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United States Environmental Protection Agency

Prevention, Pesticides And Toxic Substances (7508C)

EPA-738-F-04-012 September 2005

R.E.D. FACTS

Thidiazuron
Pesticide Reregistration
All pesticides sold or distributed in the United States must be registered by EPA (the Agency), based on scientific studies showing that they can be used without posing unreasonable risks to people or theenvironment. Because of advances in scientific knowledge, the law requires that pesticides, which were first registered before November 1, 1984, be reregistered to ensure that they meet today's more stringent standards. In evaluating pesticides for reregistration, EPA obtains and reviews a complete set of studies from pesticide producers, describing the human health and environmental effects of eachpesticide. To implement provisions of the Food Quality Protection Act (FQPA) of 1996, EPA considers the special sensitivity of infants and children to pesticides, as well as aggregate exposure of the public to pesticide residues from all sources, and the cumulative effects of pesticides and other compounds with common mechanisms of toxicity. The Agency develops any mitigation measures or regulatorycontrols needed to effectively reduce each pesticide's risks. EPA then registers pesticides that meet current health and safety standards and can be used without posing unreasonable risks to human health or the environment. When a pesticide is eligible for reregistration, EPA explains the basis for its decision with the Reregistration Eligibility Decision (RED) document. This fact sheet summarizes theinformation in the RED document.

Use Profile

Thidiazuron [1-phenyl-3-(1,2,3-thidiazol-5-yl) urea] is used as a pre-harvest cotton defoliant or growth regulator. It removes green leaves and immature fruiting structures, which contribute to cotton staining. There are no registered residential uses. Thidiazuron can be applied with aerial or ground equipment, such as groundboom sprayers. There areeighteen active products containing thidiazuron (one technical and seventeen end-use products). End-use product formulations include: wettable powders, soluble concentrates, and emulsifiable concentrates.

Regulatory History

Thidiazuron has been registered in the United States for use as a cotton defoliant since 1982.

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EPA completed the reassessment for the 22 thidiazuron tolerances onSeptember 28, 2005. Since there are no residential uses, an aggregate exposure assessment was conducted. The Agency concluded that there is a reasonable certainty of no harm to any population subgroup from aggregate exposure to thidiazuron from dietary (food and water) exposure. Some tolerances will be proposed for revocation and one new tolerance will be proposed for establishment.

Human HealthAssessment

Toxicity Thidiazuron is considered to have low acute toxicity. Thidiazuron is placed in the following acute Toxicity Categories: oral III; dermal IV; inhalation IV; eye irritation IV; and, dermal irritation IV. Thidiazuron is classified as “not likely to be carcinogenic to humans.”

Dietary Risks EPA determined that there is reasonable certainty that no harm to any population subgroup willresult from aggregate exposure to thidiazuron when considering dietary (food and water) exposure. An acute dietary assessment was not performed on thidiazuron, because there were no effects observed in the available toxicology studies that could be attributable to a single exposure (dose). However, a chronic dietary assessment was conducted for thidiazuron. Chronic dietary exposure is expected tobe less than 8% of the chronic Population Adjusted Dose (cPAD) for the general U.S. population and all population subgroups, and is therefore below the Agency’s level of concern. A cancer dietary risk assessment was not conducted for thidiazuron. Carcinogenicity studies in both rats and mice produced no treatmentrelated increase in tumor incidence and the standard battery of genotoxicity and...