**_,~~o** 

## s.,.,..ll ..;)""**~.s>** 

# i**~** 

# {,**~ ~** **UNITED** STAT E S E NVIRONMENTAL PROTECTION AG E NCY

### ~ 

# I**~** wASHINGTON D.C.
, 20460**""~ (j."~**  '1£.**PRO~~** O FF ICE OF CHEMICAL SAFETY



### MEMORANDUM

Subject:

To:

·Through:

From: AND POLLUTION PREVENTION



### PC Code: 013803



### DP 

### Barcode: 406606


### Date: March 12, 2013

Registration Review: Preliminary Problem Formulation for
Monosodium Acid Methanearsonate (MSMA)

Garland Waleko

, Chemical Review Manager

Kevin Costello, Chief
Risk Management and Implementation Branch II

Pesticide Re-evaluation Division (7508P)

James Hetrick, Ph.D., Senior Science

# Adviso~ 

# a.

Melissa Panger, Ph.D., Senior Scientist
Environmental Risk Branch III

Environmental Fate and Effects Division (7507P)

The Environmental Fate and Effects Division (EFED) has completed the problem
formulation in support of the Registration Review of the herbicide monosodiurri acid

methanearsonate [MSMA (PC code: 013803)] (attached). This document is intended to provide an overview of what is currently known regarding the environmental fate and ecological effects associated with MSMA and its transformation products

. Uncertainties regarding attributes of the parent compound and its transformation products are also

outlined. It describes the preliminary ecological risk hypothesis and the processes that
will be used during the completion of ecological risk assessment and drinking water

exposure assessment in support of registration review.

Page 1 

### of 58



# '

### Page 2 of 58 

## Contents

1. Introduction .............................................................................................................. 4

2. Conclusions from Previous Risk Assessments ........................................................ 6

2.1. Ecological Risk Assessments .......................................................................... 6

2.2. Drinking Water Exposure Assessments ........................................................... 7

2.3. Clean Water Act Programs ............................................................................... 8 3. Environmental Fate and Transport ............................................................................. 9

4. Receptors................................................................................................................ 11
4.1. Effects to Aquatic Organisms ......................................................................... 12

4.2. Effects to Terrestrial Organisms ..................................................................... 16

4.3. Ecological Incidents ....................................................................................... 17
5. Conceptual Model .................................................................................................. 19 6. Analysis Plan ........................................................................................................... 1 9
6.1. Stressors of Concern ....................................................................................... 19

6.2. Measures of Exposure ................................................................................... 20

6.3. Measures of Effect .......................................................................................... 20

6.4. Endangered Species Assessments .................................................................. 21
6.5. Endocrine Disruptor Screening Program ........................................................ 21

7. Preliminary Identification of Data Gaps ................................................................ 21
7.1. Environmental Fate ............................................................................................ 21

7.2

. Ecological Effects .............................................................................................. 22
8. References ................................................................................................................ 28 APPENDIX A: Currently Registered MSMA Products. .............................................. 29 APPENDIX B: Currently Registered MSMA USES. ................................................... 31
APPENDIX C: BEAD Chemical Profile for MSMA: ................................................. 41 APPENDIX D. Chemical Equi libria Model for As. ..................................................... 50
APPENDIX E. Results of the Screen ing Imbibation Program (SIP v. 1.0). ................ 57

### Page 3 of 58 

## Definition of Terms

Background arsenic: “Background” arsenic is used to describe arsenic in the environment that is present as a result of natural geologi cal processes and/or as a result of anything other than organic arse nical herbicide use.

Organic arsenic: The “organic” form of arse nic includes the pesticides cacodylic acid, MSMA, DSMA, and CAMA. These arsenic co mpounds can also be found naturally in
the environment.

Inorganic arsenic: Found naturally in the envi ronment, “inorganic” arsenic species are the elemental forms of arsenic (As) in the environm ent. It can exist in the oxidation states of As(III) and As(V).

Total arsenic: “Total” arsenic is used to de scribe all the arsenic present in a sample regardless of its form (i.e., organic arseni c + inorganic arsenic) and source (i.e., background + pesticidal); EPA and state/Federal agencies measure and/or establish regulatory limits in soil and water for total arsenic.

Transformation: The process of arsenic changi ng forms (i.e., organic to inorganic or vice versa).

Speciating: Quantifying the con centration of inorganic and or ganic arsenic in a soil or water sample (as opposed to only total arseni c); “speciated” data provide a breakdown of organic and inorganic arsenic whereas “unspeciated” data provide only total arsenic.

Oxidation State: The oxidation state of an atom in a molecule gives the number of valence electrons it has gain ed or lost. The oxidation stat es of As are -3,+3, and +5.

Methylation and demethylation: The chemical pr ocess that transforms metalloids such as arsenic by the addition (methylation) or rem oval (demethylation) of methyl groups (CH 3 

### )
to the molecule.

Monomethyl methanearsonate (MMA): MMA re fers to organic arsenic compounds with a single methyl group; in these assessments, the term “MMA” is used collectively to refer to MSMA, DSMA, and CAMA (salts of MMA th at readily dissociate to MMA in water).
It can form with As in the oxidation states of As(III) as MMA(III) or As(V) as MMA(V).

Dimethyl methanearsonate (DMA): DMA refe rs to organic arsenic compounds with two methyl groups such as cacodylic acid and its sa lt. It can form with As in the oxidation states of As(III) as DMA(III) or As(V) as DMA(V).

Trimethyl methanearsonate (TMA): TMA refers to organic arsenic compounds with three methyl groups. It can form with As in the oxidation states of As (III) as TMA(III) or As(V) as TMA(V).

### Page 4 of 58 

### 1. Introduction

Monosodium acid methanearsonate, or MSMA (an organic arsenical), is a broadspectrum herbicide used to control grasses and broadleaf weeds in cotton and turf. MSMA’s herbicidal mode of action, along with other organic arsenicals, is unknown. However, it is suspected that the organi c arsenicals, including MSMA, destroy cell membranes in plants, leading to the herbicidal activity.

In 2006 a Reregistration Eligibility D ecision (RED) was completed. The RED considered two groups of organic arsenicals ; the methylarsonate salts [MSMA, DSMA (PC code: 013802), CAMA (PC code: 013806)] and the cacodylates [DMA (PC code: 012501) and DMA-Na (PC code: 012502)]. The 2006 RED determined that none of the registered uses of organic arsenicals (i.e., CAMA, cacodylic acid, DSMA, and MSMA) were eligible for reregistration.

In January and February 2009, EPA reached an agreement in principle with the technical registrants of all existing or ganic arsenical pesticide produc ts to eliminate, phase out, and/or modify certain uses. The result of this agreement was the EPA issuance of a revised RED in April 2009 and a cancellati on order in September 2009 that terminated the last remaining uses of DSMA, CAMA, and DMA in the United States. The order also terminated certain MSMA product regist rations and amended ot hers (decreased rates and/or limited applications). For MSMA, only the cotton use was determined to be eligible for reregistration, based on high pot ential benefits. The remaining uses of MSMA on turf ( i.e ., golf courses, sod farms, and highw ay rights-of-way) were to be phased out with these turf uses , and use of MSMA is prohib ited after December 31, 2013.

The 2009 agreement in principle also provided fo r a scientific peer re view related to the carcinogenic mode of action (MOA) of inorganic arsenic (iAs) prior to the final phase out of the remaining MSMA uses. OPP was initia lly considering use of a joint review by the EPA Science Advisory Board (SAB) and the FIFRA Science Advisory Panel (SAP). However, since that time, the Agency ha s announced review of iAs by the National Academy of Sciences (NAS) to be used in lieu of an SAB/SAP review. Therefore, EPA will postpone any decision regarding the phase-o ut of the use of MSMA on golf courses, sod farms, and highway rights-of-way until su ch time that the NAS review is complete and the Agency has analyzed and responded to the NAS report.

The risk assessment conducted for MSMA will be based on uses registered at the time of
the assessment. Sin ce the turf uses ( i.e. , golf courses, sod farms, and highway rights-ofway) have not yet been phased out, they are considered here along with the cotton use. MSMA is currently formulated in 10 activ e end-use products as a granular, flowable concentrate, ready-to-use, and emulsifiable c oncentrate. Eight of the products contain a single active ingred ient (a.i.) ( i.e ., MSMA), while two of the products contain multiple a.i.’s (see Appendix A ). Applications to cotton are vi a aerial or ground equipment, while applications to turf are li mited to ground applications. Appendix B is a detailed list of the use patterns and maximum application rate s for the current uses of MSMA (they are
summarized below in Table 1 ).

### Page 5 of 58 TABLE 1. Currently Registered Uses of MSMA and Maximum Labeled Application Rates.

USE APP.
METHOD SINGLE
MAX.
RATE MAX NO.
APPS

PER
SEASON MIN.
APP.
INTERVAL MAX SEASONAL APP
RATE COMMENTS

Cotton Ground
Aerial 2 lb
a.i/acre 2 7-day 4 lb a.i./acre - Do not apply this product in FL, except for in the following counties: Calhoun, Columbia, Escambia, Gadsden, Hamilton, Holmes, Jackson, Jefferson, Okaloosa, Santa Rosa, Suwannee, Walton, and Washington

- 2 nd application is allowed only for a salvage operation - Some (but not all) labels have the following
restrictions: 50 ft buffer from water; cannot be applied post-bloom; in FL, only apply as a band

treatment

Golf Course (newly constructed) Ground 4 lb
a.i./acre 1 N/A 1 4.0 lb a.i./acre (does not
include
additional
spot treatments) - Do not apply in FL

Golf Course (NOT newly constructed;
spot treatment only) Ground 4 lb
a.i./acre NS NS 2 NS (not to
exceed 25% of total golf

course acreage/yr) - Do not apply in FL
- 100 ft 2 max per spot

Sod Farms (broadcast) Ground 4 lb
a.i./acre 2 NS 8 lb a.i./acre (based on 2 x max single rate) - Do not apply in FL
- 25 ft buffer from permanent water bodies or aquatic habitat

Highway Rights-of-Way Ground NS 3 2/yr 3 NS NS 3 - Do not apply in FL
- 100 ft buffer from permanent water bodies or aquatic habitat

1 N/A – Not applicable

2 NS – Not specified on the label

3 The information is specified on four labels (19713-42; 19713-528; 19713-550; and 42519-3): the highest application rate is 5 lb a.i./acre (single app.); 2 app./yr; 10 lb a.i./acre app. rate (based on 2 apps./yr); 90- day app. interval



### Private market usage data from 2000 – 2010 show that approximately one million pounds of active ingredient (lb a.i.), on average, were used per year for agricu ltural uses (97% of the agricultural use was on cotton). The average number of acres treated was 850,000

### Page 6 of 58 

### (see Appendix C for details). Most of the usage is in the Southeastern United States. For the non-agricultural uses, the available usage data show that from 2002 – 2006, there was an average of just over one million pounds of MSMA applied per year (including many of the uses that have been phased out since the usage data were collected).

2. Conclusions from Previous Risk Assessments

EFED evaluated the most recent ecological risk assessments for [MSMA (PC code: 013803)] and other arsenicals (organic and inor ganic) in association with any updated toxicity, exposure, and usage information to determine if further updates are needed to support registration review, and if so, if sufficient data are av ailable. The most recent
risk assessment for MSMA is a 2006 assessmen t that was an addendum to the ecological risk assessment conducted for the Reregist ration Eligibility De cision (RED) (D309100) (see ‘Introduction’). The RED was origina lly signed in 2006 and an amended RED was signed in 2009. The 2006 RED determined that none of the organic arsenicals ( i.e

., CAMA, cacodylic acid, DSMA, and MSMA) were eligible for reregistration. In 2009, the registrants voluntarily can celled all uses of CAMA, cac odylic acid and DSMA. At that time, most of the uses of MSMA were either voluntarily cancelled or were scheduled for a voluntary phase out. Cotton was the only MSMA use that was determined to be eligible for reregistration in 2009, ba sed on high potential benefits.

Based upon a reevaluation and reconsideration of the available data, a more refined approach than the one used for the MSMA RED document is proposed for the risk assessment to be conducted for registration re view. Because MSMA can speciate to a variety of different organic and inorganic arsenicals in the environment, the MSMA assessment will consider the available information on the fate properties and toxicity data for a variety of arsenicals (see below for details).

2.1. Ecological Risk Assessments

The EFED’s risk assessment for the or ganic arsenicals (inc luding MSMA) RED was completed in 2006 (USEPA, 2006). The RED docu ment for the organic arsenicals serves as the starting point for this problem form ulation document (USEPA, 2006). The results of the ecological assessment conducted fo r the RED are briefly summarized below.

TABLE 2. Summary of Risk Concerns Identified for Organic Arsenicals (Including MSMA) in
Previous Assessments

Birds Mammals Terrestrial

Plants Terrestrial

Inverts Fish Aquatic

Inverts Aquatic

Plants Groundwater
Contamination Persistence Degradates
of Concern 

### √ √ √ √


### -- -- -- -- √ √ 1

1-MSMA degrades to form inorganic arsenic (iAs). Because As is an element, it does not further degrade in the environment. However, it doe s form numerous inorganic and organic species in the environment. For the purposes of this assessment, only the inorganic and methylated forms of arsenic are considered in this problem formulation

.



### For aquatic organisms (fish, invertebrates, a nd plants), none of the levels of concern (LOC) were exceeded, indicating a low potentia l for risk from the use of MSMA. For terrestrial organisms (birds, mammals, and pl ants), exposures led to LOC exceedances,

### Page 7 of 58 

### indicating a potential for risk to these taxa. Risks to terre strial invertebrates were not
assessed in the RED.

The aquatic exposure assessment for MSMA wa s conducted in the RED. The daily peak estimated environmental concentration (EEC ) for MSMA ranged from 26 μg/L from use on kenaf at an annual applicati on rate of 2 lb a.i./A, to 605 μg/L from use on orchards at an annual application rate of 46.5 lb a.i./A . The daily peak EEC for MSMA was 78 μg/L from use on cotton at an annual application ra te of 6 lb a.i./A. The daily peak EEC for MSMA was 164 μg/L from use on turf at an an nual application rate of 12.6 lb a.i./A.

Surface water monitoring data for total As as well as speciated As (including arsenate, arsenite, MMA, DMA) were reported in the RED. The monitoring data for total As indicated that concentrations are typically less than 1 μg/L to severa l parts per billion. However, there are exceptions in the m onitoring data depending on local geology and anthropogenic activities. The maximum tota l As concentrations in surface water approach 1000 μg/L (1 mg/L). Speciated m onitoring programs for As were conducted in Florida and the Lower Mississippi River Basi n (Braman and Foreback and Garbarino and Burkhurdt, 1998). The maximum concentratio n of various As species was 1.8 μg/L for cacodylic acid, 5 μg/L for methylarsonic aci d, 3 μg/L for arsenite, and 5.5 μg/L for

arsenate.

2.2. Drinking Water Exposure Assessments

A drinking water assessment was conducte d to support the RED for MSMA (USEPA, 2002). The drinking water assessment was conducted using PR ZM/EXAMS modeling using the index reservoir. MS MA applications to cotton we re modeled based on 2 aerial applications at 3.6 lb a.i./A with an applic ation interval of 14 da ys. EDWCs for MSMA
are shown in Table 3

.

Table 3. Tier II PRZM/EXAMS Estimated Drinking Water Concentrations of
MSMA.

Use Pattern Arsenic Species 1 in 10 year Concentration

Peak Annual Average μg/L

Cotton MSMA 83 21

Citrus MSMA 512 136



### A more recent drinking water exposure asse ssment for organic arsenical herbicides (DSMA, CAMA, MSMA, DMA) was conduc ted for MSMA in 2006 (USEPA, 2006). This exposure assessment was designed to provide estimated drinking water concentrations for methylarsonate salt s (MSMA, CAMA, and DSMA), cacodylates (DMA) and total arsenic. PRZM/EXAMS modeling was conducted using the index reservoir ( Table 4 ). MSMA applications to turf and cotton were modeled at 2 applications at 1.74 lb acid e quivalent (ae)/A and at 4 a pplications at 3.35 lb ae/A, respectively. The modeling accounted for MS MA transformation to cacodylates (DMA)
in soil. The extent of DMA formation is based on a maximum of 35% formation of DMA from MSMA as reported in an aerobic soil metabolism study (MRID 44767601).

### Page 8 of 58 

### Ground water modeling was not conducted in this assessment. Surface water and ground water monitoring data also were considered in this assessment.

Table 4. Tier II PRZM/EXAMS Estimated Drinking Water Concentrations for Various As Species from MSMA Application.

Use Pattern Arsenic Species 1 in 10 year Concentration 30 year Annual Average Peak Annual Average μg/L

Turf MMA 250.5 127.5 74.6

DMA 102.3 46.5 28.1

Total As 135.2 68.8 40.3

Cotton MMA 37.4 11.0 5.3

DMA 23.6 7.4 4.3

Total As 20.9 7.2 3.9



### 2.4. Clean Water Act Programs

An Aquatic Life Ambient Water Quality Criteria document has not been published specifically for MSMA; however, one has b een published for arsenic (USEPA, 1995).
The criteria were derived from data for arsenic (III), but it is applie d for total arsenic. The freshwater and saltwater criteria are expr essed in terms of the dissolved As in the water column. The Aquatic Life Ambient Water Quality Criteria for arsenic are listed in the table below ( Table 5 ).

### Page 9 of 58 

### Table 5. EPA Aquatic Life Ambient Water Quality Criteria for Arsenic (μg/L).

Freshwater Saltwater

Criteria Maximum Concentration (acute) Criterion Continuous Concentration (chronic) Criteria Maximum Concentration (acute) Criterion Continuous Concentration (chronic)

340 150 69 36



### Arsenic can enter water bodies via natura l and/or anthropogenic sources. Total Maximum Daily Load (TMDL) criteria have be en developed for arsenic in several states
for several water bodies found in the U.S. The TMDLs do not distinguish the source of arsenic in water, so it is not possible to identify water bodie s that are impaired by arsenic as a result of pesticidal use using the av ailable data. Based on EPA’s WATERS Expert Query Tool ( http://iaspub.epa.gov/pls/wate rs/f?p=ASKWATERS:EXPERT:0 :::::), arsenic (total, from both natural and anthropoge nic sources) has been identified as a cause of water body impairment 2118 times under sec tion 303(d) of the Clean Water Act.

3. Environmental Fate and Transport

3.1 Fate Characterization

Unlike other pesticides that degrade over time, MSMA contains the element arsenic which does not degrade. Arseni c can, however, transform ( i.e. , change forms) or be redistributed through runoff, leaching, erosion, volatilization, or plant uptake. The extent and speed of transformation and redistribution of the organic arsenical herbicides in soil is highly variable and depends mostly on localized environmental conditions. Thus, persistence of applied organi c arsenical herbicides can ra nge from days to years, depending on soil properties and ambient conditions such as soil moisture, temperature, chemical concentration, bact erial population, and amount of organic matter. To fully describe the environmental fate of MSMA, c onsideration must be given to both the rate of transformation (demethylation/ methylation) as well as chemi cal equilibria of inorganic and organic As species in terrestr ial and aquatic environments.

The aerobic and anaerobic metabolism studies in soil and water are useful in describing
the transformation rate of MSMA into other forms of arsenic [ e.g ., As(V), As(III), TMA (III), DMA(III), MMA(III), TMA(V), DMA(V), MMA(V), etc .]. MSMA was essentially stable under all test systems, except for biotic degradation studies (Table 6). MSMA has a half-life of 240 days (Gao and Bura u, 1997; MRID 44767601) in aerobic soil. In anaerobic environments, MSMA has a ha lf-life of 776 days (MRID 44767602). It is stable to both hydrolysis and photolysis (MRID 42363001; MRID 41903902). No aerobic aquatic metabolism data are available for MSMA. Although these st udies indicate that MSMA is persistent in aquatic and te rrestrial environments, MSMA and its transformation products, in combination with As from natural background and other anthropogenic sources, represent a total arse nic load, which can be redistributed into
different forms of As in the environment. Re distribution of arsenic can be influenced by redox potential, pH, microbial activity, and presence of counter ions (Al 3+ 

### , Fe 3+ 

### , etc).

### Page 10 of 58 

### Table 6: Summary of Available Data to A ssess the Environmental Fate of MSMA.

Guideline MRID Summary Data Acceptability Hydrolysis 42363001 Stable @ pH 5,7, 9 Acceptable Photolysis in water 4190 3902 Stable in irradiated pH 7 buffer Acceptable Photolysis on soil 4190390 1 Stable on irradiated sandy loam Acceptable Aerobic Soil Metabolism 41886901 Arsenic acid major soil metabolite; Unable to reproduce formation/ decline of parent and degradation products; study did not differentiate background from introduced As. Upgradable

44767601 t 1/2 =240 days; DMA was major degradate(31% @ 2-12 months) Acceptable

Anaerobic Aquatic Metabolis m 41996501 Poor material balance Not acceptable

44767602 t 1/2 =776 days Acceptable Leaching Adsorption/Desorption 41651906 Lowest non-sand Kd 11.4 ml/g. Not acceptable

Terrestrial Field Dissipation 42526001

42616201 CA study-t 1/2 =55 days; cacodylic
acid identified AR study- t 1/2 =11 days; cacodylic
acid identified Upgradable

Accumulation in Fish 4243 2501 Mean BCF <1X in all fish tissue Acceptable



### The biogeochemical cycle of As is dependent on the microbial mediated methylation/demethylation, precipitation in to As minerals, and sorption onto soil colloids. Inorganic As is prone to under go methylation in anoxic (low redox conditions) environments. This methylation process can form various methylated forms of As including TMA (III), DMA(III), MM A(III), TMA(V), DMA(V), MMA(V), etc . The predominance and distribution of these species is dependent on pH and redox potential. The inorganic As can exist in soil pore wa ter or surface water as soluble hydrolysis species of As(III) and As(V). As(III) is the predominate i norganic As species in anoxic and suboxic environments. As(V) is the pre dominate As species in oxic environments. Hydrolysis species of As(V) and As(III) are formed through dissociation of arsenic acid (H 3 

### AsO 4 

### ) or arsenous acid (H 3 

### AsO 3 

### ), respectively. These sol uble species can be sorbed
on soil colloids or mineral surf aces. Additionally, the solubl e species can precipitate to
form As minerals.

3.2 Speciation and Transformation Products

Potential metabolites of applied organic arse nicals include volatile alkylarsines and inorganic arsenic (as arsenate or arsen ite) along with carbon dioxide. Additionally, DMA may be present as a metabolite of MMA. As with the rate, the metabolism pathway is
sensitive to environmental conditions with the major metabolites o ccurring in variable proportions under different environmental conditions. Transformation to volatile alkylarsines, the only metabolism route that w ould directly reduce soil arsenic loading, has been shown to be possible in certain circum stances but is generally not expected to be a major route of dissipation. A maximum of 35% of applie d MMA is expected to be present as DMA at any one time. Theoretical ly, there is some possibility for MMA to metabolize to DMA, but significant transfor mation has not been observed in available field or laboratory studies. Observed me tabolism rates of MMA and DMA to inorganic

### Page 11 of 58 

### arsenic greatly varies, ranging 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.

As stated in previous risk assessments fo r MSMA, the biogeochemical cycle for As is complex because it has multiple oxidation st ates (+5 and +3) which can form numerous inorganic As complexes and minerals, as well as organoarsenic compounds (for example, methylarsonic acid, methylarsini c acid, arsenocholine, arseno betaine, roxarsone). Figure 1 shows a diagram of selected As forms in the biogeochemical cycle. Although these As forms (methylated compounds, minerals, and soluble species) do not represent the complete universe of As compounds, they do represent important As species for quantifying the potential amount of inorgani c As from methylated As compounds. Speciation was not quantitativ ely considered in the 2006 Reregistration Eligibility Assessment (RED) for MSMA (013803) and disodium methylarsonic acid [DSMA (013802)], it will be considered in this updated assessment.

Chemical equilibria modeling, including solubl e inorganic and methyl ated species of As, suggest that methylated forms of arsenic are expected to be thermodynamically stable As species under anoxic (pe+pH > 4) envi ronmental conditions (Appendix D). The inorganic As(III) species are expected to be the predominate As species in suboxic (pe+pH = 4 to 8) environmental conditions. The inorganic As(V) species are expected to be the predominate As species in suboxic to oxic (pe+pH > 8) environmental conditions. These data suggest that MSMA is expected to be transforme d to inorganic As species in
most surface waters and soil conditions. This analysis, however, does not provide an
estimate on the rate of transformation of MSMA to inorganic As.

4. Receptors

The inorganic forms of arsenic are generally c onsidered more toxic (as direct toxins) than the organic forms. For aquatic species, t oxicity data for the organic (MSMA) and inorganic As species are expected in a dynami c equilibria with microbes, minerals, water, air in aquatic and/or soil conditions (see discussion above) (Lindsay, 1979). For terrestrial species, however, only the toxicity data for the MSMA will be
considered because the dynamic equilibria of As is not expected due to the limited quantity of minerals and mi crobial populations on the surfa ce of terrestrial food items ( e.g ., foliage). The most sensitive endpoint from each taxon is provided here in the tables. No toxicity data ar e currently available for methylated arsenicals with a +3 valence. Tables 11 through 15 provide a su mmary of the aquatic taxonomic groups and most sensitive surrogate species tested to characterize the poten tial acute and chronic ecological effects of MSMA, me thylated arsenicals (+5), methylated arsenicals (+3), inorganic arsenicals (+5), and inorganic arsenicals (+3). Tables 16 through 18 provide a summary of the terrestrial taxonomic groups a nd most sensitive surrogate species tested to characterize the potential acute and chr onic ecological effects of MSMA, methylated arsenicals (+5), and methylated arsenicals (+3).

### Page 12 of 58 

### 4.1. Effects to Aquatic Organisms

Table 11. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies
for MSMA.

STUDY TAXA FORM. ENDPOINT MRID STUDY
CLASSIFICATION/
COMMENTS

Acute freshwater
fish 1 Rainbow trout ( Oncorhynchus mykiss ) 51% a.i. LC 50 > 85 mg a.i./L 41747301 Acceptable; NOAEC = 85 mg a.i./L (no effects were noted in the study)

Chronic
freshwater fish No data available

Acute estuarine/
marine fish Sheepshead
minnow ( Cyprinodon variegates ) 99.4% a.i. (MAA
Methanearsoni c acid) LC 50 = 323 mg a.i./L 42414102 Acceptable; NOAEC = 170 mg a.i./L (based on mortality)

Chronic
estuarine/ marine
fish No data available

Acute freshwater
invertebrate Freshwater
invertebrate

( Daphnia

pulex ) 51% a.i. EC 50 = 77 mg a.i./L 41940605 Acceptable; no observations
of sublethal effects were made during the study; NOAEC = 12.3 mg a.i./kg (based on mortality); slope

= 2.7.

Chronic
freshwater
invertebrate No data available

Acute estuarine/
marine
invertebrate Estuarine/
Marine
invertebrate ( Americamysis
bahia
- formerly Mysidopsis bahia) 99.4% a.i. (MAA
Methanearsoni c acid) LC 50 = 173 mg a.i./L 42414101 Supplemental (the test organisms were 24-48-hr old instead of <24-hr) (adequate for RQ calculation); NOAEC = 93.5 mg a.i./L (based on mortality)

Acute estuarine/
marine
invertebrate Estuarine/
Marine
invertebrate –
oyster ( Crassostrea

virginica ) 50.4% a.i. EC 50 = 160 mg a.i./L (shell deposition) 42464801 Acceptable; NOAEC = 49 mg a.i./L (based on shell deposition); no mortality occurred during the test

Chronic
estuarine/ marine
invertebrate No data available

Vascular aquatic plant Vascular aquatic plant ( Lemna gibba ) 51% a.i. EC 50 = 104 mg a.i./L (reduced number of fronds) NOAEC = 56.9 mg a.i./L (reduced number of fronds) 41748202 Acceptable; provided meanmeasured values so assume
concentrations were
corrected for % a.i.

Non-vascular aquatic plant Non-vascular aquatic plant 51% a.i. EC 50 = 5.63 mg a.i./L (reduced cell 41748201 Acceptable; did not use the
lowest two nominal

### Page 13 of 58 STUDY TAXA FORM. ENDPOINT MRID STUDY
CLASSIFICATION/
COMMENTS ( Selenastrum capricornutum ) number) NOAEC < 0.3 mg a.i./L (reduced cell number) concentrations because no
detectable concentration could be found; provided
mean-measured values so
assume concentrations were
corrected for % a.i.

Bioconcentration factor study BCF study (bluegill sunfish) 14 C residues BCF < 1x in edible (fillet), nonedible (viscera and carcass),
and whole fish 42432501 Acceptable; fish exposed for 28 days to 0.49 mg a.i./L;
max concentrations in each tissue was measured on Day

7

1 Freshwater fish may be surrogate s for aquatic-phase amphibians.



### Table 12. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for Methylated Arsenicals (+5 Valence) (Including MSMA).

TAXA ARSENICAL (PC CODE) FORM. ENDPOINT MRID

Acute
Freshwater Fish Cacodylate acid (5) (012501 and 012502) 100% (acid) LC 50 = 17 mg a.i./L (bluegill) 40098001

Acute Estuarine/

Marine Fish Cacodylate acid Equivalence (5) (a.e.) (012501 and 012502) 29.4% (a.e.) LC 50 = 291 mg a.i./L (sheepshead minnow) 42433301

Fish Reproduction No data available

Acute
Freshwater
invertebrate Cacodylate acid Equivalence (5) (a.e.) (012501 and 012502) 29.4% (a.e.) EC 50 = 18.1 mg a.e./L (daphnid) 41747901

Acute Estuarine/
Marine
invertebrate Cacodylate acid Equivalence (5) (a.e.) (012501 and 012502) 29.4% (a.e.) LC 50 = 9.7 mg a.e./L (mysid) 42433302

Acute Estuarine/
Marine
Invertebrate

(oyster) MSMA (5) (013803) 50.4% a.i. EC 50 = 160 mg a.i./L (shell deposition) 42464801

Aquatic
Invertebrate Reproduction No data available

Vascular aquatic

plant ( Lemna gibba ) Cacodylate acid Equivalence (5) (a.e.) (012501 and 012502) 29.4% (a.e.) EC 50 = 30.9 mg/L NOAEC = 2.4 mg a.i./L 41791105

Non-vascular aquatic plant DSMA (5) (013802) 81.35% a.i. EC 50 = 1.5 mg a.i./L (bluegreen algae) NOAEC = 0.9 mg a.i./L (blue-green algae) 43184502

BCF study (fish) MSMA (5) (013803) 14 C residues BCF < 1x in edible (fillet), nonedible (viscera and carcass), and whole fish (bluegill) 42432501

### Page 14 of 58 

### Table 13. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for Methylated Arsenicals (+3 Valence).

TAXA ARSENICAL (PC CODE) FORM. ENDPOINT MRID

All No data available



### Table 14. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for Inorganic Arsenicals (+5 Valence).

TAXA ARSENICAL(3 or 5)/PC CODE FORM. ENDPOINT MRID*

Acute
Freshwater Fish Arsenic Acid (5)/

006801 75% a.i. LC 50 = 50 mg a.i./L (bluegill) 41950601 (Machado, 1991)

Acute Estuarine/

Marine Fish Arsenic Acid (5)/

006801 76.1% LC 50 = 2 mg a.i./L (mysid) 41620004 (LeLievre, 1990)

Fish Reproduction Arsenic Acid (5)/

006801 75.8% a.i. LC 50 = 50 mg a.i./L 41802201 (Machado, 1991)

Acute
Freshwater
invertebrate Arsenic Acid (5)/
006801 76.1% EC 50 = 15 mg a.i./L (daphnid) 41620001 (LeLievre, 1990)

Chronic
Freshwater
Invertebrate Chromated Arsenicals (5)/
128977 ACZA leachate (from treated wood) [copper, zinc, and arsenic (<0.95 arsenic)] NOAEC < 0.95 μg a.i./L (LOAEC <0.95 μg a.i./L based on survival, length and dry weight) ( Daphnia ) 44797501 (Putt, 1997) (supplemental)

Acute Estuarine/
Marine
invertebrate Arsenic Acid (5)/
006801 76.1% LC 50 = 2 mg a.i./L (mysid) 41620002 (LeLievre, 1990)

Acute Estuarine/
Marine
Invertebrate

(oyster) No data available

Estuarine/

Marine
Invertebrate Reproduction Chromated Arsenicals (5)/
128977 ** From OPPIN Bibliography 44797502 (Putt, 1997)

Vascular aquatic

plant ( Lemna gibba ) Arsenic Acid (5)/

006801 75.8% a.i. EC 50 >9.8 mg a.i./L [19% (statistically significant) reduction in frond number at limit dose] 42290901 (Hoberg, 1992) [Acceptable]

Non-vascular aquatic plant Arsenic Acid (5)/

006801 75.8% a.i. EC 50 = 0.0092 mg a.i./L ( Skeletonema costatum ) 42278801 (supplemental, a
NOAEC could be established)

BCF study (fish) Arsenic Acid (5)/
006801 ** From OPPIN Bibliography 40435801 (Envirosphere, 1987)

### Page 15 of 58 Table 15. Summary of the Most Sensitive Endpoi nts from Aquatic Toxicity Studies for Inorganic Arsenicals (+3 Valence).

TAXA ARSENICAL(3 or 5)/PC CODE FORM. ENDPOINT MRID*

Acute
Freshwater Fish Arsenic Trioxide (3)/
007001 99.31% a.i. LC 50 = 25.6 mg a.i./L (trout) 44423602

Acute Estuarine/

Marine Fish No data available

Acute
Freshwater
invertebrate Sodium Arsenite (3)/
013603 NaAs0 2 (99%) EC 50 = 4.89 mg a.i./L (daphnid) 00114493

Chronic
Freshwater
Invertebrate Sodium Arsenite (3)/013603 NaAs0 2 (99%) NOAEC = 0.37 mg a.i./L (daphnid) LOAEC = 0.75 mg a.i./L (based on reduced production of young and length of surviving adult) 02025917

Acute Estuarine/
Marine
invertebrate No data available

Acute Estuarine/
Marine
Invertebrate

(oyster) No data available

Estuarine/Marine
Invertebrate Reproduction No data available

Vascular aquatic

plant ( Lemna gibba ) No data available

Non-vascular aquatic plant No data available

BCF study (fish) No data available

### Page 16 of 58 

### 4.2. Effects to Terrestrial Organisms

Table 16. Summary of the Most Sensitive Endpoints from Terrestria l Toxicity Studies for MSMA.

TAXA FORM. ENDPOINT MRID STUDY
CLASSIFICATION

Acute avian oral Bobwhite quail ( Colinus virginianus ) Arsonate liquid blend

(51% a.i.) LD 50 = 425.2 mg a.i./kg-bw 41610002 Acceptable; NOAEL < 149 mg a.i./kg-bw (effects were
noted in all of the test concentrations – signs of toxicity and reduced body weight/food consumption)

Sub-acute avian dietary Bobwhite quail ( Colinus virginianus ) Arsonate liquid blend

(51% a.i.) LC 50 = 1,667 mg a.i./kg-diet 41610003 Acceptable; NOAEC < 287 mg a.i./kg-diet (effects were
noted in all test
concentrations – reduced body weight)

Chronic avian No data available

Acute oral rat Rat ( Rattus norvegicus ) 34.35% a.i. LD 50 = 157 mg a.i./kg-bw 41610003 Acceptable

Chronic rat No data available

Acute honey bee Honey bee ( Apis mellifera ) Arsonate liquid blend

(51% a.i.) LD 50 = 35 μg a.i./bee (contact) 41610007 Acceptable; endpoint corrected for purity

Terrestrial plant Seedling

emergence – Tier II 51% a.i. EC 25 = 0.116 lb a.i./acre (cabbage; reduced dry weight)
NOAEC 0.018 lb a.i./acre (cabbage; plant height) 41705501
42572501 Supplemental (a NOAEC
could not be determined for cabbage) ; Acceptable in conjunction with MRID
42572501

Terrestrial plant Vegetative vigor – Tier II 51% a.i. EC 25 = 0.418 lb a.i./acre (oat; reduced dry weight) NOAEC = 0.14 (oat, dry weight) 41705502 Acceptable

1 Birds represent surrogates for terrest rial-phase amphibians and reptiles.

### Page 17 of 58 Table 17. Summary of the Most Sensitive E ndpoints from Terrestrial Toxicity Studies for Methylated Arsenicals (+5 Valence) (Including MSMA).

TAXA ARSENICAL (PC CODE) FORM. ENDPOINT MRID

Acute Avian (oral) MSMA (5) (013803) Arsonate liquid blend (51% a.i.) LD 50 = 425.2 mg a.i./kgbw 41610002

Sub-acute Avian (dietary) MSMA (5) (013803) Arsonate liquid blend (51% a.i.) LC 50 = 1,667 mg a.i./kgdiet (quail) 41610003

Avian Reproduction No data available

Acute Mammal MSMA (5)/ 013803 34.35% a.i. LD 50 = 157 mg a.i./kg-bw (rat) 00105171

Mammal Reproduction Methanearsonic Acid (5) (128876) 99.4% a.i. NOAEL = 100 mg a.i./kgdiet 43178301

Honey bee ( Apis mellifera ) MSMA (5) (013803) Arsonate liquid blend (51% a.i.) LD 50 = 35 μg a.i./bee (contact) ; endpoint corrected for purity 41610007

Seedling emergence – Tier

II MSMA (5) (013803) 51% a.i. EC 25 = 0.116 lb a.i./acre (cabbage; reduced dry weight
NOAEC = 0.018 lb a.i./acre (cabbage; plant height) 42572501

Vegetative vigor
– Tier II DSMA (5) (013802) 82.7% a.i. EC 25 = 0.354 lb a.i./acre (corn; reduced dry weight
NOAEC < 0.30 lb a.e./acre (corn; reduced dry weight) 41905604

TABLE 18. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for Methylated Arsenicals (+3 Valence).

TAXA ARSENICAL (PC CODE) FORM. ENDPOINT MRID

All No data available



### 4.3. Ecological Incidents

For this problem formulation, the Environmenta l Incident Information System (EIIS), the Incident Database System (IDS) (for aggr egate incidents), and the American Bird Conservancy’s Avian Incident Management Sy stem (AIMS) were searched on October 9, 2012, for ecological incident reports associat ed with MSMA. Add itionally, because of the way that MSMA can speciate to other orga nic and inorganic arsenicals, the EIIS and
IDS databases were searched for incident data on all of the organic and inorganic arsenicals to help pr ovide insight on the toxicity of these chemicals to non-target organisms under natural conditions. Because of the time investment required to search
for incidents associated with each of the organic and inorganic arsenicals, only those arsenicals associated with the most ecologi cal incidents were search for in AIMS ( i.e

., MSMA, CAMA, DSMA, and cacodylic acid). The results are summarized below.

### Page 18 of 58 

### MSMA:

EIIS returned nine ecological incidents (eight involving terres trial plants and one aquatic incident) for MSMA (PC Code: 013803). The plan t incidents were associated with plant damage from direct treatment (f ive incidents) or drift to ne arby plants (three incidents). The aquatic incident involved mortality of seve ral fish (a variety of species) from runoff into a canal from the registered use of MSMA on a golf course in Louisiana. All of these incidents were listed as ‘possible’ or ‘probable’ for their certainty indices and occurred between 1972 and 2001. Three of the incidents were from registered uses, three were from accidental misuses, and the legality of use was undetermined in the remaining three
incidents. Three incidents were associated with use on rights-of-way, one was from a golf course use ( i.e ., the aquatic incident), two were fr om residential lawn use, one was from a peanut use, and two were from use on cotton.

The IDS database returned a total of 187 aggr egated incidents (all plant incidents) for MSMA (PC Code: 013803). All of the aggr egated incidents for MSMA occurred between 1998 and 2006. The AIMS database returned one incident for MSMA involving birds and rabbits. However, the certainty inde x was listed as ‘unlikely’ for this incident.

Other Organic Arsenicals:

EIIS returned 13 ecological incidents (12 involving terrestrial plants and one bird incident) for organic arsenicals, excluding MSMA. The bird incident was associated with a single bird mortality and a registered homeowner use of cacodylic acid (PC Code 012501) in 1995. The certainty index for this inci dent is classified as ‘possible’. Of the 12 plant incidents, 11 were associated with CAMA (PC Code 013806) and two were associated with DSMA (PC Code 013802). All of these incidents were listed as ‘possible’ or ‘probable’ for their certainty indices. All of the CA MA incidents occurred in 1999 and were from registered uses on residential lawns. There were no dates
associated with the DSMA incidents and th e legality of use for these incidents was undetermined. One of the DSMA incidents was from a rice use; the use for the other DSMA incident was not reported.

The IDS database returned a total of 592 aggr egated incidents (all plant incidents) for CAMA (PC Code: 013806). All of the aggr egated incidents for CAMA occurred
between 1995 and 2011. There were no incident reports for CAMA, DSMA, or cacodylic
acid in the AIMS database.

Inorganic Arsenicals:

EIIS returned 8 ecological incidents (seven terrestrial and one aquatic) for inorganic arsenicals. The aquatic incident was associated with fish mortality (several species) from the use of sodium arsenate (PC Code 013505) on cotton in 1972. The certainty index for this incident is classified as ‘possible’ a nd the legality of use was undetermined. Two of the incidents involved arsenic acid (PC Code 006801) and the death of deer [one in 1987

### Page 19 of 58 

### (forest use) and one in 1995( use not reported)]. One of the incidents involved the registered use of arsenic oxide (PC Code 006802) around a residentia l building that was associated with the death of two squirrels in 2006. The certainty index for this incident is listed as ‘probable’. There ar e four incidents associated w ith lead arsenate hydroxide (PC Code 013502). Two of these incidents are cla ssified as ‘unlikely’; the other two are reported as ‘highly probable’. Of the latter two, one involve d the death of an eagle in 1989 (use site not reported) and the other involv ed the death of four peregrine falcons in 1993 (building use). In both of these incidents, the legality of use was undetermined.

There were no aggregate incide nts reported for inorganic arse nicals in the IDS database.

5. Conceptual Model

The conceptual model for MSMA indicates that spray drift, runoff, leaching, and volatilization are poten tial exposure pathways of MS MA and its As transformation products to aquatic and terrestrial environmen ts. Because As in MSMA is an element, it will not degrade and, therefore, will be tran sformed to various organic and inorganic As species depending on site-specific environm ental conditions. The transformation of MSMA into various soluble As inorganic and As organic compounds is expected to influence the exposure pathways. For example, the inorganic As from MSMA will be
reduced under anaerobic environments to form arsine AsH 3(g). 

### Arsine is toxic gas formed from application of methylated arsenic pest icides in soil (Gao and Burau, 1997). Factors controlling the predominance of As species include pH, redox potential, microbial community, and mineralogy.

6. Analysis Plan

6.1. Stressors of Concern

The stressors of concern are parent MSMA as well as all the soluble As transformation products from MSMA in soil and aquatic enviro nments. For aquatic organisms, stressors of concern are for both methylated and inorga nic arsenicals, since MSMA can speciate to these forms in aquatic conditions. For terrestrial animals, the stressor of concern is limited to MSMA and other methylated ar senic compounds since speciation to other arsenicals is less likely in the terrestrial e nvironment (than in aquatic environments). Because the methylated (III) and inorganic As (III) are expected to form in conditions under low redox potential ( i.e ., under sub-oxic and anoxic conditions), the greatest concern for the As(III) species are for sedime nt-dwelling organisms. Arsenic minerals
are not considered as a stressor of concern be cause they simply serve to buffer the soluble As concentration. Soluble As species consid ered in this assessment are discussed in Section 3. Environmental Fate and Transport Assessment. The stressors of concern are expected to be controlled by the natural As bi ogeochemical cycle. Factors controlling the predominance of stressors of concern include pH, redox potential, microbial community, and mineralogy.

### Page 20 of 58 

### 6.2. Measures of Exposure for Ecol ogical Effects and Drinking Water

EFED will use standard available models to evaluate potential exposures to aquatic and terrestrial organisms as described at http://www.epa.gov/pesticides/science /models_db.htm

. The aquatic and drinking water expos ure assessment will be conducted using a tiered approach. PRZM/EXAMS m odeling will be conducted to estimate MSMA concentrations in the standard pond and index reservoir. The total mass of MSMA in the standard pond and index reservoir is assu med to be completely transformed into inorganic As. This assumption is used to conservatively address toxicity concerns for MSMA and inorganic As. Site-specific water quality conditions will not be considered in this exposure assessment. If additional refine ment is needed in th e exposure assessments, a chemical equilibria model using site specific wa ter quality data will be used to speciate As in the standard pond and index reservoir wa ter into the inorgani c As (III and V) and methylated arsenic compounds (MMA,DMA,TMA). Please see Appendix D for details on the chemical equilibria mode l. Summation of molar concentr ations of As species into various As forms [including inorganic As(V ) species; inorganic As(III) species; DMA, MMA, TMA(V); MMA, DMA, TMA(III)]. If additional refinement is needed then concentrations of individual inorganic and organic As species will considered.

For terrestrial animal exposures, it will be a ssumed that dietary exposures are to residues of MSMA (and other methylated arsenic com pounds), since speciation to other arsenicals is less likely (and less understood ) in the terrestrial environment [ e.g ., on potential food items ( e.g ., foliage)] than in water. Although MS MA has the potential to speciate into volatile forms (see Tables 8 and 9 ), the volatile arsenical species would only be a concern under highly reduced conditions in th e terrestrial environment. Therefore, for birds and mammals, exposure via inhalati on will not be assessed for MSMA.

To determine the potential for drinking wate r to be an exposure concern for birds and mammals the Screening Imbibation Program (S IP v. 1.0) was run. For the SIP run, the highest solubility limit for calcium arsenate (the stable mineral phase arsenical formed under most sub-oxic and oxic conditions) and corresponding toxicity data for inorganic arsenicals were used (see Appendix E ). Based on this analysis, drinking water is a potential route of concern for birds (acute exposure) and mammals (acute and chronic exposures). There are current ly no reproduction data availabl e for inorganic arsenics and birds, therefore, the potentia l for drinking water to be a potential route of concern for birds from chronic exposure could not be mode led. However, the potential risk to birds from drinking water (chronic exposure) is assumed since the risk cannot currently be precluded and the results of the acute r un (SIP) for birds and acute and chronic mammalian SIP runs indicate that drinking wa ter is a potential route of concern.

6.3. Measures of Effect

Toxicity data presented in Section 4 of this problem formulation will be used to calculate risk quotients. Any additional information submitted by the registrant or found in the open literature prior to conduct of the risk assessment will also be considered. The open literature studies are identified using EPA’s ECOTOXicology database (ECOTOX)

### Page 21 of 58 

### (USEPA, 2007 c ), which employs a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide insight in to the direct and indirect e ffects of pesticides on biotic communities from loss of species that are sens itive to the chemicals and from changes in
structure and functional characteris tics of the affected communities.

6.4. Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will evaluate risks to federally li sted threatened and/or endangered (listed) species from registered uses of pesticides in registration review. These assessments will be conducted in accordance with standard EPA procedures and good scientific judgment.

6.5. Endocrine Disruptor Screening Program

MSMA (or any arsenical) was not included in the first group of 67 chemicals issued an order to conduct Tier 1 EDSP testing. Fo r additional information the EDSP program,
visit http://www.epa.gov/endo/

.

7. Preliminary Identification of Data Gaps

7.1. Environmental Fate

Table 19 identifies environmental fate studies by MRID that offer data for each guideline requirement, as well as study clas sifications and whether or not further data are needed in order to support risk assessment.

Table 19. Submitted Environmental Fate Data for MSMA.

OCSPP
Guideline Data Requirement Submitted Studies (MRID) Study
Classifications Are data

needed to
conduct risk
assessment? Current Additional Data Need

835.2120 Hydrolysis 4 2363001 Acceptable No
835.2240 Photodegradation in

Water 41903902 Acceptable No

835.2410 Photodegradation on
Soil 41903901 Acceptable No

835.4100 Aerobic Soil 41886901 Upgradable No 44767601 Acceptable
Gao and Burau,
1997 Supplemental

151476 Supplemental 151475 Supplemental 835.4200 Anaerobic Soil Not submitted NA No Anaerobic aquatic metabolism data (MRID 44767602) provide sufficient data on MSMA degradation under
anaerobic conditions 835.4300 Aerobic Aquatic 43314801 Not classified Study is in review

### Page 22 of 58 OCSPP
Guideline Data Requirement Submitted Studies (MRID) Study
Classifications Are data

needed to
conduct risk
assessment? Current Additional Data Need

835.4400 Anaerobic Aquatic 44767602 Acceptable No

835.1230
835.1240 Leaching and adsorption/desorption 41651906

152662 Supplemental 835.1410 Volatility-Laboratory No

835.6100 Terrestrial Field Dissipation 42526001
42616201 Supplemental No

835.6200 Aquatic Field Dissipation Not submitted No

165-4 (850.1730) Fish Bioaccumulation 42432501 Acceptable No



### 7.2

. Ecological Effects

Table s 20 through 23 identify aquatic ecological effects studies by MRID that offer data for each guideline requirement, as well as study classifications and whether or not further data are needed for methylated arsenicals(V) (including MSMA), me thylated arsenicals (III), inorganic arsenicals(V), a nd inorganic arse nicals (III). Table s 24 identifies terrestrial ecological effects studies that offer data for each guideline requirement and
whether or not further data are needed fo r methylated arsenica ls(V) (including MSMA) and methylated arsenicals(III).

There are data gaps for the methylated arsenicals (both V and III valences). For aquatic species, there are currently no chronic data available for any animal for the methylated arsenicals(V). There are curren tly no toxicity data availabl e for any methylated arsenical (III). Because methylated arsenicals (II I) are most likely to form under low redox potential conditions, exposure to benthic orga nisms is of greatest toxicity concern. Therefore, EFED recommends requesting se veral toxicity studies for methylated arsenicals and aquatic organisms (see the tables below).

### Page 23 of 58 

### For the inorganic arsenicals(V), there are a fe w data gaps; however, currently available data can be used to adequa tely address the gaps (see Table 22 for details). For inorganic arsenicals(III), again, because these are most likely to form in sediments (under low redox potential conditions), benthic organi sms are of greatest toxicity concern. Therefore, EFED recommends requesting toxici ty studies for inorganic arsenicals (+3) and sediment-dwelling organisms (see Table 23 ).

For terrestrial organisms, data gaps include an acute oral study with passerines and avian reproduction studies for methylated arsenicals (V) (see Table 24 ). Therefore, EFED recommends requesting these data. The inorganic arsenicals and the methylated arsenicals (III) will not be considered in the terrestrial assessment for MSMA, therefore, toxicity data for terrestrial organisms and th ese arsenicals are not needed at this time.

Table 20. Summary of Submitted Aquatic Ecological Effects Da ta for Methylated Arsenics (+5) (Including MSMA).

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data

needed to
conduct

risk
assessment? Comment

850.1010 Freshwater
invertebrate acute toxicity 41747901 Acceptable No --

850.1025
850.1035
850.1045
850.1055 Saltwater
invertebrate acute toxicity 42433302 Decision
deferred* No This study will be reviewed prior to conducting the risk

assessment 42464801 Acceptable

850.1075 Freshwater
fish acute toxicity 40098001 Acceptable No --

850.1075 Saltwater fish acute toxicity 42433301 Acceptable No --

850.1300 Freshwater
invertebrate life cycle (None) (N/A) Yes Currently, no data are available; therefore, a guideline compliant
freshwater invertebrate life cycle test is needed.

850.1350 Saltwater
invertebrates life cycle (None) (N/A) Yes Currently, no data are available; therefore, a A guideline compliant saltwater invertebrate life cycle test is needed.

850.1400 Freshwater
fish early-life
stage (None) (N/A) No A guideline compliant freshwater fish early life-stage
test would not be needed if a fish life-cycle test was available.

### Page 24 of 58 OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data

needed to
conduct

risk
assessment? Comment

850.1400 Saltwater fish early-life
stage (None) (N/A) No – see

comment A guideline compliant saltwater fish early life-stage test would not be needed if a fish life-cycle
test was available.

850.1500 Fish life cycle (None) (N/A) Yes Currently, no data are available; therefore, a guideline compliant freshwater fish life-cycle test is
needed.

850.4400 Aquatic plant growth:
Tier II
vascular plants 41791105 Acceptable No --

850.5400 Aquatic Plant
Growth: Tier II algae 43184502 Acceptable No --



### Table 21. Summary of Submitte d Sediment Effects Data for Methylated Arsenics (+3).

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data

needed to
conduct

risk
assessment? Comment

850.1735 Whole
sediment:

acute freshwater
invertebrates (None) (N/A) Yes Methylated arsenicals are expected to form under low redox potential conditions, exposure to benthic organisms is of greatest toxicity concern. A guideline compliant whole
sediment acute freshwater
invertebrates test is needed.

Nonguideline 1 Whole
sediment:
chronic
freshwater
invertebrates (None) (N/A) Yes Methylated arsenicals are expected to form under low redox potential conditions; exposure to benthic organisms is of greatest toxicity concern. A
whole sediment chronic
freshwater invertebrates test is
needed.

1 Although there is no guideline for the chronic sediment toxicity study, the following methods by the USEPA’s Office of Research and Development may be consulted: ORD study method EPA 600/R-099- 064: chronic freshwater sediment testing flowthrough ( Hyalella azteca ); ORD study method EPA 600/R099-064: chronic freshwater sediment testing flowthrough ( Chironomus dilutus or C. tentans ).

### Page 25 of 58 

### Table 22. Summary of Submitted Aquatic Ecological Effects Data for Inorganic Arsenicals (+5).

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data

needed to
conduct

risk
assessment? Comment

850.1010 Freshwater
invertebrate acute toxicity 41620001 Acceptable No --

850.1025
850.1035
850.1045
850.1055 Saltwater
invertebrate acute toxicity 41620002 Acceptable No --

850.1075 Freshwater
fish acute toxicity 41950601 Acceptable No --

850.1075 Saltwater fish acute toxicity 41620004 Acceptable No --

850.1300 Freshwater
invertebrate life cycle 44797501 Acceptable No --

850.1350 Saltwater
invertebrates life cycle (None) (N/A) No The chronic saltwater invertebrate endpoint will be
based on an acute-to-chronic ratio using data from freshwater
invertebrates.

850.1400 Freshwater
fish early-life
stage 41802201 Acceptable No --

850.1400 Saltwater fish early-life
stage 41802201 Acceptable No --

850.1500 Fish life cycle (None) (N/A) No The chronic freshwater fish endpoint will be based on the
results from the available freshwater fish early life-stage study.

850.4400 Aquatic plant growth:
Tier II
vascular plants 42290901 Acceptable No --

850.5400 Aquatic Plant
Growth: Tier II algae 42278801 Supplemental (a NOAEC
could not be established) No --

### Page 26 of 58 

### Table 23. Summary of Submi tted Sediment Ecological Ef fects Data for Inorganic Arsenicals (+3).

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data

needed to
conduct

risk
assessment? Comment

850.1735 Whole
sediment:

acute freshwater
invertebrates (None) (N/A) Yes Arsenite is expected to form under low redox potential conditions; exposure to benthic organisms is of greatest toxicity

concern. A guideline compliant
whole sediment acute freshwater
invertebrates test is needed.

Nonguideline 1 Whole
sediment:
chronic
freshwater
invertebrates (None) (N/A) Yes Arsenite is expected to form under low redox potential conditions; exposure to benthic organisms is of greatest toxicity

concern. A whole sediment
chronic freshwater invertebrates
test is needed.

1 Although there is no guideline for the chronic sediment toxicity study, the following methods by the USEPA’s Office of Research and Development may be consulted: ORD study method EPA 600/R-099- 064: chronic freshwater sediment testing flowthrough ( Hyalella azteca ); ORD study method EPA 600/R099-064: chronic freshwater sediment testing flowthrough ( Chironomus dilutus or C. tentans ).



### Table 24. Summary of Submitted Terres trial Ecological Effects Data for Methylated Arsenics (+5) (Including MSMA).

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data
needed for
risk
assessment? Comment

850.2100 Avian oral toxicity 41610002 Acceptable Yes Acute oral toxicity data are necessary for a passerine species.

850.2200 Avian dietary toxicity 41610003 Acceptable No --

850.2300 Avian reproduction (None) (N/A) Yes No data are available to assess potential chronic toxicity to avian species. A guideline compliant avian reproduction
test is needed.

Nonguideline Avian
inhalation (None) (N/A) No Although MSMA has the potential to speciate into volatile forms, this would only be a concern under highly reduced conditions. Therefore, for birds, exposure via
inhalation will not be assessed
for MSMA and avian inhalation
data are not needed.

### Page 27 of 58 OCSPP
Guideline Data Requirement Submitted
Studies (MRID) Study
Classifications Are data
needed for
risk
assessment? Comment

850.3020 Honey bee

acute contact toxicity 00018842 Acceptable No --

850.4100 Terrestrial plant toxicity:
Tier II seedling

emergence 42572501 Supplemental No --

850.4150 Terrestrial plant toxicity:
Tier II vegetative vigor 41905604 Supplemental No --

### Page 28 of 58 

### 8. References

Dombrowski, Paul. M., Wei Long, Kevin J. Farley, John D. Mahony, Joseph F. Capitani, and Dominic M. Di Toro. 2005. Thermodynami c analysis of arsenic methylation.
Environ. Sci. Technol. 39:2169-2176.

Gao, S. and R. G. Burau. 1997. Environmental f actors affecting rates of arsine evolution
from and mineralization of arsenicals in soil. Environ. Qual. 26:753-763.

Lindsay, W.L. 1979. Chemical Equilibria in Soil s. Wiley and Sons, Inc. United States.

Sadiq, Muhammad, Tahir H. Zaidi and Attique A. Mian. 1995. Environmental behavior
of arsenic in soils: Theo retical. Water, Air, and Soil Pollution 20:369-377.

Sadiq, Muhammad. 1997. Arsenic chemistry in soils: An overview of thermodynamic predictions and field observations. Wate r, Air, and Soil Pollution 93:117-136.

### Page 29 of 58 

### APPENDIX A: Currently Registered MSMA Products.

Table 1. Currently Registered MSMA Products.

LABEL EPA
REG. NO. ACTIVE INGREDIENT(S) (A.I.) % A.I. USE(S)

QUADMEC ® TURF
HERBICIDE 2217-709 MSMA 18% a.i. [total Arsenic (as elemental) all in water soluble form 8.33%]

Golf courses; Sod farms Dimethylamine salt of 2,4- dichlorophenoxyacet
ic acid 5.83%

Dimethylamine salt of (+)-(R)-2-(2- methyl-4- chlorophenoxy)prop
ionic acid 2.93%

Dimethylamine salt of dicamba: 3,6-
dichloro-o-anisic
acid 1.46%

DrexarTM 530
Herbicide 19713-40 MSMA 35.78%) [total arsenic (aselemental), all in watersoluble form is 16.55%) Cotton; Highway rights-ofway; Golf courses; Sod
farms

MSMA 6.6 MSMA Liquid 19713-41 MSMA (51.3%) [total Arsenic as elemental) all in water soluble form is 23.61%] Cotton; Highway rights-ofway; Golf courses; Sod
farms

MSMA 6 Plus MSMA Liquid Plus
Surfactant 19713-42 MSMA 47.6% [total Arsenic (aselemental), all in watersoluble form, is 22%] Cotton; Highway rights-ofway; Golf courses; Sod
farms

MSMA 6.6 Liquid 19713-269 MSMA 51.0% a.i. [total Arsenic (as elemental) all in water soluble form is 23.61%] Cotton; Highway rights-ofway; Golf courses; Sod
farms

Diumate Herbicide 19713-528 MSMA 34.6% a.i. [Total Arsenic (as elemental) all in water
soluble form is 16.00% Cotton; Highway rights-ofway

Diuron 5.18% a.i.i

MSMA 660
Herbicide 19713-531 MSMA 51.3% a.i. [Total Arsenic (as elemental) all in water soluble form is 23.61%) Cotton; Highway rights-ofway; Golf courses; Sod
farms

MSMA 120 Arsonate Liquid for Postemergence
Weed Control 19713-550 MSMA 52.8% a.i. [Total Arsenic (aselemental), all in watersoluble form, is 23.7%] Cotton; Highway rights-ofway; Golf courses; Sod
farms

### Page 30 of 58 LABEL EPA
REG. NO. ACTIVE INGREDIENT(S) (A.I.) % A.I. USE(S)

TARGET ® 6.6 42519-1 MSMA 51.0% a.i. [Total Arsenic (as elemental) all in water soluble form 23.61%] Cotton; Highway rights-ofway; Golf courses; Sod
farms

TARGET ® 6 Plus 42519-3 MSMA 48.3% a.i. [Total arsenic (as elemental) all in water soluble form 22.3%] Cotton; Highway rights-ofway; Golf courses; Sod
farmsPage 31 of 58APPENDIX B: Currently Registered MSMA USES.Table 1. CURRENTLY REGISTERED MSMA USES:LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSQUADMEC®TURFHERBICIDE/2217-709Monosodiumacidmethanearsonate(18% a.i.) [totalArsenic (aselemental) all inwater solubleform 8.33%]Ground Newlyconstructedgolf courses(broadcast)3 lb a.i./acre 1 Notapplicable(N/A)3 lb a.i./acre(does notincludeadditionalspottreatments)None - Do not apply through anytype of irrigation system- Do not apply to newlyseeded turfgrass until afterthe third mowing- Do not apply in FL- Aerial application isprohibited- After Dec. 31, 2013,applications to golf coursesand sod farms are prohibited- Use only Medium (orcoarser) spray nozzlesaccording to ASABE- Do not apply at windspeeds > 10 mph- Do not apply with a nozzleheight > 4 ft above the cropcanopyDimethylaminesalt of 2,4-dichlorophenoxyacetic acid(5.83%)Other golfcourses(spottreatmentsonly)1.8 lba.i./acre (3 floz ofproduct/1,000 ft2)NS NS NS 100 ft2max per spot;not to exceed 25% oftotal golf courseacreage/yrDimethylaminesalt of (+)-(R)-2-(2-methyl-4-chlorophenoxy)propionic acid(2.93%)Sod farms(broadcast)3 lb a.i./acre 2 30-day 6 lb a.i./acre(total forproduct)25 ft buffer frompermanent water oraquatic habitatDimethylaminesalt of dicamba:3,6-dichloro-oanisic acid(1.46%)Sod farms(spottreatments)1.8 lba.i./acre (3 floz ofproduct/1,000 ft2)NS NS 6 lb a.i./acre(total forproduct)100 ft2max per spotDrexarTM 530Herbicide/19713-40MonosodiumacidmethanearsonateGroundAerialCotton 2 lb a.i./acre 2 (thesecondapplication7-day 4 lb a.i./acre - Postemergence (donot apply preplant)- In FL, applications- Do not apply this productin FL, except for cotton inthe following counties:Page 32 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTS(35.78%) [Totalarsenic (aselemental), all inwater- solubleform is 16.55%)is allowedfor asalvageoperation)should be confined toband treatments- 50 ft buffer frompermanent waterbodies or aquatichabitat- Do not apply postbloomCalhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- The distance of the nozzlesmust not exceed 3⁄4 the lengthof the wingspan or rotor- Applications must not bemade at a height > 10 ftabove the top of the largestplantsGround Highwayrights-ofwayNS 2/yr(broadcast)NS NS - 100 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Golf courses(newlyconstructed)(broadcast)2.75 lba.i./acre (2 floz ofproduct to1,000 ft2)1 N/A 2.75 lba.i./acre (doesnot includeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)2.75 lba.i./acre (2 floz ofproduct to1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)2.75 lba.i./acre (2 floz ofproduct to1,000 ft2)2 NS 5.5 lba.i./acre(based on 2 xthe maxsingle rate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Page 33 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSMSMA 6.6MSMALiquid/ 19713-41Monosodiumacidmethanearsonate(51.3%) [totalArsenic aselemental) all inwater solubleform is 23.61%]GroundAerialCotton 2 lb a.i./acre 2 (thesecondapplicationis allowedfor asalvageoperation)7-day 4 lb a.i./acre - Postemergence (donot apply preplant)- In FL, applicationsshould be confined toband treatments- 50 ft buffer frompermanent waterbodies or aquatichabitat- Do not apply afterfirst bloom- Do not apply through anytype of irrigation system- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- The distance of the nozzlesmust not exceed 3⁄4 the lengthof the wingspan or rotor- Applications must not bemade at a height > 10 ftabove the top of the largestplantsGround Highwayrights-ofwayNS 2/yr(broadcast)NS NS - 100 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Golf courses(newlyconstructed)(broadcast)4 lb a.i./acre(1.8 fl oz ofproduct/1,000 ft2)1 N/A 4 lb a.i./acre - Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)4 lb a.i./acre(1.8 fl oz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)4 lb a.i./acre(1.8 fl oz ofproduct/1,000 ft2)2 NS 8 lb a.i./acre(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Page 34 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSMSMA 6 PlusMSMA LiquidPlusSurfactant/19713-42Monosodiumacidmethanearsonate(47.6%) [totalArsenic (aselemental), all inwater-solubleform, is 22%]AerialGroundCotton 2 lb a.i./acre 2 (thesecondapplicationis allowedfor asalvageoperation)7-day 4 lb a.i./acre - Postplant (beforecotton emergence)and postemergence- Applications in FLshould be confined toband treatments- Do not apply afterfirst bloom- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- The distance of the nozzlesmust not exceed 3⁄4 the lengthof the wingspan or rotor- Applications must not bemade at a height > 10 ftabove the top of the largestplantsGround Highwayrights-ofway4.5 lba.i./acre(broadcast)[4.1 lba.i./acre for‘smallareas’]2/yr(broadcast)NS 9.0 lba.i./acre(broadcast)(based on 2 xmax singlerate)- 100 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Golf courses(newlyconstructed)(broadcast)4.0 lba.i./acre (2 floz ofproduct/1,000 ft2)1 N/A 4.0 lba.i./acre (doesnot includeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)4.0 lba.i./acre (2 floz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)4.0 lba.i./acre (2 floz ofproduct/1,000 ft2)2 NS 8.0 lba.i./acre(broadcast)(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Page 35 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSMSMA 6.6Liquid/ 19713-26951.0% a.i. [TotalArsenic (aselemental) all inwater solubleform is 23.61%)AerialGroundCotton 2 lb a.i./acre 2 (thesecondapplicationis allowedfor asalvageoperation)7-day 4.0 lba.i./acre- Postplant andpostemergence- Application in FLshould be confined toband treatments- 50 ft buffer frompermanent waterbodies and aquatichabitats- Do not apply through anytype of irrigation system- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and WashingtonGround Golf courses(newlyconstructed)(broadcast)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)1 N/A 4.0 lba.i./acre (doesnot includeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)2 NS 8.0 lba.i./acre(broadcast)(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Highwayrights-ofwayNS 2/yr(broadcast)NS NS - 100 ft buffer frompermanent waterbodies and aquatichabitats- Use is prohibitedafter Dec. 31, 2013Page 36 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSDiumateHerbicide/19713-528Monosodiumacidmethanearsonate(34.6% a.i.)[Total Arsenic(as elemental) allin water solubleform is 16.00%AerialGroundCotton 2 lb a.i./acre 2/yr (thesecondapplicationis allowedfor asalvageoperation)21-day 4.0 lba.i./acre- Do not apply afterfirst bloom- Applications in FLshould be limited toband treatments- 50 ft buffer frompermanent waterbodies and aquatichabitats- Do not apply through anytype of irrigation system- Use of this product incertain portions of CA, OR,and WA is subject to the Jan.22, 2004, Order forinjunctive relief inWashington Toxics Coalitionet al. v EPA C01-0143C- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- Make applications whenwinds≤10 mph- Apply with medium orcoarser spray (ASABE)- When making groundapplications, apply at aheight no more than 2 ftabove the ground or cropcanopy- For aerial, do not apply atheight greater than 10 ftabove the ground or cropcanopyDiuron (5.18%a.i.i)Ground Highwayrights-ofway5 lb a.i./acre(1.25 gallonof product/acre)2/yr 90-day 10 lb a.i/acre(based on 2 xmax. singlerate)- 100 ft buffer frompermanent waterbodies and aquatichabitats- Use is prohibitedafter Dec. 31, 2013MSMA 660Herbicide/MonosodiumacidAerialGroundCotton 2 lb a.i./acre 2/yr (thesecond7-day 4.0 lba.i./acre- Postemergenceapplications- Do not apply through anytype of irrigation systemPage 37 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTS19713-531 methanearsonate(51.3% a.i.)[Total Arsenic(as elemental) allin water solubleform is 23.61%)applicationis allowedfor asalvageoperation)- Applications in FLconfined to bandtreatments- 50 ft buffer frompermanent waterbodies and aquatichabitats- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- Applications must not bemade at a height greater than10 ft above the largest plantsGround Golf courses(newlyconstructed)(broadcast)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)1 N/A 4.0 lba.i./acre (doesnot includeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)2 NS 8.0 lba.i./acre(broadcast)(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Highwayrights-ofwayNS 2/yr(broadcast)NS NS - 100 ft buffer frompermanent waterbodies and aquatichabitats- Use is prohibitedafter Dec. 31, 2013Page 38 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSMSMA 120ArsonateLiquid forPostemergenceWeed Control/19713-550Monosodiumacidmethanearsonate(52.8% a.i.)[Total Arsenic(as elemental),all in watersoluble form, is23.7%]AerialGroundCotton 2 lb a.i./acre 2/yr (thesecondapplicationis allowedfor asalvageoperation)7-day 4.0 lba.i./acre- Postemergenceapplications- Applications in FLconfined to bandtreatments- 50 ft buffer frompermanent waterbodies and aquatichabitats- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- Do not use through anytype of irrigation systemGround Golf courses(newlyconstructed)(broadcast)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)1 N/A 4.0 lba.i./acre (doesnot includeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)4.0 lba.i./acre (1.8fl oz ofproduct/1,000 ft2)2 NS 8.0 lba.i./acre(broadcast)(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Highwayrights-ofway4.5 lba.i./acre [4.0lb a.i./acre(1.8 fl oz ofproduct/1,000 ft2) for2/yr(broadcast)NS 9.0 lb a.i/acre(based on 2 xmax. singlerate) (doesnot includeapplications- 100 ft buffer frompermanent waterbodies and aquatichabitats- Use is prohibitedafter Dec. 31, 2013Page 39 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTS‘smallerareas’]to ‘smallerareas’)TARGET®6.6/ 42519-1Monosodiumacidmethanearsonate(51.0% a.i.)[Total Arsenic(as elemental) allin water solubleform 23.61%]AerialGroundCotton 2 lb a.i./acre 2/yr (thesecondapplicationis allowedfor asalvageoperation)7-day 4.0 lba.i./acre- Postemergence only- 50 ft buffer frompermanent waterbodies and aquatichabitats- Do not apply this productthrough any type ofirrigation system- Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- Application should not bemade at a height > 10 ftabove the top of the largestplantsGround Golf courses(newlyconstructed)(broadcast)2.24 lba.i./acre (1 floz ofproduct/1,000 ft2)1 N/A 2.24 lba.i./acre (doesnot includeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)2.24 lba.i./acre (1 floz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)2.24 lba.i./acre (1 floz ofproduct/1,000 ft2)2 10-day 4.5 lba.i./acre(broadcast)(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Highwayrights-ofwayNS 2/yr(broadcast)NS NS - 100 ft buffer frompermanent waterbodies and aquatichabitats- Use is prohibitedafter Dec. 31, 2013Page 40 of 58LABEL/EPAREG. NO.A.I.(S)APPMETHODUSE(S)SINGLEMAX.APPL.RATEMAX. NO.APP./SEASONMIN. APP.INTERVALMAX.SEASONALAPP.RATESPECIFICCOMMENTSGENERAL COMMENTSTARGET®6Plus/ 42519-3Monosodiumacidmethanearsonate(48.3% a.i.)[Total arsenic (aselemental) all inwater solubleform 22.3%]AerialGround2 lb a.i./acre 2/yr (thesecondapplicationis allowedfor a salvageoperation)7-day 4.0 lba.i./acre- Postemergenceonly- 50 ft bufferfrompermanentwater bodiesand aquatichabitats- Postemergence only - Do not apply this productin FL, except for cotton inthe following counties:Calhoun, Columbia,Escambia, Gadsden,Hamilton, Holmes, Jackson,Jefferson, Okaloosa, SantaRosa, Suwannee, Walton,and Washington- Application should not bemade at a height > 10 ftabove the top of the largestplantsGround Golf courses(newlyconstructed)(broadcast)4 lb a.i./acre(2 fl oz ofproduct/1,000 ft2)1 N/A 4 lb a.i./acre(does notincludeadditionalspottreatments)- Use is prohibitedafter Dec. 31, 2013Ground Other golfcourses(spottreatmentsonly)4 lb a.i./acre(2 fl oz ofproduct/1,000 ft2)NS NS NS - 100 ft2per spot- Not to exceed 25%of the total golfcourse acreage per yr- Use is prohibitedafter Dec. 31, 2013Ground Sod farms(broadcast)4lb a.i./acre(1 fl oz ofproduct/1,000 ft2)2 NS 8 lb a.i./acre(broadcast)(based on 2 xmax singlerate)- 25 ft buffer frompermanent waterbodies or aquatichabitat- Use is prohibitedafter Dec. 31, 2013Ground Highwayrights-ofway4.5 lba.i./acre2/yr(broadcast)10 9 lb a.i./acre(broadcast)(based on 2 xmax singlerate)- 100 ft buffer frompermanent waterbodies and aquatichabitats- Use is prohibitedafter Dec. 31, 2013

### Page 41 of 58 

### APPENDIX C: BEAD Chemical Profile for MSMA:

### Page 42 of 58

### Page 43 of 58

### Page 44 of 58

### Page 45 of 58

### Page 46 of 58

### Page 47 of 58

### Page 48 of 58

### Page 49 of 58

### Page 50 of 58 

### Appendix D. Chemical Equilibria of As

The speciation of As can be roughly divided into three main forms: soluble methylated species, soluble inorganic species, and minera ls. Within each As form, the valence state
of As can be As 5+ 

### and As 3+ 

### depending on redox conditions. The As forms are discussed in the context of chemical equilibria in the As biogeochemical cycle. Chemical equilibria analysis is based on thermodynamic data from Sadiq et al ., 1982, Sadiq, 199X and Dombrowski, et al., 2005.

As Minerals

Arsenic minerals (As) can form as oxides (e.g., As 2 

### O 3 

### ,As 2 

### O 5 

### ), sulfides (AsS, As 2 

### S 2 

### , and

As 2 

### S 3 

### ), and with various metals minerals(AlAsO 4 

### , Ca 3 

### (As0 4 

### ) 2 

### , Cd(AsO 4 

### ) 2 

### , Cu(AsO 4 

### ) 2 

### , FeAsO 4 

### , Mn(AsO 4 

### ) 2 

### , Ni(AsO 4 

### ) 2 

### , Pb 3 

### (AsO 4 

### ) 2 

### , and Zn(AsO 4 

### ) 2 

### (Sadiq et al ., 1982). The solubility of each mineral is dependent on numerous factors including redox condition, counter ion chemistry, and pH. The least soluble ( i.e. , most stable) arsenate minerals

were Ca 3 

### (As0 4 

### ) 2 

### in alkaline and neutral environments and Mn(AsO 4 

### ) 2 

### in acid environments ( Figure 2 )

. 

### For the other metal arsenate (V) minerals and oxides, the mineral solubility from highest to lowest is As 2 

### O 5 > 

### Cd(AsO 4 

### ) 2> 

### Pb 3 

### (AsO 4 

### ) 2> 

### Cu(AsO 4 

### ) 2> 

### AlAsO 4> 

### FeAsO 4> 

### Zn(AsO 4 

### ) 2> 

### Ni(AsO 4 

### ) 2.

pH 456789Log (HAsO42-)

-10 -8 -6 -4 -2 0 2

Ca3(AsO4)2-Calcite AlAsO4-amorp.- Al(OH)3 AlAsO4-gibbsite FeAsO4-ferrihydrite FeAsO4-geothite Zn3(AsO4)2-Soil Zn Cu3(AsO4)2-Soil Cu

Figure 2: Arsenate Mineral Stability Diagram in Oxic Conditions (pe+pH=16)

### Page 51 of 58 Table 7: Chemical Equilibria Equations for As Minerals as a Function of pH. Mineral Equilibria Equilibrium Equation

Ca 3 (AsO 4 ) 2 ↔ CaCO 3 Log(HAsO 4 2- )=15.565-1.5pCO 2 +2pH

Ca 3 (AsO4) 2 ↔ Soil Ca Log (HAsO 4 2- )= 2.795-pH

AlAsO 4 ↔ amorp Al(OH) 3 Log(HAsO 4 2 )= -14.26+2pH

AlAsO 4 ↔ ð-Al(OH) 3 Log(HAsO 4 2 )= -13.1+2pH

FeAsO 4 ↔ amorp Fe(OH) 3 Log(HAsO 4 2 )= -12.13+2pH

FeAsO 4 ↔ Fe(OH) 3 Log(HAsO 4 2 )= -8.57+2pH

Fe 3 (AsO 4 ) 2 ↔ FeCO 3 Log(HAsO 4 2 )=12.96-2pH+3/2 pCO 2 Fe 3 (AsO 4 ) 2 ↔ Fe 2 SiO 4 Log(HAsO42-)=-23.82+log(H 4 SiO 4 )+2pH

Zn 3 (AsO4) 2 ↔ Soil Zn Log(HAsO 4 2 )= -12.8+2pH

Cu 3 (AsO4) 2 ↔ Soil Cu Log(HAsO 4 2 )= -11.68+2pH



### An important aspect of As chemistry is th e effect of redox in controlling As mineral stability. Arsenite (III) sulfide minerals ar e predicted to be the most stable arsenic mineral at suboxic to anoxic redox potentials (pe+pH ≤ 7) ( Figure 3 ). At higher redox potentials (pe+pH>7),Ca 3 

### (As0 4 

### ) 2 

### is predicted to be the most stable arsenate (V) mineral.

pe+pH 0 5 10 15 20log (HAsO42-)

-20 -15 -10 -5 0

Arsinolite (As 2 0 3 )
Claudenite(As 2 O 3 )
Realger (AsS) Orpiment (As 2 S 2 )

As 2 S 3 Ca 3 (As0 4 ) 2

Figure 3: Arsenate Mineral Stability Diagram as a Function of Redox Conditions (pe+pH)

Table 8. Chemical Equilibria Equations for As Minerals as a Function of Redox Potential. Mineral Equilibria Equilibrium Equation

As 2 0 3 ↔ HAsO 4 2 Log(HAsO 4 2- )= -29.325+2pH+ 2(pe+pH)

AsH 3 (g) ↔ HAsO 4 2- Log(HAsO 4 2- )= -28.92+2pH+ 2(pe+pH)

AsS ↔ HAsO 4 2- + SO 4 2- Log(HAsO 4 2- )= -83.13-log(SO 4 2- )+4pH+11(pe+pH)

As 2 S 2 ↔ HAsO 4 2- + SO 4 2- Log(HAsO 4 2- )= -90.21-log(SO 4 2- )+0.5pH+11(pe+pH)

As 2 S 3 ↔ HAsO 4 2- + SO 4 2- Log(HAsO 4 2- )= -109.57-1.5 log(SO 4 2- )+ 4pH + 15 (pe+pH)

Cu 3 (AsO 4 ) ↔ CuFe204 +Fe3O4 Log(HAsO 4 2- )= -26.1+2pH+(pe+pH)

### Page 52 of 58 Cu 3 (AsO 4 ) ↔ CuFe204 +Fe3(OH)8 Log(HAsO 4 2- )= -18.05+2pH+(pe+pH) Mn(AsO 4 ) 2 ↔ ß-MnO2 Log(HAsO 4 2- )= -58.58+2pH+3(pe+pH) Mn(AsO 4 ) 2 ↔ ð-MnO1.9 Log(HAsO 4 2- )= -23.73+ 0.9(pe+pH) Mn(AsO 4 ) 2 ↔ ð-MnO1.8 Log(HAsO 4 2- )= -22.24+ 0.8(pe+pH)

FeAsO 4 ↔ Amorp Fe(OH) 3 Log(HAsO 4 2- )= -12.9+2pH

FeAsO 4 ↔ Geothite ά -FeOOH Log(HAsO 4 2- )= -9.43+2pH

Fe 3 (AsO 4 ) 2 ↔ Amorp Fe(OH) 3 Log(HAsO 4 2- )= -33.74+2pH+1.5(pe+pH)

Fe 3 (AsO 4 ) 2 ↔ Geothite ά -FeOOH Log(HAsO 4 2- )= -28.53+2pH+1.5(pe+pH)



### Soluble Inorganic As Species

The soluble As species is a mixture of arsenic acid (H 3 

### AsO 4 

### ) ions, arsenious acid (As(OH) 3 

### ) ions, and halides of As (Sadiq, et al ., 1982). In oxic environments (pe+pH>8), the predominate arsenic acid species are H 2 

### AsO 4 - 

### and HAsO 4 2- 

### in environmental pH range of 5 to 8. Unde r suboxic and anoxic conditions (pe+pH<8), the predominant inorganic arsenious acid species are HAsO 2 o 

### and H 3 

### AsO 3 o 

### . Arsine gas (AsH 3 

### ) is only a predominate species in low re dox (pe+pH<0.5) and acidic environments.

Table 9. Chemical Equilibria Equations for Inorganic As Species. Equilibria Equilibrium Equation

AsBr 3 (g) ↔ HAsO 4 2- Log(AsBr 3 (g)) =14.32 + log(HAsO 4 2- )+3log(Br-)-5pH-2(pe+pH)

AsCl 3 (g) ↔ HAsO 4 2- Log(AsCl 3 (g)) =15.24 + log(HAsO 4 2- )+3log(Cl-)-5pH-2(pe+pH)

AsF 3 (g) ↔ HAsO 4 2- Log(AsF 3 (g)) =50.44 + log(HAsO 4 2- )+3log(F-)-5pH-2(pe+pH)

AsH 3 (g) ↔ HAsO 4 2 Log(AsH 3 )=28.92+log(HAsO 4 2- )-2pH-8(pe+pH)

AsO 2 - ↔ HAsO 4 2- Log(AsO 2 - )=19.32+log(HAsO 4 2- )-pH-2(pe+pH)

AsO 3 3- ↔ HAsO 4 2- Log(AsO 3 3- )=6.13+log(HAsO 4 2- )-pH-(pe+pH)

HAsO 3 2- ↔ HAsO 4 2- Log(HAsO 3 3- )=2.27+log(HAsO 4 2- )-2(pe+pH)

H 2 AsO 3 - ↔ HAsO 4 2- Log(H 2 AsO 3 - )=19.40+log(HAsO 4 2- )-pH-2(pe+pH)

H 3 AsO 3 ↔ HAsO 4 2- Log(H 3 AsO 3 )=-28.63+log(HAsO 4 2- )-2pH-2(pe+pH)

AsO 4 3- ↔ HAsO 4 2- Log(AsO 4 3- )= 11.50+log(HAsO 4 2- )+pH

HAsO 2 ↔ HAsO 4 2- Log(HAsO 2 )=28.60-2(pe+pH)-2pH+log(HAsO 4 2- )

H 3 AsO 4 ↔ HAsO 4 2- Log(H 3 AsO 4 )=-9.28+log(HAsO 4 2- )-2pH

H 2 AsO 4 - ↔ HAsO 4 2- Log(H 2 AsO 4 - )=-6.94+ log(HAsO 4 2- )-pH



### Soluble Methylated As Species

The methylation of As has been describe d using the Challenger pathway (Bentley and Chasteen, 2002) ( Figure 4; Table 10 ). This pathway is a sequen tial series of two electron reductions of arsenate (V) to arsenite (II I) which are linked to a methylation-oxidation reaction forming a sequential methylarsenate (V) species. The reducta nts in the pathwayare thiols, glutathione (GSH), and lipoic acid. The methyl donor in the pathway is Sadenosylmethionine (SAM). The methylation process of arsenic ha s been identified in mammals, fungi, and bacteria.

### Page 53 of 58 Figure 4: Proposed Challenger pathway for As Methylation



### .

Domrowski et al ., 2005 used chemical equilibria to pred ict the distributio n of methylated As species in human urine. Equilibrium constants (log K o 

### ) for methylated arsenic species
were estimated from the standard free ener gy change of the products and reactants in their standard states (25 o 

### C). Methane concentrations (CH 4 

### ) were assumed to be controlled by equilibria with CO 2. 

### Chemical equilibria reactions for methylated As species in Table 10 correspond to chemical reaction numbers in Figure 5

.

Table 10. Chemical Equilibria Equations for Methylated As Species.

Reaction Equilbria Chemical Reaction

1+2 As 5+ ↔ MMA(V) Log[MMA(V)]=53.44+log(HAsO 4 2- )-pCO 2 -2pH-10(pe+pH)

3 MMA(V) ↔ MMA(III) Log[MMA(III)]=64.86+log(HAsO 4 2- )-pCO 2 -2pH-12(pe+pH) 4 MMA(III) ↔ DMA(V) Log[DMA(V)]=106.35+log(HAsO 4 2- )-2pCO 2 -pH-20(pe+pH) 5 DMA(V) ↔ DMA(III) Log[DMA(III)]=115.90+log(HAsO 4 2- )-2pCO 2 -pH-22(pe+pH) 6 DMA(III) ↔ TMA(V) Log(TMA(V)]=122.19+log(HAsO 4 2- )-3pCO 2 -32(pe+pH) 7 TMA(V) ↔ TMA(III) Log(TMA(V)]=133.29+log(HAsO 4 2- )-34(pe+pH)



### Using the chemical equilibria equations in Tables 9 and 10 , a mole fraction diagram was developed to show their predominance of As species as a function of redox potential (pe+pH) at a specific pH ( Figure 5 ).

### Page 54 of 58 pe+pH 0 5 10 15 20log (mole fraction)

-20 -15 -10 -5 0 MMA(V) MMA(III) DMA(V) DMA(III) TMA(V) TMA(III) AsBr3(g) AsBr3(g) AsF3(g)

AsH3
AsO2-
HAsO32-
H2AsO3-
H3AsO3
AsO43-
HAsO2
H3AsO4
H2AsO4-
HAsO42-

Figure 5: Mole Fraction Diagram (pH=6) for Soluble Methylated As and Inorganic As Species



### APPENDIX E. Chemical Equilibria Model for As Speciation.

A chemical equilibria model wa s developed to predict the co ncentration of individual As species in surface water. Chemical equilibri um constants were derived from Sadiq, 1983 and Domrowski et al., 2005. The chemical e quilibria model is based on estimating the concentration of individual As species from a total soluble As concentration (expressed

as HAsO 4 2- 

### ) and general water quality data for su rface water. The total soluble As concentration is equal to the summation of molar concentratio ns of individual As species ( Equation 1).

Equation 1: Distribution of Individual As Species

[Total As]= [HAsO 4 2- 

### ]+ [H 2 

### AsO 4 - 

### ]+ [AsO 4 3- 

### ]+[H 3 

### AsO 3 

### ]+[H 2 

### AsO 3 - 

### ]+[HAsO 3 2- 

### ]+ [AsO 3 3- 

### ]+ [HAsO 2 

### ]+[AsO 2 - 

### ]+ [AsH 3 

### (g)]+ [AsF 3 

### (g)]+ [AsCl 3 

### (g)]+ AsBr 3 

### (g)] +[MMA(III)]+[DMA(III)]+[ TMA(III)] +[MMA(V)] +[DMA(V)]+[TMA(V)]

The concentrations of the individual As speci es in Equation 1 can be expressed in terms of chemical activities (or effectiv e concentration) using Equation 2.

Equation 2: Chemical Activity Equations

[Concentration]* δ (activity coefficient)= (chemical activity)

or [Concentration] = (chemical activity)/ δ (activity coefficient)

The concentration of each As species can be calculated from chemi cal activities using

### Page 55 of 58 

### Equation 3

.

Equation 3: Chemical Concentrations in Terms of Chemical Activities

[Total As]= (HAsO 4 2- 

### )/ δ HAsO42- 

### + (H 2 

### AsO 4 - 

### )/ δ H2AsO4- 

### + (AsO 4 3- 

### )/ δ AsO43- 

### + (H 3 

### AsO 3 

### )/
δ H3AsO3 

### + (H 2 

### AsO 3 - 

### )/ δ H2AsO3- 

### + (HAsO 3 2- 

### ) / δ HAsO32- 

### + (AsO 3 3- 

### )/ δ AsO33- 

### + (HAsO 2) 

### / δ HAsO2 

### + (AsO 2 - 

### )/ δ AsO2- 

### + (AsH 3 

### (g))/ δ AsH3 

### + (AsF(g)) / 

### δ AsF3 

### + (AsCl 3 

### (g))/ δ AsCl3(g) 

### + (AsBr 3 

### (g))/ δ AsBr3(g) 

### +(MMA(III))/ δ MMA(III) 

### + (DMA(III))/ δ DMA(III)+ 

### ( TMA(III))/ δ TMA(III) 

### + (MMA(V))/ δ MMA(V) 

### + (DMA(V))/ δ DMA(V) 

### + (TMA(V))/ δ TMA(V)



### The activity for each species is calculated using the equilibrium equations shown in Tables 1. The ionic strength is calcul ated using the concentrations of Na + 

### , Mg 2+ 

### , Ca 2+



### , K + 

### , SO 4 2- 

### , and Cl - 

### from surface water quality data. Ch arge balance was maintained by ensuring the molar concentration*valence fo r anions and cations are equal. Any difference in charge balance was adjusted by additional concentration of a monovalent ion (eg., NO 3 - 

### ). The ionic strength was calculated using Equation 4

.

Equation 4: Ionic Strength

μ=1/2 ∑ C i 

### Z i 2



### where: Ci= molar concentration of ion
Zi=valance of ion μ=ion strength

The Davies Equation was used to es timate the activity coefficient ( δ ) for each As species ( Equation 5 ).

Equation 5: Davies Activity Coefficient ( δ i)

Log δ i=-AZi 2 

### (μ 1/2 

### /1+μ 1/2 

### – 0.3μ)

where: δ i= activity coefficient
A= constant at 25 o 

### C
Zi=valance of ion μ=ion strength (calculated in Equation 4)

Tables 1: Chemical Equilibria E quations for Inorganic As Species Equilibria Equilibrium Equation

AsBr 3 

### (g) ↔ HAsO 4 2- 

### Log(AsBr 3 

### (g)) =14.32 + log(HAsO 4 2- 

### )+3log(Br-)-5pH-2(pe+pH)

AsCl 3 

### (g) ↔ HAsO 4 2- 

### Log(AsCl 3 

### (g)) =15.24 + log(HAsO 4 2- 

### )+3log(Cl-)-5pH-2(pe+pH)

AsF 3 

### (g) ↔ HAsO 4 2- 

### Log(AsF 3 

### (g)) =50.44 + log(HAsO 4 2- 

### )+3log(F-)-5pH-2(pe+pH)

AsH 3 

### (g) ↔ HAsO 4 2 

### Log(AsH 3 

### )=28.92+log(HAsO 4 2- 

### )-2pH-8(pe+pH)

AsO 2 - 

### ↔ HAsO 4 2- 

### Log(AsO 2 - 

### )=19.32+log(HAsO 4 2- 

### )-pH-2(pe+pH)

### Page 56 of 58 

### AsO 3 3- 

### ↔ HAsO 4 2- 

### Log(AsO 3 3- 

### )=6.13+log(HAsO 4 2- 

### )-pH-(pe+pH)

HAsO 3 2- 

### ↔ HAsO 4 2- 

### Log(HAsO 3 3- 

### )=2.27+log(HAsO 4 2- 

### )-2(pe+pH)

H 2 

### AsO 3 - 

### ↔ HAsO 4 2- 

### Log(H 2 

### AsO 3 - 

### )=19.40+log(HAsO 4 2- 

### )-pH-2(pe+pH)

H 3 

### AsO 3 

### ↔ HAsO 4 2- 

### Log(H 3 

### AsO 3 

### )=-28.63+log(HAsO 4 2- 

### )-2pH-2(pe+pH)

AsO 4 3- 

### ↔ HAsO 4 2- 

### Log(AsO 4 3- 

### )= 11.50+log(HAsO 4 2- 

### )+pH

HAsO 2 

### ↔ HAsO 4 2- 

### Log(HAsO 2 

### )=28.60-2(pe+pH)-2pH+log(HAsO 4 2- 

### )

H 3 

### AsO 4 

### ↔ HAsO 4 2- 

### Log(H 3 

### AsO 4 

### )=-9.28+log(HAsO 4 2- 

### )-2pH

H 2 

### AsO 4 - 

### ↔ HAsO 4 2- 

### Log(H 2 

### AsO 4 - 

### )=-6.94+ log(HAsO 4 2- 

### )-pH

As 5+ ↔ 

### MMA(V) Log[MMA(V)]=53.44+log(HAsO 4 2- 

### )-pCO 2 

### -2pH-10(pe+pH) MMA(V) ↔ 

### MMA(III) Log[MMA(III)]=64.86+log(HAsO 4 2- 

### )-pCO 2 

### -2pH-12(pe+pH) MMA(III) ↔ 

### DMA(V) Log[DMA(V)]=106.35+log(HAsO 4 2- 

### )-2pCO 2 

### -pH-20(pe+pH) DMA(V) ↔ 

### DMA(III) Log[DMA(III)]=115.90+log(HAsO 4 2- 

### )-2pCO 2 

### -pH-22(pe+pH) DMA(III) ↔ 

### TMA(V) Log(TMA(V)]=122.19+log(HAsO 4 2- 

### )-3pCO 2 

### -32(pe+pH) TMA(V) ↔ 

### TMA(III) Log(TMA(V)]=133.29+log(HAsO 4 2- 

### )-34(pe+pH)

The concentration of each As species was estimated using the following equation.

Equation 6: As Species Concentration Estimation

[As Species]= [Total As Concentration in Water moles/liter]*MF(As species)/ δ arsenic species

### Page 57 of 58 

### APPENDIX E. Results of the Screeni ng Imbibation Program (SIP v. 1.0).

The highest solubility limit for calcium arsenate (the stable mineral phase arsenical
formed under most sub-oxic and oxic conditions ) (between pH 5 and 9) was used since the solubility limit is pH-depende nt (solubility = 467.3 mg As+5/L).

For the mammalian and avian toxicity endpoints, the most sensitive acute and chronic endpoints from all of the inorganic arsenica ls were used. For mammals, an acute endpoint for arsenic acid (LD 50 

### = 52 mg a.i./kg-bw, rat; MRID 0026356) and a chronic endpoint for arsenic acid (NOAEL = 32 mg a.i./kg-bw, mouse; from the chromated arsenicals RED) were used for the modeling. For birds, an acute endpoint for arsenic acid (LD 50 

### = 28.9 mg a.i./kg-bw, bobwhite quai l; MRID 40409013) was used. A chronic endpoint for birds and inorganic arse nicals is not curre ntly available.

Table 1. Inputs

Parameter Value

Chemical name Arsenicals (Calcium Arsenate)
Solubility (in water at 25 o C; mg/L) 467.3

Mammalian LD 50 (mg/kg-bw) 52 Mammalian test species laboratory rat

Mammalian NOAEL (mg/kg-bw) 32 Mammalian test species other Body weight (g) of "other" mammalian species 20

Avian LD 50 (mg/kg-bw) 28.9 Avian test species northern bobwhite quail Mineau scaling factor 1.15



### Table 2. Mammalian Results

Parameter Acute Chronic Upper bound exposure (mg/kg-bw) 80.3756 80.3756 Adjusted toxicity value (mg/kg-bw) 39.9963 12.0339 Ratio of exposure to toxicity 2.0096 6.6791

Conclusion* Exposure through drinking water alone is a potential

concern for mammals Exposure through drinking water alone is a potential

concern for mammals

### Page 58 of 58 

### Table 3. Avian Results

Parameter Acute Chronic Upper bound exposure (mg/kg-bw) 378.5130 378.5130 Adjusted toxicity value (mg/kg-bw) 20.8204 0.0000 Ratio of exposure to acute toxicity 18.1799 0.0000

Conclusion* Exposure through drinking water alone is a potential
concern for birds Due to insufficient data, risk cannot be precluded

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when aggregated with other routes ( i.e ., diet, inhalation, dermal), pesticide exposure through drinking water may contribute to a total exposure that has potential for effects to non-target animals.