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Triazine Cumulative Risk Assessment and Atrazine, Simazine, and Propazine Decisions; June 22, 2006

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Introduction

EPA has completed its cumulative risk assessment for the chlorinated triazine pesticides atrazine, simazine and propazine. The Agency also has completed its Reregistration Eligibility Decision (RED) for simazine and tolerance reassessment decision (TRED) for propazine. EPA's earlier Interim RED (IRED) and revised IRED for atrazine are now considered final, and tolerance reassessment and reregistration eligibility decisions for atrazine are complete.

EPA has concluded that, with the mitigation measures in the individual atrazine and simazine decisions, the cumulative risks associated with the triazine pesticides are below the Food Quality Protection Act (FQPA) regulatory level of concern. Triazine tolerances - residue limits in food and feed - have been evaluated on the basis of cumulative risk and found to meet the safety standard established by FQPA - that the risks associated with the pesticide residues pose a reasonable certainty of no harm. The 100 reassessed triazine tolerances contribute toward meeting the Agency's tolerance reassessment goal. Comment periods are open for the cumulative assessment and the simazine RED and propazine TRED from June 21, 2006, to August 21, 2006.

EPA notes that products containing the triazine pesticides still must complete product reregistration, through which product labeling changes and associated risk mitigation measures will be implemented.

This fact sheet presents:

Background on Triazine Cumulative Risk Assessment

FQPA directs EPA to consider available information on the cumulative effects on human health resulting from exposure to multiple pesticide chemicals that have a common mechanism of toxicity.

Identifying a Common Mechanism Group EPA begins a cumulative risk assessment by identifying a group of pesticides, called a Common Mechanism Group, that bring about a common toxic effect by a common mechanism of toxicity. Pesticides share a common mechanism of toxicity if they act the same way in the body; that is, if the same toxic effect occurs in the same organ or tissue by essentially the same sequence of major biochemical events.

Triazines: A Common Mechanism Group Based on a Common Mechanism of Toxicity Certain triazine pesticides have been identified by EPA as a common mechanism group, including atrazine, simazine, propazine, and their chlorinated degradates desethyl-s-atrazine (DEA), desisopropyl-s-atrazine (DIA), and diaminochlorotriazine (DACT). These triazine pesticides share a common mechanism of toxicity. In laboratory studies in rats, at experimental dose levels higher than those encountered in the environment, the triazines have the ability to potentially cause neuroendocrine developmental and reproductive effects that may be relevant to humans. Specifically, these pesticides may disrupt part of the central nervous system (the hypothalamic-pituitary-gonadal or HPG axis), potentially causing changes to hormone levels and developmental delays. These were the primary toxicological effects of regulatory concern to EPA in assessing the triazines' food, drinking water, and residential risks.

Triazines and Cancer Evaluation Initially, EPA thought that the triazine pesticides also shared a common mechanism of toxicity based on carcinogenic effects (the formation of mammary gland tumors in rats). However, the mode of action by which the triazines cause tumors in rats depends on a reproductive aging process that does not occur in humans. The FIFRA Scientific Advisory Panel (SAP) agreed with the Agency in 2000 that "it is unlikely that the mechanism by which atrazine induces mammary gland tumors in female SD rats could be operational in humans." For the triazine cumulative risk assessment, therefore, a cancer risk assessment was not performed.

Identifying a Cumulative Assessment Group Based on the common mechanism group, EPA selects a cumulative assessment group whose uses, routes, and pathways of exposure present sufficient exposure and hazard potential to warrant including them in the cumulative risk assessment. For the triazines, only atrazine, simazine, and their three chlorinate degradates were selected for the cumulative assessment. Propazine was considered but was not included in the triazine cumulative risk assessment because no dietary, drinking water, or residential human exposure to propazine is anticipated from any of its currently registered uses.

Identifying Exposure Scenarios for the Cumulative Risk Assessment Next, EPA develops exposure scenarios for the cumulative assessment group, considering pesticide uses that result in exposures and where those uses are likely to occur. The Agency is especially interested in areas of high exposure and regions of the U.S. where residues of the pesticides in the group are likely to occur together.

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Summary of Triazine Cumulative Risk Assessment

Triazines Exposure Scenarios EPA developed exposure scenarios for the triazines considering their use and usage. Atrazine and simazine are registered for use in the U.S. on a variety of food and feed crops including grains, fruits, and nuts. Both pesticides also are registered for use on turf grasses grown in the Southeastern U.S., and are used on turf mainly in Florida. These uses result in potential exposure to residues through drinking water and/or food, and through residential activities on treated turf.

The Agency identified three regions of the U.S. where high exposures to atrazine and simazine residues are likely to co-occur: the Midwest, California, and Florida. In the U.S., the Midwest receives the highest use of atrazine, California receives the highest use of simazine, and Florida receives equally high use of both pesticides.

Analysis of Pathways of Exposure in Regions of Co-occurrence and Assessment of Cumulative Risk Next EPA analyses high-end exposures to pesticides in the group via food, drinking water, and/or residential activities in regions where co-occurrence is most likely, and assesses the resulting cumulative risks.

Analysis of Triazine Pathways of Exposure in Regions of Co-occurrence and Assessment of Cumulative Risks As a result of this analysis, cumulative exposure to residues of the triazines in food is considered negligible. Cumulative exposure to triazine residues in drinking water and/or on lawns and golf courses is possible so exposure to residues of atrazine, simazine and their metabolites were assessed for the following four exposure scenarios:

       1)    drinking water in the Midwest (using monitoring data);
       2)    drinking water in California (using modeled exposure estimates);
       3)    drinking water in Florida (also using modeled exposure estimates);
       4)    combined drinking water and home lawn and/or golf course use in Florida (using modeled exposure estimates
            &nbsp for drinking water and residential activities).

EPA's cumulative risk assessment indicates that cumulative exposures to triazine residues are not of concern in any of the four exposure scenarios. For more information on the Triazines Cumulative Risk Assessment. EPA's triazine cumulative risk assessment is available for public comment until August 21, 2006.

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Triazines Special Review

EPA initiated a Special Review for the triazine pesticides in November 1994, based on the potential for cancer risks of concern resulting from dietary or occupational exposure, as well as the potential for human health risks of concern resulting from drinking water exposure caused by ground and surface water contamination. At that time, the triazines were classified as Group C or possible human carcinogens. Atrazine and simazine were later classified as "not likely to be carcinogenic to humans." The Agency expects to complete the Special Review after considering comments from a FIFRA Scientific Advisory Panel that will meet in 2007 to review currently available data and pending epidemiological data from the National Cancer Institute regarding the carcinogenic potential of atrazine.

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Individual Triazine Decisions: Atrazine, Simazine, and Propazine

Concurrent with concluding the triazine cumulative assessment, EPA has completed decisions for three individual triazine pesticides: atrazine, simazine, and propazine. With the mitigation measures for atrazine and simazine, EPA has concluded that the cumulative risks associated with the triazines are below EPA's FQPA regulatory level of concern.

Atrazine IRED, Amended IRED, and RED

EPA completed an Interim Reregistration Eligibility Decision (IRED) for atrazine on January 31, 2003, and a Revised Atrazine IRED on October 31, 2003. In these documents, the Agency assessed whether pesticide products containing atrazine were eligible for reregistration considering all relevant issues except those relating to cumulative risks associated with potential exposures to atrazine and the other triazine pesticides. Now EPA has completed its cumulative risk assessment for the triazines and concluded that, with the mitigation measures in the individual atrazine and simazine decisions, cumulative risks are below EPA's FQPA regulatory level of concern. EPA's earlier IRED and Revised IRED for atrazine are now considered final, and the tolerance reassessment and reregistration eligibility process for atrazine is complete. Taking into account cumulative risks, EPA has determined that the established tolerances for atrazine are considered fully reassessed and meet the Federal Food, Drug, and Cosmetic Act safety standard.

No changes in atrazine risk mitigation are needed as a result of the triazine cumulative risk assessment. Monitoring programs initiated as a result of the atrazine IREDs and a Memorandum of Agreement (MOA) will continue as before, unaffected by the cumulative assessment. Individual products containing atrazine will not be considered reregistered until they have completed product reregistration, through which product labeling changes and associated risk mitigation measures will be implemented.

EPA's April 6, 2006, memorandum completing atrazine reregistration eligibility and tolerance reassessment decisions is available in the docket and on the atrazine web page.

Simazine RED

EPA has conducted human health and environmental fate and effects risk assessments and has reassessed existing tolerances for simazine. The Agency has determined that simazine will be eligible for reregistration, provided that the risk mitigation measures in the RED are adopted and product labels are amended to reflect these measures. EPA has evaluated the existing simazine tolerances and determined that there is a reasonable certainty that no harm to the general population, infants, children, or other major identifiable subgroups of consumers will result from use of simazine. The Agency has determined that tolerances for simazine meet the FQPA safety standard and are now considered reassessed.

A systemic herbicide, simazine usually is applied to soil and absorbed through leaves and roots. Simazine acts by inhibiting photosynthesis within the targeted plant. Simazine is used in growing a variety of food and feed crops, primarily corn in the Midwest, fruits and nuts in California, and citrus (oranges and grapefruit) in Florida. Simazine also is used on home lawns, golf courses, and turfgrass grown commercially for sod, as well as in forestry, and as an algaecide in ornamental ponds and aquariums.

EPA has identified potential human health risks of concern associated with the current registered uses of simazine resulting from dietary (drinking water), residential, and occupational exposures. While dietary exposure from food is estimated to be essentially zero (and therefore poses no risk of concern), simazine does pose potential chronic risks of concern from drinking water exposure in certain areas of the country, mainly to infants and children up to 6 years old (the most sensitive subpopulations). Potential aggregate risks of concern from combined drinking water and post-application turfgrass exposure also exist for this subpopulation. Simazine also poses potential risks of concern to residential turfgrass applicators using hand-held devices (belly grinders or rotary applicators); risks to handlers in a variety of scenarios, particularly those involving many acres treated or high application rates; and dermal risks to Christmas tree and turfgrass reentry workers. The Agency also has identified potential ecological risks of concern to non-target organisms including birds, mammals, and aquatic and terrestrial plants.

To reduce these exposures and address risks of concern, EPA is requiring a number of mitigation measures, such as:

Confirmatory data will be required regarding the decisions presented in the RED. EPA's Simazine RED is available for public comment [link to below where it tells the reader how to comment] until August 21, 2006.

Propazine TRED

Propazine, also a systemic herbicide, currently is registered in the U.S. for indoor greenhouse use only, and has existing tolerances established for residues on sorghum. EPA has evaluated the existing propazine sorghum tolerances and determined that there is a reasonable certainty that no harm to the general population, infants, children, or other major identifiable subgroups of consumers will result from these tolerances. Dietary exposure to propazine was determined to be essentially zero; propazine, therefore, was found to pose no risk concerns. The four propazine sorghum tolerances (forage, grain, stover, and sweet) are considered reassessed and meet FQPA safety standards. No mitigation measures are necessary for propazine at this time. The Agency has received and will consider a request for a new use of propazine on sorghum in the U.S. EPA's Propazine TRED is available for public comment until August 21, 2006.

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How to Comment and Additional Information

EPA requests public comment on the triazine cumulative risk assessment, simazine RED, and propazine TRED from June 21, 2006, to August 21, 2006. If comments are received that change any of these decisions, the Agency will issue amended decision documents.

EPA's triazines documents can be found in the following Dockets:
Triazine cumulative assessment: EPA-HQ-OPP-2005-0481
Atrazine IREDs and RED: EPA-HQ-OPP-2003-0367
Propazine TRED: EPA-HQ-OPP-2005-0496
Simazine RED: EPA-HQ-OPP-2005-0151

To review documents in these Dockets and to submit comments:

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