted for arsenical pesticide use, and very often had high total arsenic reporting limits (presumably because of established regulatory limits). What the data do clearly show, however, is the frequent presence of significant concentrations of the organic MAA and CA and generally higher concentrations of inorganic arsenic (arsenite and arsenate). The primary monitoring sources are identified briefly as follows: 1) The United States Geological Survey (USGS) has recently completed an extensive survey report entitled “Arsenic in Ground Water of the United States: Occurrence and Geochemistry” (Welch, 1999). Water analyses were almost entirely for undifferentiated or totalarsenic. Although the survey targeted ground water, it also included some useful information for surface water evaluation. 2) A separate, limited investigation by USGS research scientists (Garbarino and Burkhardt, 1998), provided data on the arsenic species CA, MAA (equivalent to MSMA/DSMA/CAMA), arsenite, and arsenate in groundwater not associated with arsenical pesticide application and in surface waters in areas which were associated with the application of MSMA.

## 32

3) The EPA Pesticides in Groundwater Database (EPA, 1992) provided monitoring data for localized areas in Texas and Washington state. 4) The BASINS and STORET databases maintained by the US EPA provided a large body of data on totalarsenic concentrations in surface waters of the United States. 5) Chemical speciation data published in 1973 (Braman, 1973) on six fresh surface water bodies, one well, and three saline waters around Tampa, Florida, revealed local background concentrations for CA, MAA, arsenite, and arsenate. 6) Chemical speciation data published in 1991 (Anderson, 1991) on a total of 14 California water bodies for concentrations of CA, MAA, and inorganic arsenic. Conclusions drawn from all sources follow below. As stated above, Appendix 5, taken from the cacodylic acid RED, has additional supporting details and references. **Groundwater Exposure Conclusions** Incremental exposure to MSMA/DSMA/CAMA or the CA metabolite from groundwater due to agricultural application is not expected to be significant. Based on soil sorption characteristics discussed in the Transport/Mobility Section above and supplemental field evidence, significant leaching of MSMA/DSMA/CAMA , CA or other metabolites to ground water from normal agricultural (diffuse or non-point source) use is not expected. Although monitoring for MSMA (MAA) and CA indicated a minor presence in ground water, this cannot be reasonably attributed to labeled agricultural use. Therefore, no modeling for ground water estimated concentrations was conducted. (Additionally, the currently available Agency SCI-GROW groundwater regression model is not well-suited for these compounds because their sorption does not correlate with soil organic matter as previously discussed.) This conclusion should not

be interpreted to mean that the U.S. population is not exposed to arsenicals (organic and inorganic) in drinking water from groundwater sources, which it certainly is, only that the labeled use of MSMA, DSMA, or CAMA should not contribute significantly to the already existing burden of arsenic from groundwater sources. In fact, a USGS map of total arsenic distribution in ground waters of the U.S., given in Appendix 10 and discussed in Appendix 5, shows surprisingly high concentrations of total arsenic at many sites. The survey authors concluded that while slightly less than half the groundwater samples had total arsenic concentrations < 1 ug/L, about 10% exceeded 10 ug/L. They further concluded that “natural” arsenic concentrations exceeding 10 ug/L are more widespread and common than previously recognized. Some areas of high arsenic concentrations (defined as > 50 ug/L) were associated with point source pollution (for example, Superfund Sites where about 30% of approximately 1200 sites list arsenic as a “contaminant of concern”), but most appear to be natural areas.

## 33

In a limited, but provocative, separate study by USGS research scientists (Garbarino and Burkhardt, 1998), 6 groundwater samples from Idaho, 10 from Illinois, and 8 from Nevada (total of 24 sites) were analyzed for arsenite, arsenate, monomethylarsonate (MMA, equivalent to MSMA/DSMA/CAMA), and cacodylic acid. Again, none of the sites were associated with the application of arsenical pesticides. With a new method detection limit of approximately 0.2 ug/L, there were no measurable concentrations of the methylated compounds in ground water. In contrast, arsenite or arsenate concentrations in these groundwater samples ranged from less than the method detection limit of approximately 0.2 ug/L to a concentration as high as approximately 900 ug/L. Their data show that either arsenite or arsenate or both were detected in all samples, typically at 10-50 ug/L. Arsenite and arsenate concentrations were unexpectedly comparable. In a personal communication, one of the study authors expressed surprise at this latter comparability, since arsenate is generally assumed to be the dominant of the two species. Therefore, as will be stated again for emphasis in the surface water conclusions below, if total arsenic concentrations at any location should exceed established levels of concern for any known, combined chemical form of arsenic, then it would be prudent to speciate to determine true individual identities and probably source(s), natural or otherwise. **Surface Water Exposure** In contrast with ground water, significant incremental exposure to MSMA /DSMA and the metabolite CA from surface water from labeled use is expected. MSMA/DSMA use is focused primarily on cotton and citrus, and such use could result in substantial areas of potential exposure. In accordance with the fate characteristics given in the environmental fate section above, eroding soil and runoff water would transport MSMA/DSMA and metabolites (cacodylic acid, for example) to surface waters. The extensive USGS report cited above on arsenic in ground water (which had a modicum of surface water information), as well as other sources (e.g., Hem, 1985), indicate that, in general, total arsenic concentration in the majority of U.S. rivers and streams is less than 1 ug/L (ppb). However, spatial and temporal variability are the rule, and manynotable exceptions of higher arsenic concentrations occur. Surface water bodies such as lakes and reservoirs appear to have higher concentrations more frequently than streams. Although in raw (untreated) surface waters in many areas there are excursions far beyond the Office of Water’s current total arsenic Maximum Contaminant Level (MCL) in drinking water of 50 ppb (a reduction to 10 ppb is pending approval), it would be difficult to associate these findings in most of these areas with current arsenical pesticide use. Highest concentrations are most likely to occur in geothermal areas and in water draining mineralized areas. The BASINS and STORET databases maintained by the US EPA have a large body of data (many tens of thousands or more of entries) on totalarsenic concentrations in surface waters of the U.S.. However, because of the wide ranging concentrations (see below) in space and time, and the multiplicity of possible major sources of arsenic, any attempt to associate these with arsenical pesticide

## 34

use would likely be a fruitless exercise, and would certainly require a major resource effort akin to that by the USGS for groundwater. Nevertheless, even casual inspection of the data from the databases shows that is not unusual for total arsenic concentrations in raw surface water in many different sites to be several parts per billion. (Reporting limits in many cases appear to be 1 ppb, but in many other cases are in excess of 10 ppb and up to approximately 50 ppb. The 10 ppb and 50 ppb limits may be associated with the human health limits currently set for total arsenic set by the World Health Organization and the US EPA, respectively.) Spatial variability is the rule. The following data for Georgia and Texas are illustrative of this variability, and are not meant to imply a special situation. For example, in Georgia, as presented in BASINS, upper 85th percentile concentrations of total arsenic at different sites ranged from less than 1 ppb to 338 ppb. More typical high values would fall in the range of 10 to 50 ppb. The most probable concentration appears to fall in the range of <1 to 2 or 3 ppb. The STORET database for Georgia and Texas show similar results, with Texas seeming to average several parts per billion more. Some of the highest values reported in STORET for Georgia and Texas (79,000 entries) approach 1000 ppb and can often be associated with past point-source pollution by humans. Such pollution is becoming less serious through environmental conscientiousness and governmental regulation. However, as previously mentioned, natural sources (especially in places in the western U.S.) also produce such high concentrations. As stated above, speciated arsenic data are sparse, but informative in clearly showing the presence of significant concentrations organic arsenic and generally higher concentrations of inorganic arsenic. In 1997, very limited USGS surface water monitoring data in arsenical pesticide use areas targeted four arsenic species: MAA (MSMA/DSMA/CAMA equivalent), cacodylic acid (CA), arsenite, and arsenate. USGS research scientists collected surface water samples from streams at one or two week intervals from early March through the middle of September of 1997 from each of three sites associated with different basins or sub-basins in an agricultural region potentially impacted by application of MSMA (application is normally from May through July). A total of 24 samples were analyzed from each site. Unfortunately, there were no baseline data for areas not associated with application. Analyses showed maximum concentrations of MAA at the three sites were approximately 2, 3, and 5 

## : g/L (ppb), and were relatively short-lived. (The multiplicative factor for converting MAA to MSMA is 1.2; thus 5 ppb of MAA converts to 6 ppb of MSMA.) Although it was apparently not in use, concentrations of CA, a metabolite of MAA, were at or below the detection limit of 0.2 

## : g/L, except for one sample which registered approximately 0.6 

## : g/L. For comparison, maximum measured arsenite and arsenate concentrations were approximately 3 ppb and 5.5 ppb, respectively. The extent of MSMA application and distance of the streams from application sites were not published, and there were no baseline data for comparable areas not associated with MSMA application.. Sampling for the Florida study, published in 1973, was for 10 natural waters in the vicinity of Tampa. There were six surface fresh water bodies (two rivers, two ponds, two lakes), three saline waters (two bays, one tidal flat), and one water well at a remote camping area. Tampa tap water was also

## 35

analyzed. Presumably, all water sites were sampled once with two or more replicates analyzed; however, the study authors did not report specifics on sampling dates and the number of samples analyzed. Concentrations of CA in the natural waters ranged up to 1.0 ppb. At one site, the Hillsborough River, concentrations were below the detection limit of 0.02 ppb, while the median value for CA at the other nine sites was approximately 0.3 ppb. The well water concentration was 0.2 ppb. MAA, detected in eight of the ten sites, was generally present at lower concentrations, the highest being 0.22 ppb. Total arsenic concentrations ranged from approximately 0.3 to 3.6 ppb. The extent to which these concentrations represented the natural background (baseline) in the Tampa area or were influenced by introduction of artificial sources is unknown. However, the study authors considered the sampled sites as “natural” waters. Tampa tap water contained only traces of arsenate at the time. Sampling for the cited California study published in 1991 was brought to our attention by the Office of Water’s proposed rule for the regulation of arsenic (22 June 2000). MAA and CA concentrations in a total of 14 California water bodies were measured (total of ten lakes, estuaries, or reservoirs, and a total of four rivers or creeks). Highest measured concentrations of MAA and CA were equivalent to 1.2 ppb and 4.6 ppb, respectively (excluding one anomalous site that was so high in inorganic arsenic as to swamp the analysis for the organic). There were no detectable concentrations (<0.1 nM) of MAA or CA in the four streams, but eight of the ten other sites had measurable concentrations of MAA and all ten had measurable concentrations of CA. Inorganic arsenic was present at all sites. Except for the Davis Creek Reservoir, inorganic arsenic was in much higher concentrations than the organic. At five sites, total arsenic concentrations were far above the current MCL of 50 ppb. The extent to which these measurements may be affected by agriculture or the use of arsenical pesticides is unclear. It is informative to compare the various actual measured results presented above with environmental simulation model predictions, and then draw appropriate conclusions for surface water exposure. For surface drinking water, the Agency has recently adapted the standard PRZM/EXAMS simulation model to estimate runoff to an Index Drinking Water Reservoir (IR), and also made an allowance for the portion of surrounding land which may be cropped. The resulting acute and chronic drinking water concentrations for MSMA/DSMA for the IR scenario for cotton and citrus were based on 1) current labeled application rates, and 2) field trial data application rates. Field trial data, from which the dietary (food) exposure assessment was based, were collected at application rates lower than the label rates. The Agency is recommending that the labels be amended to reflect the lower rates (or that field trial data be conducted at the current label rates). Details of the modeling inputs and assumptions used to calculate index reservoir concentrations (IRC) given below can be found in Appendix 6.

## 36

**Index Drinking Water Reservoir Simulation Results for MSMA and DSMA Use**

**Cotton**: application rates and intervals Labeled rate MSMA: 2 aerial applications, each at 3.0 lb a.i./acre, 14 days apart Field trial rate MSMA: 2 aerial applications, each at 2.0 lb a.i./acre, 14 days apart Labeled rate DSMA: 2 aerial applications, each at 3.6 lb a.i./acre, 14 days apart Field trial rate DSMA: 2 aerial applications, each at 2.0 lb a.i./acre, 14 days apart

**Cotton**: Drinking Water Index Reservoir Concentrations (IRC)

Labeled / Field Trial Labeled / Field Trial Acute IRC* Chronic IRC* MSMA 83 / 56 

## : g/L (ppb) 21 / 14 

## : g/L DSMA 100 / 56 

## : g/L 25 / 14 

## : g/L *Acute = 1-in-10 year peak concentration, Chronic = 1-in-10 year average annual mean



## Citrus application rates and intervals Labeled rate MSMA: 3 ground applications each, at 4.7 lb a.i./acre, 14 days apart Field trial rate MSMA: 3 ground applications, each at 4.0 lb a.i./acre, 14 days apart Labeled rate DSMA: 3 ground applications, each at 6.3 lb a.i./acre, 14 days apart Field trial rate DSMA: 3 ground applications, each at 4.9 lb a.i./acre, 14 days apart

**Citrus** : Drinking Water Index Reservoir Concentrations (IRC)

Labeled / Field Trial Labeled / Field Trial Acute IRC Chronic IRC MSMA 512 / 436 

## : g/L (ppb) 136 / 116 

## : g/L DSMA 687 / 534 

## : g/L 182 / 141 

## : g/L
Modeled concentrations are roughly and, at least superficially, akin to the higher totalarsenic concentrations reported in the BASINS and STORET databases. Modeled results for MSMA and DSMA can be converted to arsenic equivalent concentrations by multiplying the tabulated results by a factor of approximately one-half (0.46 and 0.41, respectively) and inversely, but this factor is really

## 37

immaterial when considering variabilities and uncertainties. However, as stated above, any attempt to correlate the monitoring data for total arsenic with pesticidal use is a major resource effort, and requires establishing natural background concentrations in use areas. Even if there were correlation, there would still be niggling doubt of association without knowledge of arsenic speciation. The USGS sampling results for individually speciated arsenic components (approx. 5-6 ug/L max. for MSMA/DSMA) are seemingly lower than those from modeling for cotton by a rough factor of ten. (We do not have similar data for citrus use areas for comparison.) However, the USGS surface water results were from flowing water bodies in non-targeted, general use areas, limited to a few months in 1997, and limited to so few samples over the time period as to have little statistical weight. The speciated data from the Tampa, Florida, area were from “natural” waters and even sparser than that of the USGS. Likewise, the representativeness of the California measurements which yield organic arsenic results similar to those of the USGS is uncertain. In contrast, the index reservoir scenario yields values intended to represent reservoirs in the upper 90% of susceptibility to runoff/erosion when viewed over many years, and represents a rather quiescent water body in an area where use would be most extensive. Agency regulations currently assure that community water systems will provide public drinking water which contains total arsenic at no more than the maximum contaminant level (MCL) of 50 

## : g/L (ppb). At the time of this writing, a new rule for a proposed MCL of 10 ppb is pending final approval. Consequently, community water systems are protected against all the modeled surface water concentrations in excess of these limits. **Surface Water Exposure Conclusions** Runoff/erosion of applied surface deposits to surface waters and sediments is expected to cause significant local, temporal perturbations above background concentrations for MSMA/DSMA and CA. The higher measured totalarsenic concentrations agree qualitatively with the Index Reservoir model for uses on cotton. However, this agreement is probably coincidental because the measured values are entangled with undetermined, highly variable natural background concentrations for which there has been no attempt to separate use and non-use areas. The total arsenic data are therefore inconclusive about arsenic origin. Speciated data are too sparse, not suitably targeted, and also generally open-ended about origin. However, the speciated data do clearly and consistently show the presence of MAA and CA, as well as comparable or larger amounts of arsenite and arsenate, regardless of source . Also, independent of source, the limited available speciated data may underestimate potential concentrations of pesticide-related arsenicals in drinking water reservoirs in major use areas. Therefore, whatever the source of arsenic, if there are toxicological concerns near the monitored, modeled, and/or regulatory limit concentrations, then, clearly, this invites broader scale, systematic environmental sampling and analysis for speciated arsenic, not just total arsenic, in order to determine

## 38

statistically the associations, ranges of exposure, and possible effects. Adequate analytical methods for speciating arsenic are now readily available. The effects of water treatment on raw water concentrations are known, and should be considered for “public water systems” (as defined in 40 CFR 141.2). However, it also should be acknowledged that many users of surface drinking water do not drink from regulated public water systems. According to the USEPA Office of Drinking Water (personal communication from Charles Abernathy), which is currently engaged in new regulation for total arsenic in drinking water in public water systems, many larger water treatment facilities use sedimentation-flocculation procedures that are capable of lowering total arsenic to 1 ppb or less. However, in smaller public water systems, the method is less effective, and can lower concentrations to only approximately 20-25 ppb. At the present time, public water systems only assure protection against excursions of total arsenic beyond the 50 ppb MCL (10 ppb if pending regulation is enacted). Furthermore, within the regulatory limit for total arsenic in drinking water are inorganic forms that are most often in higher concentrations and generally accepted to be far more toxic than the organic. Based on our surface water assessment, it is certain that application of arsenical pesticides will result in a superposition upon existing local background concentrations of arsenic species in surface drinking water. In some locations, these incremental amounts caused by pesticidal application would be relatively small compared to some of the existing or “non-pesticidal” background concentrations. In other locations where the background is low, the superposition could be relatively large. Provided repeated, long-term pesticidal applications at the higher labeled rates do not occur, it is most likely that local biogeochemistry of arsenic (redistribution, transformation, recycling) would moderate or prevent significant alteration in local, long-term arsenic equilibria (for possible long-term accumulations, see above Environmental Fate Subsection, Transformation Is By Microbes , third paragraph). Therefore, provided local biogeochemistry is not overwhelmed by excessive application of arsenical pesticides, local, long-term average concentrations of available arsenic should remain relatively unaffected. Determining the kind (chemical speciation) and degree of acceptable arsenic exposure in drinking water involves many regulatory considerations (for example, cost/benefit) representing complex issues for EPA Program Offices. However, the Office of Drinking Water, after extensive project funding, protracted deliberations with expert panels, practical considerations, and public/stakeholder input, has set the regulatory limit for public water systems at 50 ppb (10 ppb if current proposed regulation is enacted) for total arsenic (which includes organic and the more toxic inorganic forms), even if that limitshould happen to exceed the Office of Pesticide’s level of concern for arsenical pesticides or their byproducts.

## 39

**AQUATIC EXPOSURE AND RISK ASSESSMENT Exposure Assessment**  Estimated environmental concentrations (EECs) for MSMA and DSMA are reported in Table 13. The values were calculated using GENEEC with constant input parameters for interval between applications (5 days), Koc (1121 ml/g), aerobic soil half-life (240 days), aerobic aquatic half-life (480 days), and solubility in water (104,000 mg/L). The variable input parameters were application rate (conservativelyused maximum rate), number of applications, and application method (aerial for cotton, ground for noncrop, turf, and orchard). Depending on application rates and the number of applications, the values for DSMA ranged from 98 ppb near cotton applications to 270 ppb near turf applications. MSMA values ranged from 26 ppb near Kenaf applications to 605 ppb near orchard applications. **Hazard Asessment** Freshwater Animals Toxicity data for freshwater organisms are presented in Table 9. DSMA could be considered practically non-toxic to the tested fish species as the LC50s were greater than 112 ppm. MSMA toxicity range from slightly to moderately toxic to the tested fish species with the majority of LC50sbeing between 10 and 100 ppm. The toxicity categories ranged from slightly toxic to practically nontoxic to the tested freshwater invertebrates. The LC50s of MSMA and DSMA to the water flea ( Daphnia magna) were 77.5 and 156 ppm, respectively. The guidelines (72-1, 72-2) are fulfilled for DSMA and MSMA. Data are not required for CAMA.

Marine/Estuarine Animals MSMA toxicity to sheepshead minnows was classified as practically non-toxic while the categories for MSMA toxicity to marine/estuarine invertebrates ranges from moderately toxic to practically non-toxic (Table 11). The LC50 of MSMA to the sheepshead minnow was considerably higher (323ppm) than the range of LC50s reported for the tested marine/estuarine invertebrates (>1 to 173ppm). The guidelines (72-3a,b,c) are fulfilled for MSMA but not for DSMA since no data were reported for DSMA. Data were not required for CAMA. Aquatic Plants The EC50s of DSMA to different plant species range from 1.5 to 96.2ppm (Table 14). The EC50s of MSMA to green algae and duckweed were 5.6ppm and 104.1ppm, respectively. Although a complete

## 40

complement of aquatic plant studies were not submitted for MSMA, EFED previously determined that testing either DSMA or MSMA would suffice for both active ingredients. Testing was not required for CAMA. The guideline (123-2) is fulfilled for all three active ingredients. **Risk Assessment** Aquatic Animals Based on the acute toxicity information provided to EFED, and the model generated EEC values, the overall risk of MSMA toxicity to aquatic organisms would be considered low at any use site. The risk quotients (EEC/effects endpoint concentration) were all below 0.5, the acute risk presumption RQ for aquatic organisms (Table 11). No risk is presumed for aquatic fish and invertebrates exposed to DSMA at the predicted environmental concentrations (Table 9). Risk quotients remained <0.01 for all applications for all marine fish and invertebrates, and for freshwater invertebrates. No toxicity data were presented for freshwater fish so no RQs could be calculated. Aquatic Plants The acute LOC for non-endangered and endangered aquatic plants (RQ = 1) was not exceeded for either MSMA or DSMA (Table 12) allowing for a presumption of low risk to aquatic plants exposed to the predicted MSMA and DSMA concentrations. **TERRESTRIAL EXPOSURE AND RISK ASSESSMENT Exposure Assessment**  Food items The EECs on potential bird and mammal food items are based on Hoerger and Kenaga (1972) as modified by Fletcher et al. (1994), which presumes a 1 lb ai/acre pesticide application yielding the following maximum EECs: 240 ppm for short grass; 135 ppm for broadleaved plants and insects; and 15 ppm for seeds, pods, and fruits. Using those values, the EECs for DSMA and MSMA ranged from 108 to 3078 ppm and 30 to 6277 ppm, respectively, depending on application rates, number of applications, and food item (Table 2). Typically, fruits and seeds had lower predicted residue levels as compared to short grasses and broad-leaved plants. The exposure levels for insects are predicted to be similar to that for broad-leaved plants because the surface area of a leaf is assumed to approximate that of an insect.

## 41

Off-site exposure for plants Due to sheet runoff and spray drift, the EECs of upland plant exposure range from 0.12 to 3.36 lb ai/A for MSMA and 0.216 to 0.403 lb ai/A for DSMA (Table 6). For semi-aquatic plants, the EECs range from 1.12 to 8.68 lb ai/A for MSMA and 1.836 to 3.876lb ai/A for DSMA. EECs for upland (dry) and lowland (semi-aquatic) off-site areas are for a single application. **Hazard Assessment** Birds Based on acute oral (LD50) and dietary tests (LC50) with northern bobwhite quail (Colinus virginianus) and mallard ducks ( Anas platyrhynchos), DSMA, MSMA, CAMA (all 82% a.i.) were classified as being moderately to practically non-toxic (Table 5). For DSMA, the LD50 to bobwhite was 627 mg/kg (moderately toxic) while the LC50s for bobwhite and mallards were 4695 ppm (slightly toxic) and >5620 ppm (practically non-toxic), respectively. The disparity between the LD50s and LC50s is likely due to absorptive efficiency differences between the mode of exposure for oral and dietary tests, i.e. absorption efficience is likely to be greater for an oral test as compared to a dietary test. Therefore, in comparison to an oral dose, a greater dose will be necessary in a dietary test in order to get the same amount of active ingredient to the site of toxic action. The LD50 of MSMA (51% a.i.) to bobwhite was 834 mg/kg (slightly toxic), while the LC50s were 3269 ppm (slightly toxic) and 5620 ppm (practically non-toxic) for the bobwhite and mallard, respectively. When the MSMA LC50 values were adjusted to toxicity for 100% a.i., the values for the bobwhite and mallard decreased to 425 ppm (moderately toxic) and 1667 ppm (slightly toxic), respectively. CAMA was classified as practically non-toxic to both bobwhite quail and mallard ducks. However, the percent active ingredient was 10% indicating significant uncertainty about CAMA’s toxicity to avian species. Avian reproduction studies (71-4) are required but have not been submitted for any of these chemicals. Guidelines 71-1 and 71-2 are fulfilled for DSMA and MSMA but not for CAMA for which the required studies have not been submitted. Guideline 71-4 is not fulfilled for any of these active ingredients.

## 42

Mammals The acute toxicity classifications of MSMA, DSMA, and CAMA to laboratory rats range from moderately toxic to practically non-toxic (Table 1). The LD50s for MSMA (34.35% a.i.), DSMA (82.7% a.i.), and CAMA (10.3% a.i.) are reported to be 458 (moderately toxic), 1934 (slightly toxic), and >5000 mg/kg (practically non-toxic), respectively. Extrapolating the toxicity to 100% a.i. yields LD50s of 157 mg/kg (moderately toxic), 1599mg/kg (slightly toxic), and 500mg/kg (moderately toxic. A no-observeable-adverse-effect-level (NOAEL) of 100ppm was determined for laboratory rats exposed to methanearsonic acid (anion of MSMA, DSMA, and CAMA) during a two generation, reproductive toxicity tests (Table 1).
Insects MSMA, DSMA, and CAMA are practically non-toxic to honey bees (Table 15). The LD50s for each were 68 (51% a.i.), >20.7 (82.7% a.i.), and >25 ug/bee (10.1% a.i.), respectively, for MSMA, DSMA, and CAMA. Extrapolating the toxicity of MSMA to 100% a.i. would approximately double the toxicity (35 ug/bee) of MSMA to honey bees. Because all the active ingredients are practically nontoxic to the honey bee, precautionary labeling is not needed. The guideline (141-1) is fulfilled. Non-target Terrestrial Plants (Tier II) DSMA (82.7% a.i.) and MSMA (51% a.i.) toxicity to non-target agricultural plants are reported in Table 16. Very little information was presented for the EC25 on seedling emergence. The most sensitive species to MSMA, with respect to the EC25, was cabbage (0.116 lb a.i./A). The remainder of the EC25 values for both chemicals ranged from 1.07 to 1.44 lb a.i./A. The majority of the seedling emergence toxicity values were the NOECs. These ranged from <0.3 to 4.86 lb a.i./A for DSMA, and 0.018 to 2.24 lb a.i./A for MSMA. More toxicity information was presented for vegetative vigor. The EC25s ranged from 0.354 to 2.43 lb a.i./A for DSMA and from 0.418 to >2.24 lb a.i./A for MSMA. The NOECs ranged from <0.30 to 4.86 lb a.i./A for DSMA and from 0.14 to 2.24 lb a.i./A for MSMA. Only the most sensitive endpoint is reported for each species.

## 43

**Risk Assessment** Birds The RQ values for acute lethality to avian species is divided into three categories: herbivores, insectivores, and granivores (Table 4). For DSMA, acute risk (RQ = 0.5) to herbivorous birds is presumed for all applications except on cotton, for which the restricted use LOC (RQ = 0.2 is exceeded. The RQs range from 0.38 to 1.2, the highest RQ from turf applications. The acute risk LOC is also exceeded for insectivorous birds for cotton and non-crop applications of DSMA. None of the DSMA applications exceeded the LOCs for granivores. For MSMA, the acute risk LOCs are exceeded for herbivorous species non-crop, orchard, and turf applications, for insectivorous species near non-crop and orchard applications, and not at all for granivorous species. The restricted use LOC was exceeded for herbivorous species near cotton and seed grass applications, for insectivorous species near cotton, seed grass, and turf applications, and not at all for granivorous species. CAMA, while the tested formulation would be classified as practically nontoxic to birds, it must be understood that the formulation was only 10% a.i. The acute LOC was exceed for herbivorous species, while the restricted use LOC was exceeded for insectivorous species. No levels of concern were exceed for granivorous species. Avian reproductive risk cannot be assessed until toxicity data are submitted. A potential for reproductive risk exists from avian exposure to DSMA and MSMA, because applications may occur in at use sites during the avian reproductive season. Mammals The acute risk LOC (RQ >0.5) is exceed for small herbivorous mammals exposed to DSMA in all uses (Table 3). The RQs ranged from 0.5 to 1.45 for DSMA. The RQs were greatest for DSMA use on turf grass. The acute risk LOC was also exceed for insectivorous mammals for all uses except on cotton, a use for which the restricted use LOC (RQ >0.2) was exceeded. All MSMA uses except Kenaf resulted in acute risk exceedences for both herbivorous and insectivorous species. The only exceedence for granivorous species was for endangered species near orchard applications. While CAMA was classified as practically non-toxic to mammals, the percent active ingredient was 10%. Considerable uncertainty exists about CAMA’s inherent toxicity. The acute toxicity LOC was exceeded for herbivorous species, while the restricted use LOC was exceeded for insectivorous species. No LOC was exceeded for granivorous species.

## 44

The reproductive risk LOC (RQ = 1) was exceeded for all MSMA, DSMA, and CAMA uses except for granivores exposed to DSMA near cotton fields, and to MSMA near cotton fields, seed grass, and kenaf applications (Table 17). Non-endangered plants Risk is presumed for non-endangered plant species inhabiting upland and especially lowland areas that are exposed to MSMA runoff and drift (i.e., total loading) from all use sites as the LOC (RQ >1) is exceeded for all uses (Table 7). Also at risk are non-endangered plants inhabiting lowland areas receiving runoff and drift of DSMA from all use sites. Minimal risk from DSMA is presumed for upland plants and areas receiving only drift exposure. Endangered Species LOCs for endangered species are exceeded for birds (MSMA, DSMA), mammals (MSMA, DSMA), freshwater fish (MSMA), and terrestrial plants (MSMA, DSMA). The Agency has developed the Endangered Species Protection Program to identify pesticides whose use may cause adverse impacts on endangered and threatened species, and to implement mitigation measures that address these impacts. The Endangered Species Act requires federal agencies to ensure that their actions are not likely to jeopardize listed species or adversely modify designated critical habitat. To analyze the potential of registered pesticide uses to affect any particular species, EPA puts basic toxicity and exposure data developed for REDs into context for individual listed species and their locations by evaluating important ecological parameters, pesticide use information, the geographic relationship between specific pesticides uses and species locations, and biological requirements and behavioral aspects of the particular species. This analysis will include consideration of the regulatory changes recommended in this RED. A determination that there is a likelihood of potential impact to a listed species may result in limitations on use of the pesticide, other measures to mitigate any potential impact, or consultations with the Fish and Wildlife Service and/or the National Marine Fisheries Service as necessary. At present, the program is being implemented on an interim basis as described in a Federal Register notice (54 FR 27984-28008, July 3, 1989). A final program, which may be altered from the interim program, will be proposed in a Federal Register notice scheduled for publication in autumn of 2001.

## 45 **APPENDIX 1 Toxicity, EEC, and Risk Quotient Tables** 

## 46

Table 1. Toxicity of DSMA, MSMA, and CAMA to laboratory rats.

Chemical/ Test species % ai Acute LD50 (mg/kg) Reproductive

NOAEL (ppm) Toxicity

Classification MRID No.

**DSMA** Lab. rat 82.7 1934*/1599 1 NA slightly toxic 418920-04 **MSMA** Lab. rat 34.35 458*/ 157 1 NA moderately toxic 00105171 **CAMA** Lab. rat 10.3 >5000/500 1 NA # 010991

**Methanearsonic acid** Lab. rat 99.4 NA 100 431783-01

1 adjusted for the purity of the test material * Acute values utilized for risk quotient calculation # No toxicity classification was designated since actual toxicity is unknown.

## 47

Table 2. Estimated environmental concentrations (EECs) (ppm) of DSMA, MSMA, and CAMA on terrestrial food items resulting from direct application of active ingredient.

Chemical/Site Max. Appl. Rates (lb ai/A) No.

Appl. Predicted Maximum EEC on Food items 1 Short grasses Broadleaf plants and Insects Seeds

**DSMA** cotton 3.6 2 1519 854 95 non-crop 5.7 3 3190 1795 199 orchard 6.3 3 3526 1983 220 turf 7.6 3 4253 2393 266 **MSMA** cotton 3 2 1265 712 79 non-crop 6 3 3358 1889 210 orchard 15.5 3 8676 4880 542 Kenaf 2 1 480 270 30 seed grass 6 1 1440 810 90 turf 4.2 3 2351 1322 147 **CAMA** turf 5 3 2799 1574 175 * See appendix four for assumptions and formulae used to calculate residue levels on food items.

## 48

Table 3. Risk quotients for small mammal exposure to DSMA and MSMA.

Chemical/Site Appl. Rate (lb ai/A) EEC (ppm) Acute RQ 1,2

Grasses Insects Seeds Herbivores 3 Insectivores 3 Granivores 4
**DSMA** Cotton 3.6 1519 854 95 0.52 *** 0.29 ** <0.1

Noncrop 5.7 3190 1795 199 1.09 *** 0.61 *** <0.1 Orchard 6.3 3526 1983 220 1.20 *** 0.68 *** <0.1 Turf 7.6 4253 2393 266 1.45 *** 0.82 *** <0.1 **MSMA** Cotton 3 1265 712 79 1.82 *** 1.02 *** <0.1

Noncrop 6 3358 1889 210 4.84 *** 2.72 *** <0.1 Orchard 15.5 8676 4880 542 12.50 *** 7.03 *** 0.18 * Kenaf 2 480 270 30 0.69 *** 0.39 ** <0.1 Seed grass 6 1440 810 90 2.07 *** 1.17 *** <0.1 Turf 4.2 2351 1322 147 3.39 *** 1.90 *** <0.1 **CAMA** turf 5 2799 1574 175 0.37 *** 0.21 ** <0.1

1 RQ = EEC / [LD50 / food eaten expressed as % of bw] 2LD50s = 1934 mg/kg for DSMA, 458 mg/kg for MSMA, and 5000 mg/kg for CAMA 3for a 35 g mammal that consumes an amount of green vegetation or insects equivalent to 66% of its body weight 4for a 35 g mammal that consumes an amount of seeds equivalent to 15% of its body weight *** exceeds the LOCs for high risk (RQ > 0.5), restricted use (RQ> 0.2), and endangered species (RQ > 0.1) ** exceeds the LOCs for restricted use and endangered species * exceeds the LOC for endangered species

## 49

Table 4. Risk quotients for avian species exposure to DSMA and MSMA.

Chemical/Site Appl. Rate (lb ai/A) EEC (ppm) Acute RQ 1,2

Grasses Insects Seeds Herbivores Insectivores Granivores **DSMA** Cotton 3.6 1519 854 95 0.32 ** 0.18 * <0.1

Noncrop 5.7 3190 1795 199 0.68 *** 0.38 ** <0.1 Orchard 6.3 3526 1983 220 0.75 *** 0.42 ** <0.1 Turf 7.6 4253 2393 266 0.90 *** 0.51 *** <0.1 **MSMA**

**CAMA** Cotton 3 1265 712 79 0.39 ** 0.22 ** <0.1

Noncrop 6 3358 1889 210 1.03 *** 0.58 *** <0.1 Orchard 15.5 8676 4880 542 2.65 *** 1.49 *** 0.17 * Kenaf 2 480 270 30 0.15 * <0.1 <.0.1 Seed Grass 6 1440 810 90 0.44 ** 0.25 ** <0.1 Turf 4.2 2351 1322 147 0.72 *** 0.40 ** <0.1

turf 5 2799 1574 175 0.50 *** 0.28 ** <0.1

1 RQ = EEC/LC50 2LC50s = 4695 (northern bobwhite) for DSMA, 3269 ppm (northern bobwhite) for MSMA, and 5620 for CAMA *** exceeds the LOCs for high risk (RQ > 0.5), restricted use (RQ> 0.2), and endangered species (RQ > 0.1) ** exceeds the LOCs for restricted use and endangered species * exceeds the LOC for endangered species

## 50

Table 5. Acute toxicity of DSMA and MSMA to northern bobwhite (Colinus virginianus) and mallard ducks ( Anas platyrhynchos).

Chemical/ Test species Test % ai Toxicity Value* Toxicity

Classification MRID No. Study Classification **DSMA** Northern bobwhite Acute oral 82 627/514 1 slightly toxic 418920-01 core Northern bobwhite Dietary 82 4695 * */3850 1 slightly toxic 418920-03 core Mallard Dietary 82 >5620/4606 1 practically non-toxic 418920-02 core Northern bobwhite Reproduction no data outstanding Mallard Reproduction no data outstanding **MSMA** Northern bobwhite Acute oral 51 834/425 1 moderately toxic 416100-02 core Northern bobwhite Dietary 51 3269 * */1667 1 slightly toxic 416100-03 core Mallard Dietary 51 >5620/2912 1 practically non-toxic 416100-04 core Northern bobwhite Reproduction no data outstanding Mallard Reproduction no data outstanding **CAMA** Northern bobwhite Acute oral 10.1 >2250/>227 1 # 433164-03 outstanding Northern bobwhite Dietary 10.1 >5620 **/>564 1 # 433164-02 outstanding Mallard Dietary 10.1 >5620/>564 1 # 433164-01 outstanding Northern bobwhite Reproduction no data outstanding Mallard Reproduction no data outstanding 1 adjusted value based on the purity of the test material * toxicity values for acute oral and dietary tests are in mg/kg and ppm, respectively * * Acute values utilized for risk quotient calculations

## 51

# No toxicity classification was designated since actual toxicity is unknown.

## 52

Table 6. Estimated environmental concentrations* (EECs) (lb ai/A) in terrestrial environments off-site from the application site resulting from drift and runoff from different application rates.

Chemical/Site Appl. Rate (lb ai/A) Runoff (lb ai/A) Drift (lb ai/A) Total Load (lb ai/A) Sheet Channelized Upland 1 Semi-aquatic2
**DSMA** cotton 3.6 0.18 1.8 0.036 0.216 1.836

non-crop areas 5.7 0.285 2.85 0.057 0.342 2.907 orchard 6.3 0.315 3.15 0.063 0.378 3.213 turf 7.6 0.38 3.8 0.076 0.403 3.876 **MSMA** cotton 3 0.15 1.5 0.03 0.18 1.53

noncrop areas 6 0.3 3 0.06 0.36 3.36 orchard 15.5 0.775 7.75 0.155 0.93 8.68 Kenaf 2 0.100 1.000 0.020 0.120 1.120 seed grass 6 0.300 3.000 0.060 0.360 3.060 turf 4.200 0.210 2.100 0.042 0.240 2.142 **CAMA** turf 5 0.25 2.5 0.05 0.3 2.55

1 sheet runoff plus drift 2channelized runoff plus drift
*See appendix three for formulae and assumptions utilized for calculating off-site terrestrial exposure levels.

## 53

Table 7. Risk quotients for non-endangered terrestrial plants from a single application.

Chemical/Site Appl. Rate (lb ai/A) Appl.

Method Total Loading (lb ai/A) Drift (lb ai/A) RQ 3,4 Upland 1 Lowland2 Upland Lowland Drift **DSMA**

Cotton 3.6 ground 0.216 1.836 0.036 <1 <1 - 2 * <1 aerial 0.315 1.530 0.18 <1 <1 - 1 * <1 Noncrop 2.3 - 5.7 ground 0.138 - 0.342 1.173 - 2.907 0.023 - 0.057 <1 <1 - 2 * <1 Orchard 4.0 - 6.3 ground 0.204 - 0.378 2.040 - 3.213 0.040 - 0.063 <1 2 - 3 * <1 Turf 2.3 - 7.6 ground 0.138 - 0.403 1.173 - 3.876 0.023 - 0.076 <1 <1 - 3 * <1 **MSMA** Cotton 1 - 3 ground 0.060 - 0.180 0.510 - 1.530 0.010 - 0.030 <1 - 2 * 4 - 13 * <1 aerial 0.088 - 0.263 0.430 - 1.280 0.050 - 0.150 <1 - 2 * 4 - 11 * <1 Noncrop 2.1 - 6 ground 0.126 - 0.360 1.070 - 3.360 0.021 - 0.060 1 - 3 * 9 - 29 * <1 Orchard 2 - 15.5 ground 0.120 - 0.930 1.120 - 8.680 0.020 - 0.155 1 - 8 * 10 - 75 * <1 Kenaf 2 ground 0.120 1.120 0.020 1 * 10 * <1 aerial 0.175 0.850 0.100 2 * 7 * <1 Seed grass 6 ground 0.360 3.060 0.060 3 * 26 * <1 aerial 0.525 2.550 0.300 5 * 22 * <1 Turf 3 - 4.2 ground 0.180 - 0.240 1.530 - 2.142 0.030 - 0.042 2 * 13 - 19 * <1

1 sheet runoff and drift 2channelized runoff and drift 3RQ = lb ai/A / EC25 (seedling emergence for total loading and vegetative vigor for drift) 4Seedling emergence EC25s = 1.25 and 0.116 lb ai/A for DSMA and MSMA, respectively; vegetative vigor EC25s = 0.354 and 0.418 lb ai/A for DSMA and MSMA, respectively * exceeds the LOC (RQ > 1) for nontarget plants

## 54

Table 8. Risk quotients for endangered terrestrial plants from a single application.
Chemical/Site Appl. Rate (lb ai/A) Appl.

Method Total Loading (lb ai/A) Drift (lb ai/A) RQ 3,4 Upland 1 Lowland2 Upland Lowland Drift 5 **DSMA** Coton 1.1 - 3.6 ground 0.066 - 0.216 0.561 - 1.836 0.011 - 0.036 <1 2 - 6 * <1 aerial 0.096 - 0.315 0.465 - 1.530 0.055 - 0.180 <1 - 1 * 2 - 5 * <1 Noncrop 2.3 - 5.7 ground 0.138 - 0.342 1.173 - 2.907 0.023 - 0.057 <1 - 1 * 4 - 10 * <1 Orchard 4.0 - 6.3 ground 0.204 - 0.378 2.040 - 3.213 0.040 - 0.063 <1 - 1 * 7 - 11 * <1 Turf 2.3 - 7.6 ground 0.138 - 0.403 1.173 - 3.876 0.023 - 0.076 <1 - 1 * 4 - 13 * <1 **MSMA** Cotton 1 - 3 ground 0.060 - 0.180 0.510 - 1.530 0.010 - 0.030 3 - 10 * 28 - 85 * <1 aerial 0.088 - 0.263 0.430 - 1.280 0.050 - 0.150 5 - 15 * 24 - 71 * <1 - 1 * Noncrop 2.1 - 6 ground 0.126 - 0.360 1.070 - 3.360 0.021 - 0.060 7 - 20 * 59 - 187 * <1 Orchard 2 - 15.5 ground 0.120 - 0.930 1.120 - 8.680 0.020 - 0.155 7 - 52 * 62 - 482 * <1 - 1 * Kenaf 2 ground 0.120 1.120 0.020 7 * 62 * <1 aerial 0.175 0.850 0.100 10 * 47 * <1 Seed grass 6 ground 0.360 3.060 0.060 20 * 170 * <1 aerial 0.525 2.550 0.300 29 * 142 * 2 * Turf 3 - 4.2 ground 0.180 - 0.240 1.530 - 2.142 0.030 - 0.042 10 - 13 * 85 - 119 * <1

1 sheet runoff and drift 2channelized runoff and drift 3RQ = lb ai/A / NOEC (seedling emergence for total loading and vegetative vigor for drift) 4Seedling emergence NOECs = 0.30 and 0.018 lb ai/A for DSMA and MSMA, respectively; vegetative vigor NOECs = <0.30 and 0.14 lb ai/A for DSMA and MSMA, respectively * exceeds the LOC (RQ > 1) for nontarget plants 5used NOEC of 0.3 for DSMA affect on vegetative vigor

## 55

Table 9. Acute toxicity of DSMA and MSMA to various freshwater fish species and an aquatic invertebrate.

Chemical/ Test Species % ai Test Conditions LC50

(ppm) Toxicity Classification MRID No. Study Classification **DSMA** Bluegill 82.7 flow-through >112 * practically non-toxic 419056-01 core Rainbow trout 82.7 flow-through >114 practically non-toxic 419056-02 core Water flea 82.7 static 153 * practically non-toxic 419406-04 core **MSMA** Bluegill 51 flow-through >93/<47.4 1 # 417480-01 core Bluegill 51.2 static >100/<51 1 # 400980-01 core Bluegill 34.8 static 12 */ 4.1 1 slightly - moderately toxic 400980-01 core Bluegill 37.7 static 49.2 / 18.5 1 slightly toxic 400980-01 core Rainbow trout 51 flow-through >167/<85 1 # 417473-01 core Rainbow trout 51.2 static 78 / 40 1 slightly toxic 400980-01 core Fathead minnow 34.8 static 13.3 / 4.6 1 slightly - moderately toxic 400980-01 supplemental Channel catfish 37.7 static 26.8 / 10.1 1 slightly toxic 400980-01 supplemental Goldfish 34.8 static 31.1 / 10.8 1 slightly toxic 400980-01 supplemental Water flea static 77.5 */40 1 slightly toxic 419406-05 core Scud 34.8 static >100<51 1 # 400980-01 supplemental

1 adjusted LC50 or EC50 is based on the purity of the test material * Acute toxicity values used for risk quotient calculation # No toxicity classification was designated since actual toxicity is unknown.

## 56

Table 10. Risk quotients for DSMA and MSMA exposure to aquatic organisms.

Chemical/ Site Appl.

Rate (lb ai/A) No.

Appl. Peak

EEC (ppb) Acute RQ 1 - Freshwater Acute RQ 1 - Estuarine/marine

Fish2 Invert.3 Fish5 Invert.4 **DSMA** Cotton 3.6 2 98 <0.05 <0.05 * * Non-crop 5.7 3 202 <0.05 <0.05 * * Orchard 6.3 3 270 <0.05 <0.05 * * Turf 7.6 3 224 <0.05 <0.05 * * **MSMA** Cotton 3 2 78 <0.05 <0.05 <0.05 <0.05 Non-crop 6 3 234 <0.05 <0.05 <0.05 <0.05 Orchard 15.5 3 605 0.05 * <0.05 <0.05 <0.05 Kenaf 2 1 26 <0.05 <0.05 <0.05 <0.05 Seed grass 6 1 78 <0.05 <0.05 <0.05 <0.05 Turf 4.2 3 164 <0.05 <0.05 <0.05 <0.05

1 RQ = EEC/LC50 (fish) or EC50 (invertebrates) 2LC50s = 112 ppm for DSMA and 12 ppm for MSMA 3EC50s = 153 ppm for DSMA and 77.5 ppm for MSMA 4EC50 = 160 ppm for MSMA 5LC50 = 323 ppm for MSMA * No toxicity data for DSMA and marine/estuarine organisms were presented, so no RQs were calculated.

## 57

Table 11. Acute toxicity of DSMA and MSMA to various estuarine and saltwater fish and invertebrate species.

Chemical/ Test Species % ai Test Conditions LC50/EC50

(ppm) Toxicity

Classification MRID No. Study Classification **DSMA** Sheepshead minnow no data outstanding Mysid shrimp no data outstanding Oyster no data outstanding **MSMA** Sheepshead minnow 99.4 static 323 * practically non-toxic 424141-02 core Mysid shrimp 99.4 static 173 practically non-toxic 424141-01 supplemental Eastern oyster 50.4 flow-through 160* / 80 1 practically non-toxic / moderately toxic 424648-01 core
Eastern oyster 63 flow-through >1/>0.63 1 # 400980-01 supplemental Pink shrimp 63 flow-through >1/>0.63 1 # 400980-01 supplemental

1 adjusted for the purity of the test material * Acute toxicity values utilized for risk quotient calculation # No toxicity classification was designated since actual toxicity is unknown

## 58

Table 12. Risk quotients for non-endangered aquatic plant exposure to DSMA and MSMA.

Chemical/ Site Appl. Rate

(lb ai/A) No.

Appl. Peak EEC

(ppb) RQ 1,2

non-endangered vascular spp. non-endangered

non-vascular spp. endangered vascular spp. **DSMA** Cotton 1.1 - 3.6 2 32 - 98 <0.1 <0.1 <0.1 Noncrop 2.3 - 5.7 3 67 - 202 <0.1 <0.1 0.13 Orchard 4 - 6.3 3 90 - 270 <0.1 <0.1 0.18 Turf 2.3 - 7.6 3 74 - 223 <0.1 <0.1 0.15 **MSMA** Cotton 1 - 3 2 26 - 78 <0.1 <0.1 <0.1 Noncrop 2.1 - 6 3 82 - 156 <0.1 <0.1 <0.1 Orchard 2 - 15.5 3 78 - 605 <0.1 0.2 <0.1 Kenaf 2 1 26 <0.1 <0.1 <0.1 Seed grass 6 1 78 <0.1 <0.1 <0.1

1 RQ = EEC / EC50 (non-endangered species) or NOEC (endangered species) 2vascular (duckweed) EC50's and NOECs are 72.7 ppm and 20.5 ppm for DSMA and 53 and 29 ppm for MSMA; non-vascular (algae or diatom) EC50's are 1.5 ppm for DSMA and 2.8 ppm for MSMA

## 59

Table 13. Estimated environmental concentrations (EECs) for MSMA and DSMA in the aquatic environment.
Application rate (lbs a.i./A) Number of

Applications Peak EEC (ppb) **DSMA** Cotton 3.6 2 98 Non-crop 5.7 3 202 turf 7.6 3 270 orchard 6.3 3 223 **MSMA**
cotton 3 2 78

noncrop areas 3 3 234

orchard 15.5 3 605

Kenaf 6 1 26
seed grass 6 1 78

turf 4.2 3 164

## 60

Table 14. Acute toxicity of DSMA and MSMA to aquatic algal, diatom, and plant species.

Chemical/ Test Species % ai EC50 (ppm) NOEC

(ppm) MRID No. Study Classification **DSMA** Duckweed 82.7 72.7 20.5 419406-03 core Green algae 82.7 96.2 <67 417911-01 core Marine diatom 81.35 38.8 <26.6 431845-03 core Marine diatom 81.35 211 32.9 431845-01 core Blue-green algae 81.35 1.5 0.9 431845-02 core **MSMA** Duckweed 51 104.1 / 53 1 * 56.8 / 29 1 * 417482-02 core Green algae 51 5.6 / 2.8 1 * <0.3 417482-01 core * Acute toxicity values utilized for risk quotient calculation 1 adjusted value based on the purity of the test material

## 61

Table 15. Acute toxicity of MSMA, DSMA, and CAMA to honey bees.

Chemical % ai LD50 (μg/bee) Toxicity

Classification MRID No. Study Classification **DSMA** Honey bee 82.7 >20.7 practically non-toxic 419354-01 core **MSMA** Honey bee 51 68 35 1 practically non-toxic 416100-07 core

**CAMA** Honey bee 10.1 >25 practically non-toxic 430511-01 core

1 adjusted value based on the purity of the test material

## 62

Table 16. Acute toxicity of DSMA, MSMA, and CAMA to non-target algricultural plants (Tier II).

Chemical/ Test Species Seedling Emergence Vegetative Vigor

Endpoint 1 EC25

(lb ai/A) NOEC

(lb ai/A) Endpoint 1 EC25 (lb ai/A) NOEC

(lb ai/A) **DSMA** 1,2 **monocots:** Corn none n/a 4.86 dry weight 0.354 * <0.30 Oat phytotoxicity <0.30 phytotoxicity n/a 0.61 Ryegrass none n/a 4.86 none n/a 4.86 Onion none n/a 4.86 none n/a 4.86 **dicots:** Soybean phytotoxicity n/a 1.22 none n/a 4.86 Carrot none n/a 4.86 phytotoxicity n/a 2.43 Tomato none n/a 4.86 dry weight 0.666 0.30 Cabbage dry weight 1.25 * 1.22 dry weight 0.419 <0.30 * Cucumber none n/a 4.86 dry weight 2.43 0.61 Lettuce dry weight 1.44 0.30 * dry weight 0.705 0.30 **MSMA** 4,5 **monocots:** Corn none n/a 2.24 none n/a 2.24 Oat none n/a 1.12 dry weight 0.418 * 0.14 * Ryegrass none n/a 2.24 none n/a 2.24 Onion none n/a 2.24 plant height >2.24 0.56 **dicots:** Soybean none n/a 2.24 dry weight 0.712 0.56 Carrot none n/a 2.24 none n/a 2.24 Tomato none n/a 2.24 plant height 1.104 0.28 Cabbage dry weight 0.116 * 0.018 4 * plant height 0.516 0.28 6 Cucumber none n/a 2.24 dry weight >2.24 0.56

1only the most sensitive endpoint has been tabulated for each species
2the test material was 82.7% ai DSMA
3MRID Nos 419056-03 for seedling emergence (supplemental) and MRID No. 419056-04 for vegetative vigor (supplemental)

## 63 4the test material was 51% ai MSMA
5MRID Nos 417055-01 and 425725-01 for seedling emergence (core) and 417055-02 for vegetative vigor (core)
6based on phytotoxicity * Acute toxicity values utilized for risk quotient calculations

## 64

Table 17. Chronic risk quotients for small mammals from exposure to methanearsonic acid (MMA)*.

Chemical/Site Max. Appl. Rates (lb ai/A) No.

Appl. Predicted Maximum EEC on Food items 1 Reproductive Risk Quotients 1 **

Short grasses Broadleaf plants

and Insects Seeds Herbivores Insectivores Granivores

**DSMA** cotton 3.6 2 1519 854 95 15.19 8.54 0.95

non-crop 5.7 3 3190 1795 199 31.90 17.95 1.99 orchard 6.3 3 3526 1983 220 35.26 19.83 2.20 turf 7.6 3 4253 2393 266 42.53 23.93 2.66 **MSMA** cotton 3 2 1265 712 79 12.65 7.12 0.79

non-crop 6 3 3358 1889 210 33.58 18.89 2.1 orchard 15.5 3 8676 4880 542 86.76 48.80 5.42 Kenaf 2 1 480 270 30 4.80 2.70 0.3 seed grass 6 1 1440 810 90 14.40 8.10 0.9 turf 4.2 3 2351 1322 147 23.51 13.22 1.47 **CAMA** turf 5 3 2799 1574 175 27.99 15.74 1.75 * Methanearsonic acid is the anion of MSMA, DSMA, and CAMA, and is generated upon dissolution of MSMA, DSMA, and CAMA in water. ** The level of concern for reproductive risk is 1. 1 Reproductive risk RQ = EEC/NOEC (100ppm)

## 65 **APPENDIX 2**
**DEFINITIONS AND EXPLANATIONS OF TERMS AND ACRONYMS** RISK QUOTIENTS AND LEVELS OF CONCERN Risk quotients (RQs) are compared to levels of concern (LOCs) to assess the potential for adverse ecological effects to nontarget organisms. An RQ is an index comparing estimated environmental concentrations (EECs) with the most sensitive ecotoxicity values, where RQ = EEC / TOXICITY Risk presumptions are made by comparing acute and chronic RQs to LOCs for birds, mammals, plants, and aquatic organisms. Exceedance of an LOC indicates the potential for serious risk to nontarget organisms and the need for the Agency to consider regulatory action. LOCs address the following risk presumption categories: acute high risk: regulatory action may be warranted to eliminate or reduce risk; acute restricted use: risk may be mitigated by restricted use classification; acute endangered species: regulatory action may be warranted to protect endangered species; and reproductive and chronic risk: regulatory action may be warranted to eliminate or reduce reproductive or chronic risk. The ecotoxicity values for acute effects are:
LC50: birds and fish LD50: mammals EC50: aquatic plants and aquatic invertebrates EC25: terrestrial plants NOAEL: endangered terrestrial and aquatic plants The NOAEL is the ecotoxicity value for reproductive and chronic effects for birds, mammals, fish, and aquatic invertebrates. Risk presumptions are tabulated below.

## 66

Risk Presumption RQ LOC **Birds and Mammals** Acute High Risk EEC **1**/LC50 or LD50/sqft **2**or LD50/day **3** 0.5 Acute Restricted Use EEC/LC50 or LD50/sqft or LD50/day (or LD50 < 50 mg/kg) 0.2

Acute Endangered Species EEC/LC50 or LD50/sqft or LD50/day 0.1 Reproductive Risk EEC/NOAEL 1 

## Aquatic Animals Acute High Risk EEC**4**/LC50 or EC50 0.5 Acute Restricted Use EEC/LC50 or EC50 0.1 Acute Endangered Species EEC/LC50 or EC50 0.05 Chronic Risk EEC/NOAEL 1 

## Plants Acute Risk EEC**5**/EC25 (terrestrial) or EEC4/ EC50 (aquatic) 1 Endangered Species EEC/EC05 or NOAEL 1

**1**ppm ai on avian and mammalian food items (grass, insects, seeds) **2**mg ai per ft 2÷ [LD50 * animal wt (kg)] **3**mg ai consumed per day ÷ [LD50 * animal wt (kg)] **4**aquatic concentration of ai **5**lb ai/A

## 67 **APPENDIX 3**
**FORMULAS AND ASSUMPTIONS FOR OFF-SITE TERRESTRIAL PLANT EXPOSURE EECs for Terrestrial Plants Inhabiting Upland Areas Adjacent to Treatment Sites**  **Ground application:** Runoff = maximum application rate (lb ai/A) x runoff value (1%, 2%, or 5%) Drift = maximum application rate (lb ai/A) x 1% (drift) Total Loading = runoff (lb ai/A) + drift (lb ai/A) **Aerial application:** Runoff = max. appl. rate (lb ai/A) x 75% (application efficiency) x runoff value Drift = max. appl. rate (lb ai/A) x 5% (drift) Total Loading = runoff (lb ai/A) + drift (lb ai/A) **EECs for Terrestrial Plants Inhabiting Lowland Areas Ground application:**  Runoff = max. appl. rate (lb ai/A) x runoff value x 10 acres Drift = max. appl. rate x 1% Total Loading = runoff (lb ai/A) + drift (lb ai/A) **Aerial application:** Runoff = max. appl. rate (lb ai/acre) x 75% x runoff value x 10 acres Drift = max. appl. rate (lb ai/A) x 5% Total Loading = runoff (lb ai/A) + drift (lb ai/A) Terrestrial plants inhabiting dry and semi-aquatic areas may be exposed to pesticides from runoff, spray drift or volatilization. Semi-aquatic areas are those low-lying wet areas that may be dry at certain times of the year. EFED's runoff scenario is: (1) based on a pesticide's water solubility and the amount of pesticide present on the soil surface and its top one inch, (2) characterized as "sheet runoff" (one treated acre to an adjacent acre) for dry areas, (3) characterized as "channelized runoff" (10 treated acres to a distant low-lying acre) for semi-aquatic areas, and (4) based on % runoff values of 0.01, 0.02, and 0.05 for water solubility of <10 ppm, 10-100 ppm, and >100 ppm, respectively. Spray drift exposure from ground application is assumed to be 1% of the application rate. Spray drift from aerial, airblast, forced-air, and chemigation applications is assumed to be 5% of the application rate. EECs are calculated for the following application methods: (1) unincorporated ground applications, (2) incorporated ground application, and (3) aerial, airblast, forced-air, and chemigation applications. Formulas for calculating EECs for dry areas adjacent to treatment sites and EECs for semi-aquatic areas are in an addendum.

## 68 **APPENDIX 4**
**ESTIMATING RESIDUES ON TERRESTRIAL FOOD ITEMS** The Agency estimates the residues on terrestrial food items from multiple applications and over time by taking into account: - application rate for a single application, - number of applications, - application interval, and - dissipation rate The model of Hoerger and Kenega (1972), as modified by Fletcher et al. (1994) was used to estimate pesticide concentrations on selected avian or mammalian food items. This model predicts the maximum concentrations that may occur immediately following a direct application at 1 lb ai/A. For 1 lb ai/A applications, concentrations on short grass, broadleaf plants, and fruits are predicted to be 240 and 85 ppm, 135 and 45 ppm, and 15 and 7 ppm for maximum and mean residues, respectively. The predicted maximum concentration for broadleaf plants and fruits are used to represent maximum concentrations that may occur on small and large insects, respectively. Linear extrapolation is then used to estimate maximum terrestrial EEC’s for single applications at other application rates. The Agency uses this as a screening level exposure assessment tool to determine peak terrestrial EECs resultingfrom multiple applications. After application, residues on food items are predicted to decline according to a firstorder exponential model. If the maximum initial concentration is C 0and the half-life for the exponential dissipation of the active ingredient is t 1/2 , the remaining concentration at time t is given by the following formula:

or Ct = C 0(1/2) t/t1/2(the latter form shows the direct use of the half-life concept). 

# C C e t tt 

# = − 0 2 1/ 2 ln

The general formula for the peak EEC (Cpeak ) following multiple applications is: or in simpler, directly calculable, single equation form, 

# C C e peak i n I n i t 

# =

= − − 

# ∑ 0 1 2

1 2 ( )ln /

Cpeak = C 0 [1-(1/2) nI/t1/2] [1- (1/2) I/t1/2]
where C

0is the maximum initial concentration after one application, I is the time interval between applications, nis the number of applications, and t 1/2is the half-life of the active ingredient.1 Typical or conventional laboratory analysis does not differentiate among the various inorganic species

and organic species of arsenic. Analysis for total arsenic, of course, sets an upper bound for all arsenic-containing species from all sources. Any contribution specifically from cacodylic acid would be masked. 

## 69 **APPENDIX 5*** [*This appendix is a verbatim copy of the expanded drinking water assessment which was a major portion of Appendix 6 of the **Cacodylic Acid** RED. It has coequal information on cacodylic acid and MDMA/DSMA, as well as other arsenical species. References are listed at the end.]
**DRINKING WATER EXPOSURE ASSESSMENT Background and Basis.**  As stated in the introduction, cacodylic acid is one of several arsenical pesticides which the Agency is or will soon be considering for reregistration. Ultimately, in another action, the Agency will assess the potential overall (aggregate, cumulative) drinking water exposure to these compounds and common transformation products. The EPA Office of Water (OW) is scheduled to issue a proposed and final regulation on the larger issue of “arsenic” in drinking water by the years 2000 and 2001, respectively

. This drinking water assessment is based primarily on 1) fate studies reviewed in the Environmental Fate Assessment Section of this document, 2) limited monitoring for cacodylic acid and other speciated forms of arsenic in a mixed assortment from pesticidal use or non-use areas, and 3) extensive monitoring for total 1 arsenic. Although monitoring for individual chemical forms of arsenic is sparse, the available measured data are revealing. Surface water conclusions from these sources are compared with simulation model predictions. The primary monitoring sources are identified briefly as follows: 1) The United States Geological Survey (USGS) has recently completed an extensive survey report entitled “Arsenic in Ground Water of the United States: Occurrence and Geochemistry” (Welch, 1999), which is soon to be published in the journal Groundwater . Alan H. Welch, a principal investigator, has provided the Agency with an advance version of the report and, through telephone discussions, provided valuable insights. Water analyses were almost entirely for undifferentiated or total arsenic, as footnoted. Although the survey was dedicated to ground water, it also includes some useful information for surface water. In addition to survey information and statistical analysis, it provides a comprehensive bibliography and discusses the many of the facets of the biogeochemistry of arsenic. 2) A separate, limited investigation by USGS research scientists (Garbarino and Burkhardt, 1998), provided data on the arsenic species cacodylic acid, monomethylarsonate, arsenite, and arsenate in ground water not associated with arsenical pesticide application and in surface waters in areas which are associated with the application of MSMA, a compound closely related to cacodylic acid. 3) The EPA Pesticides in Groundwater Database (EPA, 1992) provided groundwater monitoring data for a localized area in Texas and another in the State of Washington. 4) The BASINS and STORET databases maintained by the US EPA provided a large body of data (many tens of thousands or more of entries) on total arsenic concentrations in surface waters of the U.S. 5) Chemical speciation data published in 1973 on six fresh surface water bodies, one well, and three saline waters around Tampa, Florida, revealed background concentrations for cacodylic acid, monomethylarsonate, arsenite, and arsenate.

## 70

**Groundwater Exposure** The USGS (Welch, 1999) retrieved water-quality data for about 50,000 samples from about 30,000 sample locations from the USGS’s National Water Information System (NWIS, which includes National Water Quality Assessment (NAWQA) data), and additional data from many other sources. A subset of about 20,000 analyses from the years 1973-1997 which met certain criteria were selected (censored) for statistical testing. Only a single analysis for a particular well or spring was used to avoid bias towards frequently sampled sources. Sample sites were not uniformly distributed across the country and were not specifically targeted for areas where arsenical pesticides were applied. The survey authors conclude that while slightly less than half the groundwater samples had total arsenic concentrations < 1 ug/L, about 10% exceeded 10 ug/L. They further conclude that “natural” arsenic concentrations exceeding 10 ug/L are more widespread and common than previously recognized. Some areas of high arsenic concentrations (defined as > 50 ug/L) were associated with point source pollution (for example, Superfund Sites where about 30% of approximately 1200 sites list arsenic as a “contaminant of concern”), but most appear to be natural areas. A USGS map of total arsenic distribution in ground waters of the U.S. is given in Appendix 7. Based on a few regional studies of agricultural use of inorganicarsenical pesticides (not the “organic” cacodylic acid), the survey authors conclude that groundwater arsenic concentrations do not correlate well with use, and that groundwater is largely unaffected by their use in those areas (North Dakota, South Dakota, Wisconsin, Minnesota). Almost all instances of significant detections of the inorganics are associated with disposal or other types of point source pollution. The survey authors report that even in areas that tend to have naturally high arsenic concentrations there exists some ground water with low to very low arsenic concentrations. Steep lateral and vertical concentration gradients exist, showing inherent local spatial variability. The USGS scientists state that a statistically based evaluation of these observations requires work on, among other things, development of lithochemical geologic/aquifer relationships. Similar reports of high spatial variability over small, localized areas come from scientists investigating numerous recent newsworthy instances of serious arsenic poisoning deriving from drinking water wells in India (West Bengal) and Bangladesh (Nickson, et al., 1998; Masud, 2000; numerous others)

. The USGS reports few analyses of groundwater samples specifically for methylated arsenic compounds such as cacodylic acid. However, about 30 groundwater samples taken in northwestern Nevada where these compounds were not used were analyzed for background monomethylarsonate and cacodylic acid (also identified as dimethylarsinate). The data suggested to the authors that groundwater in areas where arsenical pesticides are not applied contains < 1ug/L of methylated arsenic (all analyses were < 0.3 ug/L). In a separate study by USGS research scientists (Garbarino and Burkhardt, 1998), 6 groundwater samples from Idaho, 10 from Illinois, and 8 from Nevada (total of 24 sites) were analyzed for arsenite, arsenate, monomethylarsonate, and cacodylic acid. Again, none of the sites were associated with the application of arsenical pesticides. With a detection limit of approximately 0.2 ug/L, there were no measurable concentrations of the methylated compounds in ground water. In contrast, arsenite or arsenate concentrations in these groundwater samples ranged from less than the method detection limit of approximately 0.2 ug/L to a concentration as high as approximately 900 ug/L. Their data show that either arsenite or arsenate or both were detected in all samples, typically at 10-50 ug/L. Arsenite and arsenate concentrations were comparable. In a personal communication, one of the study authors expressed surprise at this latter comparability, since arsenate is generally assumed to dominate. As part of a study of 10 natural waters (one ground water, nine surface waters) in the vicinity of Tampa, Florida (Braman and Foreback,1973), one water well at a remote camping area was sampled. Tampa tap water was also analyzed. Details of this study are given below in the Surface Water Exposure Section. The well water concentration for cacodylic acid was 0.4 ug/L (ppb); for methylarsonic acid, 0.2 ug/L; and for arsenate (as arsenic), 0.3 ug/L. Concentration of arsenite (as arsenic) was less than the detection limit of 0.02 ug/L (20 parts per trillion). Tampa tap

## 71

water “contained only traces of arsenate”. Reported monitoring data in the EPA Pesticides in Groundwater Database show relatively high concentrations of total arsenicin a high percentage of water wells in localized areas of Texas [concentrations of 10-680 ppb in 91 of 247 wells with limits of detection (LODs) for most samples of 25 ppb; fewer with LODs of 10 ppb]; and in the State of Washington (1.6-13.3 ppb in 15 of 20 wells with LOD of 0.2 ppb). The Texas data (paragraph 1 below) were associated with use of cacodylic acid; the Washington data (paragraph 2 below) were not. 1) From the Texas report (Aurelius, 1988), the Agency independently concludes that these detections are not reasonably attributable to labeled pesticidal application (non-point source) of cacodylic acid or other currently used arsenicals. Rather, the high concentrations were most likely caused by cacodylic acid-treated cotton gin waste which was spread in the vicinity of poorly cased wells, and by somewhat higher natural concentrations of arsenic. 2) In Washington (Erickson, 1990), natural conditions including historical volcanic activity; strongly alkaline, sandy soils; hydrology favorable to the migration of soluble constituents; former heavy use of calcium or lead arsenates (sometimes hundreds of pounds/acre annually) in orchards; thermal waters; or wastes from mining operations may have contributed to the elevated concentrations.
Groundwater Conclusion. In view of 1) the extensive USGS survey report on arsenic (principally total arsenic); 2) the limited, monitoring data for speciated arsenicals, including cacodylic acid; 3) the relative immobility of cacodylic acid indicated by laboratory sorption and comparison with phosphate; and 4) the insignificant leaching of cacodylic acid observed in a supplemental field study, it is reasonable for the Agency to conclude that highly variable background concentrations of arsenic species in groundwater (including arsenite and arsenate,the mineral allies/metabolites of cacodylic acid) should be largely unaffected by the labeled, agricultural (nonpoint source) use of cacodylic acid on cotton. This conclusion should not be interpreted to mean that humans are not exposed to arsenicals in their drinking water from groundwater sources. It is patently clear from all sources that humans are exposed to significant concentrations of chemical forms of arsenic (including cacodylic acid) in their drinking water from groundwater sources. However, labeled use of cacodylic acid should not contribute significantly to the already existing burden of arsenic in groundwater from all sources, natural and anthropogenic. Furthermore, the prevalence of so much natural total arsenic, including arsenite and arsenate, suggests that any concerns be directed toward other arsenic species. It is therefore desirable that whenever future groundwater samples are analyzed for total arsenic (as has usually been the case), that arsenic be speciated whenever total arsenic concentrations justify possible toxicity concerns. **Surface Water Exposure** As discussed under “mobility” in the environmental fate section above, eroding soil and runoff water would transport cacodylic acid and metabolites to surface waters. The extensive USGS report cited above on arsenic in ground water (which had a modicum of surface water information), as well as other sources (e.g., Hem, 1985), indicate that total arsenic concentration in the majority of U.S. rivers and streams is less than 1 ug/L. However, as for ground water, many notable exceptions of higher arsenic concentrations occur; the highest most likely to occur in geothermal areas and in water draining mineralized areas. The BASINS and STORET databases maintained by the US EPA have a large body of data (many tens of thousands or more of entries) on total arsenic concentrations in surface waters of the U.S.. However, because of the wide ranging concentrations (see below) in space and time, and the multiplicity of possible major sources of arsenic, any attempt to associate these with cacodylic acid use would likely be a fruitless exercise, and would certainly require a major resource effort akin to that by the USGS for groundwater. Nevertheless, even casual inspection of the data

## 72

from the databases shows that is not unusual for total arsenic concentrations in raw surface water in many different sites to be several parts per billion. (Reporting limits in many cases appear to be 1 ppb, but in many other cases are in excess of 10 ppb and up to approximately 50 ppb. The 10 and 50 ppb limits may be associated with the human health limits currently set for total arsenic set by the World Health Organization and the US EPA, respectively.) Spatial variability is the rule. The data for Georgia and Texas given below are illustrative of this variability and are not meant to imply a special situation. For example, in Georgia, as presented in BASINS, upper 85th percentile concentrations of total arsenic at different sites ranged from less than 1 ppb to 338 ppb. More typical high values would fall in the range of 10 to 50 ppb. The most probable concentration appears to fall in the range of <1 to 2 or 3 ppb. The STORET database for Georgia and Texas show similar results, with Texas seeming to average several parts per billion more. Some of the highest values reported in STORET for Georgia and Texas (79,000 entries) approach 1000 ppb and can often be associated with past point source pollution by humans. Such pollution is becoming less serious through environmental conscientiousness and governmental regulation. However, as previously mentioned, natural sources (especially in places in the western U.S.) also produce such high concentrations. It is noteworthy that most major drinking water facilities which use surface water often use water treatment techniques (e.g., flocculation with compounds of aluminum or iron) which are generally effective in reducing total arsenic concentrations in the observed ranges to less than 1 ppb. As was established above, if desired, it is possible to measure and speciate lower concentrations. As previously stated, data specifically on methylated forms of arsenic in surface waters are sparse. One precocious study (partially described in the groundwater section above) for 10 natural waters in the vicinity of Tampa, Florida, published in 1973 (Braman and Foreback) revealed background concentrations of cacodylic acid to range up to 1.8 ug/L. There were six surface fresh water bodies (two rivers, two ponds, two lakes), three saline waters (two bays, one tidal flat), and one water well at a remote camping area. Tampa tap water was also analyzed. Analysis was for the four arsenic species: cacodylic acid (dimethylarsenic acid), methylarsonic acid (methyl arsonate, MMA or MSMA), arsenite, and arsenate. Presumably, all water sites were sampled once with two or more replicates analyzed; however, the study authors did not report specifics on sampling dates and the number of samples analyzed or replicated. All concentrations reported below are as arsenic equivalents (to get cacodylic acid concentrations, for example, multiply all values given below for cacodylic acid by the relative chemical weights of approximately 138/75 or 1.8). [In addition to the water samples, human urine(15ppb cacodylic acid, N=8; 3 ppb methylarsonic acid, N=8; 2 ppb arsenite, N=4; and 4 ppb arsenate, N=4), bird eggshells, seashells, and a limestone rock, were analyzed.] Concentrations of cacodylic acid (reported as arsenic) in the natural waters ranged up to 1.0 ppb (1.0 x 1.8 = 1.8 ppb cacodylic acid). At one site, the Hillsborough River, concentrations were below a remarkably low detection limit of 0.02 ppb, while the median value for cacodylic acid (as arsenic) at the other nine sites was approximately 0.3 ppb (0.5 ppb cacodylic acid). The well water concentration, as given previously, was 0.2 ppb (0.4 cacodylic acid). Concentrations of arsenate, detected at all ten sites, were similar to cacodylic acid. Arsenite was detected at only six of the ten sites, but had the highest concentration (2.7 ppb) of all species. Methylarsonic acid, detected in eight of the ten sites, was generally present at lower concentrations, the highest being 0.22 ppb. However, in a broader sense, considering the few samples, surface water concentrations of all four were similar. Total arsenic concentrations ranged from approximately 0.3 to 3.6 ppb. The extent to which these concentrations represent the natural background in the Tampa area or are influenced by introduction of artificial sources is unknown. However, the study authors considered the sampled sites as “natural” waters. As previously given, Tampa tap water “contained only traces of arsenate”. In another arsenic speciation study, USGS research scientists (Garbarino and Burkhurdt, 1998) collected surface water samples at one or two week intervals from early March through the middle of September of 1997 from each of three sites associated with different basins or sub-basins in an agricultural region potentially impacted by application of MSMA (application is normally from May through July). MSMA can be used as a surrogate for cacodylic acid because it is chemically closely related to cacodylic acid; produces cacodylic acid as a metabolite; is a minor metabolite of cacodylic acid; and has a similar use and environmental fate profile (cacodylic acid is slightly

## 73

more mobile). Sampling dates and times varied between sites and were not correlated. A total of 24 samples were analyzed from each site. Analyses were for MSMA (as the acid MMA), cacodylic acid (DMA), arsenite, and arsenate. Maximum concentrations of MMA at the three sites were approximately 2, 3, and 5 ug/L, and were relatively short-lived. As a surrogate and with adjustment for application rates, similar concentrations would be expected for cacodylic acid. Concentrations of cacodylic acid (a possible metabolite of MSMA), were at or below the detection limit of 0.2 ug/L, except for one sample which registered approximately 0.6 ug/L. Maximum arsenite concentrations were approximately 2, 3, and 3 ug/L. Maximum arsenate concentrations were approximately 2, 5.5, and 5.5 ug/L. The comparable concentrations of arsenite and arsenate is again noteworthy. The inorganic species generally increased later in the summer, possibly indicating alkylarsenic degradation (oxidation) or a secondary source of inorganic arsenic. However, until similar baseline data for surface water sources where no arsenicals are applied are compared, no conclusions can be reached about whether the fluctuations are part of the natural arsenic cycle or influenced by pesticide application. It is informative to compare the preceding surface water results with environmental simulation model predictions for potential increases in surface water concentrations. The Agency has recently adapted the standard PRZM/EXAMS model for runoff to an Index Drinking Water Reservoir (IR), and also makes an allowance for an estimated maximum of surrounding land which may be cropped. Model input values specific to cacodylic acid are given in an attachment. Resulting acute and chronic drinking water concentrations for the IR scenario for cotton grown in Mississippi with one annual application of cacodylic acid at a rate of 0.60 lb/acre and with a multiplicative factor for percent cropped area (PCA) of 0.20 (20% cropped) are: Acute (one-in-ten year peak concentration x PCA): 29 ug/L x 0.20 ~ 6 ug/L (ppb) Chronic (one-in-ten year peak concentration x PCA): 7.0 ug/L x 0.20 ~ 1 ug/L (ppb) **Conclusion for Surface Drinking Water.**Whether coincidence or not, and whatever the source, the modeled values for cacodylic acid for surface drinking water are similar to those measured and discussed above for both use and non-use areas, and would, therefore, generally represent an additional, localized burden above background. If there are toxicological concerns at or near the monitored and modeled concentrations, then, clearly, this observation invites broader scale, systematic environmental sampling and analysis for cacodylic acid and other speciated arsenicals in order to determine statistically the associations, ranges of exposure, and possible effects. As is obvious from the Florida and USGS work, adequate analytical methods for arsenical chemical speciation are available. While all of the pesticidal arsenicals certainly can contribute to total arsenic in surface water in use areas, their additive effects would be generally comparable to the lower limits of most observed concentrations of total arsenic (including arsenite and arsenate) or a small superposition on larger collective contributions at the upper limits of concentrations from other sources, natural or anthropogenic. However, considering the speciated measurements by the USGS researchers, those by Braman and Foreback, and the similarity of model predictions, if there is concern for concentrations of cacodylic acid per se, then its pesticidal application clearly appears to represent an additional, localized exposure burden of magnitude comparable to background concentrations.

## 74 **APPENDIX 6**
**MSMA/DSMA INDEX RESERVOIR DRINKING WATER CONCENTRATIONS** 
**PRZM/EXAMS MODEL INPUTS AND OUTPUTS FOR DEFOLIANT/HERBICIDAL USE WITH COTTON AND CITRUS**  **Note: Modeled uses (cotton and citrus) for MSMA and DSMA are the same. Except for differences in application rates, any differences in model inputs for MSMA and DSMA, the mono- and disodium salts methanearsonic acid**  **(MMA), are virtually inconsequential to model output. Thus, only the simulations for DSMA on cotton (aerial spray) and citrus (ground spray) are given below. MSMA and DSMA concentrations for other rates, as given in the Drinking**  **Water Section of the main text from which this appendix is referenced, are proportional to the application rates. PRZM (Version 3.12) INPUTS**  **Application Information, including Rates and Intervals (also given in table below):**
**Cotton** : **Aerial** spray applied to mature cotton for defoliation of cotton plant prior to harvest. **Two**applications

of **DSMA** , each at **4.0 kg/ha**(3.6 lb/acre) with a **14-day interval** (seasonal max. of 8.0 kg/ha). No incorporation.
**Citrus: Ground** 

spray applied for weed control around citrus. **Three**applications of **DSMA** , each at **7.1 kg/ha** (6.3 lb/acre) applied at 14-day intervals (seasonal max. of 21 kg/ha). No incorporation.

**Variable (units)**  **Variable**

**Description Input Value**  **Source of Info/Reference**  DWRATE(1) 1 (day -1 ) Dissolved phase

pesticide decay rate constant in surface horizon DWRATE(1) = DSRATE(1)

k = ln2/t1/2 = ln2/242
k = 2.9 x 10-3/day Aerobic soil metabolism study (GLN 162-1) 2 soils (t /2 = 240 and 241days), upper 90% C.L. = 242 days DSRATE(1) 1 (day -1 ) Adsorbed phase

pesticide decay rate constant in surface horizon DWRATE(2) (day -1 ) DWRATE(3) (day -1 ) Dissolved phase

decay rate const. in 1 st, and 2nd subsurface horizon DWRATE(2) = DSRATE(2)

k = ln2/t1/2 = ln2/2300 k = 3.0 x 10-4/day DWRATE(3) = DSRATE(3) Same as above: k = 3.0 x 10-4/day Anaerobic soil/ anaerobic aquatic metabolism study (GLN 162-2/3) One anaerobic aquatic study, t1/2 = 2.1 years 3 x 2.1 = 6.3 years = 2300 days DSRATE(2) (day -1 ) DSRATE(3) (day -1 ) Adsorbed phase

decay rate const. in 1 st and 2nd subsurface horizon

## 75

KD(1) KD(2) KD(3) (cm3gm-1 or mL g -1 or L kg -1 ) Pesticide

partition or distribution coefficients for each horizon Kd = 13 mL/g (loamy sand) (use for all horizons) Mobility - Adsorption/Desorption study (GLN 163-1) No OC correlation. Lowest non-sand Kd of 21 U.S. soils =13 mL/g

DEPI (cm) Incorporation

depth Actual or pesticide label

0 cm (no incorporation) Product label

TAPP (kg ha-1 ) Application rate Maximum label rate DSMA on Cotton : Aerial spray

. Two applicationsof 4.0 kg/ha

with a 14-day interval (seasonal max. of 8.0 kg/ha).
DSMA on Citrus : Ground spray

. Three applications , each at 7.1 kg/ha with a 14-day interval (seasonal max. of 21 kg/ha). Product label

APPEFF (decimal) Application

efficiency 0.95 for aerial spray and ground spray Current default

DRFT Spray drift

fraction 0.16 for aerial spray; 0.014 for ground spray. Current defaults

## 76 **MSMA/DSMA USES ON COTTON AND CITRUS Input Parameters for EXAMS (Version 2.97.5)** 
**Variable (units) Variable** 

**Description Input Value**  **Source of Info/Reference**  HENRY (atm-m3 -mole-1 ) Henry's law

constant MSMA: 1.5 x 10 -13atm m3mole -1 DSMA: 7.1 x 10 -14atm m3mole-1 Calculated from V.P.and solubility KBACW 1 (cfu/mL) -1 hour-1 Bacterial biolysis

in water column Aerobic soil t 1/2x 2 = 242days x 2 x 24hr/day

t 1/2= 1.16 x 104hr k = ln2/1.16 x 104/hr

= 6.0 x 10-5/hr Aerobic aquatic metabolism (GLN 162-4) half-life ( units change) KBACS 1 (cfu/mL) -1 hour-1 Bacterial biolysis

in benthic sediment Anaerobic aquatic study

One value, t1/2= 2.1 years 2.1 x 3 = 6.3 years = 2300 days x 24hr/da = 5.5 x 104hr k = ln2/t 1/2= 1.3 x 10-5/hr Anaerobic aquatic metabolism (GLN 162-3) (units change) Anaerobic soil (GLN 162-2) KDP (hour-1 ) Direct

photolysis Stable (0.0) Photolysis in water (161-2) KBH (mole-1 hour-1 ) KNH (hour-1 ) KAH (mole-1 hour-1 ) Base hydrolysis

Neutral hydrolysis Acid hydrolysis 0.0

0.0

0.0 Hydrolysis study (GLN 161-1)
Stable

KOC (mL g -1 O.C. ) Partition

coefficient for organic carbon Lowest non-sand Kd

Kd = 13 mL/g Mobility - Ads/Des study (GLN 163-1) No OC corr.Lowest nonsand Kds for 21 soils. MWT (g mole-1 ) Molecular

weight MSMA: 162

DSMA: 184 Chemical formula SOL (mg L-1 ) Aqueous

solubility MSMA: 1.0 x 10 6mg/L

DSMA: 3.4 x 10 5mg/L Product Chem.

QUANT Direct

photolysis quantum yield 0 NA

VAPR (torr) Vapor pressure MSMA: 7.5 x 10-7Torr DSMA: 1 x 10 -7Torr Product Chem.

## 77 Output for DSMA use on cotton - Yazoo County, Mississippi Major Land Resource Area 134: Southern Mississippi Valley Silty Uplands Loring Silt Loam (Hydraulic Soil Group: C) 2 aerial applications at 3.6 lb a.i./ac

MS cotton - IR w/PCA for drinking water (PPB)
YEAR PEAK 96 HOUR 21 DAY 60 DAY 90 DAY YEARLY

---- ---- ------- ------ ------ ------ ------ 1948 362.000 352.000 338.000 299.000 224.000 67.800 1949 281.000 274.000 250.000 224.000 201.000 122.000 1950 156.000 152.000 136.000 115.000 109.000 61.800 1951 269.000 262.000 254.000 239.000 191.000 74.590 1952 218.000 213.000 196.000 162.000 143.000 86.110 1953 143.000 140.000 129.000 111.000 95.890 46.070 1954 177.000 173.000 165.000 144.000 134.000 65.230 1955 228.000 222.000 205.000 165.000 146.000 87.050 1956 135.000 132.000 128.000 108.000 95.190 61.370 1957 552.000 537.000 503.000 416.000 341.000 107.000 1958 332.000 323.000 294.000 252.000 217.000 116.000 1959 180.000 176.000 160.000 133.000 125.000 71.060 1960 459.000 446.000 426.000 358.000 316.000 114.000 1961 247.000 242.000 229.000 157.000 125.000 82.730 1962 200.000 194.000 177.000 158.000 138.000 68.220 1963 245.000 238.000 218.000 153.000 116.000 44.210 1964 207.000 202.000 180.000 150.000 146.000 112.000 1965 280.000 272.000 243.000 192.000 164.000 83.390 1966 218.000 212.000 129.000 117.000 104.000 50.500 1967 204.000 199.000 178.000 157.000 143.000 100.000 1968 164.000 159.000 142.000 125.000 117.000 53.420 1969 396.000 379.000 303.000 262.000 205.000 79.310 1970 385.000 375.000 335.000 275.000 244.000 126.000 1971 129.000 126.000 112.000 78.020 69.510 38.640 1972 539.000 525.000 489.000 424.000 337.000 115.000 1973 315.000 308.000 278.000 228.000 196.000 127.000 1974 153.000 148.000 135.000 108.000 91.900 54.250 1975 155.000 150.000 141.000 136.000 110.000 46.200 1976 166.000 161.000 151.000 123.000 117.000 76.100 1977 162.000 158.000 152.000 130.000 129.000 57.220 1978 568.000 552.000 498.000 418.000 387.000 142.000 1979 484.000 471.000 425.000 348.000 299.000 144.000 1980 197.000 192.000 175.000 150.000 147.000 65.280 1981 374.000 364.000 331.000 273.000 221.000 80.820 1982 283.000 278.000 254.000 221.000 205.000 117.000 1983 146.000 142.000 127.000 101.000 85.690 41.250

upper 10th 500.500 487.200 444.900 375.400 322.300 126.300 percentile

MEAN OF ANNUAL VALUES = 82.906 STANDARD DEVIATION OF ANNUAL VALUES = 30.285 UPPER 90% CONFIDENCE LIMIT ON MEAN = 90.380 **PCA for cotton = 0.20**

## 78

**Acute: 1-in-10-year peak concentration x PCA = 500.5 x 0.20 =**  **100 ug/L**
**Chronic: 1-in-10-year average annual mean x PCA = 126.3 x 0.20 =**  **25 ug/L**

## 79 Output for DSMA use on citrus- Osceola County, Florida Major Land Resource Area 156A: Florida Everglades and Associated Area Adamsville Sand (Hydraulic Soil Group: C) 3 ground applications at 6.3 lb a.i./ac

FL citrus - IR w/ PCA for drinking water (PPB) YEAR PEAK 96 HOUR 21 DAY 60 DAY 90 DAY YEARLY

---- ---- ------- ------ ------ ------ ------ 1948 622 602 550 488 429 165 1949 360 347 308 293 266 109 1950 473 460 414 350 328 140 1951 334 326 292 242 242 116 1952 571 553 494 428 401 191 1953 586 568 543 519 478 203 1954 443 429 406 354 324 144 1955 310 300 269 232 221 107 1956 565 553 513 430 368 138 1957 844 817 747 627 556 223 1958 389 376 338 296 266 116 1959 554 538 494 441 387 160 1960 766 741 705 578 489 186 1961 328 318 279 253 231 106 1962 532 515 473 421 368 142 1963 654 633 575 460 384 150 1964 1094 1059 928 766 682 243 1965 506 490 446 385 354 172 1966 363 352 320 266 239 109 1967 576 565 513 435 410 168 1968 695 672 599 511 474 179 1969 454 440 406 346 309 134 1970 414 401 359 279 233 95 1971 396 389 358 285 260 111 1972 438 425 382 315 298 120 1973 623 608 550 462 396 150 1974 562 544 487 402 342 135 1975 278 270 251 219 212 97 1976 667 646 585 490 421 158 1977 429 417 367 298 266 118 1978 156 152 139 119 118 62 1979 419 405 361 337 331 137 1980 593 579 552 471 419 171 1981 1155 1120 1015 901 774 279 1982 274 266 248 202 194 105 1983 501 485 445 374 323 124 upper 10th 789 764 718 592 508 208 percentile

MEAN OF ANNUAL VALUES = 146 STANDARD DEVIATION OF ANNUAL VALUES = 44 UPPER 90% CONFIDENCE LIMIT ON MEAN = 157 PCA for citrus = 0.87 (default)

Acute: 1-in-10-year peak concentration x PCA = 789 x 0.87 = 687 ug/L

## 80

Chronic: 1-in-10-year average annual mean x PCA = 208 x 0.87 = 182 ug/L

## 81 **APPENDIX 7 GENEEC MODEL INPUT/OUTPUT TABLES FOR AQUATIC ECOLOGICAL ASSESSMENT**  **EXAMPLE: DSMA USE ON COTTON**

**DSMA INPUT**  Two applications, each at 3.6 lb/acre, 14 days apart

------------------------------------------------------------------------------------------------------------------------------------------- RATE (#/AC) APPLICATIONS SOIL SOLUBILITY % SPRAY INCORP ONE(MULT) NO.-INTERVAL Koc (Kd) (PPM) DRIFT DEPTH(IN)

------------------------------------------------------------------------------------------------------------------------------------------- 3.6 (7.06) 2 14 1120 (13) 3 x 105 5.0 0

FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

---------------------------------------------------------------------------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND)

---------------------------------------------------------------------------------------------------------------------------------------- 240 0 N/A .00- .00 ***** 480

**DSMA OUTPUT**  **:** GENERIC EECs (IN PPB)

--------------------------------------------------------------------------- PEAK AVERAGE 4 AVERAGE 21 AVERAGE 56 GEEC DAY GEEC DAY GEEC DAY GEEC

--------------------------------------------------------------------------- **97 95**  **81 64** 

________________________________________________

## 82 **APPENDIX 8** Data Requirements for: **DSMA** Chemical Number: 013802

Data Requirement Use Pattern 1 Does EPA Have

Data To Satisfy This Requirement? (Yes, No, or Partially) Bibliographic Citation MRID # Must Additional

Data Be Submitted Under FIFRA 3(c)(2)(B)?

**§158.490 WILDLIFE AND AQUATIC ORGANISMS 71-1(a) Acute Avian Oral, Quail/Duck**  Yes 418920-01 **71-2(a) Acute Avian Diet, Quail** Yes 418920-03 **71-2(b) Acute Avian Diet, Duck** Yes 418920-02 71-3 Wild Mammal Toxicity No 71-4(a) Avian Reproduction, Quail No Yes 71-4(b) Avian Reproduction, Duck No Yes 71-5(a) Simulated Terrestrial Field Study No 71-5(b) Actual Terrestrial Field Study No

**72-1(a) Acute Fish Toxicity, Bluegill** Yes 419056-01

72-1(b) Acute Fish Toxicity, Bluegill (TEP) No **72-1(c) Acute Fish Toxicity, RainbowTrout**  Yes 419056-02

72-1(d) Acute Fish Toxicity, Rainbow Trout (TEP) No

**72-2(a) Acute Aquatic, Invertebrate** Yes 419406-04 72-2(b) Acute Aquatic, Invertebrate (TEP) No 72-3(a) Acute Est/Mar Toxicity, Fish No Yes 72-3(b) Acute Est/Mar Toxicity, Mollusk No Yes 72-3(c) Acute Est/Mar Toxicity, Shrimp No Yes 72-3(d) Acute Est/Mar Toxicity, Fish (TEP) No

72-3(e) Acute Est/Mar Toxicity, Mollusk (TEP) NoData Requirement Use Pattern 1 Does EPA Have

Data To Satisfy This Requirement? (Yes, No, or Partially) Bibliographic Citation MRID # Must Additional

Data Be Submitted Under FIFRA 3(c)(2)(B)?



## 83 72-3(f) Acute Est/Mar Toxicity, Shrimp (TEP) No

72-4(a) Early Life Stage, Fish No Yes 72-4(b) Life Cycle, Aquatic Invertebrate No Yes 72-5 Life Cycle, Fish No Yes 72-6 Aquatic Organism Accumulation No 72-7(1) Simulated Aquatic Field Study No 72-7(b) Actual Aquatic Field Study No **§158.540 PLANT PROTECTION** 122-1(a) Seedling Emergence (Tier I) No 122-1(b) Vegetative Vigor (Tier I) No 122-2 Aquatic Plant Growth (Tier I) No 123-1(a) Seedling Emergence (Tier II) Yes 417055-01, 425725- 01 123-1(b) Vegetative Vigor (Tier II) Yes 417055-02 123-2 Aquatic Plant Growth (Tier II) Yes 419406-03, 417911- 01, 431845-03, 431845-02 124-1 Terrestrial Field Study (Tier III) No 124-2 Aquatic Field Study (Tier III) No **§158.490 NONTARGET INSECT TESTING** 141-1 Honey Bee Acute Contact Yes 419354-01 141-2 Honey Bee Residue on Foliage No
141-5 Field Test for Pollinators No **§158.290 ENVIRONMENTAL FATE Degradation Studies-Lab:**  161-1 Hydrolysis 161-2 Photodegradation In Water 161-3 Photodegradation On Soil **Metabolism Studies-Lab:**Data Requirement Use Pattern 1 Does EPA Have

Data To Satisfy This Requirement? (Yes, No, or Partially) Bibliographic Citation MRID # Must Additional

Data Be Submitted Under FIFRA 3(c)(2)(B)?



## 84 162-1 Aerobic Soil 162-3 Anaerobic Aquatic 162-4 Aerobic Aquatic **Mobility Studies:** 163-1 Leaching- Adsorption/Desorp. 163-2 Volatility (Lab) **Dissipation Studies-Field:** 164-1 Soil 164-2 Aquatic (Sediment) 164-3 Forestry 164-5 Soil, Long-term **Accumulation Studies:** 165-4 In Fish **Ground Water Monitoring Studies:** 166-1 Small-Scale Prospective **§158.440 SPRAY DRIFT** 201-1 Droplet Size Spectrum
202-1 Drift Field Evaluation

**FOOTNOTES:**1. 1=Terrestrial Food; 2=Terrestrial Feed; 3=Terrestrial Non-Food; 4=Aquatic Food; 5=Aquatic Non-Food(Outdoor); 6=Aquatic NonFood (Industrial); 7=Aquatic Non-Food (Residential); 8=Greenhouse Food; 9=Greenhouse Non-Food; 10= Forestry; 11=Residential Outdoor; 12=Indoor Food; 13=Indoor Non-Food; 14=Indoor Medicinal; 15=Indoor Residential.

## 85

Data Requirements for: **MSMA** Chemical Number: 013803

Data Requirement Use Pattern 1 Does EPA Have

Data To Satisfy This Requirement? (Yes, No, or Partially) Bibliographic Citation MRID # Must Additional Data

Be Submitted Under FIFRA 3(c)(2)(B)?

**§158.490 WILDLIFE AND AQUATIC ORGANISMS 71-1(a) Acute Avian Oral, Quail/Duck**  Yes 416100-02 **71-2(a) Acute Avian Diet, Quail** Yes 416100-03 **71-2(b) Acute Avian Diet, Duck** Yes 416100-04 71-3 Wild Mammal Toxicity No 71-4(a) Avian Reproduction, Quail No Yes 71-4(b) Avian Reproduction, Duck No Yes 71-5(a) Simulated Terrestrial Field Study No 71-5(b) Actual Terrestrial Field Study No

**72-1(a) Acute Fish Toxicity, Bluegill** Yes 400980-01, 417480-01 72-1(b) Acute Fish Toxicity, Bluegill (TEP) **72-1(c) Acute Fish Toxicity, RainbowTrout** Yes 417473-01

72-1(d) Acute Fish Toxicity, Rainbow Trout (TEP) No

**72-2(a) Acute Aquatic, Invertebrate** Yes 419406-05 72-2(b) Acute Aquatic, Invertebrate (TEP) 72-3(a) Acute Est/Mar Toxicity, Fish Yes 424141-02 72-3(b) Acute Est/Mar Toxicity, Mollusk Yes 424648-01, 400980-01 72-3(c) Acute Est/Mar Toxicity, Shrimp Yes 424141-01, 400980-01 72-3(d) Acute Est/Mar Toxicity, Fish (TEP) 72-3(e) Acute Est/Mar Toxicity, Mollusk (TEP) 72-3(f) Acute Est/Mar Toxicity, Shrimp (TEP) 72-4(a) Early Life Stage, Fish No YesData Requirement Use Pattern 1 Does EPA Have

Data To Satisfy This Requirement? (Yes, No, or Partially) Bibliographic Citation MRID # Must Additional Data

Be Submitted Under FIFRA 3(c)(2)(B)?



## 86 72-4(b) Life Cycle, Aquatic Invertebrate No Yes 72-5 Life Cycle, Fish No Yes 72-6 Aquatic Organism Accumulation No 72-7(1) Simulated Aquatic Field Study No 72-7(b) Actual Aquatic Field Study No **§158.540 PLANT PROTECTION** 122-1(a) Seedling Emergence (Tier I) No 122-1(b) Vegetative Vigor (Tier I) No 122-2 Aquatic Plant Growth (Tier I) No 123-1(a) Seedling Emergence (Tier II) Partial 419056-03 123-1(b) Vegetative Vigor (Tier II) Partial 419056-04 123-2 Aquatic Plant Growth (Tier II) Yes 417482-02, 417482-01 124-1 Terrestrial Field Study (Tier III) No 124-2 Aquatic Field Study (Tier III) No **§158.490 NONTARGET INSECT TESTING** 141-1 Honey Bee Acute Contact Yes 416100-07 141-2 Honey Bee Residue on Foliage No
141-5 Field Test for Pollinators No **§158.290 ENVIRONMENTAL FATE Degradation Studies-Lab:**  161-1 Hydrolysis 161-2 Photodegradation In Water 161-3 Photodegradation On Soil **Metabolism Studies-Lab:** 162-1 Aerobic Soil 162-3 Anaerobic Aquatic 162-4 Aerobic AquaticData Requirement Use Pattern 1 Does EPA Have

Data To Satisfy This Requirement? (Yes, No, or Partially) Bibliographic Citation MRID # Must Additional Data

Be Submitted Under FIFRA 3(c)(2)(B)?



## 87 **Mobility Studies:** 163-1 Leaching- Adsorption/Desorp. 163-2 Volatility (Lab) **Dissipation Studies-Field:** 164-1 Soil 164-2 Aquatic (Sediment) 164-3 Forestry 164-5 Soil, Long-term **Accumulation Studies:** 165-4 In Fish **Ground Water Monitoring Studies:** 166-1 Small-Scale Prospective **§158.440 SPRAY DRIFT** 201-1 Droplet Size Spectrum
202-1 Drift Field Evaluation

**FOOTNOTES:**1. 1=Terrestrial Food; 2=Terrestrial Feed; 3=Terrestrial Non-Food; 4=Aquatic Food; 5=Aquatic Non-Food(Outdoor); 6=Aquatic NonFood (Industrial); 7=Aquatic Non-Food (Residential); 8=Greenhouse Food; 9=Greenhouse Non-Food; 10= Forestry; 11=Residential Outdoor; 12=Indoor Food; 13=Indoor Non-Food; 14=Indoor Medicinal; 15=Indoor Residential.

## 88 **APPENDIX 9** REFERENCES ACS, 1975. Woolson, E.A., Ed. Arsenical Pesticides. American Chemical Society Symposium Series 7. American Chemical Society, Washington, DC. Abernathy, C.O., Calderon, R.L., Chappel, W.R. (Eds.), 1997. Arsenic Exposure and Health Effects. Chapman and Hall, New York. Anderson, Linda C.D. and Bruland, Kenneth W., 1991. Biogeochemistry in Natural Waters: The Importance of Methylated Species. Environ. Sci. Technol. , 25, 420-427. Aurelius, Lea., 1988. Investigation of Arsenic Contamination of Groundwater Occurring Near Knott, Texas. Report from the Texas Dept. of Agriculture, Austin, TX. Bartsch, H, J Nair. 2000. New DNA-based biomarkers for oxidative stress and cancer chemoprevention studies. Eur J Canc36:1229-1234. Bostwick, DG, EE Alexander, R Singh, A Shan, J Qian, RM Santella, LW Oberley, T Yan, W Zhong, X Jiang, TD Oberley. 2000. Antioxidant enzyme expression and reactive oxygen species damage in prostatic intraepithelial neoplasia and cancer. Cancer 89:123-134. Braman, Robert S. and Foreback, Craig C., 1973. Methylated Forms of Arsenic in the Environment. Science182:1247-1249. Bright, DA, M Dodd, KJ Reimer. 1996. Arsenic in subArctic lakes influenced by gold mine effluent: the occurrence of organoarsenicals and "hidden" arsenic. Sci Tot Environ180:165-182. Dickens, R., and Hiltbold, A.E., 1967. Movement and Persistence of Methanearsonates in Soil. Weeds 15:299-304. Eisler, Ronald. 1988. Arsenic Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review. Contaminant Hazard Reviews, Fish and Wildlife Service Report No. 12; Biological Report 85(1.12), January, 1988. Emsley, John, 1991. The Elements, 2nd ed. Oxford University Press, New York. Erickson, Denis and Norton, Dale, 1990. Washington State Agricultural Chemicals Pilot Study, Final Report. Washington State Dept. of Ecology, Ground Water Monitoring Section; Olympia, Washington 98504-8711.

## 89

Fletcher, JS, JE Nellessen, TG Pfleeger. 1994. Literature review and evaluation of the EPA food-chain (Kenaga) nomogram, and instrument for estimating pesticide residues on plants. Environ Chem 13:1383-1391. Garbarino, J. R. and Burkhardt, M. R., 1998; "Determination of Four Arsenicals in Natural Water Samples by HPLC-Hydride Generation-ICPMS." 40th Rocky Mountain Conference on Analytical Chemistry , Denver, Colorado; July 25-August 1, 1998. Gao, S, RG Burau. 1997. Environmental factors affecting rates of arsine evolution from and mineralization of arsenicals in soil. J Environ Qual 26:753-763. Goering, PL, HV Aposhian, MJ Mass, M Cebrian, BD Beck, MP Waalkes. 1999. The enigma of arsenic carcinogenesis: role of metabolism. Toxicol Sci49:5-14. Hem, J.D., 1985. Study and Interpretation of the Chemical Characteristics of Natural Water, Third Edition. U.S. Geological SurveyWater-Supply Paper 2254. Hughes, MF, LMD Razo, EM Kenyon. 2000. Dose-dependent effects on tissue distribution and metabolism of dimethylarsinic acid in the mouse after intravenous administration. Toxicol 143:155-166. Kreppel, H, JW Bauman, J Liu, JM McKim Jr, CD Klaasen. 1993. Induction of metallothionein by arsenicals in mice. Fun App Toxicol20:184-189. Lederer, W.H. and Fensterheim, R.J., Eds., 1983. Arsenic: Industrial, Biomedical, Environmental Perspectives. Proceedings of the Arsenic Symposium. Van Nostrand Reinhold Co., Inc., New York. Lindsay, W.L., 1979. Chemical Equilibria in Soils. John Wiley & Sons, Inc., New York. Masud, Karim, 2000. Arsenic in Groundwater and Health Problems in Bangladesh. Water Research 34:304-310. Moore, MM, K Harrington-Brock, CL Doerr. 1997. Relative genotoxic potency of arsenic and its methylated metabolites. Mut Res386:279-290

. NAS, 1977. National Academy of Sciences (Levander, O.A.; Committee Chair). Arsenic: Medical and Biological Effects of Environmental Pollutants. National Academy of Sciences , Washington, DC. NRC, 1999. Arsenic in Drinking Water. National Research Council. National Academy Press

.

## 90

Washington, DC. Nickson, R. McArthur, J., Burgess, W., Ahmed, K.M., Ravenscroft, P., Rahman, M. 1998. Arsenic Poisoning of Bangladesh Groundwater. Nature395:338-340.
Pierzynski, G.M, Sims, J.T., and Vance, G.F. 1994, Soils and Environmental Quality. CRC Press, Inc., Boca Raton, FL. Schlenk, D, L Wolford, M Chelius, J Steevens, KM Chan. 1997. Effect of arsenite, arsenate, and the herbicide monosodium methyl arsonate (MSMA) on hepatic metallothionein expression and lipid peroxidation in channel catfish. Comp Biochim Physiol 118C:177-183. Sposito, G. 1989. The Chemistry of Soils. Oxford University Press, Inc., New York. USEPA, 1997. Engineering Bulletin (EPA/540/S-97/500). Technology Alternatives for the Remediation of Soils Contaminated with As, Cd, Cr, Hg, and Pb. USEPA, Washington, DC. USEPA, 1992. Pesticides in Ground Water Database (EPA 734-12-92-001). USEPA, Washington, DC. Vahter, M. 2000. Genetic polymorphism in the biotransformation of inorganic arsenic and its role in toxicity. Toxicol Letters112-113:209-217. Wauchope, R.D. 1975. “Fixation of Arsenical Herbicides, Phosphate, and Arsenate in Alluvial Soils”, J. Environ. Qual., Vol. 4, no. 3 (1975) 355-358. EPA Accession No. 260782 and associated Nos. 259582 and 260061. Welch, Alan H., Westjohn, D.B., Helsel, Dennis R., Wanty, Richard B. United States Geological Survey Advance Report. Arsenic in Ground Water of the United States: Occurrence and Geochemistry. To be published in the Journal Ground Water in 2000. Yamanaka, K, S Okada. 1994. Induction of lung-specific DNA damage by metabolically methylated arsenics via the production of free radicals. Environ Health Pers102:37-40.

## 91 **APPENDIX 10**

ARSENIC IN GROUND WATER; USGS DATA

Printed March 2, 2000 http://co.water.usgs.gov/trace/pubs/usgs_as_county.jpeg