OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTA L PROTECTION A GENCY

WA SHINGTON, D.C. 20460

January 31 , 2011 PC Code: 122804 MEMORANDUM DP Barcode: 3 80524 SUBJECT: Abamectin : Drinking Water Exposure Assessment for Proposed Section 3 New

Use s on Chives, Dried Beans, and the Bulb Onion Subgroup 3
- 07A. FROM: Greg Orrick, Environmental Scientist

E nvironmental Risk B ranch II E nvironmental Fate and Effects Division (7507P) THR O U GH : Brian Anderson , C hief

Environmental Risk B ranch II E nvironmental 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 Regi stration 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 (bo th fresh and dried). These uses were proposed b y 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 currentl y l abeled uses of abame ctin
. Water monitoring data on abamectin have not been located. The previous drinking water exposure assessment identified the use pattern s of maximum exposure as tomatoes and cucurbits, based on aquatic exposure modeling (DP 335118 ; USEPA,2

2007 ). However, the proposed use on dried beans result s 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 avai lable environmental fat e data for abamectin are poor. Submitted aqueous photoly sis, soil photoly sis, aerobic soil metabol ism, and anaerobic soil metabolism are not acceptable
. Also, aerobic aquatic metabolism and anaerobic aquatic metabolism studies of a bamectin 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 photoly sis and biodegradation in the absence of acceptable data (it is known to be stable to abiotic hydrol ys is). Therefore, exposure estimates reflect per sistence of the compound mixture’s residues
. Submission of acceptable data (especiall y 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 an y 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 adequatel y 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 “moderatel y polar” fra ction that was not identified, and a major polar fraction that consisted of multiple unidentified components. Acceptable studies would, among other criteria, adequatel y 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), maj or amounts of radiolabeled material (up to 52% of the applied) were lost from each study ( i.e. , each combination of soil and treatment concentration). M ajor abamectin degradates included a mixture of 8
- α - hydroxy and ring
- opened aldehyde derivative s of the parent compound mixture (“Compound 7”; maximum of 20 % of the applied 56 day s after treatment) and two other unidentified compounds or mixtures (“Compound 4”, maximum of 12% of the applied at 84 day s, and “Compound 12”, maximum of 12% of the applied at 28, 56, 112 day s). These major degradates appear to have be en 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 structurall y si milar to the parent compound mixture, and provide mass balances accounting for >90% and <110% of the applied radiolabeled test material.3

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 fore casted 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
.