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, 
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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.
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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.