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Federal Register / Vol. 86, No. 30 / Wednesday, February 17, 2021 / Rules and Regulations generated with the Pesticide Root Zone Model for GroundWater PRZMGW, version 1.07 for use in sulfonylurea dietary risk assessments. Rather than using chemical-specific estimated drinking water concentrations EDWCs following the usual assessment procedures, these coarse-screen estimates should exceed upper-bound, chemical-specific EDWCs for any sulfonylurea SU. This was achieved by using model inputs that represent the use pattern of highest exposure from any SU, the highest soil mobility of any SU residue of concern, and the highest persistence to any route of degradation over time. The resulting coarse-screen EDWC from PRZMGW was used as the conservative estimate of exposure. The chronic dietary assessment for orthosulfamuron used the coarse-screen maximum daily concentration of 0.751
ppm.
3. Non-dietary exposure. The term residential exposure is used in this document to refer to non-occupational, non-dietary exposure e.g., for lawn and garden pest control, indoor pest control, termiticides, and flea and tick control on pets. Orthosulfamuron is not registered for any specific use patterns that would result in residential exposure.
4. Cumulative effects from substances with a common mechanism of toxicity.
Section 408b2Dv of the FFDCA
requires that, when considering whether to establish, modify, or revoke a tolerance, the Agency consider available information concerning the cumulative effects of a particular pesticides residues and other substances that have a common mechanism of toxicity.
The Agency has assessed orthosulfamuron, and its chemical class, sulfonylureas, and determined that the SUs do not share a common mechanism of toxicity EPAHQOPP201104538
0024. The SUs share a core chemical structure with varying degrees of structural similarity based on individual substituents on either side of the molecule. In addition, the SUs share a pesticidal mode of action MOA
inhibition of acetolactate synthase ALS, although the function of ALS in humans is unknown and the relevance of this MOA in humans in unclear.
Based on toxicity studies, the SUs do not share a common toxicological profile; instead the target organs vary among the class and are often nonspecific, such as changes in body weight or general effects on the liver. Further dividing the SUs into subclasses based on the urea substituent did not result in a clear association of a target organ with any particular substructure.

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Based on the weight of the evidence, which includes the lack of a common toxicological profile, the uncertainty in the human relevance of ALS inhibition, and the lack of mammalian MOA data, a testable hypothesis for a common mechanism of action cannot be identified. Therefore, the Agency concludes that no common mechanism of toxicity exists among these pesticides and a cumulative risk assessment approach is not appropriate for this class of pesticides.
D. Safety Factor for Infants and Children Section 408b2C of the FFDCA
provides that EPA shall apply an additional tenfold 10X margin of safety for infants and children in the case of threshold effects to account for prenatal and postnatal toxicity and the completeness of the database on toxicity and exposure unless EPA determines based on reliable data that a different margin of safety will be safe for infants and children. This additional margin of safety is commonly referred to as the FQPA Safety Factor SF. In applying this provision, EPA either retains the default value of 10X, or uses a different additional safety factor when reliable data available to EPA support the choice of a different factor.
EPA has determined that reliable data show the safety of infants and children would be adequately protected if the FQPA SF were reduced to 1x. The rationale for that decision remains the same as in the February 28, 2007 final rule establishing tolerances for a use on rice. See 72 FR 8928 FRL81134 for the full rationale in Unit III.D.
E. Aggregate Risks and Determination of Safety EPA determines whether acute and chronic dietary pesticide exposures are safe by comparing aggregate exposure estimates to the acute PAD aPAD and chronic PAD cPAD. Short-, intermediate-, and chronic-term risks are evaluated by comparing the estimated aggregate food, water, and residential exposure to the appropriate PODs to ensure that an adequate MOE
exists.
1. Acute risk. An acute aggregate risk assessment takes into account acute exposure estimates from dietary consumption of food and drinking water. No adverse effect resulting from a single oral exposure was identified and no acute dietary endpoint was selected. Therefore, orthosulfamuron is not expected to pose an acute risk.
2. Chronic risk: Using the exposure assumptions described in this unit for chronic exposure, EPA has concluded
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that chronic exposure to orthosulfamuron from food and water will utilize 81% of the cPAD for all infants less than 1 year old, the population group receiving the greatest exposure. There are no residential uses for orthosulfamuron.
3. Short-term and intermediate-term risk. Short-term and intermediate-term aggregate exposure takes into account short-term or intermediate-term residential exposure plus chronic exposure to food and water considered to be a background exposure level.
Short-term and intermediate-term adverse effects were identified in the toxicity database e.g., kidney and liver effects; however, orthosulfamuron is not registered for any use patterns that would result in short-term or intermediate-term residential exposure.
Short-term risk is assessed based on short-term residential exposure plus chronic dietary exposure. Intermediateterm risk is assessed based on intermediate-term residential exposure plus chronic dietary exposure. Because there is no short-term or intermediateterm residential exposure and chronic dietary exposure has already been assessed under the appropriately protective cPAD which is at least as protective as the POD used to assess short-term or intermediate-term risk, no further assessment of short-term or intermediate-term risk is necessary, and EPA relies on the chronic dietary risk assessment for evaluating short-term and intermediate-term risk for orthosulfamuron.
4. Aggregate cancer risk for U.S.
population. As stated in Unit III.C.1.iii, EPA has concluded that the chronic reference dose RfD will adequately account for all repeated exposure/
chronic toxicity, including carcinogenicity, which could result from exposure to orthosulfamuron. As there is no chronic risk of concern, EPA
concludes that exposure to orthosulfamuron will not pose an aggregate cancer risk.
5. Determination of safety. Based on these risk assessments, EPA concludes that there is a reasonable certainty that no harm will result to the general population, or to infants and children from aggregate exposure to orthosulfamuron residues.
IV. Other Considerations A. Analytical Enforcement Methodology Adequate enforcement methodology utilizing high-performance liquid chromatography with tandem mass spectrometric detection LC/MS/MS is available to enforce the tolerance expression.

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