On May 30, 2017, the U.S. Court of Appeals for the Ninth Circuit responded to two petitions for review of the U.S. Environmental Protection Agency’s (EPA) conditional registration of a nanosilver pesticide product and vacated the conditional registration. NRDC v. EPA, No. 15-72308. The Natural Resources Defense Council (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 is in the public interest.” When EPA granted the conditional registration, EPA did so on the basis that NSPW had a lower application rate and a lower mobility rate when compared to conventional-silver pesticides, and thus had the potential to reduce environmental loading and risk caused by silver release. Petitioners disputed these facts. While the court found that substantial evidence supports EPA’s findings that NSPW has lower application and mobility rates, the court agreed that the third premise, that current users of conventional-silver pesticides will switch to NSPW and/or that NSPW will not be incorporated into new products, “impermissibly relies on unsubstantiated assumptions.” According to the court, EPA cites no evidence in the record to support its assumption that current users of conventional-silver pesticides will switch to NSPW (“the substitution assumption”), but contends that it will occur as a “logical matter.” The court states that the lack of evidence supporting the substitution assumption is problematic in light of EPA’s other unsupported assumption, that there will be no new products. The court notes that EPA assumes current users of conventional-silver pesticides will switch to NSPW because of its benefits, but that these same benefits will not prompt manufacturers to incorporate NSPW into new products. EPA could have proved these assumptions, but without evidence in the record to support the assumptions, the court states that it “cannot find that the EPA’s public-interest finding is supported by substantial evidence as required by [the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)].” According to the court, the public interest finding is an “essential prerequisite to conditional registration,” and EPA failed to support that finding for NSPW with substantial evidence. The court vacated the conditional registration in whole, and did not consider the remaining issues raised by petitioners. More information will be available in Bergeson & Campbell, P.C.’s forthcoming memorandum.