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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 methyldithiocarbamate salts (metam sodium, metam potassium) and 

methyl isothiocyanate (MITC). This work plan addresses public comments received concerning 

the Preliminary Work Plan (PWP), which was posted in the methyldithiocarbamate salts (metam 

sodium, metam potassium) registration review docket (EPA-HQ-OPP-2013-0140) and the MITC 

registration review docket (EPA-HQ-OPP-2013-0242). Metam sodium and metam potassium 

(hereafter referred collectively as “metam”) are non-selective fumigant biocides registered for 

use as pre-plant soil fumigants for use on a variety of food, feed, fiber crops, forest trees, 

ornamentals and turf, including golf courses, to kill soil dwelling pests (fungi, weeds, insects, 

and nematodes). There are several non-agricultural registered uses of metam, including 

antimicrobial uses and sewer root-control use. After application, metam breaks down quickly to 

the primary toxic degradate, MITC gas. MITC is highly volatile and is responsible for the 

biocidal properties of these fumigants. In addition to being a degradate of metam, MITC is also 

registered itself as an antimicrobial active ingredient for wood pole/timber use. There are no 

registered residential uses of metam or MITC products. MITC is also the primary degradate of 

the fumigant active ingredient dazomet, which is addressed as a separate registration review 

case.

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.

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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 metam and MITC. Lastly, there is a discussion of next steps.

UPDATES SINCE THE PWP WAS ISSUED

• Changes to data requirements, Table 1

o The table now clarifies that data are not required for antimicrobial metam and 

MITC products registered only for wood pole/timber use. 

o In the PWP, the honey bee acute contact toxicity study (850.3020) was incorrectly 

marked as “under review.” The study was waived in 2010. Therefore, it has been 

removed from Table 1.

 1 http://www.epa.gov/oppsrrd1/registration_review/
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o The avian acute inhalation study was not listed in the PWP table for previously 

required data. It is now included in Table 1 below. The study is under review.

o Reviews of the prenatal developmental toxicity study (870.3700) and the acute 

neurotoxicity study (870.6200) are now complete and classified as acceptable. 

Therefore, these studies have been removed from Table 1.

o Data received for sewer uses of metam have been reviewed and found acceptable. 

Therefore, the sewer use studies have been removed from Table 1.

o The timeframe for the ambient air monitoring program has been extended from 

March 2014 to December 2016. Since the PWP was issued, the registrants have 

been working with the Agency to develop a protocol for this study.

o The metam registrant with antimicrobial products registered for cooling tower and 

industrial water purification system uses has agreed to remove those uses from 

product labels. These uses triggered the need for post-application exposure data. 

Therefore, when the uses are removed from labels, then metam antimicrobial

post-application exposure data (875.2500 and 875.2900) will no longer be 

required.

• Changes to risk assessments, Table 2

o The Agency has concluded that a drinking water assessment will not be required 

for metam and MITC. Based on use patterns and the volatile nature of MITC, the 

Agency does not expect MITC to adversely impact drinking water sources such as 

surface water and ground water. 

SUMMARY OF COMMENTS AND AGENCY RESPONSES

During the 60-day public comment period on the Metam and MITC Preliminary Work Plan, 

which opened on September 25, 2013 and closed on November 25, 2013, the Agency received 

28 total public comments on both the MITC and metam dockets. Comments were submitted by 

growers, grower groups, state agricultural offices, University of Georgia Extension, the Center 

for Biological Diversity, the task force representing metam pesticide registrants, and the FIFRA 

Endangered Species Task Force (FESTF). Two comments addressed the timeline described in 

the PWP by requesting an extension to the comment period. Comments from the Metam Task 

Force specifically addressed the planned ecological and human health risk assessments and data 

requirements. Most comments expressed strong support for the continued registration for metam 

soil fumigant products and provided benefits information. Some comments expressed concern 

over recently implemented risk mitigation measures, which were the result of the previous reevaluation program, known as reregistration for metam. No comments were received regarding 

the antimicrobial uses of metam or MITC. 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.

None of the public comments resulted in changes to the anticipated registration review data 

needs, risk assessments, or timeline, or are of a broader regulatory nature. Public comments in 

their entirety are located in the dockets, EPA-HQ-OPP-2013-0140 and EPA-HQ-OPP-2013-

0242. Summarized public comments and Agency responses related to the anticipated ecological

risk assessment or data needs are in the EFED Response to Metam Task Force Comments to 
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Data Call-In and Problem Formulation on the Registration Review of Metam Sodium, Metam 

Potassium and Methyl Isothiocyanate (MITC) (DP Barcode: D416688, dated February 10, 2014.

Comments relevant to the anticipated human health risk assessment or data needs are in the 

RESPONSE TO COMMENTS. The Health Effects Division’s Response to the Idaho State 

Department of Agriculture on the Metam Sodium, Metam Potassium, Methyl Isothiocyanate 

Registration Review Scoping Document for Human Risk Assessment, dated February 18, 2014.

Responses to all other comments are in the Responses to Public Comments on the Metam and 

MITC Preliminary Work Plan.

PLANNED DATA NEEDS

Table 1 below summarizes the planned data needs for metam and MITC based on the EFED and 

AD Registration Review Problem Formulation for Metam Sodium, Metam Potassium, and MITC,

dated September 19, 2013, and Metam Sodium, Metam Potassium, and MITC. Human Health 

Assessment Scoping Document in Support of Registration Review, dated September 4, 2013.

Some minor changes were made to the planned data needs table from what was included in the 

PWP. Timeframes for some previously required data have been updated. Also, the table now 

clarifies that data will not be required for antimicrobial metam and MITC products registered 

only for wood pole use. Therefore, the Agency does not anticipate any data call in for the MITC 

product, which is registered only for wood pole use. For an explanation, see pages 34-35 of the 

Problem Formulation.

Table 1: Planned Data Needs for Metam Registration Review

Guideline 

Number Study Title Test Material

Estimated 

Timeframe

(Months from 

receipt of DCI)

Anticipated Data Needs for Soil Fumigant and Antimicrobial (other than wood pole/timber use)

Uses of Metam

835.4300 Aerobic aquatic metabolism MITC 24

850.4100 Terrestrial plant toxicity, seedling emergence MITC 12

850.6100

Environmental chemistry methods and associated 

independent laboratory validations for air and 

water

MITC 12

Nonguideline Acute vapor exposure honey bee study MITC 12

Anticipated Data Needs for Soil Fumigant Uses of Metam

835.8100 Field volatility – shank bedded application Metam TEP 12
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Table 1: Planned Data Needs for Metam Registration Review

Guideline 

Number Study Title Test Material

Estimated 

Timeframe

(Months from 

receipt of DCI)

Outstanding Data Requirements from Post-RED DCIs for All Uses2

870.3800 Reproduction and fertility effects MITC Due April 2014

870.4200 Carcinogenicity MITC Due April 2014

835.8100 Field volatility from soil – center pivot application

Metam – TEP 

(metam soil 

fumigant product)

Under review

850.1025 Oyster acute toxicity test (shell deposition) MITC Under review

850.1035 Mysid acute toxicity test MITC Under review

850.1075 Fish acute toxicity test, freshwater and marine MITC Under review

850.4150 Vegetative vigor (Tier II) MITC Under review

850.4400 Aquatic plant growth toxicity (Tier II) MITC Under review

Nonguideline Avian acute inhalationMITC Under review

Outstanding Data Requirements from Post-RED DCIs for Soil Fumigant Uses Only3

NonguidelineAmbient air monitoring program Metam – TEP Due December 

2016

Outstanding Data Requirements from Post-RED DCIs for Antimicrobial Uses Only4

875.1200 Dermal exposure--indoor TEP Extension 

requested*

875.1400 Inhalation exposure--indoor TEP Extension 

requested*

875.1600 Application exposure monitoring data reporting TEP Extension 

requested*

875.1700 Product use information TEP Extension 

requested*

 2 The studies listed in this section were previously required through generic metam sodium (metam-Na) and metam 

potassium (metam-K) data call-ins (DCI) issued in March 2010 and are still outstanding. The DCI numbers are as 

follows: Soil Fumigant Registrants (Metam-Na: GDCI-039003-28196, Metam-K: GDCI-039002-28888); 

Antimicrobial Registrants (Metam-Na: GDCI-039003-29028, Metam-K: GDCI-039002-29030); Sewer Use 

Registrants (Metam-Na: GDCI-039003-29029); MITC registrants (GDCI-068103-29026). These studies will not

be included in the anticipated Registration Review DCI because they are already required through the earlier 

DCIs. 3 The studies listed in this section were previously required through generic metam sodium (metam-Na) and metam 

potassium (metam-K) data call-ins (DCI) issued in March 2011 and are still outstanding. The DCI numbers are as 

follows: Metam-Na: GDCI-039003-840, Metam-K: GDCI-039002-839. These studies will not be included in the 

anticipated Registration Review DCI because they are already required through the earlier DCIs. 4 The studies listed in this section were previously required through generic metam sodium (metam-Na) and metam 

potassium (metam-K) data call-ins (DCI) issued in March 2010 and are still outstanding. The DCI numbers are as 

follows: Metam-Na: GDCI-039003-29028, Metam-K: GDCI-039002-29030. These studies will not be included in 

the anticipated Registration Review DCI because they are already required through the earlier DCIs.
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Table 1: Planned Data Needs for Metam Registration Review

Guideline 

Number Study Title Test Material

Estimated 

Timeframe

(Months from 

receipt of DCI)

875.2500 Inhalation exposure

TEP Data may be 

waived pending 

use deletion

875.2700 Product use information – post-application TEP Extension 

requested*

875.2800 Description of human activity TEP Extension 

requested*

875.2900 Data reporting and calculations

TEP Data may be 

waived pending 

use deletion

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

*After the PWP was issued, antimicrobial metam registrants submitted an updated extension request, which is 

currently under review.

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 metam and MITC. For human health,

EPA will conduct revised residential and occupational risk assessments during registration 

review. 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 

Problem Formulation and Scoping Document and has been updated since the PWP to reflect a 

change to one of the planned risk assessments. This change was based on discussion within EPA 

and not as a result of public comments.

Table 2: Planned Risk Assessments for the Registration Review of Metam and MITC

Type of Risk Assessment Conduct? Notes

Ecological and Environmental Fate

Comprehensive ecological 

(species to be assessed 

include terrestrial and 

aquatic organisms), 

including endangered 

species 

Y MITC will be considered the main stressor in the 

risk assessment. Due to the rapid conversion of 

metam to MITC, it is not expected that metam 

sodium and metam potassium will be bioavailable 

to terrestrial or aquatic organisms in any 

environmentally relevant concentration. 
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Incidents Will check for 

updates

For a discussion of reported ecological incidents 

for metam and MITC, see page 28 of the Problem 

Formulation.

Human Health

Dietary

Food N There is no reasonable expectation of finite 

residues to be incurred in/on food and feed crops 

when metam sodium and metam potassium are 

used on the labeled use sites as preplant soil 

fumigants, so these uses are considered non-food 

uses, and tolerances are not needed. There is also 

no reasonable expectation of finite residues in/on 

food for the antimicrobial uses of metam 

sodium/potassium and MITC.

Drinking water N Based on use patterns and the volatile nature of 

MITC, the Agency does not expect MITC to 

adversely impact drinking water sources such as 

surface water and ground water. A drinking water 

assessment will not be required for metam and 

MITC.

Occupational

Handlers (mixers, loaders, 

applicators)

Y For soil fumigant, sewer, and antimicrobial uses, 

updates to handler risk assessments are 

anticipated.

Post-application Y An updated occupational post-application risk 

assessment for some antimicrobial uses is 

anticipated. 

N The Agency does not anticipate conducting postapplication risk assessments for soil fumigant and 

sewer use in registration review.

Residential

Handlers N There are no registered residential uses of 

metam/MITC.

Post-application N There are no registered residential uses of 

metam/MITC.
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Bystander Y A revised residential risk assessment is 

anticipated in registration review to update risk to 

bystanders from inhalation exposure to MITC 

during and following soil fumigant uses of metam 

products. 

Additionally, the Agency anticipates updating the 

fumigant factors document, which provides a 

discussion of values and parameters used as the 

basis for buffer zone reduction credits as well as 

for establishing Good Agricultural Practices 

(GAPs) for the soil fumigants. Buffer zones and 

GAPs were required by the 2009 amended RED 

as measures to mitigate occupational and 

bystander risk.

Other

Aggregate N Evaluates the combined risk from dietary and 

residential exposures. No dietary risk is 

anticipated from metam and MITC uses. 

Therefore, an aggregate assessment is not 

anticipated.

Cumulative N Metam and MITC are not members of a 

cumulative group, so no cumulative risk 

assessment is planned.

Tolerances N Currently labeled uses are considered non-food 

uses, so tolerances are not needed.

Incidents Will check for 

updates

For a discussion of reported human incidents for 

metam and MITC, see page 12 of the Scoping 

Document and the Metam Sodium, Metam 

Potassium, MITC: Review of Human Incidents.

August 29, 2013.

TIMELINE

EPA has created the following estimated timeline for the completion of the metam and MITC 

registration review in Table 3 below. The projected timeline has been updated since the PWP to 

reflect the lengthening of the timeframe between posting of the draft risk assessment and the 

proposed decision by one quarter.

Table 3: Registration Review for Metam and MITC – Projected Registration Review 

Timeline

Activities Estimated Date

Opening the Docket

Open Docket and 60-day Public Comment Period Sept. 2013 –

Completed

Close Public Comment Nov. 2013 –

Completed
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Table 3: Registration Review for Metam and MITC – Projected Registration Review 

Timeline

Activities Estimated Date

Case Development

Final Work Plan March. 2014 -

Completed

Issue DCI 2014: April - June

Data Submission 2016: April - June

60-day Public Comment Period for Draft Risk Assessments7[1] 2017: Oct. – Dec.

Registration Review Decision

60-day Public Comment Period for Proposed Registration Review 

Decision 

2018: July – Sept.

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 and ecological 

effects studies for metam and MITC through a Data Call-In Notice, expected to be issued in 

2014 to metam sodium and metam potassium soil fumigant and antimicrobial registrants. 

Registrants that only register products with wood pole/timber use will not be issued a Data CallIn Notice. Therefore, the registrant for MITC will not receive a Data Call-In Notice.

 7 The regulations governing Registration Review generally 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). For conventional pesticides, the 

Agency plans to provide a 60 calendar day public comment period generally for draft risk assessments.