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Common Mechanism Groups; Cumulative Exposure and Risk Assessment

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Common mechanism of toxicity pertains to two or more pesticide chemicals or other substances that cause a common toxic effect(s) by the same, or essentially the same, sequence of major biochemical events (i.e., interpreted as mode of action).

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Organophosphates

Organophosphates

Organophosphates (OPs) are a group of closely related pesticides used in agriculture and non-agricultural sites that affect functioning of the nervous system. They are among the Agency's first priority group of pesticides to be reviewed under the Food Quality Protection Act.

OP Cumulative Assessments

A key step in the process of reassessing tolerances for the organophosphate pesticides was the assessment of cumulative exposure and risk to human health from these pesticides.  In December 2001, EPA released a preliminary version of the OP cumulative assessment.  A revised version of the assessment was released in June 2002.  In August 2006, EPA issued the 2006 Update to the OP Cumulative Assessment. The Agency concluded that with the adoption of risk mitigation measures for over 40 individual OPs from risk management decisions completed during the previous several years, the cumulative risks associated with the OP pesticides do not exceed the Agency's level of concern.

OP Pesticides Review Status

EPA has also assessed uses and risks associated with each individual organophosphate pesticide.  Decisions were captured in Interim Reregistration Eligibility Decision (IRED) or Tolerance Reassessment Decision (TRED) documents for these pesticides, as reflected in the OP status table.  In completing the cumulative risk assessment for the OPs, EPA concluded that, with the mitigation measures encompassed in the individual Interim REDs and TREDs, the cumulative risks associated with the OPs are below the Agency’s level of concern.  Based on the results of the OP cumulative assessment, the Interim REDs and TREDs for the OP pesticides are now considered final, and the associated tolerance reassessment and reregistration eligibility decisions are considered complete.

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N-methyl Carbamates

N-methyl Carbamates

The N-methyl carbamates are a group of closely related pesticides used in homes, gardens and agriculture that may affect the functioning of the nervous system. In 2004, EPA described its reasoning and identified the N-methyl carbamate pesticides designated as a common mechanism group for the purposes of its cumulative risk assessment. The cumulative risk assessment, along with individual risk assessments was the basis for completing tolerance reassessment for the N-methyl carbamate pesticides.

N-methyl Carbamate Revised Cumulative Risk Assessment

EPA issued the N-methyl carbamate revised cumulative risk assessment for comment on September 26, 2007. The Agency concluded that, with the adoption of the risk mitigation measures required in the individual N-methyl carbamate pesticide risk management decisions, the cumulative risks associated with the N-methyl carbamate pesticides do not exceed the Agency's level of concern.

N-methyl Carbamate Pesticides Review Status

EPA also has assessed uses and risks associated with each individual N-methyl carbamate pesticide (that is, for aldicarb, carbaryl, carbofuran, formetanate hydrochloride, methiocarb, methomyl, oxamyl, pirimicarb, propoxur, and thiodicarb). Decisions are captured in reregistration eligibility and tolerance reassessment decision documents for these pesticides, as reflected in the carbamates status table.

Preliminary N-methyl Carbamate Cumulative Risk Assessment

The following information is available in the docket. For more information on the N-methyl carbamates and these tolerances, go to Regulations.gov, in Docket ID EPA-HQ-OPP-2003-0360.

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Triazines

Triazines

The triazine pesticides and their metabolites are a group of closely related herbicides used widely in agriculture and non-agricultural sites. After taking public comment, EPA concluded in 2002 that the triazine-containing pesticides atrazine, simazine, and propazine and their three chlorinated degradates should be included in a common mechanism group and considered through a cumulative risk assessment. In laboratory animal studies, the triazines share a common neuroendocrine mechanism of toxicity which results in both developmental and reproductive effects. Propazine was not included in the cumulative assessment because no dietary, drinking water, or residential human exposure to propazine is anticipated from any of the currently registered uses. The triazines have been given a high priority in EPA's review of older pesticides and associated tolerances.

Triazine Cumulative Assessment

EPA issued the triazine cumulative risk assessment for comment on June 21, 2006. The Agency concluded that, with mitigation measures for atrazine and simazine, the cumulative risks associated with the triazines are below the Agency's level of concern.

Triazine Pesticides Review Status

EPA also has assessed uses and risks associated with each individual triazine pesticide (that is, for atrazine, simazine, propazine, and their three chlorinated degradates). Decisions are captured in reregistration eligibility and tolerance reassessment decision documents for these pesticides, as reflected in the triazine status table.

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Chloroacetanilides

Chloroacetanilides

The chloroacetanilides are a group of closely related herbicides used in agriculture for general weed control in food and feed crops. After taking public comment in 2001, EPA grouped together three of the choloracetanilides - acetochlor, alachlor, and butachlor - for cumulative assessment based on their ability to cause nasal tumors. Because butachlor no longer has active product registrations or tolerances, only acetochlor and alachlor were considered in the chloroacetanilide cumulative assessment, released in March 2006.

Chloroacetanilide Cumulative Assessment

EPA issued the completed chloroacetanilide cumulative risk assessment for comment on March 29, 2006. The Agency concluded that the cumulative risk associated with the chloroacetanilide pesticides is below the Agency's level of concern.

EPA simultaneously issued the last individual chloroacetanilide decision, the Acetochlor TRED (PDF) (12 pp, 108 KB, About PDF), on March 29, 2006.

Chloroacetanilide Pesticides Review Status

EPA also has assessed uses and risks associated with both of the individual chloroacetanilide pesticides (that is, for acetochlor and alachlor). Decisions are captured in RED and TRED documents for these pesticides, as reflected in the chloroacetanilide status table.

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Pyrethrins/Pyrethroids

Pyrethroids are a class of synthetic insecticides which are structurally based on the pyrethrins, botanical insecticides extracted from Chrysanthemum cinerariaefolium. In conducting the screening-level cumulative risk assessment, EPA considered all registered uses of pyrethrins/pyrethroids and exposure from food, drinking water, and residential use through oral, dermal, and inhalation routes of exposure.

Pyrethrins/Pyrethroid Cumulative Risk Assessment

EPA completed the Pyrethrins/Pyrethroid Cumulative Risk Assessment on October 4, 2011. This screening-level cumulative risk assessment is highly conservative, overestimating actual risk. That is, the assessment assumes that people are exposed to the highest levels of residues in food, water, and in their homes, all on the same day. Even with these conservative and protective assumptions, the assessment shows that cumulative risks for both children and adults are not of concern for the currently registered uses of pyrethrins/pyrethroid pesticides. Further, the assessment shows that there is sufficient room in the pyrethroid cumulative risk cup to support consideration of additional individual pyrethroid pesticide uses.

Pyrethrins/Pyrethroid Pesticides Review Status

The Agency will update individual pyrethrins/pyrethroid pesticide risk assessments as these pesticides come up for review.

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