UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D. C., 20460 OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES PC Codes: 012501, 012502, 013802, 013803, 013806 DP Barcode: D327974 Date: March 29, 2006 ADDENDUM TO RED CHAPTER SUBJECT: Response to Registrant Phase I Error Only Comments:

Addendum to EFED RED Chapters for Organic Arsenicals Accounting for Updated Label Rates and Potential for Long Term Buildup in Soil [ Cacodylic Acid and its Sodium Salt ( D210451, D212449, D255226) and Sodium and Calcium Salts of Methanearsonic Acid ( MSMA / DSMA / CAMA; D277233)]

TO: Lance Wormell, Chemical Review Manager Reregistration Branch II Special Review and Reregistration Division ( 7508C)

FROM: Keara Moore, Chemist Environmental Risk Branch III Environmental Fate and Effects Division ( 7507C)

Thuy Nguyen, Senior Environmental Scientist Environmental Risk Branch III Environmental Fate and Effects Division ( 7507C)

THROUGH: Mark Corbin, Senior Environmental Scientist Environmental Risk Branch III Environmental Fate and Effects Division ( 7505C)

APPROVED Daniel Rieder, Branch Chief BY: Environmental Risk Branch III Environmental Fate and Effects Division ( 7507C) 2 Attached, please find the revised addendum to the EFED RED Chapters for Organic Arsenicals Accounting for Updated Label Rates and Potential for Long Term Buildup in Soil. Revisions have been made to the previous EFED RED Addendum ( DP Barcode 309100; February 3, 2006) to correct any mathematical/ typographical errors and provide clarification in areas identified by the registrants in their Phase 1 response. Additional comments were received regarding EPA's methodology and environmental fate results; these comments will be addressed after the 60 day Phase 3 public comment period scheduled to begin in April 2006.

The revisions made in this document do not alter any EFED conclusions from the previous assessment. Where appropriate, references to " degradation" have been replaced with the more suitable term " metabolism." Language has been added to clarify the discussion of the potential for transformation of organic arsenicals to inorganic arsenic and for transformation of dimethylated arsenical species to monomethylated species. A more thorough discussion of terrestrial field dissipation data is also included, presented in the soil accumulation section in the environmental fate appendix. 3 I. EXECUTIVE SUMMARY This addendum updates the ecological risk assessments for the organic arsenicals, which include cacodylic acid ( DMA; dimethylarsinic acid), sodium cacodylate ( DMA Na), monosodium methanearsonate ( MSMA), disodium methanearsonate ( DSMA), and calcium acid methanearsonate ( CAMA). Originally, these pesticides were assessed as two separate groups: the methylarsonate salts ( MSMA, DSMA, CAMA; DP Barcode D277233) and the cacodylates ( DMA and DMA Na; DP Barcodes D210451, D212449, D255226). Although risk estimates are still calculated based on the original groupings, these two groups are being included in a single document because the discussion of their fate characteristics has been combined. They all have similar chemical structures and similar environmental fate profiles, and they all contribute to total arsenic environmental loading, an important issue in the current assessment. The updated drinking water assessment ( DP Barcode D309098) also considers these compounds as a group.

For MSMA and DSMA, risk estimates are updated based on new master labels that have lowered application rates for most uses. The new master label for cacodylic acid ( dimethylarsinic acid; DMA) had not been completed at the time of this assessment and so has not been included here. No new toxicity data have been considered and so calculation of risk is all based on toxicity conclusions from the original assessment. With the lower application rates, most risk quotients ( RQs) have dropped as well, but the overall risk conclusions have not changed. There are no exceedances of levels of concern ( LOC) for aquatic species, including fish, invertebrates, and plants. All categories of terrestrial exposure lead to exceedances of LOCs, including small mammals, avian species, and upland and semi aquatic plants. Because of lower applications rates, in many cases the terrestrial exceedances are not as great as in the original assessment and there are fewer exceedances in the highest risk category. The endangered species portion of this assessment has not been updated. The original assessment found that endangered species risk quotients exceed the Agency's LOC for birds, mammals and terrestrial plants from exposure to DSMA and MSMA. There are still exceedances in each of these categories. In the original assessment, however, one use led to exceedances for freshwater fish and the new rates lead to RQs below the LOC.

The discussion of the environmental fate and transport of organic arsenicals has been expanded. Greater attention is paid to the possibility of transformation of these compounds to the more toxic inorganic arsenic. Additionally, the issue of long term accumulation of total arsenic in soil after repeated applications of organic arsenicals has been considered. Field studies, monitoring data, and modeling all indicate that accumulation of arsenical in soil is likely. Based on PRZM modeling of soil concentrations, maximum rates of MSMA, DSMA, and DMA on turf are expected to exceed the ecological soil screening levels set by the EPA's Office of Solid Waste and Emergency Response ( OSWER). Modeling suggests that applications of these products to cotton will not lead to soil level exceedances. 4 II. PESTICIDE USE CHARACTERIZATION This update is based on master labels for MSMA and DSMA. These labels, provided by the registrants on 11/ 14/ 05, have not yet been finalized but are assumed to invalidate all previous labels. Variance from these rates could change the conclusions of this assessment.

The main agricultural application for both MSMA and DSMA is as a pre/ post emergent herbicide on cotton applied prior to the first bloom. The only other agricultural uses of MSMA and DSMA supported by master labels are in non bearing orchards, citrus, and vineyards. Non agricultural uses of MSMA and DSMA include use on turf and non crop uses. The turf use is both residential and commercial, including residential lawns, sod farms, golf courses, parks, and other areas. The non crop use includes drainage ditch banks, rights of way, storage yards and similar areas.

The maximum application rates for all of these uses are included in Table 1. Although applied as different parent compounds, MSMA and DSMA end up as the same chemical in the environment, monomethyl arsonic acid ( MMA). Rates for both are reported here in acid equivalents ( ae) to represent the amount applied as MMA. Labels for all uses specify that the maximum number of applications applies to " either DSMA or MSMA or their combination per crop, per year." Exposure was therefore estimated based on the maximum MMA application rate for each use for either MSMA or DSMA. The maximum rate for each use, marked in bold on Table 1, was considered in exposure estimates. For the non crop use, the master label single application rate is lower than that allowed by previous labels, but the number of applications has increased so the annual application rate has not changed. For all other uses, the master label annual application rate is lower than the rates considered in the previous assessment.

III. EXPOSURE CHARACTERIZATION A. Environmental Fate and Transport Summary The environmental fate section has been updated to discuss the organic arsenicals ( MSMA, DSMA, CAMA, DMA) as a group rather than in separate documents. It has been expanded to include consideration of the potential for long term accumulation of total arsenic in soil and of metabolism of organic arsenicals to inorganic arsenic. The general conclusions about the fate and transport of organic arsenicals have not changed, but re evaluation of the available data has led to revision of several modeling inputs. A detailed discussion of environmental fate properties is provided in Appendix A and summarized here. References to all of the registrant studies and open literature reports taken into account in this fate characterization are included in the Appendix.

MSMA, DSMA, and CAMA are salts of the dibasic weak acid MMA. In aqueous solution, they dissociate to MMA and the associated companion cations. DMA is a weak acid with two methyl groups attached to the central arsenic atom, rather than one as in MMA. These pesticides are all non volatile solids that are highly soluble in water. 5 Table 1. Application Rates for MSMA and DSMA, based on 11/ 14 Master Labels.

Use Maximum App. Rate ( lb ae/ A) Max. No. Apps. Application Interval Application Method DSMA 1.7 1 n/ a g round or aerial Cotton 1.7 2 1   3 weeks ground ( directed)

Turf 2.5 4 14 days ground spray Orchards, Citrus, Vineyards 1 3.7 3 not specified ground ( directed)

Non crop 2 3.9 4 10   14 days ground spray Grass for seed 3 3.3 1 n/ a n ot specified MSMA 1.7 1 n/ a g round or aerial Cotton 1.7 2 not specified ground ( directed)

Turf  Sod Farms4  Golf Course4 3.4 2.2 4 10   14 days ground spray Orchards, Citrus, Vineyards 1 3.7 3 10   14 days ground spray Non crop 2 3.9 4 10   14 days ground spray Grass for seed 3 5.3 1 n/ a n ot specified 1 Non bearing only  not to be used within one year of harvest. Restricted to spot treatments in Florida. 2 Non crop = " drainage ditchbanks, rights of way, storage yards and similar areas". 3 Pacific Northwest only. 4 Sod farm rate allowed on sod farms and established Bermuda and Zoysiagrass. Golf course rate allowed on athletic fields, golf courses, and parks.

Environmental fate laboratory studies show that organic arsenicals are stable under all tested abiotic conditions; they do not degrade by hydrolysis or by aquatic or soil photolysis. Arsenicals can be subject to microbial metabolism in soil under aerobic and anaerobic conditions. The occurrence, rate, and products of this metabolism are variable, dependent on environmental conditions. Persistence of applied parent compounds can range from days to years, depending on soil properties and ambient conditions such as soil moisture, temperature, chemical concentration, bacterial population, and amount of organic matter. Regardless of the form it takes, however, the total amount of arsenic present does not change; these arsenicals and their transformation products, in combination with arsenic from the natural background and from other anthropogenic sources, maintain the total, immutable arsenic load. Arsenic from pesticides is not lost but redistributed and transformed throughout the environment ( plants, animals, air, soil, sediment, water) into other arsenic containing substances.

Metabolism rates do not appear to depend linearly on arsenical concentration; the kinetics are therefore not necessarily first order and so " half life" may not be an appropriate 6 constant for all concentrations. Despite the uncertainty, first order half lives have been calculated for modeling purposes and as a convenient measure to compare laboratory results. The estimated half lives, used in EFED's current models, may underestimate the faster initial rate of metabolism but adequately portray the overall transformation and so are assumed to be protective for chronic exposure, a major concern for arsenicals. The modeled aerobic soil half life for MMA, based on two studies with similar results, is 240 days. No anaerobic soil half life was determined for MMA. For DMA, the Agency derived aerobic soil half life is 173 ± 115 days with a standard upper 90% confidence limit on the mean of 240 days. The anaerobic soil half life for DMA was calculated to be 128 ± 38 days with a standard upper 90% confidence limit on the mean of 168 days.

The effects of environmental factors on the rate of arsenical metabolism are complex and poorly defined, with different studies leading to conflicting results. An increase in temperature leads to increased metabolism. The observed influences of soil organic matter or applied arsenical concentrations are contradictory. The effect of aerobic versus anaerobic conditions on metabolism rates is also ambiguous.

Potential metabolites of applied arsenicals include volatile alkylarsines and inorganic arsenic ( as arsenate or arsenite) along with carbon dioxide. Additionally, DMA may be present as a metabolite of MMA as well as applied directly. As with the rate, the metabolism pathway is sensitive to environmental conditions in indeterminate ways with the major metabolites occurring in widely variable proportions. Transformation to volatile alkylarsines, the only metabolism route that would directly reduce soil arsenic loading, has been shown to be possible in certain circumstances but is generally not expected to be a major route of dissipation. A maximum of 35% of applied MMA is expected to be present as DMA at any one time. Theoretically, there is some possibility for MMA to metabolize to DMA, but significant transformation has not been observed in current acceptable field or laboratory studies. Observed metabolism of MMA and DMA to inorganic arsenic has ranged from undetected after several years to more than 80% transformation in several months. Generally, arsenate [ As( V)] is expected to be the dominant species of inorganic arsenic, but in reducing conditions, arsenite [ As( III)] may be more stable.

Some of the variability in metabolism processes is associated with variability in sorption, because microbial transformation is only likely to occur while compounds remain dissolved in pore water. Mobility of arsenicals is typically very low to intermediate and appears to be independent of organic matter content. Instead, sorption is higher in soils with higher percentage of clay or with more iron or aluminum content. One study found by direct comparison that all arsenicals were more strongly sorbed than phosphate in the increasing order: phosphate < DMA < arsenate ~ MMA. The lowest non sand Kd for MMA is 11.4 mL/ g. For 20 tested soils, the range of Kds spans two orders of magnitude ( 0.5 to 95 mL/ g, mean 37 mL/ g). For DMA, the lowest non sand Kd from 16 soils is 8.2 mL/ g ( range 8.2 to 33 mL/ g, mean 18 mL/ g).

Surface Water Exposure Conclusions. Arsenical pesticides and their metabolites may be transported to surface waters and sediments through runoff water, eroding soils, or drift 7 during application. These routes of exposure are likely to lead to local, temporal elevations above background arsenic levels in surface water bodies. Tier I surface water modeling for MSMA and DSMA estimated surface water concentrations as high as 360 ppb, as MMA. Limited targeted monitoring has found elevated total arsenic levels in surface water bodies in MMA use areas. In cotton growing areas in Mississippi, surface water concentrations of MMA up to 5 ppb were detected. In golf courses in Florida, 6 of 10 ponds tested had elevated arsenic levels with a maximum of 34 ppb, as total arsenic. These monitoring results are discussed in more detail in the organic arsenical Drinking Water Assessment ( DP Barcode 309098).

Soil Accumulation Conclusions. The relative immobility of arsenicals along with arsenic's elemental nature make buildup in soil after repeated applications an important consideration. Controlled field studies, monitoring targeted to pesticide use areas, and soil modeling results all indicate that soil buildup is a likely result of long term organic arsenical application. Arsenic accumulation is likely to be limited to the top layers of soil, with studies suggesting that it is unlikely to occur at depths greater than 30 cm. These conclusions are discussed in more detail in the terrestrial exposure section.

B. Aquatic Exposure For surface water contamination, the estimated environmental concentrations ( EEC) were calculated using GENEEC2 ( GENeric Estimated Environmental Concentration). This Tier I model uses the soil/ water partition coefficient and degradation kinetic data to estimate runoff from a ten hectare field into a one hectare by two meter deep " standard" pond. This model is designed as a coarse screen and estimates conservative pesticide concentrations in surface water from a few basic chemical parameters and pesticide label use and application information. This model is used to screen chemicals in order to determine which ones potentially pose sufficient risk to warrant higher level modeling. Additional information on this model can be found at: http:// www. epa. gov/ oppefed1/ models/ water/ index. htm.

The input parameters used to estimate the surface water EECs for aquatic exposure assessment were selected from the environmental fate data submitted by the registrant and from the open literature, and in accordance with USEPA OPP EFED water model parameter selection guidelines, Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version II, February 28, 2002. The maximum rate for each use, either from MSMA or DSMA, was modeled. Both are present in aqueous solution as monomethyl arsonic acid ( MMA) and are therefore modeled in acid equivalents ( ae) to represent the amount applied as MMA. With the exception of the sorption coefficient, which was reduced from 13 mL/ g to 11.2 mL/ g, all modeling inputs are the same as in the original RED ( DP Barcode 277233). The general input values used in the model runs are included in Appendix B, along with the model outputs. The results are presented in Table 2. 8 Table 2. EECs for MMA in the aquatic environment.

1 The pesticide with the highest application rate for each use was modeled as the acid equivalent MMA. 2 All application rates are based on ground application. The cotton use is labeled for aerial application as well but a higher rate is allowed for ground application.

C. Terrestrial Exposure 1. Animals Terrestrial wildlife are exposed to pesticides through the plant or animal material that they consume as food. The Kenaga nomogram as modified by Fletcher, a series of tables that relate food item residues to pesticide application rate based on a database of actual measured pesticide residue values on plants, are used to estimate exposure to terrestrial organisms. The TREX model ( version 1.22) was used to calculate EECs, presented in Table 3, for MMA from application of MSMA and DMSA. The equations and assumptions used by TREX are discussed in Appendix C.

Table 3. EECs ( ppm MMA) on terrestrial food items resulting from direct applications of DSMA and MSMA.

1 The pesticide with the highest application rate for each use was modeled as the acid equivalent MMA. Crop ( Chemical) 1 Application rate 2 ( lbs ae/ A) Number of Applications Peak EEC ( ppb as MMA)

Cotton ( DSMA) 1.74 2 84 Non crop ( MSMA) 3.86 4 360 Orchard ( DSMA) 3.70 3 260 Turf; max ( MSMA) 2.23 4 310 Turf; golf ( MSMA) 3.35 4 210 Predicted Maximum EEC on Food Items Crop ( Chemical) 1 Appl. rate ( lbs ae/ A) No. of Appl. Short grasses Broadleaf plants & insects Seeds Cotton ( DSMA) 1.74 2 734 413 46 Non crop ( MSMA) 3.86 4 2557 1438 160 Orchard ( DSMA) 3.70 3 2071 1165 129 Turf; max ( MSMA) 3.35 4 2225 1251 139 Turf; golf ( MSMA) 2.23 4 1482 833 93 9 2. Plants Exposure to upland and wetland plants is estimated using the TerrPlant ( v1.0) screening model and the EECs are presented in Table 4. TerrPlant estimates potential exposure using default assumptions for runoff and spray drift. It should be emphasized that TerrPlant is only used for estimating environmental concentrations based on a single application. Most uses of MSMA and DSMA allow for multiple applications. TerrPlant model details are included in Appendix D.

Table 4. EECs ( lb MMA/ A) in off site terrestrial environments resulting from drift and runoff from single applications of DSMA and MSMA.

1 The pesticide with the highest application rate for each use was modeled, both as the acid equivalent MMA. 2 All application rates are based on ground application. The cotton use is labeled for aerial application as well but a higher rate is allowed for ground application. 3 Sheet runoff + drift. 4 Channelized runoff + drift.

3. Soil Accumulation Long term accumulation of pesticides in soil is not generally considered in ecological risk assessments. Organic arsenicals are unique, however, due to the elemental nature of arsenic. Arsenic does not degrade; along with arsenicals' relative immobility in soil, this makes long term impacts an important consideration. Field studies, monitoring of soil in use areas, and modeling all suggest that it is likely that applied arsenicals will build up in soil over time. Arsenic accumulation is likely to be limited to the top layers of soil, with studies suggesting that it is unlikely to occur at depths greater than 30 cm. A more detailed discussion of the potential for arsenic to accumulate in soil is included in the Environmental Fate and Transport section in Appendix A.

Registrant terrestrial field dissipation studies have measured the impact of one season of pesticide applications on soil concentrations. Two studies at rates similar to the maximum labeled cotton and turf rates found that a single year of application is unlikely Runoff ( lb ae/ A) Total Load Crop ( Chemical) 1 Appl. rate2 ( lbs ae/ A) Upland3 Semi Aquatic4 Drift only ( lb ae/ A) Upland3 Semi Aquatic4 Cotton ( DSMA) 1.74 0.087 0.87 0.017 0.104 0.887 Non crop ( MSMA) 3.86 0.193 1.93 0.039 0.232 1.969 Orchard ( DSMA) 3.70 0.185 1.85 0.037 0.222 1.887 Turf; golf ( MSMA) 2.23 0.167 1.67 0.033 0.201 1.709 Turf; max ( MSMA) 3.35 0.111 1.11 0.022 0.134 1.137 10 to lead to significantly elevated soil arsenic levels. Since most of the applied arsenic remained in the top 6 inches of soil, however, repeated application may lead to significant accumulation. Higher application rates of DMA, possible in some of the non crop uses, led to elevated soil arsenic levels after a single year of application. Few studies have evaluated the longer term impact of repeated application of organic arsenicals. Those that have been conducted have conflicting results, with some reporting no arsenic buildup despite very high application rates and others finding substantial buildup at rates similar to current labels. Most reports do not contain adequate explanations to account for observed loss of arsenic. Monitoring of soil in areas where arsenicals are known to have been applied, including golf courses and roadside areas, has found significant increases of arsenic levels relative to background concentrations. In Miami, an area with low background arsenic levels, arsenic was the most common contaminant found in documented soil violations at golf courses.

Soil accumulation values are generated by PRZM as part of the process of modeling runoff concentrations. PRZM was run with a modified version of the pe4 v01 shell program to estimate arsenic accumulation in the top 10 cm of soil. Results are presented in Table 5. Maximum application rates for MMA and DMA on turf and cotton were used and the modeling assumed median sorption ( Kd = 30 for MMA and Kd = 20 for DMA). The annual application rates for DMA on non crop areas and ornamentals are nearly 50% higher than the turf rate, and so would be expected to lead to higher soil concentrations. Because of limitations in the available data and modeling capabilities, soil concentrations were modeled as total arsenic, rather than speciated forms. Application rates were therefore calculated to represent applied arsenic and infinite half lives were used to capture all forms of arsenic that may be present. Routes of dissipation accounted for in the modeling include runoff, leaching, and soil erosion; transformation to volatile species and plant uptake are not accounted for. Of available scenarios, PA turf and NC cotton scenarios led to the highest soil concentrations. Because soil concentrations are based on local application rather than input from an entire watershed, use of a percent cropped area ( PCA) factor was unnecessary.

Table 5. Modeled soil concentrations for total arsenic resulting from long term application of MMA or DMA.

Parent Compound Use App. rate ( lbs As/ A) No. of Applications Chronic EEC 1 ( ppm, total arsenic)

MSMA Cotton 0.95 2 13 Turf 1.80 4 45 DMA Cotton 0.65 1 2 Turf 2 ( lawn edging) 4.18 4 77 1 " Chronic" concentrations are the upper 90th percent confidence limit on the annual average, or the 1 in 10 year peak annual concentration. 2 Application rate based on master label from 12/ 12/ 05. 11 IV. RISK CHARACTERIZATON A. Risk Estimation A risk quotient ( RQ) based approach is used in this assessment, comparing the ratio of exposure concentrations to effects endpoints with predetermined levels of concern ( LOCs). Although risk is often defined as the likelihood and magnitude of adverse ecological effects, the risk quotient based approach does not provide a quantitative estimate of likelihood and/ or magnitude of an adverse effect. The primary change in these RQs, compared to those in the 2001 RED ( DP Barcode D277233), is that they are calculated using EECs based on application rates from updated master labels. No new toxicity data have been considered and most toxicity endpoints used in calculations have not changed. For terrestrial avians and small mammals, the LD50s that were used in calculating acute RQs was adjusted for the purity of the test material. This calculation is reported in the original RED, but for those earlier calculations, the unadjusted LD50s were used. Further discussion of the toxicity can be found in the 2001 RED.

1. Non target Aquatic Animals Acute RQs for aquatic organisms, based on the aquatic EECs listed in Table 2, are shown below in Table 6. All calculated RQs for fish and aquatic invertebrates are < 0.05 and below the level of concern ( LOC). ( This table updates Table 10 from the 2001 RED).

Table 6. Acute risk quotients for MMA exposure to aquatic organisms.

Freshwater RQ 1 Estuarine/ marine RQ 1 Crop ( Chemical) Peak EEC ( ppb) Fish2 Invert. 3 Fish4 Invert. 5 Cotton ( DSMA) 84 < 0.05 < 0.05 * *

Non crop ( MSMA) 360 < 0.05 < 0.05 < 0.05 < 0.05 Orchard ( DSMA) 260 < 0.05 < 0.05 * *

Turf; max ( MSMA) 310 < 0.05 < 0.05 < 0.05 < 0.05 Turf; golf ( MSMA) 210 < 0.05 < 0.05 < 0.05 < 0.05 1 RQ = EEC/ LC50 ( fish) or EC50 ( invertebrates) 2 LC50s = 112 ppm for DSMA and 12 ppm for MSMA 3 EC50s = 153 ppm for DSMA and 77.5 ppm for MSMA 4 LC50 = 323 ppm for MSMA 5 EC50 = 160 ppm for MSMA * No toxicity data for DSMA and marine/ estuarine organisms were presented, so no RQs were calculated. 12 2. Non target Aquatic Plants Risk quotients for aquatic plants, based on toxicity values from the original RED and EECs determined using GENEEC2, are summarized below in Table 7. ( This table updates Table 12 from the 2001 RED). No risks to non endangered or endangered aquatic plants exceed the level of concern of 1.

Table 7. Risk quotients for MMA exposure to aquatic plants. RQ 1 Crop ( Chemical) Peak EEC ( ppb) Non endangered Vascular spp. 2 Non endangered Non vascular3 Endangered Vascular spp. 2 Cotton ( DSMA) 84 < 0.1 < 0.1 < 0.1 Non crop ( MSMA) 360 < 0.1 0.13 < 0.1 Orchard ( DSMA) 260 < 0.1 0.17 < 0.1 Turf; max ( MSMA) 310 < 0.1 0.11 < 0.1 Turf; golf ( MSMA) 210 < 0.1 < 0.1 < 0.1 1 RQ = EEC / EC50 ( non endangered species) or NOEC ( endangered species) 2 vascular ( duckweed) EC50' s and NOECs: 72.7 ppm & 20.5 ppm ( DSMA), 53 ppm & 29 ppm ( MSMA) 3 non vascular ( algae or diatom) EC50' s: 1.5 ppm ( DSMA), 2.8 ppm ( MSMA) 13 3. Non target Terrestrial Animals Acute and chronic risk quotients for terrestrial small mammals are summarized below in Table 8. These RQs are calculated based on toxicity values from the original RED, adjusted for the purity of the test material, and EECs determined using TREX. ( This table updates Tables 3 and 17 from the 2001 RED). These RQs are applicable to mammals with body weights of 35 g that consume green vegetation or insects equivalent to 66% of their body weight ( herbivores and insectivores) or seeds equivalent to 15% of their body weight ( granivores). The purpose of this addendum is only to update RQs from the 2001 RED, so RQs have not been calculated for mammals with body weights of 10 g or 1000 g, as would be done for a current assessment. Most of these acute RQs, excepting those for granivores, exceed the endangered species LOC of 0.1 while some also exceed the restricted use and high risk LOCs of 0.2 and 0.5. All but 2 of the chronic RQs exceed the chronic risk LOC of 1.

Table 8. Risk quotients for small mammals ( 35 g) from exposure to MMA.

1 Acute RQ = EEC / LD50, corrected for body weight; LD50s = 1599 mg/ kg ( rat) for DSMA, 157 mg/ kg ( rat) for MSMA, adjusted for purity of test material. 2 Chronic RQ = EEC/ NOEC, corrected for body weight; NOEC = 100 ppm ( rat) for MMA *** exceeds LOCs for high risk ( 0.5), restricted use ( 0.2), and endangered species ( 0.1) ** exceeds the LOCs for restricted use and endangered species * exceeds the LOC for endangered species * exceeds the chronic risk LOC ( 1) Acute RQs 1 Chronic RQs 2 Crop ( Chemical) Herbivore Insectivore Granivore Herbivore Insectivore Granivore Cotton ( DSMA) 0.17* 0.10* < 0.1 7.3* 4.1* 0.46 Non crop ( MSMA) 6.04*** 3.39*** < 0.1 26* 14* 1.6*

Orchard ( DSMA) 0.48** 0.27** < 0.1 21* 12* 1.3*

Turf; max ( MSMA) 5.25*** 2.95*** < 0.1 22* 13* 1.4*

Turf; golf ( MSMA) 3.50*** 1.97*** < 0.1 15* 8.3* 0.93 14 Acute RQs for avian species are presented below in Table 9. These values are based on toxicity values from the original RED, adjusted for the purity of the test material, and EECs determined using TREX. ( This table updates Table 4 from the 2001 RED). As with terrestrial mammals, most RQs, with the exception of granivores, exceed the restricted use and endangered species LOCs of 0.2 and 0.1 while some also exceed the high risk LOC of 0.5.

Table 9. Risk quotients for avians from exposure to MMA. Acute RQ 1 Crop ( Chemical) Herbivores Insectivores Granivores Cotton ( DSMA) 0.16* < 0.1 < 0.1 Non crop ( MSMA) 1.53*** 0.86*** 0.1*

Orchard ( DSMA) 0.54*** 0.30** < 0.1 Turf; max ( MSMA) 1.33*** 0.75*** < 0.1 Turf; golf ( MSMA) 0.89*** 0.50*** < 0.1 1 RQ = EEC / LC50; LC50s = 4695 mg/ kg ( DSMA) and 1667 mg/ kg ( MSMA), both for northern bobwhite, adjusted for purity of the test material. *** exceeds LOCs for high risk ( 0.5), restricted use ( 0.2), and endangered species ( 0.1) ** exceeds the LOCs for restricted use and endangered species * exceeds the LOC for endangered species 15 4. Non target Terrestrial and Semi Aquatic Plants Risk quotients for terrestrial and semi aquatic plants exposed to drift and/ or runoff are summarized below in Table 10. These are based on toxicity values from the 2001 RED and EECs determined using TerrPlant. Most RQs for endangered and non endangered plants, both upland and semi aquatic, exceed the LOC of 1 for exposure from runoff and drift. None of the drift only RQs exceed the LOC.

Table 10. Risk quotients for terrestrial and semi aquatic plants from a single application of DSMA or MSMA.

1 RQ = EEC / EC25. For total loading use seedling emergence EC25 ( 1.25 and 0.116 lb ai/ A for DSMA and MSMA, respectively). For drift use vegetative vigor EC25 ( 0.354 and 0.418 lb ai/ A for DSMA and MSMA, respectively) 2 RQ = EEC / NOEC. For total loading use seedling emergence NOEC ( 0.30 and 0.018 lb ai/ A for DSMA and MSMA, respectively). For drift use vegetative vigor NOEC (< 0.30 and 0.14 lb ai/ A for DSMA and MSMA, respectively) 3 Upland EEC based on sheet runoff + drift; Semi Aquatic EEC based on channelized runoff + drift. * exceeds the LOC ( RQ > 1) for nontarget plants Non Endangered RQs 1 Endangered RQs 2 Crop ( Chemical) Upland3 Semi Aquatic 3 Drift Only Upland3 Semi Aquatic 3 Drift Only Cotton ( DSMA) < 1 < 1 < 1 < 1 3* < 1 Non crop ( MSMA) 2* 17* < 1 13* 109* < 1 Orchard ( DSMA) < 1 1.5* < 1 < 1 6* < 1 Turf; golf ( MSMA) 1.7* 15* < 1 11* 95* < 1 Turf; max ( MSMA) 1.1* 9.8* < 1 7.4* 63* < 1 16 5. Soil Accumulation Because it is not typical for EFED to assess environmental risk resulting from accumulation of pesticides in soil, there are no established methods for calculating RQs based on this type of exposure. The EPA's Office of Solid Waste and Emergency Response ( OSWER) has established procedures for dealing with the issue of contaminated soils. Rather than calculating RQs resulting from accumulation of arsenic in soil, EFED has compared the estimated soil concentration to ecological soil screening levels ( SSL) for arsenic set by OSWER in March, 2005 ( OSWER, 1995). SSLs are defined as " concentrations of contaminants in soil that are protective of ecological receptors that commonly come into contact with soil or ingest biota that live in or on soil." More information about how these levels were set can be obtained at http:// www. epa. gov/ ecotox/ ecossl/ pdf/ eco ssl_ arsenic. pdf.

Table 11 presents the SSLs set to protect plants, birds, and mammals. Insufficient data were available to set an SSL for soil invertebrates. Arsenic SSLs are based on concentrations of total arsenic. The soil concentrations estimated using PRZM, also as total arsenic, are included for comparison. Application of either MMA or DMA at the maximum rate for cotton does not lead to exceedance of any SSLs, but the maximum rates of MMA or DMA applied to turf exceed SSLs for all groups.

Table 11. Soil EECs for MSMA and DMA compared to OSWER arsenic SSLs.

Parent Compound Use Chronic EEC ( ppm, total arsenic) OSWER Eco SSLs ( mg/ kg dry weight)

MSMA Cotton 13 Plants 18 Turf 45 Avian Wildlife 43 DMA Cotton 2 Mammalian Wildlife 46 Turf ( lawn edging) 77 Soil Invertebrates NA B. Risk Description 1. Risks to Aquatic Organisms Use of MSMA and DSMA present minimal risk to aquatic species, including fish, invertebrates, and plants. In the original assessment, the one exception found to this conclusion was risk to freshwater fish from the very high application rate of MSMA to orchards. The lower application rates on the current master label have reduced this risk quotient below the LOC. 17 2. Risks to Terrestrial Organisms With the lower application rates, most terrestrial risk quotients ( RQs) have dropped but the overall risk conclusions have not changed. Application of organic arsenicals presents risk to all categories of terrestrial organisms, including small mammals, avian species, and upland and semi aquatic plants. Because of lower applications rates, in many cases the exceedances are not as great as in the original assessment. Additionally, there are fewer exceedances in the highest risk category.

3. Federally Threatened and Endangered ( Listed) Species Concerns The endangered species portion of this assessment has not been updated. The original assessment found that application of DSMA and MSMA present risk to endangered species for birds, mammals and terrestrial plants. There are still exceedances in each of these categories. The original assessment found risk to endangered freshwater fish from the high application rate for MSMA on orchards. Limiting this application rate lowered the risk for freshwater fish below the LOC.

The Agency's preliminary risk assessment for endangered species indicates that organic arsenic applied as a pesticide results in a determination of " no effect" to listed aquatic animal and plant species on an acute or chronic basis. RQs exceed endangered species LOCs for terrestrial plants, birds, and mammals. These findings are based solely on EPA's screening level assessment and do not constitute " may affect" findings under the Endangered Species Act.

4. Uncertainties The uncertainties of this risk assessment were discussed in the original assessments. Further discussion of the uncertainty regarding the environmental fate and transport properties of organic arsenicals has been included in Appendix A, the Environmental Fate and Transport section. Uncertainties in the modeling input parameters are discussed in the organic arsenicals Drinking Water Assessment ( DP Barcode D309098).

One additional source of uncertainty is relevant to this addendum. All exposure estimates for MSMA and DSMA in this document are based on application rates as MMA, the acid equivalent of the methanearsonate salts. For determining terrestrial risk, in some cases it is unclear which form of the parent compound was used as the active ingredient used to determine toxicity. Some of these endpoints may have been based on concentrations as MSMA rather than as MMA. If the toxicity is based on arsenic as MSMA, the units of the toxicity estimate would have to be converted MMA to be appropriately compared to the exposure as MMA. This would lead to a lower toxicity value and therefore a higher risk quotient and a higher estimate of risk. It is possible, then, that risk was underestimated in some of the terrestrial categories. Even if true, though, this would not lead to significant changes in the risk conclusions. 18 APPENDIX A:

ENVIRONMENTAL FATE OF ORGANIC ARSENICALS 19 Physicochemical Properties MSMA, DSMA, and CAMA are salts of the dibasic weak acid monomethylarsonic acid ( MMA; also variously abbreviated in other documents and the published literature as MMAA or MAA, for methanearsonic acid). In aqueous solution these compounds dissociate into MMA and the associated ions, either sodium or calcium. Cacodylic acid ( DMA, for dimethylarsonic acid) is a weak acid with two methyl groups attached to the central arsenic atom, rather than one as in MMA. In some formulations, DMA is mixed with its sodium salt ( DMA Na), which in aqueous solution is also dissociated to DMA and a sodium ion. Chemical structures and some physicochemical properties for MSMA, DSMA, DMA, and DMA Na are presented in Tables A1a and A1b below. This group of compounds is referred to as " organic arsenicals" throughout this document. Most environmental fate studies have been conducted on MSMA or DMA as representatives of the monomethylated and dimethylated species, respectively.

Table A1a. Physicochemical Properties for MSMA and DSMA DSMA MSMA Molecular Structure As O O O C H 3 Na + Na + As OH O O C H 3 Na +

Empirical Formula CH3AsNa2O3 CH4AsNaO3 Molecular Weight 183.92 161.94 CAS No. 144 21 8 2163 80 6 PC Code 013802 013803 Melting Point ( º C) > 300 116 121 Density ( g/ mL) 1.04 1.65 Vapor Pressure ( mm Hg) 1 x 10 7 7.5 x 10 7 log Kow < 1 < 1 Solubility: Water ( mg/ L) 3.4 x 105 104 Methanol 2.6 x 105 16 Hexanol 25 0.005 pKa1,2 ( approx.) 4.0, 9.0 4.0, 9.0 20 Table A1b. Physicochemical Properties for Cacodylic Acid Cacodylic Acid ( DMA) Sodium Cacodylate ( DMA Na)

Molecular Structure O || CH3  As  OH | CH3 O || CH3  As  O Na+ | CH3 Empirical Formula C2H7AsO2 C2H6AsNaO2 Molecular Weight 138.0 160.0 CAS No. 75 60 5 124 65 2 PC Code 012501 012502 Melting Point ( º C) 192 194 77   79.5 Density ( g/ mL) 1.10 1.10 Vapor Pressure ( mm Hg) Non volatile No data Kow < 0.028 No data Solubility: Water ( mg/ L) ~ 1 to 3 x 106 No data Methanol 3.63 x 105 No data Hexanol 1.02 x 10 1 No data pKa 6.2 6.2 As weak acids, the form in which MMA and DMA are present is dependent on pH, which affects the degree of association with hydrogen ions and therefore the charge of the species. For MMA, the three possible species are symbolized H2MMA, HMMA1, and MMA2. Reported titration studies for MSMA and DSMA yield base strengths for the anions corresponding to pKa values for the acid MMA of 4 and 9. Under agriculturally relevant conditions, then, HMMA1 would dominate at pH 5 to 7 as approximately 90% to 99% of the total, while at pH 9, it would be approximately equal to the amount present as MMA2. DMA can be present as neutral cacodylic acid or as the cacodylate anion and has a pKa of 6.2. At a pH of 5, then, neutral cacodylic acid dominates at approximately 94% of the total, while at pHs of 7 to 9, the anionic species is dominant, going from 87% of the total to more than 99%. In the environment, chemical speciation is in dynamic flux, depending on variations in pH and affected by transport, mixing, diffusion, etc., in accordance with principles of chemical equilibria and kinetics. 21 Degradation and Metabolism ( Rate and Environmental Conditions) Environmental fate laboratory studies show that organic arsenicals are stable under all tested abiotic conditions. Registrant submitted studies of DMA and MMA found both compounds to be stable to hydrolysis at all pHs ( MRIDs 42059201 and 42363001). DMA and MMA were also found to be stable to photolysis in both aquatic and soil environments ( DMA: MRIDs 41662601 & 41662602; MMA: MRIDs 41903902 & 41903901).

Organic arsenicals can be subject to microbial metabolism in soil under aerobic or anaerobic conditions. The occurrence, rate, and products of this metabolism are variable, dependent on environmental conditions. The observed persistence of organic arsenicals in aerobic soil has ranged from weeks to years, depending on soil properties and ambient conditions such as soil moisture, temperature, chemical concentration, and amount of organic matter. The extreme of this range is seen in several registrant submitted studies of microbial metabolism which observed no transformation at all ( MRIDs 42616001, 42572601, 43036101). These studies were determined to be scientifically sound but were found to be not fully acceptable because they provided no explanation for this result in light of well established evidence of organic arsenical metabolism. Although these studies demonstrate that there are conditions in which metabolism does not occur, possibly due to non viable soils, this assessment is based on the understanding that transformation of organic arsenicals is an important, although variable, process.

Adding to the complexity is that metabolism rates do not appear to depend linearly on organic arsenical concentration; in some studies, transformation decreased with increasing concentration while in others, concentration had no effect on metabolism. Hence, the kinetics are not necessarily first order, and " half life" is therefore not necessarily an appropriate constant for all concentrations. Keeping this uncertainty in mind, first order half lives have been calculated as required by EFED's current models and also as a convenient measure to compare results from laboratory studies. The Agency derived values for a DMA half life from four studies representing a total of six soils. Together, these yielded an effective average aerobic soil half life for DMA of 173 + 115 days with a standard upper 90% confidence limit on the mean of 240 days ( Woolson and Kearney, 1973; Woolson, 1982; Gao and Burau, 1997; and MRID 44767601). The average half life of DMA in three anaerobic ( flooded) soils was 128 + 38 days with a standard upper 90% confidence limit on the mean of 168 days ( Woolson and Kearney, 1973). For MMA, two studies in two soils both resulted in aerobic soil half lives of approximately 240 days ( Gao and Burau, 1997; MRID 44767601). No anaerobic soil half life was determined for MSMA. The studies on which these estimates are based are discussed in more detail below and the calculations are also described in the surface water modeling section of the Drinking Water Assessment ( DP Barcode D309098).

Some of the variability in metabolism processes is associated with variability in sorption processes. Soil microbial metabolism of organic arsenicals only occurs while the compounds remain dissolved in pore water ( NRC, 2003). As the organic arsenicals sorb 22 to soil, they become less accessible to microbes and therefore less likely to be metabolized ( Woolson and Kearney, 1973). Sorption variability, discussed in more detail in the mobility section ( p. 28), is largely controlled by soil properties including the clay content, the iron and aluminum content, and the soil pH ( Wauchope, 1975; Matera and La Hecho, 2001). Laboratory studies have shown that in some situations, significant sorption of arsenic compounds may occur within hours of application, while in others, a large portion of applied arsenic remains in water soluble forms for days or months after application ( Onken and Adriano, 1997; Sarkar et al., 2005). Remobilization of sorbed arsenic with changing environmental conditions is also possible ( Matera and La Hecho, 2001).

The effects of other environmental factors on the rate of organic arsenical metabolism are complex and poorly defined with different studies leading to conflicting results. An increase in temperature has been shown to lead to increased metabolism ( Akkari et al., 1986; Gao and Burau, 1997) but results on the impact of soil organic matter or applied organic arsenical concentrations are contradictory ( Dickens and Hiltbold, 1967; Von Endt et al., 1968; Woolson and Kearney, 1973; Woolson, 1982; Akkari et al., 1986; Gao and Burau, 1997).

The influence of aerobic versus anaerobic conditions on metabolism rates is also ambiguous. Based on a comparison of the results of studies of MMA applied to an aerobic soil and to an anaerobic sediment/ aquatic system, the registrants conclude that aerobic metabolism is more significant than anaerobic metabolism ( MAATF, 2005). After one year of incubation, 35% of the parent MMA remained in aerobic soil ( MRID 44767601), while in the anaerobic system, only 3% of applied MMA had been metabolized ( MRID 44767602). Both studies ended with a significant amount of unidentified arsenic compounds bound to the soil ( 10 25%). Two studies by Woolson also concluded that greater metabolism occurred in aerobic than in anaerobic conditions. In one study, an average of 24% of 14C from applied DMA remained after 24 weeks incubation of 100 ppm DMA in three aerobic soils while 39% remained in flooded soils ( Woolson, 1973). In the other study, the amounts of applied DMA remaining after 60 days were similar at soil moisture levels between 77% and 125% of field capacity but in flooded soils ( 230% field capacity), more parent compound remained, indicating slower metabolism in anaerobic conditions ( Woolson, 1982).

Two more recent studies led to the opposite result, finding that metabolism of organic arsenicals is more significant in anaerobic conditions. In 3 soils incubated at 30 ° C for 120 days, Akkari found half lives in flooded conditions ( 150% field capacity) of approximately 1 month while in low moisture conditions, ( 20% field capacity), the halflives were 2 to 5 months. One of these soils was also tested at 75% field capacity and found to have a half life between the flooded and low moisture soils. In this study, the reported half life also includes " deactivation by processes such as salt formation, irreversible absorption, and ion exchange" ( Akkari et al, 1986). Gao and Burau ( 1997) incubated one soil at a range of soil moistures for 70 days and found significantly higher mineralization in flooded conditions (> 350 g H20/ kg soil). In soil with moisture levels   350 g H20/ kg soil, 88% to 97% of applied DMA was recovered as parent compound, 23 while for flooded soils, recovered parent compound was as low as 13%, indicating a significant increase in metabolism in anaerobic conditions.

Of the studies reviewed for this document, the most complete, systematic investigation of the metabolism of organic arsenicals under variable conditions is by Gao and Burau ( 1997). In particular, this study is valuable because the products are speciated, including trapping of volatiles, with very good recovery. The mass balance is greater than 90%, even for inorganic arsenic, so, unlike some studies reviewed here, these half lives include only metabolism and not other routes of dissipation such as sorption. Gao and Burau were motivated by noticing differences in published results on transformation processes ( rates and products) and by a concern for the potential for arsenic to accumulate in soils. The extent to which an applied organic arsenical and its arsenic containing byproducts accumulate locally depends on both mineralization and volatilization. The 1997 Gao and Burau study serves to systematically complement, and, to a great extent, unify existing data. The study is designed to measure the influence of four factors concentration, soil moisture, temperature, and soil amendment with organic carbon ( cellulose) on the rates and routes of transformation of organic arsenicals in soil. Gao and Burau primarily tested DMA in the form of sodium cacodylate, although production of volatile arsines was measured for MMA, sodium arsenate ( AsV), and sodium arsenite ( AsIII), and one treatment compared the metabolism rates of DMA and MMA under the same conditions. The study was limited to one California soil, a Sacramento silty clay ( noncalcareous).

Gao and Burau's results show the great influence of soil environmental conditions on transformation rates. After 70 days of incubation, depending on conditions, the amount of parent cacodylate remaining ranged from a high of about 97% to a low of about 13% 1. Under all conditions, production of volatile arsines was less than 0.5% of the applied arsenic. Arsenite was not a detected product under these conditions and both DMA and MMA metabolized without detection of methylation or demethylation. The amount of parent compound remaining at the end of the study depended strongly on all tested factors. Unless noted otherwise, the following tests were all carried out with DMA at 100 mg As/ kg soil and soil moisture content of 350 g water/ kg soil ( approximately 1/ 3 bar suction [ 0.03 Mpa]).

1) Soil Moisture. As mentioned above, metabolism of DMA was measured at five soil moisture contents of 50, 250, 350, 450, and 550 g water/ kg soil [ from approximately 7% ( 23.7 MPa suction) to 81% ( 0.0005 MPa) of saturation], at 22 oC. Mineralization to arsenate increased with soil moisture from 2.7% at the lowest soil moisture to 86.6% at the highest, showing the tremendous influence of soil water.

1 Gao and Burau report some of their results as " percent mineralized", calculated as 100% minus the measured percent of parent compound remaining. The authors explain this as an assumption for the sake of consistency. The reported percent mineralized, then, includes the < 0.5% volatilized as well as any unrecovered arsenic. The actual concentrations of inorganic arsenic resulting from degradation were measured directly with 91% recovery, so 9% is the most unrecovered arsenic which may be accounted for in the reported demethylation. In this discussion, in order to avoid this uncertainty, the percentage of parent compound remaining was determined based on the reported percent mineralized. 24 2) Temperature. At 5 and 25 oC, mineralization was approximately 5.2 and 23.8%, respectively. This result is roughly as would be predicted from the Arrhenius relationship which yields rate doubling for every 10 oC increase in temperature. [ The 23.8% mineralization result can be compared with the result of 12.1% mineralization, from the soil moisture series, as a measure of variability under essentially the same conditions, except for an uncorrected 3 oC difference in temperature.]

3) Concentration. At increasing cacodylate concentrations equivalent to arsenic concentrations of 10, 30, and 100 mg As/ kg soil at 25 oC, decreasing percentages of cacodylate mineralized were approximately 82, 31 and 24%, respectively, indicating that the rate process is not first order in concentration. One possible reason for the slowing of metabolism at increasing concentrations could be toxicity to soil microorganisms, however, the two upper concentrations correspond to application rates much higher than those currently labeled.

4) Organic Matter. Increasing cellulose additions of 0.0 ( unamended), 0.2, 1.0, and 5.0 g per 100 g of soil ( original soil organic carbon content of 1.8%) with sodium cacodylate added at the arsenic equivalent of 10 mg As/ kg soil at 250C decreased mineralization from around 77% down to around 49%. ( As a measure of variability in this experiment under the same conditions, the first value of 77% can be compared directly with the 82% result from the concentration experiment above.) Some reports show the same trend of decreasing mineralization with increasing concentration of organic matter ( e. g., Woolson, 1982), but others report the opposite trend ( e. g., Dickens and Hiltbold, 1967). Types of added organic matter were generally different, and could perhaps account for the differences. However, in view of the sensitivity of metabolism to the other cited factors, lack of extremely careful control of experimental conditions could also be a major factor for the difference.

5) Arsenical Species. Metabolism rates of MMA and DMA were compared by applying both at 100 mg As/ kg soil under the same environmental conditions. After 70 days at 220C, more than twice as much DMA as MMA had metabolized. Parent DMA remained at only 26.7% of the applied, while 57.1% of the applied MMA remained.

Using the Gao and Burau data to estimate an " effective half life" for DMA ( realizing that the process is apparently not first order with concentration), the Agency calculated halflives for each trial, based on the initial and final concentrations of parent compound. These were interpolated as a function of soil moisture at the tested arsenic equivalent concentration of 100 mg/ kg soil to the standard 75% of 1/ 3 bar soil moisture content using the soil moisture retention function ( the logarithm of the absolute value of soil tension vs. soil water concentration) which the authors gave for the Sacramento silty clay soil. The interpolation gives a moisture concentration of approximately 27%, or 266 g water per kilogram of dry soil, and a corresponding DMA half life of 642 days ( 1.8 years). In tandem, the Agency then made a simple, proportionate adjustment of the rate constant corresponding to this half life at the 100 mg/ kg concentration to the more agriculturally relevant 10 mg/ kg arsenic equivalent ( 18 mg/ kg cacodylic acid). This range is relatively low when compared to most study concentrations which were typically 25 10 to 180 ppm in cacodylic acid. This calculation leads to a normalized DMA half life ( at 75% of 1/ 3 bar soil moisture and an arsenic equivalent concentration of 10 mg/ kg) of 102 days. The more limited data for MMA was converted by comparison to the DMA normalization, resulting in a normalized half life of 241 days. Additional reports contributing to the discussion of organic arsenical soil metabolism include two published laboratory studies authored by Woolson and others2. In the first, 14C cacodylic acid was applied at three concentrations ( 1, 10 and 100 ppm DMA; arsenic equivalent 0.5, 5, and 54 ppm) to each of three soils of varying iron and aluminum content ( Woolson and Kearney, 1973). Soil moistures were brought to 75% of field capacity and the temperature was 25 0C. For several reasons this study does not meet current guideline standards but was not specifically cited as deficient in the 1986 Agency review and provides valuable information. The authors found that " rate of application had no appreciable effect on disappearance" and so reported the amount of 14C remaining in each soil after 32 weeks as an average from the three application rates. Based on these final values, the Agency calculated assumed first order aerobic half lives of 325, 245, and 106 days, from a loamy sand, a silty clay loam, and a clay loam, respectively. These are considerably longer than the half lives reported in the 2001 RED ( 117, 89, and 48 days; DP Barcodes D210451, D212449, D255226), which were calculated based on the 14C remaining at 24 weeks rather than 32 weeks. Recalculation based on the complete length of the study led to these longer half lives which are more representative of the long term behavior of applied organic arsenicals and closer to the guideline standard of a study length of one year. Less data were reported for anaerobic ( flooded) soil metabolism and so half lives were calculated based on data from 24 weeks for cacodylic acid applied at 100 ppm. Apparent anaerobic half lives, as reported in the 2000 RED, were 86, 138, and 159 days. Due to the different dataset used, these half lives are not directly comparable to the calculated aerobic half lives. They would be expected to follow the same trend, with the cacodylic acid metabolizing more slowly over time. Again, these estimated results are dependent on professional judgment and interpretation. The nature of transformation products revealed in this and other studies is integrated below in the " metabolites" subsection.

Woolson et al ( 1982) applied cacodylate at an initial arsenic equivalent concentration of 10 ppm to a Mattapeake silt loam soil treated under several different conditions of soil moisture ( 77 230% of field capacity) with unamended soil and with a variety soil amendments. After 60 days of aerobic incubation at 25 0C, the residual cacodylic acid was reported to average approximately 15 30%. Results were similar under all conditions. Based on these published data, the estimated average aerobic soil half life ( assumed first order) for all unamended treatments was approximately 20 days. The estimated half life from amended soil, with a higher organic matter content, was approximately 31 days.

2 These studies were submitted under Accession No. 259582 and associated Accession Nos. 260061 and 260782. The study by Woolson and Kearney ( 1973) was specifically evaluated at the time but Woolson et al, 1982 was not. Both studies were discussed in the 1986 Agency review and in the 2000 RED for cacodylic acid. 26 Again, none of these published studies meet current Guideline and GLP criteria. Halflife estimates for all were based on single time intervals, rather than complete time series. The Woolson studies generally had poor recoveries with the loss accounted for through inferred metabolism. These studies appeared formally in peer reviewed scientific publications, however, as is normal for most scientific work outside of the regulatory process. They have been cited in the literature numerous times and they were submitted by the registrant in the past. These studies provide a body of evidence on the environmental fate of organic arsenicals that cannot be dismissed.

One GLP aerobic soil metabolism study is available for MSMA and has been rated acceptable according to guideline standards ( MRID 44767601). In this study, 14C labeled MSMA was applied to a sandy loam soil at 6.1 ppm ( 2.7 ppm as arsenic) and incubated at 25 ° C and 75% of field moisture capacity for 1 year. Based on measurements taken throughout the course of the study, the estimated first order half life for MMA was 240 days. This half life is calculated from the percent of the applied dose remaining as the parent compound. As much as 11% of the applied dose was bound to soil and unextractable, so it is possible that this half life takes into account some amount of sorption as well as transformation. The metabolism did not occur at a constant rate; 50% of the parent compound had dissipated by 60 days, but after this time, metabolism slowed to the extent that approximately 35% of the applied dose remained after one year. DMA was formed as a metabolite in this study and data on its formation and decline led to a half life of 242 days, as discussed in the surface water modeling section.

Metabolites Potential metabolites of applied DMA and MMA include volatile alkylarsines and inorganic arsenic ( as arsenate or arsenite) along with carbon dioxide. Cacodylic acid may be present as a metabolite of MMA as well as an applied parent compound. The formulas and names of the principal species are listed below in Table A2. 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 likely associated with the sensitivity to the ambient conditions, mentioned above, although some variability is likely due to difficulty in analysis as well. Regardless of the form it takes, however, the total amount of arsenic present does not change; these organic arsenicals and their transformation products, in combination with arsenic from the natural background and from other anthropogenic sources, maintain the total, immutable arsenic environmental load. Arsenic from pesticides is not lost but redistributed and transformed throughout the environment ( plants, animals, air, soil, sediment, water) into other arsenic containing substances.

The only metabolism pathway that could directly reduce soil arsenic loading is transformation to volatile alkylarsines. Microbial species capable of metabolizing dissolved organic arsenical compounds to gaseous arsines have been identified ( Cox and Alexander, 1973; Turpeinen, 2001). Dimethylarsine and trimethylarsine are the most likely volatile products of soil metabolism ( Cox and Alexander, 1973; Woolson, 1977). Some early studies of arsenic fate in soil concluded that volatilization was a major route of dissipation. Woolson ( 1973) attributed losses of applied arsenic of up to 60% to 27 Table A2. Arsenic species commonly found in environmental samples.

" Organic" Species " Inorganic" Species dimethylarsine ( CH3) 2AsH arsenate [ As( V)] AsO4 3

trimethylarsine ( CH3) 3As arsenite [ As( III)] AsO3 3

cacodylic acid ( dimethylarsenic acid, hydroxydimethylarsine oxide) ( CH3) 2AsO( OH)

volatilization. This conclusion was inferred indirectly from mass balance calculations and was not confirmed analytically. In a later study designed to investigate the possibility of volatilization, Woolson found that less than 0.5% of applied arsenic was trapped as volatile arsines from unamended soils, and only 1.4% was found in amended soils ( 1982). Several other studies found volatilization of up to 15% of applied arsenic from amended soils, but no more than 2.2% volatilization was found in unamended soils ( Woolson, 1977; Akins and Lewis, 1976; Cheng and Focht, 1979). More recent studies with improved analytical techniques have achieved mass balance without volatilization ( Onken and Adriano, 1997; MRID 44767601) and other experiments designed specifically to consider volatilization have not found alkylarsines produced at greater than 0.5% of applied arsenic ( Gao and Burau, 1997; Turpeinen et al, 2001). Metabolism to volatile alkylarsines is possible under certain conditions but is generally not likely to be a major route of dissipation. The possibility of volatilization was therefore not included in calculations on the fate of applied organic arsenical pesticides.

Other routes of metabolism include methylation and demethylation. DMA has two methyl groups attached to a central arsenic, MMA has one, and inorganic arsenic has none. Theoretically, any of the methyl groups on DMA or MMA are subject to removal, while one methyl group could be added to convert inorganic arsenic to MMA which could be further methylated to DMA. In fact, not all of these transformations are likely to occur. There is some uncertainty associated with all speciation of soil arsenic due to limitations in extraction and analytical techniques. Organic arsenical species may be transformed to some extent during the process of extraction and measurement. This is not an issue when results are reported as total arsenic, as done in many studies, but those results are less useful in a discussion of metabolites.

Application of MMA may lead to both DMA and iAs as end products. A registrant aerobic soil metabolism study found that after 1 year, 35% of MMA applied at 6.1 ppm remained present as the parent compound, 32% was present as DMA, and 19% had evolved as carbon dioxide, indicating demethylation to inorganic arsenic ( MRID 44767601; Acceptable). Conversely, Gao and Burau ( 1997) detected no DMA resulting from application of MMA despite significant metabolism to inorganic arsenic. In the few other laboratory studies reviewed for this document that speciated end products, variable DMA resulting from application of MMA was found up to a maximum of 9% ( MRID 43314801; MRID 44767602; Von Endt et al., 1968). Field studies found some DMA 28 after application of MMA, but typically in very small amounts ( MRID 42526001; MRID 42616201). Transformation to inorganic arsenic is discussed further below.

For metabolism of DMA, there are fewer studies available with speciated results. A registrant submitted aerobic soil metabolism study detected MMA in soil samples following application of DMA, but both the study author and the EPA reviewer concluded that the MMA detected was an artifact of the analytical methodology ( MRID 42616001; Unacceptable). Gao and Burau ( 1997) found that after 70 days, up to 82% of applied DMA had metabolized, but only inorganic arsenic, and not MMA, was detected. Given the relative stability of MMA, it is unlikely that MMA metabolized too quickly to accumulate, so this result suggests that DMA metabolizes directly to inorganic arsenic by loss of both methyl groups, rather than stepwise going through a monomethylated intermediate. As discussed above, other experiments have shown that Gao and Burau's results with respect to MMA are not true in all situations. Their results for DMA are more conclusive than those for MMA, however, because DMA's metabolism was investigated under at least 15 sets of varying conditions, while MMA was only studied in one. In another laboratory study, Woolson et al. ( 1982) applied DMA at 10 ppm ( as arsenic) in aerobic and anaerobic soils, either unamended or amended with sewage sludge, dairy manure, or hay. In unamended soils, the highest reported detection of MMA was at 0.8 ppm as arsenic. In amended soils in anaerobic conditions, detection of MMA went as high as 3.6 ppm as arsenic. A registrant submitted terrestrial field dissipation study looked for MMA in soil after two applications of DMA at 24 lb/ A ( MRID 43485301; Supplemental). A small amount of MMA ( 1.65 ppm as MSMA, equivalent to 0.76 ppm as arsenic) was detected immediately after the second application and was undetected by the end of the study. Based on the lack of significant transformation seen in these studies, MMA was not treated as a metabolite of DMA in modeling potential exposure to both species, although there is some uncertainty in this assumption.

Inorganic forms of arsenic are generally more toxic than the organic forms, so it is very important to assess the possibility of mineralization of organic arsenical pesticides to arsenate [ As( V)] and arsenite [ As( III)]. Results of studies investigating conversion to inorganic arsenic are extremely variable, ranging from no mineralization in one year to approximately 80% mineralization in 2 months. The only GLP study carried out for a full year, as required by FIFRA guidelines, found that 19% of MMA applied at 6.1 ppm mineralized to inorganic arsenic. Mineralization, as measured by production of carbon dioxide, was most rapid in the first three months and then slowed, with very little, if any, occurring in the period from 9 to 12 months ( MRID 44767601; Acceptable). These results are consistent with the findings of several shorter term published studies which determined that metabolism to inorganic arsenic is most likely to occur soon after application ( Abdelghani et al., 1977; Von Endt et al., 1968; Dickens and Hiltbold, 1967). All of those studies, which lasted several weeks to several months, ended with inorganic arsenic at less than 19% of the applied amount, suggesting that as a reasonable upper bound. 29 Two other studies, however, present very different conclusions. One study applied DMA at the arsenic equivalent of 10 ppm and found that in aerobic conditions, 52% was demethylated after 60 days, while in anaerobic conditions, 27% mineralization occurred. Mineralization was significantly lower in soils amended with sewage sludge, manure, or hay ( Woolson, 1982). In another study, DMA was applied at 10 to 100 ppm in a variety of conditions and incubated for 70 days. The least amount of mineralization, all less than 7% of the applied, occurred in low moisture soils and at low temperatures. In moister soils at 22 25 ° C, demethylation ranged from approximately 12% to approximately 86% ( Gao and Burau, 1997). In the one treatment where MMA was applied, approximately 43% demethylation occurred, relative to 73% for DMA in the same conditions ( 100 ppm as arsenic, 22 ° C, soil moisture approximately at field capacity). Terrestrial field dissipation studies also suggest that conversion to inorganic arsenic can occur, with total soil arsenic levels remaining elevated over control values even after applied parent compounds are no longer detectable ( MRIDs 43485301, 42526001). These results are discussed in more detail in the soil buildup section ( p. 30).

In the one available aerobic soil laboratory study where there was analysis for arsenite [ As( III)], a possible mineral transformation product, it was not detected ( Gao and Burau, 1997). Consistent with this result, and as part of the same study, applied arsenite was converted to arsenate. It is generally accepted and consistent thermodynamically that arsenate rather than arsenite is the prevalent form in aerobic soils. There were no reported tests for arsenite production from cacodylic acid under anaerobic or flooded conditions. However, comparable concentrations of arsenate and arsenite can thermodynamically coexist under certain environmental conditions, including those found in groundwater and surface water and such concentrations have been measured, as discussed in the monitoring section of the Drinking Water Assessment ( DP Barcode D309098).

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 varies tremendously, but indicates intermediate to low mobility. Laboratory studies have shown that in some situations, significant sorption of arsenic compounds may occur within hours of application, while in others, a large portion of applied arsenic remains in water soluble forms for days or months after application ( Onken and Adriano, 1997; Sarkar et al., 2005). Remobilization of sorbed arsenic with changing environmental conditions is also possible ( Matera and La Hecho, 2001).

To fulfill data requirements, the registrant submitted a published non FIFRA, non GLP study by Wauchope ( 1975) for Agency review ( part of 27 June 1986 review package, EPA Accession No. 260061) as well as one FIFRA GLP study ( MRID 41651906; 30 Supplemental). Additional information about the pH dependency of sorption of arsenic was obtained from an open literature report by Smith ( 1999).

Wauchope measured the simple batch equilibrium adsorption of 16 Mississippi River alluvial flood plain soils, none of which were in the " sand" textural class, two of which had a " clay" texture, and 14 of which had a " loam" texture. The main study objectives were to correlate sorption with soil properties and to make direct experimental comparison of the relative sorptions of phosphate ( as H2PO4 1 , a relatively immobile soil chemical), cacodylate/ cacodylic acid, arsenate/ arsenic acid, and methylarsonate/ methylarsonic acid ( at an adjusted pH of 5.6 for all soils and chemicals). Phosphate, a large magnitude agricultural, industrial, and naturally occurring mineral with established relative immobility, is a well suited benchmark for comparing the suite of organic arsenicals. Phosphorous and arsenic are also adjacent periodic table group Vb.

Wauchope equilibrated arsenical slurries at a 1: 20 soil: solution ratio in systems experimentally fixed at a pH of 5.6. Wauchope did not explicitly calculate sorption coefficients, so the Agency calculated simple soil sorption coefficients ( Kd) based on the results at the low end initial concentrations, 3.2 x 10 4 M for cacodylate and 2.5 x 10 4 M for arsenate and MMA. The Kds for cacodylate ranged from 8.2 to 33 mL/ g with a median of 16 mL/ g and for MMA, the range was from 17 to 95 mL/ g with a median of 28 mL/ g. The results were relatively independent of organic matter content. ( Pseudo organic carbon sorption coefficients ( Koc) range from around 700 to 7000 mL/ g oc, but do not correlate with the Kd values given above.) Wauchope found that sorption was best correlated with clay and iron and aluminum oxide content. In this respect, the two organic arsenicals behaved like the inorganic arsenate and phosphate. By direct comparison, all arsenicals were more strongly sorbed than phosphate in the increasing order: phosphate < DMA < arsenate ~ MMA. Although arsenicals sorb more strongly than phosphate, phosphate is still expected to strongly compete for binding sites ( Matera and Le Hecho, 2001).

Additional Kd values for MMA were obtained from a registrant adsorption/ desorption study following standard FIFRA guidelines ( MRID 41651906). MMA was equilibrated with soil at a 1: 10 ratio with initial concentrations ranging from 1 to 18 ppm. Four soils were tested with average Kds of 0.5 mL/ g ( sand), 11.4 mL/ g ( silty loam), 18.7 mL/ g ( silty clay), and 39.4 mL/ g ( sandy loam). Again, there was no correlation between organic matter content and sorption. Based on these two studies, the lowest non sand Kd values for DMA and MMA were 8.2 mL/ g and 11.4 mL/ g, respectively.

pH could have a major influence on sorption because of the anionic nature of the tested chemicals. Wauchope experimentally fixed the pH at 5.6 for the 16 soil/ water systems ( natural soil pHs ranged from 4.8 to 7.6) so correlation with pH cannot be determined from this study. At a pH of 5.6, DMA would be expected to be present primarily in the protonated, uncharged form. At neutral to alkaline pHs, however, the negatively charged cacodylate ion dominates. Generally, anionic ( negatively charged) species tend to be less strongly sorbed by soil surfaces which tend to maintain a negative ( repelling) charge; the surface charge also tends to increase ( become more negative) at higher pHs. Thus, at 31 more nearly neutral or alkaline pHs, sorption coefficients could be considerably lower than those given above, and mobility correspondingly higher. A recent publication on arsenate and arsenite sorption in Australian soils ( Smith et al., 1999) provides some insight on the potential degree of importance of pH on sorption of acid and anion couples. Although somewhat tenuous, Wauchope's four species might be considered a homologous series with the congeners phosphorus or arsenic at the central core. Therefore, Smith's arsenate and arsenite data would serve as a relational link to the possible effect of pH on the mobility of cacodylic acid/ cacodylate.

In four soils selected to vary widely in chemistry and mineralogy, Smith showed that in the experimentally adjusted pH range of 2.0 to 8.5 ( adjusted with dilute nitric acid or sodium hydroxide) and ionic strength range of 0.003 to 0.3 mol/ L ( adjusted with sodium nitrate) there are complicated pH and ionic strength dependencies. However, the Agency observes from the data in the more environmentally relevant range of pHs from 5 to 8.5 and ionic strength of 0.003 molar, that arsenate decreased in sorption with increasing pH by a maximum factor of only approximately two. This decrease is not dramatic compared with the much larger variability in simple, standard sorption Kds which Wauchope measured above and which Smith measured for a total of 10 soils ( the four for the detailed pH and ionic strength dependencies plus six others for a rudimentary subset for Kd measurement and soil correlations). Smith's simple Kds for arsenate in the 10 soils were distributed in the range from 1.7 to 62 mL/ g.

Although Smith did not report any calculated sorption coefficients for arsenite, his comments and plotted data of sorbed amounts show arsenite to be moderately less sorbed than arsenate, consistent with its lower negative charge. A more recent study comparing sorption of arsenate and arsenite confirms this results, finding that arsenite is more available to dissolution in water than arsenate ( Onken and Adriano, 1997) However, in contrast with the decreasing sorption of arsenate in the four soils in the pH range of 5 to 8.5 and ionic strength of 0.003 M, Smith found sorption of arsenite in two soils was fairly constant from approximately pH 2 to pH 5, but increased significantly from approximately pH 5 to the maximum reported pH 7 for arsenite. Sorption increased by a maximum factor of approximately five in the most sensitive of the two soils. Effect of ionic strength on sorption of arsenite was small and complex in the tested ranges of pH and ionic strength. Overall, the Agency concludes from Smith's surrogate data in the more environmentally relevant range of pHs from 5 to 8.5 and ionic strength of 0.003 molar, that sorption of cacodylate/ cacodylic acid should not decrease ( increase mobility) dramatically with pH when compared to the much larger variability in soil sorption found with different soils.

Soil Buildup/ Field Studies The relative immobility of arsenicals along with arsenic's elemental nature make buildup in soil after repeated applications an important consideration. Arsenic does not break down; it can only be redistributed through runoff, leaching, erosion, volatilization, or plant uptake. Even at the lowest non sand Kds of 8.2 and 11.4 mL/ g, sorption of arsenicals would be significant, and the range of possible Kds extends to much higher values, especially if the possibility of transformation to more strongly sorbing inorganic 32 arsenic is considered. As a result, significant leaching is unlikely in most conditions and the potential for runoff is likely to decrease over time. Volatilization is also likely only in specific circumstances, leaving soil erosion and plant uptake as the sole routes of dissipation of organic arsenicals applied to soil.

Several terrestrial field dissipation studies have been conducted by registrants to explore the environmental fate of applied organic arsenicals. They are discussed here with the qualification that, although most have been determined to be scientifically sound, unless otherwise indicated here, they have not been recognized as fulfilling the data requirement because they do not provide an adequate theoretical explanation for observed loss of arsenic.

In the most recent study, rated supplemental, DMA was applied twice at 24 lb a. i./ A to bare ground plots of sandy loam soil ( MRIDs 42843101 and 43485301). The annual application rate used in this study, 48 lb a. i./ A, is considerably higher than that allowed on cotton ( 1.2 lb a. i./ A/ yr; 12/ 12/ 05 Master Label) but it is similar to the labeled rate on non crop areas and ornamentals ( 44 lb a. i./ A/ yr; 12/ 12/ 06 Master Label). DMA in the top 6 inches of soil reached a peak concentration of 32.8 ppm ( as DMA) 10 days after the second application and was non detectable by 243 days. MSMA reached a peak concentration of 1.65 ppm immediately following the second application.

Total arsenic peaked at 20.37 ppm ( as As), also 10 days after the second application. Following the peak, total arsenic decreased more slowly than DMA with little dissipation in the final 6 months, reaching 10.68 ppm on day 366. These values can be compared to the average arsenic background of 2.00 ± 0.24 ppm found in the top 6 inches of the control plot. Some of the dissipation in the top soil layer can be accounted for by increasing arsenic in the next soil layer. At the 6 to 12 inch depth, total arsenic increased steadily from 1.95 ppm prior to DMA application to 4.47 ppm ( as As) on day 366. Beginning on day 182, slightly elevated arsenic levels were observed in the 12 to 18 inch soil layer as well but a statistical evaluation found these results to be inconclusive. This shows a significant persistence of applied arsenic, with the study author concluding that " by [ day 93] the organic arsenicals  were largely mineralized, leaving elemental arsenic in the surface soil."

Two other registrant studies monitored the terrestrial field dissipation of MSMA. In one, MSMA was applied twice to cotton in a silty loam soil at 2 lb a. i./ A ( MRID 42616201). In the other, turf application was simulated by applying MSMA three times at 4.95 lb a. i./ A to bare ground sandy loam ( MRIDs 42526001 and 4322801). In both, residual MSMA decreased to undetectable levels, by 2 months in the cotton field and by day 365 in the bare ground plot. Both studies showed some transformation to DMA, but at very low levels, peaking at less than 0.5 ppm in a short time frame after application. In the cotton study, soil arsenic levels were " variable with no discernable pattern of increase or decline." In the bare ground study, total arsenic levels in the top 6 inches of soil were consistently higher in treated plots than in control plots and higher than initial values. Total soil arsenic peaked three times, corresponding to the three applications. In the study period following the third peak, days 41 to 365, the average total arsenic in the 33 treated plots was 12.16 ± 0.77 ppm compared to an average in the control plot over the same period of 9.79 ± 1.76 ppm. It is difficult to quantify the impacts on total soil arsenic, in large part due to the variability in measurements in the control plot, but these results suggest that arsenic levels in the treated plot were elevated over background levels by at least 2 ppm.

These studies show that except at high application rates, a single year of application is unlikely to lead to quantifiable buildup of soil arsenic, but they show that a large fraction of applied arsenic remains in the top layers of soil, opening the possibility that soil buildup is a long term concern. As a worst case scenario, all applied arsenic would remain in the top soil layer with no dissipation. In the DMA field dissipation study ( MRIDs 42843101 and 43485301), the worst case scenario would lead to arsenic levels in the top 6 inches of soil approximately 12.9 ppm3 higher than background. As discussed above, by the end of the study, total arsenic in the top layer of soil is elevated at least 8 ppm over background levels, meaning that nearly two thirds of the applied arsenic remained in the top layer of soil at the end of a year, and additional arsenic was found from 6 to 12 inches.

At the application rates used in the studies of MSMA on cotton and turf, the worst case scenario would have led to soil arsenic levels of approximately 0.9 ppm and 3.3 ppm above background, respectively3. The first value is low enough to be within the natural range of variation in measurements of background arsenic levels, so it is impossible to identify arsenic resulting from pesticide application. For the bare ground plot, the elevated soil level, at least 2 ppm greater than the control, is a significant portion of the worst case level of 3.3 ppm, showing that a substantial amount of the applied arsenic remained in the top 6 inches of soil. After repeated applications for multiple years, then, soil arsenic levels could be expected to increase, possibly to levels of concern.

Because long term impacts are of concern, it is important to look at studies conducted over a longer period of time. One older registrant study applied MSMA and DMA to cropped fields at annual rates of up to 6 lb ai/ A and 7.5 lb ai/ A, respectively ( MRID 117165). After 6 years soil arsenic levels in the top 6 inches of soil, although somewhat uncertain because of large variation in residue levels, were as high as 14 ppm and 15.5 ppm, respectively, compared to an average background level of 11 ppm. This shows some buildup, although less than worst case calculations would predict. The study authors hypothesized that the arsenic loss was due to volatilization. The authors concluded, however, that " after 6 annual applications all rates of MSMA and DMA resulted in poorly defined but significant buildup of arsenic" in the 0 6 inch layer.

An incomplete review of the open literature found several long term field dissipation studies with some reporting no arsenic buildup despite very high application rates and others finding substantial buildup at rates similar to current labels. Robinson ( 1975)

3 Calculations of soil arsenic levels for worst case scenarios assumed that all applied arsenic remained in the top 15 18 cm of soil. The applied rate was converted to mg As/ ha and then divided by the mass of one hectare of soil to a depth of 15 18 cm, estimated to be approximately 2.25 million kg. 34 applied MSMA for 5 years at annual rates varying from 4.4 to 288 kg MSMA/ ha and observed an increase in total arsenic only for application rates greater than 36 kg ai/ ha. Hiltbold et al ( 1974) applied MSMA to plots in three different cotton fields at variable rates. After 6 years at an application rate comparable to the maximum labeled MSMA rate4, the amounts of soil arsenic in the top 15 cm, corrected for background levels, were 13.0, 13.2, and 8.0 ppm. These levels represent 57%, 53%, and 32% of the applied pesticide, respectively. In the second soil, an additional 15% of the applied arsenic was detected in the 15 30 cm soil layer, while in the other soils no residual arsenic was detected below 15 cm. The authors suggest that the unrecovered arsenic could be accounted for through gaseous losses. In another field study, Woolson and Isensee ( 1981) monitored soil arsenic levels in soybean fields in which DMA, MSMA, and sodium arsenite were applied annually. The data are presented only as line plots, but show that in most cases, after 6 years, at least half of the applied arsenic was recovered in the top 15 cm of soil. For MSMA applied at 11.2 kg ai/ ha ( compare to maximum labeled MSMA rate on turf of 17.5 kg ai/ ha/ yr), the line plot shows recovered soil arsenic of approximately 8 ppm. DMA applied at 11.2 kg ai/ ha ( a higher application as total arsenic than the same rate for MSMA) led to soil levels of approximately 10 ppm arsenic after 6 years.

Additional information about the potential for arsenic soil buildup comes from monitoring studies in areas where organic arsenicals are known to be used. One of these studies measured soil arsenic concentrations at 5 Florida golf courses that use MSMA. 9 samples from greens, tees, and fairways found arsenic levels ranging from non detectable to 50 ppm. The median value was 13 ppm and the 90th percentile approximately 30 ppm. The estimated mean background arsenic level in this area is 1.2 ppm ( DERM, 2002). Another study measured arsenic levels in roadside areas where the Louisiana Department of Transportation applied arsenicals. Out of 559 samples, 42% had concentrations between 21 and 50 ppm and 22% had concentrations greater than 50 ppm. Background arsenic in this area was found to be between 4 and 14 ppm ( LDOTD, 1984). Detailed histories of pesticide applications are not available in these studies and other potential sources of arsenic, including historical land uses, are not accounted for. These results, then, are inconclusive as to the source of the arsenic buildup, but they add to the weight of evidence from controlled field studies and modeling.

Soil accumulation values are generated by PRZM as part of the process of modeling runoff concentrations. PRZM was run with a modified version of the pe4 v01 shell program to estimate soil accumulation. Except for exceptions described here, the modeling inputs were the same as those included for surface water modeling ( DP Barcode D309098). Maximum application rates for MMA and DMA on turf and cotton were used and the modeling assumed median sorption ( Kd = 30 for MMA and Kd = 20 for DMA). Because of limitations in the available data and modeling capabilities, soil 4 Hiltbold indicates MSMA was applied at rates of 10, 20, and 40 kg/ ha for 6 years. The total applied, as arsenic, over the course of the study amounted to 27, 55, and 110 kg/ ha, indicating average annual application rates, as arsenic, of 4.5, 9, and 18 kg/ ha/ yr. The current MSMA label allows a maximum application rate ( on turf) of 3.9 lb ae/ A, 4 times a year. This is equivalent to an annual rate as arsenic of 8.5 kg/ ha/ yr, comparable to the experimental average annual rate of 9 kg/ ha/ yr leading to a total of 55 kg/ ha. 35 concentrations were modeled as total arsenic, rather than speciated forms. Application rates were therefore calculated to represent applied arsenic and infinite half lives were used to capture all forms of arsenic that may be present. A wide range of sorption is possible; lower sorption, used to provide protective estimates for surface water modeling ( Kd = 11.4 for MMA and Kd = 8.2 for DMA), would lead to lower soil concentrations, while greater sorption leading to higher concentrations is also possible. The possibility of transformation to volatile species was not included in modeling, and modeling does not account for the possibility of plant uptake of soil arsenic. The results presented are for the scenarios that led to the highest soil concentrations ( PA turf and NC cotton). Because soil concentrations are based on local application rather than input from an entire watershed, use of a percent cropped area ( PCA) factor was unnecessary.

In the top 10 cm of soil, modeling predicts that arsenic will accumulate with very little dissipation for several years and then level off. Over the long term, the buildup of total arsenic from MMA application is predicted to reach chronic concentrations of approximately 13 ppm and 45 ppm on cotton and turf, respectively. For DMA on turf, the highest application rate leads to a modeled chronic soil concentration of approximately 77 ppm, assuming annual application at that rate. For DMA on cotton, the chronic soil concentration is 2 ppm. (" Chronic" concentrations are the upper 90th percent confidence limit on the annual average, or the 1 in 10 year peak annual concentration.) Considering another 10 cm, the modeled concentrations reach similar levels, but after longer periods time. If deeper soils are included, the overall concentrations would be lower. Most studies suggest that concentrations are highest in the surface layers and buildup is typically limited to the top 30 cm.

The same issue of arsenic buildup, supported for soil by field studies, monitoring, and modeling, is relevant to concentrations of arsenic in sediment as well. Arsenic that reaches surface water is likely to end up in sediments. A registrant study in an aerobic aquatic/ sediment system found that after 30 days, 25% of applied DMA was found in the sediment ( MRID 43036101). For MMA, 39% of the applied amount ended up in sediment after 30 days, most of it out of the water within the first week ( MRID 43314801; Acceptable). In an anaerobic system, after 1 year 61% to 95% of applied MMA was found in the sediment ( MRID 44767602; Acceptable). For DMA, approximately 95% of the applied amount was found in the sediment after one year, most of it reaching there within the first month ( MRID 42572601). A literature review of arsenic fate reports that in Lake Michigan, arsenic concentrations in water are generally much less than in the sediments, and refers to oceanic sediments as " the ultimate sink for arsenic" ( Woolson, 1977). 36 REFERENCES Abdelghani, A.; Anderson, A.; Englande, A. J.; Mason, J. W.; Dekemion, P. 1977. Demethylation of MSMA by soil microorganisms. In Trace Substances in Environmental Health, Part XI ( Ed: Hemphill, D. D), University of Missouri, Columbia, pp. 419 426.

Akins, M. B.; Lewis, R. J. Chemical distribution and gaseous evolution of arsenic 74 added to soils as DSMA 74As. Soil Sci. Soc. Am. J., 1976, 40, 655 658.

Akkari, K. H.; Frans, R. E., Lavy, T. L. Factors affecting degradation of MSMA in soil. Weed Sci. 1986, 34, 781 787.

Bednar, A. J; Garbarino, J. R.; Ranville, J. F.; Wildeman, T. R. Presence of organoarsenicals used in cotton production in agricultural water and soil of the Southern United States. J. Agric. Food Chem., 2002, 50, 7340 7344.

Cheng, C. N.; Focht, D. D. Production of arsine and methylarsines in soil and in culture. Applied Environ. Microbiol. 1979, 38, 494 498.

Cox, D. P.; Alexander, M. Production of trimethylarsine gas for various arsenic compounds by three sewage fungi. Bull. Environ. Contam. Toxicol. 1973, 9, 84 88.

DERM, 2002. Environmental Quality Monitoring at Five Municipal Golf Courses in Miami Dade County. DERM Technical Report; Florida Department of Environmental Resources Management: Florida. http:// www. miamidade. gov/ derm/ land/ library/ golf_ course. pdf Dickens, R.; Hiltbold, A. E. Movement and persistence of methanearsonates in soil. Weeds. 1967, 15( 4), 299 304.

Gao, S.; Burau, R. G. Environmental factors affecting rates of arsine evolution from and mineralization of arsenicals in soil. J. Environ. Qual. 1997, 26, 753 763.

Hiltbold, A. E.; Hajek, B. F.; Buchanan, G. A. Distribution of arsenic in soil profiles after repeated applications of MSMA. Weed Sci. 1974, 22, 272 275.

Kuhlmeier, P. D. Partitioning of arsenic species in fine grained soils. J. Air & Waste Management Association. 1997, 47, 481 490.

Louisiana Department of Transportation and Development ( LDOTD), 1984. Environmental and Health Effects of MSMA Application along Louisiana Highways. Prepared by Perry, D. L., Germany, R. D., and Flourney, R. W. Enviromed Laboratories, Inc. Baton Rouge, LA. June, 1984. Rpt. No. FHWA/ LA 84 1. 37 MAATF, 2005. The Environmental Fate of Monosodium Methane Arsonate ( MSMA): A Review of Important Processes. MAA Research Task Force, Washington, D. C. 2005.

Matera, V; Le Hecho, I. 2001. Arsenic behavior in contaminated soils: Mobility and speciation. In Heavy Metals Release in Soils ( Eds: Selim, H. M.; Sparks, D. M.), CRC Press, Boca Raton, pp. 207 235.

National Research Council ( NRC), 2003. Bioavailability of Contaminants in Soils and Sediments. National Academies Press, Washington, D. C. Onken, B. M.; Adriano, D. C. Arsenic availability in soil with time under saturated and subsaturated conditions. Soil Sci. Soc. Am. J. 1997, 61, 746 752.

Robinson, E. L. Arsenic in soil with five annual applications of MSMA. Weed Sci. 1975, 23( 5), 341 345.

Sarkar, D.; Datta, R.; Sharma, S. Fate and bioavailability of arsenic in organo arsenical pesticide applied soils. Part I. Incubation study. Chemosphere. 2005, 60, 188 195.

Smith, E., Naidu, R., Alston, A. M. Chemistry of arsenic in soils: I. Sorption of arsenate and arsenite by four australian soils. J. Environ. Qual. 1999, 28, 1719 1726.

Swancar, A. Water Quality, Pesticide Occurrence, and Effects of Irrigation with Reclaimed Water at Golf Courses in Florida: U. S. Geological Survey Water Resources Investigation Report 95 4250; U. S. Geological Survey: Tallahassee, 1996. http:// fl. water. usgs. gov/ PDF_ files/ wri95_ 4250_ swancar. pdf Tu, C.; Ma, L. Q.; Zhang, W.; Cai, Y.; Harris, W. G. Arsenic species and leachability in the fronds of the hyperaccumulator Chinese brake ( Pteris vittara L.). Environmental Pollution. 2003, 124, 223 230.

Turpeinen, R.; Pantsar Kallio, M.; Kairesalo, T. Influence of microbes on the mobilization, toxicity, and biomethylation of arsenic in soil. Sci. Total Environ. 1999, 236, 173 180.

Turpeinen, R.; Pantsar Kallio, M.; Kairesalo, T. Role of microbes in controlling the speciation of arsenic and production of arsines in contaminated soils. Sci. Total Environ. 2001, 285, 133 145.

Von Endt, D. W.; Kearney, P. C.; Kaufman, D. D. Degradation of MSMA by soil microorganisms. Ag. Food Chem. 1968, 16( 1), 17 20.

Wauchope, R. D. Fixation of arsenical herbicides, phosphate, and arsenate in alluvial soils. J. Environ. Qual. 1975, 4( 3), 355 358. ( EPA Accession No. 260782 and associated Nos. 259582 and 260061.) 38 Woolson, E. A.; Kearney, P. C. Persistence and reactions of 14C cacodylic acid in soils. Environ. Sci. Technol., 1973, 7, 47 50. ( EPA Accession Nos. 259582.)

Woolson, E. A. Fate of arsenicals in different environmental substrates. Environ. Health Perspectives. 1977, 19, 73 81.

Woolson, E. A.; Isensee, A. R. Soil residue accumulation from three applied arsenic sources. Weed Sci. Soc. Am. J. 1981, 29, 17 21.

Woolson, E. A.; Aharonson, N.; Iadevaia, R. Application of high performance liquid chromatography  flameless atomic absorption method to the study of alkyl arsenical herbicide metabolism in soil. J. Agric. Food Chem., 1982, 30, 580 584. ( EPA Accession Nos. 259582, 260061, 260782.) 39 APPENDIX B: GENEEC2 INPUTS Table B1. GENEEC2 Input Parameters for DSMA and MSMA Property Value Comments Source / MRID Solubility ( water) 1 x 106 mg/ L at 20 E C  2000 RED ( D210451, D212449, 255226)

Hydrolysis t1/ 2 0 day stable at all pHs 42059201 Aquatic Photolysis t1/ 2 0 day stable 41662601 Aerobic Soil Metabolism t1/ 2 240 days 90th percentile, based on 3 values Woolson & Kearney, 1973; Woolson 1982; Gao & Burau, 1997; 44767601 Aerobic Aquatic Metabolism t1/ 2 480 days 2x240 days. No data available, 2 x aerobic soil t1/ 2 since hydrolysis assumed stable Kd 11.4 mL/ g lowest non sand, from 20 soils Wauchope, 1975 41651906 Application Rate ( MMA  lb ae/ A) / No. of Appl per year cotton: 1.74 / 2 ( ground) orchard: 3.70 / 3 non crop: 3.86 / 4 turf ( max): 3.35 / 4 turf ( golf): 2.23 / 4 40 APPENDIX C. T REX Model ( T REX Version 1.22, July 11, 2004)   Model Overview and Results 1. Introduction This spreadsheet based model calculates the decay of a chemical applied to foliar surfaces for single or multiple applications. It uses the same principle as the batch code models FATE and TERREEC for calculating terrestrial estimates exposure ( TEEC) concentrations on plant surfaces following application. A first order decay assumption is used to determine the concentration at each day after initial application based on the concentration resulting from the initial and additional applications. The decay is calculated by from the first order rate equation: CT = Cie kT or in log form:

ln ( C T / Ci) = kT Where:

CT = concentration at time T = day zero.

Ci = concentration, in parts per million ( PPM) present initially ( on day zero) on the surfaces. Ci is calculated based on Kenaga and Fletcher by multiplying the Ci based on the Kenega nomogram ( Hoerger and Kenaga, ( 1972) as modified Fletcher ( 1994). For maximum concentration the application rate, in pounds active ingredient per acre, is multiplied by 240 for Short Grass, 110 for Tall Grass, and 135 for Broad leafed plants/ small insects and 15 for fruits/ pods/ lg insects. Additional applications are converted from pounds active ingredient per acre to PPM on the plant surface and the additional mass added to the mass of the chemical still present on the surfaces on the day of application.

k = If the foliar dissipation data submitted to EFED are found scientifically valid and statistically robust for a specific pesticide, the 90% upper confidence limit of the mean half lives should be used. When scientifically valid, statistically robust data are not available TETT recommends the using a default half life value of 35 days. The use of the 35 day half life is based on the highest reported value ( 36.9 days) reported by Willis and McDowell ( Pesticide persistence on foliage, Environ. Contam. Toxicol, 100: 23 73, 1987).

T = time, in days, since the start of the simulation. The initial application is on day 0. The simulation is designed to run for 365 days. 41 The program calculates concentration on each type of surface on a daily interval for one year. The maximum concentration during the year are calculated for both maximum and mean residues. The inputs used to calculate the amount of the chemical present are in highlighted in light blue on the spread sheet. Outputs are in yellow. The inputs required are:

Application Rate: The maximum label application rate ( in pounds ai/ acre) Half life: The degradation half life for the dominant process( in days) Frequency of Application: The labeled interval, in days, between repeated applications Maximum # Application per year: From the label The calculated concentrations are used to calculate Avian and Mammalian RQ values. The maximum calculated concentration is divided by user input values for acute and chronic endpoints to give RQs for each type of plant surface.

2. Avian Species For calculating dose based RQs in birds, the maximum and mean Kenaga residue values are adjusted for avian class and food consumption based on the following scaling factor ( USEPA, 1993):

FI ( g/ d) = 0.648 ( g bw)^ 0.651 For the 3 avian weight classes considered ( 20, 100 and 1000 g), this results in % body weight consumption of:

Weight( g) FI wet FI % bw consumed 20 4.555599463 22.77799731 114 100 12.98897874 64.94489369 65 1000 58.15338588 290.7669294 29 A. Dose Based Acute RQs Dose based acute RQs are then calculated using the formula: RQ = adjusted EEC/ LD50 or NOAEL where the adjusted EEC is considered to be the daily dose weighted for % body weight consumed of a given food source. 42 B. Dietary Based RQs For dietary based RQs, two values are given for each food group. First, the consumption weighted RQ for each weight class ( 20, 100, and 1000g birds) is displayed and calculated using the equation:

RQ = EEC/(( LC50 or NOAEC)/(% bw consumed))

In the second method, no adjustment is made for consumption differences among the weight classes. This RQ is calculated:

RQ = EEC/ LC50 or NOAEC 3. Mammalian Species A. Dose Based RQs For calculating dose based RQs in mammals, the maximum and mean Kenaga values are adjusted for mammalian class and food consumption ( 0.95, 0.66 and 0.15 body weight for herbivores and insectivores and 0.21, 0.15, and 0.03 body wt. for granivores). Dosebased acute and chronic RQs are then calculated by dividing the adjusted EECs ( daily dose) by the LD50 or NOAEL.

B. Dietary Based RQs Dietary based RQs are calculated using the equation:

RQ = EEC/(( LC50 or NOAEC)/(% bw consumed))

4. Graph A graph of concentration on each plant surface vs time is plotted and a concentration of concern line can be added at a user specified level. The concentration of concern ( e. g., avian LC50, mammalian NOAEL) label should be entered in the cell underneath the value. The graph automatically plots a line at this concentration and the label is extracted from that cell. The graph is plotted for the first 100 days post application. Graphs displaying acute and chronic LOCs for both birds and mammals are displayed in the " Graph" worksheet. These graphs may be useful as a visual aid to communicate risk in your assessment and can be copy/ pasted into your document. To help with scaling issues on the y axis, you may want to delete one of the endpoints.

5. New Version Notes A new look is used in this update in an effort to decrease confusion and increase transparency in the risk assessment process. This version of T REX ( v1.12) incorporates the ability to calculate EECs and RQs for maximum and mean residues. Mean residues 43 are calculated exactly as the maximum residues are, except the corresponding Kenaga values are: 85 for Short Grass, 36 for Tall Grass, and 45 for Broad leafed plants/ small insects and 7 for fruits/ pods/ lg insects. Version 1.22 provides additional improvements.

6. References Fletcher, J. S., J. E. Nellesson and T. G. Pfleeger. 1994. Literature review and evaluation of the EPA food chain ( Kenaga) nomogram, an instrument for estimating pesticide residues on plants. Environ. Tox. and Chem. 13( 9): 1383 1391.

Hoerger, F. and E. E. Kenaga. 1972. Pesticide residues on plants: correlation of representative dada as a basis for estimation of their magnitude in the environment. IN: F. Coulston and F. Corte, eds., Environmental Quality and Safety: Chemistry, Toxicology and Technology. Vol 1. Georg Theime Publishers, Stuttgart, Germany. pp. 9 28.

USEPA. 1993. Wildlife Exposure Factors Handbook. Volume I of II. EPA/ 600/ R 93/ 187a. Office of Research and Development, Washington, D. C. 20460. Willis and McDowell. 1987. Pesticide persistence on foliage. Environ. Contam. Toxicol. 100: 23 73. 44 Appendix D: TerrPlant 1.0 Details Exposure to Terrestrial Plants including Wetlands ( August 8, 2001; version 1.0)

Terrestrial plants inhabiting dry and semi aquatic ( wetland) areas may be exposed to pesticides from runoff and/ or spray drift. Semi aquatic areas are low lying wet areas that may dry up at times throughout the year.

EFED's runoff scenario is ( 1) based on a pesticide's water solubility and the amount ot 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 " channel runoff" ( 10 acres to a distant low lying acre) for semi aquatic or wetland areas, and ( 4) based on percent runoff values of 0.01, 0.02, and 0.05 for water solubilities of < 10, 10 100, and > 100 ppm, respectively.

EFED's Spray Drift scenario is assumed as ( 1) 1% for ground application, and ( 2) 5% for aerial, airblast, forced air, and spray chemigation applications. The spray drift ratio used here is in agreement with the policy procedures at the time the worksheet was designed.

Currently, 1) this worksheet is designed to derive the plant exposure concentrations from a single, maximum application rate only. 2) For pesticide applications with incorporation of depth of less than 1 inch, the total loading EECs derived for the incorporation method will be same as the unincorporated method.

To calculate RQ values for Non Endangered Terrestrial Plants:

Terrestrial Plants Inhabiting Areas Adjacent to Treatment Site:

Emergence RQ = Total Loading to Adjacent Area or EEC/ Seedling Emergence EC25 Drift RQ = Drift EEC/ Vegetative Vigor EC25 Terrestrial Plants Inhabiting Semi aquatic Areas Adjacent to Treatment Site:

Emergence RQ = Total Loading to Semi aquatic Area or EEC/ Seedling Emergence EC25 Drift RQ = Drift EEC/ Vegetative Vigor EC25 To calculate RQ values for Endangered Terrestrial Plants:

Endangered Terrestrial Plants Inhabiting Areas Adjacent to Treatment Site:

Emergence RQ = Total Loading to Adjacent Area or EEC/ Seedling Emergence EC05 Drift RQ = Drift EEC/ Vegetative Vigor EC05 or NOAEC Endangered Terrestrial Plants Inhabiting Semiaquatic Areas Near Treatment Site:

Emergence RQ = Total Loading to Semiaquatic Area or EEC/ Seedling Emergence EC05 Drift RQ = Drift EEC/ Vegetative Vigor EC05 or NOAEC 45 Formulas used to calculate EEC values ( 8/ 08/ 01; version 1.0)

To calculate EECs for terrestrial plants inhabiting in areas adjacent to treatment sites Un incorporated Ground Application ( Non granular):

Sheet Runoff = Application Rate ( lb ai/ A) x Runoff Value Drift = Application Rate ( lb ai/ A) x 0.01 Total Loading = EEC = Sheet Runoff + Drift Incorporated Ground Application with Drift ( Non granular):

Sheet Runoff = [ Application Rate ( lb ai/ A)/ Incorporation Depth ( inch)] x Runoff Value Drift = Application Rate ( lb ai/ A) x 0.01 Total Loading = EEC = Sheet Runoff + Drift Un incorporated Ground Application ( Granular):

Sheet Runoff = EEC = Application Rate ( lb ai/ A) x Runoff Value Incorporated Ground Application without Drift ( Granular):

Sheet Runoff = EEC = [ Application Rate ( lb ai/ A)/ Incorportion Depth ( inch)]

x Runoff Value Aerial/ Airblast/ Spray Chemigation Applications:

Sheet Runoff = Application Rate ( lb ai/ A) x Runoff Value x Application Efficiency of 0.6 Drift = Application Rate ( lb ai/ A) x 0.05 Total Loading = EEC = Sheet Runoff + Drift Runoff Value = 0.01, 0.02, or 0.05 when the solubility of the chemical is < 10 ppm, 10 100 ppm, or> 100 ppm, respectively Incorporation Depth: Use the minimum incorporation depth reported on the label.