UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

DATE: February 18, 2014 

SUBJECT: 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 Seeping Document for Human Risk 

Assessment (OPP Docket# OPP-2013-0140). 

PC Code: Metam Sodium PC Code: 039003, 

Metam Potassium PC Code: 039002, MITC PC 

Code: 068103 

DP Barcode: 0416917 

MRIDNo.: NA Registration No.: NA 

Petition No.: NA Regulatory Action: Registration Review 

Assessment Type: Single Chemical/ Aggregate Reregistration Case No.: NA 

TXR No.: NA CAS No.: Metam Sodium: 6734-80-l , Metam 

Potassium: 137-41-7, MITC: 556-61-6 

FROM: 

THRU: 

TO: 

Shalu Shelat, Industrial Hygienist Y...0A ~~ . \ _.1-'\ 

Risk 

Healt

Assessment 

h Effects Division 

Branch 

(7509P) 

VI 0 f\A\L.U ~ 

Donna Davis, Acting Branch Chief 

Risk Assessment Branch VI 

Health Effects Division (7509P) 

Jose Gayoso, Chemical Review Manager 

Risk Management and Implementation Branch II (7508P) 

Pesticide Re-evaluation Division 

In response to the letter submitted by Mr. Robert Spencer, Bureau Chief for the Division of 

Agricultural Resources with the Idaho State Department of Agriculture (ISDA) in regards to the 

use and application of fumigants as part of the metam sodium, metam potassium, and methyl 

isothiocyanate Preliminary Work Plan (Docket ID No. EPA-HQ-2013-0140). 

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ISDA Comment: 

Wind Speed 

ISDA encourages EPA to look at wind speed as an option for giving buffer zone credits for all 

applications. EPA already requires applicators to observe weather forecasts prior, during and 

after the soil fumigant application. Odors from off-gassing of soil fumigants do not present a 

major problem when wind is present. The majority of the issues occur during calm or inversion 

type conditions. ISDA proposes that if a 5 - 7 mph wind is forecasted, the applicator could 

apply a 10 - 15% buffer credit. If an 8- 10 mph wind is forecasted, the applicator could apply a 

20% buffer credit. If a wind exceeding 10 mph is forecasted, the applicator could apply a 90% 

credit, but not exceed a minimum buffer zone of 25 feet. Maximum wind restrictions for 

chemigation should remain the same. 

EPA Response: 

Currently established buffers take into account actual emissions data measured from field studies 

along with modeling programs. The Probabilistic Exposure and Risk Model for FUMigants 

(PERFUM) modeling program used in the risk assessment process, incorporates a variety of 

weather conditions, including a range of wind conditions, over a 5 year span. This approach 

allows for a generalization of the data to adequately assess fumigant use across the various use 

sites. A significant analysis would need to be performed to determine how the buffers would 

change when considering the ranges proposed by ISDA. In addition, wind is variable by nature. 

Therefore, implementing this approach over the entire course of the emission profile (duration of 

application plus 48 hours after) may be difficult to reasonably predict and may be unrealistic over 

the course of several days of an emissions profile. At this time, EPA does not believe the wind 

speed buffer zone credit proposal presented by ISDA is feasible or appropriate. 

ISDA Comment: 

25' Buffer Criteria 

EPA should allow buffer zones for all ground (shank, bedded, rototilled, etc.) applications to be 

25 feet when followed by~ inch of irrigation. This 25 foot buffer zone should not be limited 

only for broadcast applications. 

EPA Response: 

As stated previously, currently established buffers take into account actual flux data measured 

from field studies using multiple different application techniques along with PERFUM. The 25' 

buffer for shank injection broadcast (with water seal) applications is based on data that has been 

submitted for this specific application method. This buffer distance was not selected for all 

ground (shank, bedded, rototilled, etc) application methods because the currently available flux 

data and PERFUM outputs show that larger buffer zones are appropriate for those methods. 

Stakeholders may submit additional flux studies demonstrating good agricultural practices for 

these application methods if they believe the available flux data do not represent those current 

practices. If such data are submitted, they would be reviewed and assessed during registration 

review to determine how or if they would impact the current buffer distances. 

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