              OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                               January 31, 2011

                                                                PC Code: 122804
MEMORANDUM	DP Barcode: 380524	

SUBJECT:	Abamectin: Drinking Water Exposure Assessment for Proposed Section 3 New Uses on Chives, Dried Beans, and the Bulb Onion Subgroup 3-07A.

FROM:	Greg Orrick, Environmental Scientist
      Environmental Risk Branch II
      Environmental Fate and Effects Division (7507P)
      
THROUGH:	Brian Anderson, Chief 
      Environmental Risk Branch II
      Environmental Fate and Effects Division (7507P)

TO:		Paula Deschamp, Chief
		Risk Assessment Branch II
		Health Effects Division (7509P)

      Laura Nollen, Risk Manager Reviewer
      Barbara Madden, Minor Use Team Leader, RM Team 5
      Risk Integration Minor Use and Emergency Response Branch
      Registration Division (7505P)
      
      Thomas Harris, Risk Manager Reviewer
      John Hebert, Team Leader, RM Team 7
      Insecticide-Rodenticide Branch
      Registration Division (7505P)

      This Environmental Fate and Effects Division (EFED) memorandum includes a drinking water assessment in support of human health risk assessment for proposed Section 3 new use registrations of abamectin on bulb onions (crop subgroup 3-07A), dried beans, and chives (both fresh and dried).  These uses were proposed by the Interregional Research Project No. 4 (IR-4).  This assessment quantifies potential surface water and ground water exposure due to the maximum use patterns of proposed and currently labeled uses of abamectin.  Water monitoring data on abamectin have not been located.
      
      The previous drinking water exposure assessment identified the use patterns of maximum exposure as tomatoes and cucurbits, based on aquatic exposure modeling (DP 335118; USEPA, 2007).  However, the proposed use on dried beans results in higher exposure even with the addition of seed treatments on tomatoes and cucurbits (regardless of the environmental fate assumptions used for modeling).  If the screening exposure estimates listed in this memorandum result in dietary risk exceedances, contact Greg Orrick (703-305-6140) of Environmental Risk Branch II (7507P) to explore further refinements to this drinking water exposure assessment.
      
      Exposure estimates are conservative because the available environmental fate data for abamectin are poor.  Submitted aqueous photolysis, soil photolysis, aerobic soil metabolism, and anaerobic soil metabolism are not acceptable.  Also, aerobic aquatic metabolism and anaerobic aquatic metabolism studies of abamectin have not been submitted.  The field studies were identified as not acceptable in the previous ecological risk assessment for abamectin (USEPA, 2010; DP barcode 372885); however, MRID 41191501 appears to have been upgraded with the submission of MRID 42627601 (DP 187271; USEPA, 1993) and MRID 42900002 is in review.  Therefore, additional field dissipation data are not needed at this time.  Abamectin is assumed stable to photolysis and biodegradation in the absence of acceptable data (it is known to be stable to abiotic hydrolysis).  Therefore, exposure estimates reflect persistence of the compound mixture's residues.  Submission of acceptable data (especially aqueous photolysis, aerobic soil metabolism, aerobic aquatic metabolism, and anaerobic aquatic metabolism studies) showing ready degradation to much less toxic degradates would reduce the conservatism of exposure estimates and should be the first step in any efforts to refine the drinking water exposure assessment, if necessary.

      In the submitted aqueous and soil photolysis studies (MRID 159163), the photoperiods under sunlight and the sunlamps used for degradate characterization were not adequately described.  Mass balances were not provided and degradates were not characterized in the definitive studies.  In degradate characterization studies under sunlamps, three chromatographic fractions representing degradates were described, including a major non-polar fraction consistent with the delta-8,9-isomers of abamectin, a major "moderately polar" fraction that was not identified, and a major polar fraction that consisted of multiple unidentified components.  Acceptable studies would, among other criteria, adequately describe the lighting conditions, identify and quantify all major degradates, quantify all minor degradates structurally similar to the parent compound mixture, and provide mass balances accounting for >90% and <110% of the applied radiolabeled test material.

      In the submitted aerobic and anaerobic soil metabolism studies (MRID 159163), major amounts of radiolabeled material (up to 52% of the applied) were lost from each study (i.e., each combination of soil and treatment concentration).  Major abamectin degradates included a mixture of 8-α-hydroxy and ring-opened aldehyde derivatives of the parent compound mixture ("Compound 7"; maximum of 20% of the applied 56 days after treatment) and two other unidentified compounds or mixtures ("Compound 4", maximum of 12% of the applied at 84 days, and "Compound 12", maximum of 12% of the applied at 28, 56, 112 days).  These major degradates appear to have been more persistent in soil than the parent compound mixture.  Acceptable studies would, among other criteria, identify and quantify all major degradates, quantify all minor degradates structurally similar to the parent compound mixture, and provide mass balances accounting for >90% and <110% of the applied radiolabeled test material.
      
	The environmental hazards statements on the proposed labels (EPA Reg. No. 100-898, 100-1154, 100-1351) do not include the following surface water advisory that is recommended in Chapter 8 of the current Label Review Manual (November, 2008):

      "This product may impact surface water quality due to runoff of rain water.  This is especially true for poorly draining soils and soils with shallow ground water.  This product is classified as having a medium potential for reaching both surface water and aquatic sediment via runoff for several weeks to months after application.  A level, well-maintained vegetative buffer strip between areas to which this product is applied and surface water features such as ponds, streams, and springs will reduce the potential loading of abamectin from runoff water and sediment. Runoff of this product will be reduced by avoiding applications when rainfall is forecasted to occur within 48 hours."
      
      Because of its low mobility in soil, a ground water advisory for abamectin is not recommended.
      

References

USEPA, 1993.  Mastradone, P.  EFGWB Review Transmittal Memorandum.  DP Barcode 187271.  U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances, Environmental Fate and Effects Division.  Memorandum to the Registration Division.  May 10, 1993.

USEPA.  2010.  Abdel-Saheb, I.  Ecological Risk Assessment Evaluating Abamectin for the Registration of a New End-use Product (Athena Miticide/Insecticide) for Use on Field Crops, Vegetables and Small Fruits, Tree, Bush, and Vine Crops.  DP Barcode 372885.  U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances, Environmental Fate and Effects Division.  Memorandum to the Registration Division.  Jun. 22, 2010.

