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INTRODUCTION

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP) for 

the registration review of MSMA. This work plan addresses public comments received 

concerning the Preliminary Work Plan (PWP), which was posted in the MSMA registration 

review docket (EPA-HQ-OPP-2013-0107). MSMA is a broad-spectrum, post-emergent, organic 

arsenical herbicide currently registered for use to selectively control grasses and broadleaf weeds 

in cotton and turf grass (i.e., golf courses, sod farms, and highway rights-of-way). MSMA 

cannot be used in Florida, except for on cotton in certain counties. 

The remaining uses on turf grass were to be phased out and prohibited after December 31, 2013 

according to a 2009 Agreement in Principle with the technical registrants. However, the 2009 

Agreement also provided for a scientific peer review related to the carcinogenic mode of action 

(MOA) of inorganic arsenic (iAs), prior to the final phase-out of the remaining MSMA turf uses. 

In light of a Congressional directive to the National Academy of Sciences (NAS) (House Report 

112-151 accompanying HR 2584) to evaluate the carcinogenic mode of action of inorganic 

arsenic, EPA and the MSMA registrants recently agreed to modify the 2009 Agreement (letter 

from Richard P. Keigwin Jr., Director, Pesticide Re-evaluation Division, to Lynn Bergeson on 

behalf of the Organic Arsenical Products Task Force, dated Sept. 14, 2012) to include the NAS 

as a potential peer review body. It is EPA’s current intention to rely on the NAS for the peer 

review of the mode of action, although EPA retains the right to utilize either of the Agency’s 

scientific peer review bodies (Science Advisory Board or FIFRA Science Advisory Panel) if it 

later determines that utilization of an Agency peer review body would be more appropriate. The 

NAS final report is currently scheduled to be completed in late 2015. Therefore, EPA will 

postpone any decision regarding the phase-out of the uses of MSMA on golf courses, sod farms, 

and highway rights-of-way until the NAS review is complete and the Agency has analyzed and 

responded to the NAS report. The Agency documents discussed above can be found in the 

Organic Arsenicals; Amendment to Reregistration Eligibility Decision docket EPA-HQ-OPP2009-0191. 

The Agency is implementing the registration review program pursuant to Section 3(g) of the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each registered 

pesticide every 15 years to determine whether it continues to meet the FIFRA standard for 

registration. Changes in science, public policy, and pesticide use practices occur over time. The 

registration review program is intended to make sure that, as the ability to assess risk evolves and 

as policies and practices change, all registered pesticides continue to meet the statutory standard. 

The public phase of registration review begins when the initial docket is opened for each case. 

Information on this program is provided on the Agency’s website.1

The FWP begins with any updates since the PWP was issued. Next is a summary of substantive 

comments received during the public comment period for the PWP concerning anticipated data 

needs, expected risk assessments, or the estimated timeline identified in the PWP, and a 

summary of the Agency’s responses to those comments. This section is followed by registration 

review planned data needs, risk assessments expected to be conducted, and the projected 

registration review timeline for MSMA. Lastly, there is a discussion of next steps. 

 

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 http://www.epa.gov/oppsrrd1/registration_review/ 
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UPDATES SINCE THE PWP WAS ISSUED

There are no additional updates on MSMA since the PWP. 

SUMMARY OF COMMENTS AND AGENCY RESPONSES

During the 60-day public comment period on the MSMA Preliminary Work Plan, which opened 

on March 27, 2013 and closed on May 28, 2013, the Agency received one comment from the 

Organic Arsenicals Product Task Force (OAPTF), addressing several issues including the 

timeline described in the PWP, as well as the planned ecological and human health risk 

assessments and data requirements. In the PWP, EPA also solicited comments on the specific 

topics of environmental justice, water quality concerns, and trade irritants, but no comments or 

information were received on those issues. 

The OAPTF comment did not result in changes to the anticipated registration review data needs, 

risk assessments, or timeline. Public comments and EPA responses in their entirety are located 

in the docket, EPA-HQ-OPP-2013-0107. Agency responses related to the anticipated ecological 

risk assessment and data needs are in the EFED Response to Public Comments on the 

Monosodium Methanearsonate (MSMA) Problem Formulation for Ecological Risk and Drinking 

Water Exposure while those relevant to the anticipated human health risk assessment and data 

needs are in the HED Monosodium Methanearsonate (MSMA): Response to Comments on the 

Registration Review Workplan. 

 
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PLANNED DATA NEEDS

Table 1 below summarizes the planned data needs for MSMA based on the Registration Review: 

Preliminary Problem Formulation for Monosodium Acid Methanearsonate (MSMA), the 

Monosodium Methanearsonate (MSMA): Revised Registration Review Scoping Document for 

Human Health Assessments, and the Response to Comments documents. The planned data needs 

have not changed from what was included in the PWP. 

Table 1: Planned Data Needs for the MSMA Registration Review 

Guideline 

Number2 Study Title2 

Test Material 

Estimated 

Timeframe 

(Months from 

receipt of DCI) 

835.4300 Aerobic aquatic metabolism3 

TGAI or 

PAIRA; 

Methylated 

arsenics (V) 

24 

850.1300 Aquatic invertebrate life cycle (freshwater) 

TGAI; 

Methylated 

arsenics (V) 

12 

850.1350 Aquatic invertebrate life cycle (saltwater) 

TGAI; 

Methylated 

arsenics (V) 

12 

850.1500 Fish life cycle (Freshwater) 

TGAI; 

Methylated 

arsenics (V) 

24 

850.1735 Whole sediment: acute freshwater invertebrates 

TGAI; 

Methylated and 

inorganic 

arsenics (III) 

24 

Nonguideline 

Whole sediment: chronic freshwater invertebrates 

(Hyalella or Chironomus) 

TGAI; 

Methylated and 

inorganic 

arsenics (III) 

24 

850.2100 Avian oral toxicity (passerine) 

TGAI; 

Methylated 

arsenics (V) 

12 

850.2300 Avian reproduction 

TGAI; 

Methylated 

arsenics (V) 

24 

 

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 On June 27, 2012, EPA announced certain revisions in harmonized guideline series 850 – Ecological Effects Tests 

– including renumbering and other designations or changes for some guideline studies. See “Final Test 

Guidelines; OCSPP 850 Series; Notice of Availability” 77 FR 38282, June 27, 2012. 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-0028 3

 A study is under Agency review for the aerobic aquatic metabolism data requirement. This data requirement has 

not been included in a DCI previously, therefore it will be included in the Registration Review DCI. 
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Table 1: Planned Data Needs for the MSMA Registration Review 

Guideline 

Number2 Study Title2 

Test Material 

Estimated 

Timeframe 

(Months from 

receipt of DCI) 

860.1500 Crop Field trials (cotton gin byproducts) 4 TEP 24 

870.7800 Immunotoxicity 

TGAI; 

Methylated 

arsenics (V) 

12 

TGAI = technical grade active ingredient; TEP = typical end-use product; 

 

 

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 The data requirement for crop field trials for cotton gin byproducts has not been included in a DCI previously; 

therefore it will be included in the Registration Review DCI. 
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RISK ASSESSMENTS FOR REGISTRATION REVIEW

During registration review, the Agency will conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, for all uses of MSMA. For human health, EPA will 

conduct revised dietary, residential, occupational, and aggregate risk assessments. If 

toxicological endpoints or points of departure are revised based on the data that are required for 

registration review, they will be considered in the new assessments, as well as any changes to the 

standard operating procedures or default exposure assumptions. 

Table 2 below summarizes the planned registration review risk assessments based on the EFED 

Problem Formulation and HED Scoping Document. The planned assessments have not changed 

from what was included in the PWP. 

Table 2: Planned Risk Assessments for the MSMA Registration Review 

Type of Risk Assessment Conduct? Notes 

Ecological and Environmental Fate 

Comprehensive ecological 

(species to be assessed 

include terrestrial and aquatic 

organisms), including 

endangered species 

Yes 

Arsenic speciation was not quantitatively considered 

in the Reregistration Eligibility Assessment (RED) 

for MSMA and DSMA, but will be considered in this 

updated assessment. 

Incidents 

Will check for 

updates 

A formal review is not planned, but the agency will 

continue to monitor incident data throughout 

registration review. For a discussion of MSMA’s 

reported ecological incidents, see page 17 of the 

Problem Formulation. 

Human Health 

Dietary 

Food 

Yes 

These assessments may be required, and would use 

existing data for monomethylarsonic acid, 

dimethylarsinic acid, and iAs; the most updated 

information and policies, revised points of departure 

(PoDs) or uncertainty factors including any NAS 

Review revised cancer MoA; updated consumption 

information and the latest dietary exposure model; 

and updated estimated drinking water concentrations 

(EDWC’s). 

Drinking water 

Occupational 

Handlers (mixers, loaders, 

applicators) Yes 

An updated assessment may be required due to 

changes to the use pattern and revisions to scenario 

specific surrogate handler exposure data since the 

assessment done for the RED. 
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Table 2: Planned Risk Assessments for the MSMA Registration Review 

Post-application 

Yes 

An updated dermal assessment may be necessary. A 

quantitative post-application inhalation exposure 

assessment is not required at this time; however, if 

new policies and procedures are put into place to 

incorporate volatilization of pesticides as a potential 

source of post-application inhalation exposure, the 

need for this assessment may be revisited. 

Residential 

Handlers 

Yes 

A revised non-cancer assessment may be required 

that includes post-application exposure to treated golf 

courses and will incorporate as necessary updated 

SOP’s, human factor assumptions, and currently 

registered use patterns. The need for spray drift and 

volatilization assessments will also be evaluated. 

Post-application 

Other 

Aggregate 

Yes 

Evaluates the combined risk from dietary and 

residential exposures. This assessment may be 

required because of the potential for short-term 

residential post-application exposure from the golf 

course use. Updated PoDs, uncertainty and safety 

factors, and drinking water assessment revisions and 

residential assessment findings will be incorporated. 

Cumulative 

No 

At this time, EPA does not have available data to 

determine whether MSMA has a common mechanism 

of toxicity with other substances. 

Tolerances 

No 

The current tolerance expression as listed in the 40 

CFR § 180.289(a) will need to be revised to reflect 

product cancellations following the 2006 RED and 

subsequent agreements with the registrants. These 

changes are detailed in the Monosodium 

Methanearsonate (MSMA): Registration Review 

Scoping Document for Human Health Assessments.

Incidents 

Will check for 

updates 

A formal review is not planned, but the agency will 

continue to monitor incident data throughout 

registration review. For a discussion of MSMA’s 

reported human incidents, see page 11 of the Scoping 

Document. 

TIMELINE

EPA has created the following estimated timeline for the completion of the MSMA registration 

review in Table 3 below. The projected timeline has been revised since the PWP, because it is 

expected that less time will be required to issue the Data Call-In (DCI). 
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Table 3: Registration Review for MSMA– Projected Registration Review Timeline

Activities Estimated Date 

Opening the Docket 

Open Docket and 60-day Public Comment Period March 2013– Completed 

Close Public Comment May 2013 – Completed 

Case Development 

Final Work Plan August 2013 – Completed 

Issue DCI 2014 – January - March 

Data Submission 2016 – January - March 

60-day Public Comment Period for Draft Risk Assessments5 2017- July - September 

Registration Review Decision 

60-day Public Comment Period for Proposed Registration Review 

Decision 

2019 – January - March 

Registration Review Decision and Begin Post-Decision Follow-up 2019 

Total (years) 6 

NEXT STEPS

As noted previously, the Agency plans to require several environmental fate, ecological effects, 

and human health studies for MSMA through a Data Call-In Notice, expected to be issued in 

January – March 2014. 

 

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 The regulations governing Registration Review require the Agency to provide a public comment period of at least 

30 calendar days for draft risk assessments; see 40 CFR Part 155.53(c). The Agency plans to provide a 60 calendar 

day public comment period for draft risk assessments as a general standard of practice.