In a significant ruling on November 7, the Ninth Circuit Court of Appeals vacated USEPA’s first-ever decision to register a pesticide containing nanosilver as its active ingredient under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The Ninth Circuit held that USEPA  failed to follow its own risk assessment rules by concluding that use of the nanosilver product to treat clothing and other textiles did not present a risk concern to toddlers for short- and intermediate-term aggregate oral and dermal exposure.

In December 2011, USEPA granted a conditional pesticide registration under FIFRA to HeiQ Materials AB for AGS-20, a nanosilver product intended to be used as an antimicrobial agent for textiles by slowly releasing silver ions that inhibit the growth of bacteria that cause odor, stains and other damage to textiles. In January 2012, the Natural Resources Defense Council (NRDC) filed a petition with the Ninth Circuit challenging USEPA’s decision to grant the conditional registration for AGS-20.

USEPA’s evaluation and conditional approval of AGS-20 was the first time that USEPA had deliberately registered a pesticide product with nanomaterial as an active ingredient. FIFRA requires USEPA to determine that a pesticide will not have any “unreasonable adverse effects” on the environment or human health before the pesticide is approved. As part of its assessment of the potential risks presented by a pesticide, USEPA sets a numerical “margin of exposure” (MOE) for vulnerable subpopulations, which essentially sets an acceptable level of exposure to the pesticide. In its review of AGS-20, USEPA identified 3-year old toddlers as the most vulnerable subpopulation because of their habit of chewing on textiles.  It set the target MOE at 1,000, indicating that exposures calculated to be 1,000 or less presented a risk concern to toddlers that required mitigation, while MOEs calculated as exceeding 1,000 did not present such a concern. The Ninth Circuit found that USEPA had granted the conditional registration for AGS-20 even though the Agency’s assessment indicated that the actual MOE for 3-year old toddlers was 1,000 and the Agency had not required mitigation for this exposure. The Ninth Circuit remanded the matter to USEPA.

Although the Ninth Circuit’s decision turned on such a highly technical issue, it has potentially significant implications for USEPA’s review of pesticide products containing nanomaterials. To date, USEPA has generally taken a cautious approach to such pesticides, and the issuance of the conditional registration for AGS-20 was a milestone. In fact, since its decision on AGS-20, USEPA has been reviewing registration applications for other nanomaterial pesticides, and in late August 2013 the agency announced a proposed conditional registration for another nanosilver pesticide called “NanoSilva.” A coalition of groups led by the NRDC has submitted comments to USEPA strongly opposing the proposed conditional registration for NanoSilva, and in light of the Ninth Circuit’s decision, likely would file a judicial challenge to the NanoSilva registration if finalized. Close attention should be paid to how the Ninth Circuit’s decision affects USEPA’s reconsideration of the conditional registration for AGS-20, the proposed conditional registration of NanoSilva, and the Agency’s approach to nanomaterial pesticides (and other nano-substances) overall.