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


                                                                PC Code: 053001
                                                            DP Barcodes: 428697


MEMORANDUM	February 17, 2016


SUBJECT:	Metaldehyde: Drinking Water Exposure Assessment for New Use on Garden Beets, Hops, Rutabaga, Turnips, and Wheat in the Pacific Northwest for Interregional Research Project No.4 (IR-4).

TO:			Barbara Madden, Team Leader
            Sidney Jackson, Reviewer
         Minor Use, and Emergency Response Branch
         Registration Division
		
FROM:	James Hetrick, Ph.D., Senior Science Advisor
                              Rosanna Louie-Juzwiak, Risk Assessment Process Leader
               Environmental Fate and Effects Division

THROUGH:	Dana Spatz, Branch Chief
               Environmental Risk Branch 3
         Environmental Fate and Effects Division (7507P)\
         

The Interregional Research Project #4 (IR-4) has proposed new uses of metaldehyde (2,4,6,8-tetramethyl-1,3,5,7-tetraoxacyclooctane) on garden beets, hops, rutabaga, turnips, and wheat in the Pacific Northwest. The proposed maximum metaldehyde application rates are 2 lb a.i./A/year for garden beets, 4 lb a.i./A/year for hops, rutabaga, turnip, and 6 lb ai/A/year for wheat.

Previous drinking water assessments for metaldehyde were conducted to support the APHIS exotic mollusk eradication use on to grass (seed crop), forage and hay (DP Barcode 404861, 7/17/13).  The application rate used in the assessment was 2 lb a.i./acre applied in 6 broadcast (ground) applications for a total maximum annual application of 12 lb a.i./acre.  The estimated drinking water concentrations (EDWCs) are shown in Table 1. The highest estimated 1-in-10-year annual peak (acute), annual average (chronic) and 30-year annual average (cancer) concentrations of metaldehyde in surface water sources of drinking water are 205, 136, and 83 μg/L, respectively.  For groundwater sources of drinking water, the estimated peak and post-breakthrough average concentrations were 1,740 μg/L and 635 μg/L, respectively (Error! Reference source not found.).  

 

Table 1. Maximum Tier II estimated drinking water concentrations (EDWCs) in parts per     billion (μg/L) resulting from applications of metaldehyde at an annual application rate of 12 lb a.i./acre.
Drinking water source (model)
                                 1-in-10 year 
                              30-year simulation

                                     Acute
                                    Chronic
                                     Acute
                                    Chronic
Surface water    
(PRZM-EXAMS)
                                      205
                                      136
                                       -
                                      83
Groundwater     
(PRZM-GW)
                                       -
                                       -
                                     1740
                                      635

Because the proposed new metaldehyde uses on the US-LON-A label (EPA Reg. No. 6836-350) have application rates lower than assessed in previous drinking water assessments (DP Barcode 404861, 7/17/13), the EDWCs reported in the previous drinking water assessment for metaldehyde continue to be the recommended values for use in the human health assessment. These EDWCs provide the most conservative concentrations in surface and ground source drinking water for current metaldehyde uses.    

