                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                                                      OFFICE OF
                                                            CHEMICAL SAFETY AND
                                                           POLLUTION PREVENTION


MEMORANDUM

DATE: 6/30/2021

SUBJECT:	Dimethenamid and Dimethenamid-p.  Response to the USDA Comment on the Mixer/Loader Risk of Concern in the Human Health Draft Risk Assessment.

PC Code:  129051/120051
DP Barcode:  D462479 
Decision No.:  576514
Registration No.:  NA
Petition No.:  Not Applicable (NA)
Regulatory Action:  Registration Review
Risk Assessment Type:  NA
Case No.:  7223
TXR No.:  NA
CAS No.:  87674-68-8/163515-14-8
MRID No.:  NA
40 CFR:  §180.464
For
For
FROM:	Christopher Severini, Biologist 
            Risk Assessment Branch IV
            Health Effects Division (7509P)

THROUGH:	Shalu Shelat, Branch Chief
            Risk Assessment Branch IV
            Health Effects Division (7509P)

TO:		Lauren Weissenborn, Chemical Review Manager (CRM)
            Jill Bloom, Team Lead
            Cathryn Britton, Branch Chief 
            Risk Management and Implementation Branch V
      Pesticide Reevaluation Division (7508P)

The Pesticide Re-Evaluation Division (PRD) of the Office of Pesticide Programs (OPP) has requested that the Health Effects Division (HED) respond to the United States Agricultural Department (USDA) comment on the dimethenamid/dimethenamid-p Proposed Registration Review Interim Decision (or PID, dated December 17, 2020) related to potential risks to mixer/loaders involved in the commercial impregnation of dry bulk fertilizers with liquid formulations of dimethenamid/dimethenamid-p. HED has addressed this comment below. 

USDA comment (summary): 
In the USDA Comments on the Proposed Interim Decision for Dimethenamid/Dimethenamid-p for Registration Review (USDA; Document ID EPA-HQ-OPP-2015-0803-0033), USDA noted that EPA identified a potential inhalation risk to mixers/loaders of liquid formulations used to impregnate dry bulk fertilizer in commercial facilities (MOE = 670, LOC = 1,000). To address this risk, EPA proposes to reduce mixer/loader exposure by increasing the minimum amount of impregnated fertilizers applied to the field from 200 to 300 lbs/acre (i.e., to maintain the rate of dimethenamid applied to fields, but lower the concentration of dimethenamid being handled per ton of fertilizer). USDA expressed concern that the proposed mitigation could result in growers applying more fertilizer than is typically needed and increase production costs for growers. USDA recommended several alternative approaches to addressing the risks, including using updated Agricultural Handler Exposure Task Force (AHETF) data, which includes a new unit exposure value for the fertilizer impregnation scenario. 

HED Response:
In the human health draft risk assessment for dimethenamid/dimethenamid-p (Dimethenamid/Dimethenamid-P: Draft Human Health Risk Assessment for Registration Review, dated June 19, 2020, hereafter referred to as the DRA), HED assessed potential risks to mixer/loaders involved in the commercial impregnation of dry bulk fertilizers with liquid formulations of dimethenamid/dimethenamid-p. The handler mixer/loader assessment resulted in an inhalation MOE of 670 (based on the use of closed mixing/loading systems), determined to be a risk of concern at the LOC of 1,000. 

In May 2021, after the issuance of the PID, OPP  adopted an Office-wide update to the unit exposures values to be used for occupational handler assessments (the update can be found at https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/occupational-pesticide-handler-exposure-data and  Occupational Pesticide Handler Unit Exposure Surrogate Reference Table - Revised May 2021 (PDF)). In the DRA, HED used an inhalation unit exposure value of 0.083 μg/lb ai for the mixer/loaders involved in the commercial impregnation of dry bulk fertilizer using closed systems with liquid formulations of dimethenamid/dimethenamid-p scenario. As part of the 2021 update to the occupational handler surrogate table, the inhalation unit exposure has been updated to 0.011 μg/lb ai and therefore has resulted in a revision to the  inhalation MOE for this scenario (using closed mixing/loading systems) to 5,100, no longer resulting in a risk of concern at the LOC of 1,000. The updated mixer/loader scenario can be found in Table 1 below.

Table 1.  Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethenamid/Dimethenamid-p.
                               Exposure Scenario
                                Crop or Target
                    Inhalation
Unit
Exposure[1]
(μg/lb ai)
                      Level of PPE or
Engineering control
                    Maximum
Application Rate (in lb ai/ton)
                Area Treated or
Amount Handled Daily (in tons)
                                  Inhalation






                               Dose (mg/kg/day)
                                      MOE
                                 Mixer/Loader
                  Liquid, Impregnation, Commercial treatment
                       Fertilizer, dry bulk, impregnated
                                     0.011
                                    EC/No-R
                                      15
                                      960
                                    0.00198
                                     5100
 The updated Inhalation Unit Exposure can be found at: https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/occupational-pesticide-handler-exposure-data and Occupational Pesticide Handler Exposure Calculator (XLSX) (version date: May 2021) (XLSX)
