UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C.

, 20460

OFFICE OF

CHEMICAL SAFETY AND

POLLUTION PREVENTION

July 11

, 2013

PC Code: 013803

Barcode: D412157

MEMORANDUM

SUBJECT:

TO:

THROUGH:

FROM: Response to Public Comments on the Monosodium Methanearsonate (MSMA)

Problem Formulation for Ecological Risk and Drinking Water Exposure

Assessment.

Garland Waleko

, Chem i cal Review Manager

Risk Management and Imp l ementation Branch II

Pesticide Re-eva l uation Division (7508P)

Dana Spatz, Branch

## Chie~ -- -

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Environmental R i sk

### ranc~~ Environmental Fate and Effects Division (7507P)

Jame s A. Hetrick, Ph.D., Senior Science

# Adviso~ 

# C.

Meli ssa Panger, Ph. D

., Senior Biologi st

, Environmental Risk Branch 3

-- Environmental Fate and Effect s Division (7507P)

This memorandum provides EFED's responses to Organic Arsenical Products Task Fo r ce (OAPTF) comments on the preliminary problem formulation for the ecological risk and drinking

water exposure asse ss ment to be conducted for MSMA. OAPTF comments and the respective

EFED respon s e s are s hown below.



### ENVIRONMENTAL FATE AND EXPOSURE MODEUNG



### OAPTF Comment 1:

OPP should utilize more realistic modeling to estimate transformation of MSMA to inorganic

arsenic As(i) and tran spo rt from treated fields to s urface water.2 EFED Response :

The exposure assessment section in the problem formulation describes the uni que and complex

processes involved in controlling the environment fate and transport of MSMA and its degradation products in soil and aquatic environments

. T o predict the fate of MSMA and its degradation products

, we plan to conduct exposure modeling that consider s the rate of

transformation of MSMA (de methylation /methylation) as well as chemical equilibria of inorganic and organic As species in terrestrial and aquatic environments.

OAPTF Comment 2 :

The OAPTF believes th at PRZM/EXAMS modeling is not an appropriate Tier 2 modeling approach because of conservative assumptions regarding extent of demethylation of MSMA into As(i), MSMA application rate, percent of crop treated with MSMA, and frequency of MSMA applications.

E FED Response :

EFED plans to account for the rate of demethylation of MSMA into As(i) in the PRZM/EXAMS modeling. Additionally, the modeling will be conducted to represent the maximum MSMA application rate and application frequency as stipulated on the cu rrent label. Although t he percent crop treated is not currently a factor considered in the drinking water or ecological exposure

assessment modeling , the appropriate percent crop area ( s ) will be used in the drinking exposure

assessment

.

OAPTF Comment 3 :

The OAPTF believes index reservoir modeling is only screening level assessment. Therefore, a more refined modeling approach is needed.

EFED Response :

The index reservoir scenario serves as a representative scenario for representing a vulnerable community water system ( FIFRA SAP, 1998 ). Refined modeling approaches can be employed

t o account for the rate of transformation of MSMA (de methylation /methylation) as well as chemical equilibria of inorganic and organic As species in terrestrial and aquatic environments

.

OAPTF Comment 4 :

The OAPTF believes a Tier 3 model for MSM A exposure should consider soil kinetics and transformation. OAPTF believes the PRZM/EXAMS modeling should be modified to account

for soil kineti cs and transformation of MSMA.3 EFED Response :

See response to comment 1.

OAPTF Comment 5 :

The OAPTF believes that incorporation of a speciation model for As would improve the exposure modeling.

EFED Response :

Although the exposure modeling for MSMA is a difficult and complex exercise , the complexity

of As sp eciation is an important consideration in the exposure assessment. Chemical speciation modeling can provide a bounding level assessment on the thermodynamic stability of various As species. This type of modeling, however, does not account for the rate of transformations among the various As species. In order to consider chemical kinetics, demethylation rates of MSMA (DMA) to As(i) are intended to be used in PRZM/EXAMS modeling. Appropriate fate properties for DMA and As(i) will be considered in both PRZM and EXAMS modeling to provide an estimated concentration of DMA and As(i) in soil and aquatic enviro nments. Chemical speciation modeling of As in the water column of the standard pond and index reservoir will be conducted to provide bounding estimate s on the variety of inorganic and methylated As species and their concentration

.

OAPTF Comment 6 :

The OAPTF believes MSMA transformation into As(i) in soil needs to be considered in the modeling. This modeling should be compared to experimental data to allow for calibration of the modeling.

EFED Response :

The plan is to use d emethylation rates of MSMA (DMA) in PRZM/EXAMS modeling

. Appropriate fate properties for DMA and As(i) will be considered in both PRZM and EXAMS modeling to provide an estimated concentration of DMA and As(i) in soil and aquatic environments. Chemical speciation modeling o f As in the water column of the standard pond and

index reservoir is planned to provide a bounding estimate of the concentration s and variety of inorganic and methylated As species

.

OAPTF Comment 7 :

The OAPTF believes the exposure modeling should represent actual use conditions in watersheds with MSMA usage. The modeling should consider risk mitigation measures for currently registered MSMA uses (cotton, golf courses, sod farms, and highway rights

- of

- way).4 EFED Response :

T he exposure modeling is conducted to represent current labels. The mitigation measures on the current label will be considered, when possible, in the PRZM/EXAMS modeling.

ECOLOGIAL EFFECTS

OAPTF Comment 8 :

“O P P h a s p r opos e d to re qui r e a qu a tic inv e r t e b ra te li f e c y c l e t e sting wi t h m e t h y l a t e d p e n t a v a l e nt

a r s e nic f or f re shw a t e r ( G u id e line 850.1300) a nd f or s a ltw a t e r ( Gui d e line 850.1350 )

. I n

e v a lu a ti n g li f e c y c le t e sting n e e ds f or ino r g a nic p e nt a v a l e nt ar s e n i c
, E F ED d e t er min e d th a t

a c h r o n ic e ndpoint f or s a ltw a t e r inv er t e b r a t e s ca n b e “ b a s e d on a n ac u t e

- to

- c h r onic r a tio using d a ta f r om fre sh w a t e r in v er t e b r a t e s. ” OA P TF no t e s th a t th er e is a n e x isting ac ute to x i c i t y

stu d y wi t h m y sid sh r imp ( a s a lt w a t e r inv er t e b ra t e ) th a t indi ca t e s th a t M S MA is p rac ti ca l l y

non

- to x ic with a n LC 50/E C 50 of 173 m g / L

. J ust a s E F ED d e t er min e d th a t li f e c y c le t e sti n g with s a ltw a t e r a q u a tic inv er t e b ra t e s i s not n ee d e d f or ino r g a nic p e nt a v a l e nt ar s e ni c, it should

a lso be p rac ti ca ble to utili z e a n ac u t e

- to

- c h r on i c ra tio d e r iv e d fr om the f r e shw a t e r

a qu a tic inv e r t e b r a te li f e c y c le t e sting p r opos e d b y E P A a nd the a v a il a ble ac ute d a ta to d e t e r mine

c h r onic to x i c i t y to s a lt w a t e r in v er t e b r a t e s.” (p. 21

– 22; footnotes have been omitted)

EFED Response :

Based on the available information, there is no indication that estuarine/marine animals are more

sensitive to inorganic pentavalent arsenic than freshwater animals. Therefore, unless data become available that indicate otherwise, EFED agrees that a n ac u t e

- to

- c h r on i c ra tio d er iv e d

fr om an acceptable fre shw a t e r a qu a tic inv er t e b ra te li f e cyc le te st could be used with the a v a il a ble

ac ute da ta to d e t er mine c h r onic to x i c i t y to s a lt wa t e r in ver t e b ra t e s (using an acute

- to

- chronic ratio). Therefore, EFED could concur with a w aiv er of the requirement for an estuarine/marine

invertebrate life cycle test with methylated pentavalent arsenic if an acceptable freshwater invertebrate life cycle test with methylated pentavalent arsenic is submitted.

OAPTF Comment 9 :

In lieu of a freshwater fish life cycle test with methylated pentavalent arsenic, OAPTF suggests using the acute and chronic data for freshwater fish and sodium arsenite [As(III)] to derive a chronic endpoint for MSMA using an acute

- to chronic ratio. Thi s is based on the following: 1) EPA used the AS(III) chronic fish data to derive the ambient water quality criteria for arsenic; and 2) the acute toxicity of As(III) to fish appears similar to that of MSMA. OAPTF state that it is not necessary to require either a life

- cycle study or an early life

- stage study with freshwater fish and methylated pentavalent arsenic for these reasons.

EFED Response:

EPA’s national recommended water quality criteria provide guidance for states and tribes to use in adopting water quality standards for the protection of aquatic life and human health and, for5 aquatic life, are not taxon specific. EPA’s ecological risk as sessments conducted for pesticide registrations are taxon specific. Therefore, data adequate for use in setting national water quality standards may not be fully adequate for assessing taxon

- specific risks associated with pesticide use. Additionally, the re are currently no acceptable chronic data available for methylated arsenicals (including both III and V valences) for any aquatic species. Therefore, the relative toxicities among the arsenicals (organic and inorganic arsenicals, valences III and V) to fish on a chronic basis are unknown at this time. Therefore, EFED recommends requesting chronic toxicity data for freshwater fish and methylated pentavalent arsenic ( i.e ., an early life stage and/or a life cycle study).

OAPTF Comment 10 :

OAPTF states that whole sediment acute tests for freshwater invertebrates should not be required for methylated trivalent arsenic or for inorganic trivalent arsenic because, “...EFED has not cited any data that demonstrate conversion of MSMA to trivalent ars enic compounds in sediment”. (p. 23). They continue, “(i)t appears that EFED has based its recommendation that the two forms of trivalent arsenic be tested in whole sediment solely on chemical equilibria modeling” (p. 23

– 24) and the analysis has not bee n provided. OAPTF states that it is unreasonable to require these data without a detailed explanation for the conclusion that MSMA will transform to trivalent arsenic in sediment. They also argue that it will be costly and redundant to conduct the tests with more than one compound.

EFED Response :

Based primarily on the chemical equilibria modeling described in the MSMA Problem Formulation (USEPA, 2013), both methylated trivalent arsenic and inorganic trivalent arsenic are expected to form under low redo x potential conditions

. Therefore, unless data to show otherwise become available, EFED has a concern for benthic organisms and their potential exposure to trivalent arsenic from the use of MSMA. Additionally, there are currently no data

available to ind icate the relative toxicities of methylated trivalent arsenic and inorganic trivalent

arsenic to benthic organisms. Therefore, EFED recommends requesting whole sediment tests for acute exposure to both methylated trivalent arsenic and inorganic trivalent arsenic

.

OAPTF Comment 11 :

“OPP has also proposed to require testing whole sediment for chronic effects in freshwater invertebrates using technical grade active ingredients for methylated trivalent arsenic and for inorganic trivalent arsenic. These woul d both be non

- guideline studies. EPA’s ecological effects testing requirements for pesticides state that chronic sediment toxicity t ests will only be required if: ‘ The estimated environmental concentration (EEC) in sediment is > 0.1 of the acute

LC50/EC50 values....’ Thus, any proposal by EPA to require chronic sediment toxicity testing for trivalent arsenic is premature, and imposition of such a requirement should be deferred until completion of any acute sediment toxicity testing.

In addition, OAPTF not es that existing methods for chronic sediment toxicity tests with freshwater invertebrates are based on the testing of contaminated sediments and do not6 appropriately address method modifications needed for testing with pesticides or pesticide degradates. Contract laboratories are encountering a number of difficulties in trying to implement chronic sediment testing. Accordingly, MSMA registrants should not be required to conduct this type of test until OPP has issued further guidance on the methodology fo r this test.” (p. 23

– 24; footnotes have been omitted)

EFED Response:

As stated above, EFED has a concern for benthic organisms and their potential exposure to trivalent arsenic from the use of MSMA (this concern is for both acute and chronic exposure). EFED recommends requesting these data if ‘(t) he estimated environmental concentration (EEC)

in sediment is > 0.1 of the acute LC50/EC50 values....’. EFED defers to PRD on whether or not to delay the studies until the completion of the acute sediment tox icity testing.

As stated in the MSMA Problem Formulation, “ (a) lthough 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/R

- 099

- 064: chronic freshwater sediment testing flowthrough ( Chironomus dilutus or C. tentans ). ” (USEPA, 2013, p. 26). EFED recommends that the regis trant submit a protocol for review before conducting the studies. EFED is not aware of any ‘difficulties’ that contract laboratories are encountering when conducting chronic sediment testing with freshwater organisms.

REFERENCES :

USEPA, 2013. Registration Review: Preliminary Problem Formulation for Monosodium Acid Mathanearsonate (MSMA) . Environmental Fate and Effects Division, Office of Pesticide Programs, United States Environmental Protection Agency. Washington, DC. March 12, 2013.

USEP A. 1998. FIFRA Scientific Review Pane l : Proposed Methods for Basin

- scale Estimation of Pesticide Concentrations in Flowing Water and Reservoirs for Tolerance Reassessment

.