### 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 Hea lth Effects Di v ision 's Respon s e t o the Idaho State Department of Agriculture on the Me tam Sodium, Metam Potassium , Methyl Isothiocyanate Registration Review Seepi n g Document for Human Risk Assessment (OPP Docket# OPP -2 013

- 0140). PC Code: Metam Sodium PC Code: 039003, Metam Potass ium PC Code: 039002, MITC PC Code: 068103 DP Barcode: 0416917
MRIDNo .: NA Registration No.: NA Petition No. : NA Regulatory Action: R egist ration Review Reregistration Case No.: NA Asse ssment Type: Single Chemical / Aggregate TXR No.: NA CAS No.: Metam Sodium: 6734-80

- l , Metam Potassium : 1 37 -41-7 , M IT C: 556-61-6


### FROM:

THRU:

TO : Shalu Shelat, Indu s trial Hygienist 

# Y...0A**~~** 

# . \ _.1-'\ Risk Assessment Branch VI 

# 0 f\A\L.U**~** Healt h Effects Division (7509P) Donna Davi s, Acting Branch Chief Risk Assessme n t Branch VI Health E ffects Divis ion (7509P) Jose Gayoso, Chemical Review Manager Risk Management and Implementation Branch II (7508P) Pest icide Re-evaluation Di v is ion
In response to the lette r submi tted by Mr. Robert Spencer, Bureau Chief for the Division of Agricultural Resources with the Idaho S tate D epartment of Agricu l ture (ISDA) in regards to the use and application of fu migants as part of the me tam sodium, metam potassium , and methyl isothiocyanate Preliminary Work Plan (Docket ID No. E PA-HQ-2013

- 0140).

Page 1 of2ISDA Comment: Wind Speed ISDA encou rages EPA to look at wind speed as an optionfor 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 notpresent 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 isforecasted, 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 chemigati on should remain the same. EPA Response: Currently estab li s h ed buffe rs take into account actual emiss io n s data measured from field studies al ong with mod eling programs. T he Probab ili stic Exposure and Risk Model for FUMigants (PERFUM) modeling p rogram used i n t he r i sk assessment process, incor p orates a variety of weather cond i tions, i ncl u di ng a range of wind condi tions, over a 5 year span . Th i s approach a ll ows for a generalization of the data to adequate ly assess fumigant use across the various use s ites . A s i gnifica n t analysis would need to be performed to dete rm i ne how th e buffers would change when cons ide r in g th e ranges proposed by ISDA. 

### In addition, wind is variable by nat ure. Therefore, implementing this a p proach over th e e n ti re course of th e emi ssion pro fil e (durat i o n of application p lus 48 hours after) may be difficult to reasonably pred ic t and may be unrealistic over the course of severa l days of an emissions profi l e. At this time , EPA does not b e li eve the w i nd speed buffer zone credit p r oposal presented by I SDA i s feasib l e or appropriate. ISDA Comment : 25' B u ffer 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 prev iously, currently es t abl ished buffers take into account ac tu al flux data measured from field studies us i ng mu ltiple differ ent appli cation techniques al ong 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 selec ted for all ground (shank, bedded, rotot ill ed, etc) applicati on methods b ecause the currently available flux data and PERFUM outputs s h ow that larger buffer zones are appropriate fo r those methods. Stakeholders may subm i t additional flux studies demonstrating good agric u ltural pract ices for these appl icat i o n me thods if they be li eve the availab l e flux data do n ot represent those current practices. If such data are submitted , they would be reviewed an d assessed during registration rev iew to determin e how or if they wou ld impact the current bu ffer distances
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