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October 10, 2023

EPA OPP Work Group Reconsidering 100-nm Threshold for Nanomaterials

Lynn L. Bergeson Carla N. Hutton

Bergeson & Campbell, P.C. understands that the U.S. Environmental Protection Agency (EPA) Office of Pesticide Programs (OPP) has formed a work group to review data and information related to whether the current 100-nanometer (nm) threshold for determining whether a substance is a nanomaterial should be reviewed. Our May 10, 2022, blog item reported on a May 2022 news item published by EPA, “Advancing EPA’s Understanding of the Next Generation of Pesticides.” According to the item, the research team developed a review framework “that includes a simple decision tree to determine what products should be classified and evaluated as a nanopesticide.” Products determined to contain nanomaterials are subject to additional assessment or data needs from the manufacturer.


Readers may recall that the Natural Resources Defense Council (NRDC) challenged EPA’s conditional registration of HeiQ AGS-20 and AGS-20 U, pesticide products that EPA determined contain nanosilver. As reported in our November 12, 2013, blog item, a panel of the U.S. Court of Appeals for the Ninth Circuit issued a decision granting in part and denying in part NRDC’s petition, finding that although EPA’s decision was supported by substantial evidence, EPA’s decision with respect to the specific issue addressed by the supplemental briefing was not supported by substantial evidence, vacating that part of the decision. Specifically, the court found that EPA did not follow its own “rule of decision,” under which “there is a risk concern requiring mitigation when the short- or intermediate-term [margin of exposure (MOE)] is less than or equal to 1,000.”

On May 30, 2017, the U.S. Court of Appeals for the Ninth Circuit responded to two petitions for review of EPA’s conditional registration of a nanosilver pesticide product and vacated the conditional registration. NRDC v. EPA, No. 15-72308. NRDC, as well as the Center for Food Safety (CFS) and the International Center for Technology Assessment (ICTA), filed petitions in 2015 asking the court to set aside EPA’s final order granting a conditional registration for a nanosilver-containing antimicrobial pesticide product named NSPW-L30SS (NSPW). The court vacated the conditional registration because, according to the court, “EPA failed to support its finding that NSPW was in the public interest.” More information is available in our May 31, 2017, blog item.

In 2020, EPA announced that it registered NSPW Nanosilver as a new active ingredient that helps suppress odor-causing bacteria, and algae, fungus, mold, and mildew that can cause deterioration or staining in textiles. EPA noted that NSPW Nanosilver is registered only for use in specified textiles, including fabrics, sportswear, footwear, linens, and awnings. Although NSPW Nanosilver is the same active ingredient in the 2015 conditional registration challenged by NRDC, CFS, and ICTA, EPA stated that the 2020 registration has a modified use pattern that is expected to limit exposures compared to the previous conditional registration. According to EPA, additional data were submitted and reviewed to update the risk assessment for NSPW Nanosilver, allowing for an unconditional registration. More information is available in our July 2, 2020, blog item.