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OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

January 7, 2016

PC Code: 079801

MEMORANDUM DP Barcode: 430964

SUBJECT: Thiram: Response to Comments on the EFED Problem Formulation for Registration 

Review

FROM: Elyssa Arnold, Risk Assessment Process Leader

Ron Parker, Senior Environmental Engineer

Environmental Risk Branch 2

Environmental Fate and Effects Division (7507P)

THROUGH: Brian Anderson, Branch Chief

Environmental Risk Branch 2

Environmental Fate and Effects Division (7507P)

TO: Wilhelmena Livingston, Chemical Review Manager

Kevin Costello, Branch Chief

Risk Management and Implementation Branch 4

Pesticide Re-evaluation Division (7508P)

The Environmental Fate and Effects Division (EFED) reviewed comments from the Thiram Task Force 

and the Physicians Committee for Responsible Medicine on the “Registration Review: Preliminary 

Problem Formulation for Environmental Fate, Ecological Risk, Endangered Species, and Human 

Health Drinking Water Exposure Assessments for Ferbam and Thiram” (DP427810, 427924, Docket ID 

EPA–HQ–OPP–2015–0433). The purpose of this memorandum is to respond to these comments. 

Comments from the Thiram Task Force

1. Comment summary: The Thiram Task Force believes that the Agency should reconsider the need 

for the pollinator studies identified in the preliminary Work Plan. The EPA categorizes pesticides as 

“toxic to bees” if the acute contact LD50 is >11 μg/bee. Available data indicate that the contact LD50

for thiram is 73.72 μg/bee and was considered by the Agency to be practically nontoxic to bees. 

Additionally, it is not believed that there have been any adverse incidents involving thiram and bees.

EFED response: Although thiram is categorized as practically non-toxic to adult honeybees via 

acute contact exposure, there is considerable uncertainty regarding the potential effects of the 

compound on honey bee larval development and survival as well as potential for chronic effects.

Additional data on pollinators are needed to fully characterize the risk associated with thiram use to 

all developmental stages of honey bees, as sensitivity may vary according to life-stage (adult vs. 

eggs, larvae, and pupae), length of exposure (acute vs. chronic), and route of exposure (contact vs. 
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oral). As indicated in EPA guidance issued in 20141, assessing risks to bees involves a battery of 

laboratory-based studies. These studies are intended to examine effects to individual bees and 

provide insight on potential effects to solitary species of bees. Depending on the outcome of those 

studies, semi-field and full-field studies involving whole bee colonies may be required to refine risk 

estimates and provide insight into the potential effects of a pesticide on social bees. Additionally, as 

the risk assessment process is intended to provide information on non-Apis as well as honey bees, 

there are solitary and social non-Apis bees which feed directly on pollen and would likely be 

exposed to any residues that are sorbed to pollen.

An absence of reported incidents does not necessarily equate to an absence of incidents given the 

nature of incident reporting. Incidents that do not involve acute mortality events can be difficult to 

identify and are very rarely reported.

2. Comment summary: The members of the Thiram Task Force hold segmented labels for foliar and 

seed treatment uses. It would be helpful to the Task Force if the Final Work Plan could designate 

which data requirements are for foliar uses, for seed treatments and for both.

EFED response: OCSPP 850.4150, Vegetative Vigor, is applicable to foliar uses only. All other 

requested ecotoxicity studies apply to both foliar uses and seed treatments.

Comment from the Physicians Committee for Responsible Medicine (PCRM)

1. Comment summary: PCRM has identified acute avian oral toxicity data for a passerine species via 

Extoxnet (http://extoxnet.orst.edu/pips/thiram.htm). The stated LD50 is >100 mg/kg in red-winged 

blackbirds. If additional data are needed, PCRM recommends using the OECD Test Guideline 223 

(TG223) instead of EPA Guideline 850.2100 in the interest of reducing the numbers of animals used. 

EFED response: EFED will review the red-winged blackbird study referenced by PCRM if it is 

submitted to the Agency for that purpose. However, EFED notes that a limit dose of 100 mg/kg is 

unlikely to be sufficient for risk assessment. EFED will accept TG223 studies in place of 850.2100 

studies under the conditions laid out in EFED’s 2011 Guidance for Classifying Studies Conducted 

Using the OECD Test Guideline 223 (TG223) (Acute Avian Oral Sequential Dose Study) 

(http://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/guidance-classifying-studiesconducted-using-oecd).

 1 USEPA. 2014. Guidance for Assessing Pesticide Risks to Bees. Office of Pesticide Programs United States Environmental 

Protection Agency, Health Canada Pest Management Regulatory Agency, California Department of Pesticide Regulation. 

June 19, 2014. Available at: http://www.epa.gov/pollinator-protection/pollinator-risk-assessment-guidance