EPA’s conditional registration of a pesticide containing nanosilver was remanded to the Agency by a three-judge panel of the U.S. Court of Appeals for the 9th Circuit (NRDC v. EPA).  The case involved a pesticide called AGS-20, which the Swiss company HeiQ Materials developed to control microbes that cause odors, stains, discoloration, and degradation of clothing, blankets, and carpets. 

The court had a favorable view of two parts of the risk assessment the EPA performed for AGS-20.  But in assessing the risk from oral plus dermal aggregate exposure, the EPA failed to base its approval on criteria the Agency itself had established, the court ruled.

Conditional registration

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) allows the EPA to conditionally register a pesticide that contains a new active ingredient such as nanosilver until the Agency receives sufficient data from an applicant such as HeiQ to decide whether to issue an unconditional registration. 

But the Natural Resources Defense Council (NRDC) argued that in granting the conditional registration, the EPA failed to properly assess the risks posed by nanosilver in AGS-20.  The NRDC cited three aspects of the assessment—EPA’s use of the body weight of a toddler instead of that of an infant as the subpopulation that would be most susceptible to the risks; EPA’s decision not to account for potential sources of the nanosilver other than HeiQ’s products; and the Agency’s conclusion that risks from dermal and oral exposure to AGS-20 were not severe enough to require mitigation. 

MOE criteria not satisfied

The panel’s decisions in these three areas are summarized as follows:

1. EPA’s use of toddlers as the most vulnerable subpopulation when assessing the effects of dermal and nondietary oral exposure to AGS-20 is in line with the Agency’s existing guidelines and past practices.  The court noted that EPA’s assessment of risks posed by chemicals on fabrics was based on the aggressive chewing of fabrics observed in toddlers, which would potentially release more nanosilver than the sucking or mouthing typical with infants.  The court denied NRDC’s petition in this matter.
2. While both parties agreed that nanosilver exists in other products, the EPA did not conduct an aggregate risk assessment to account for additional exposure from other products.  The NRDC charged that it was unreasonable for the EPA to effectively assume that consumers will never be exposed to nanosilver that is chemically similar to the nanosilver used in HeiQ’s products.  The panel did not disagree with this argument, but pointed out that the EPA is required to perform aggregate assessments only when granting unconditional registrations for pesticides.  In contrast, conditional registrations may be based only on the data available, and the court accepted EPA’s view that there is no data whatsoever on whether other types of nanosilver are chemically similar to the nanosilver used in HeiQ’s products.  Therefore, the court did not disagree with EPA’s decision not to conduct a risk assessment that included other products.
3. The EPA determined that the margin of exposure (MOE) to nanosilver in HeiQ’s products as experienced by toddlers was not a risk concern.  EPA’s MOE is a target number the Agency calculates mathematically using a number of factors such as results from tests wherein laboratory animals are exposed to the chemical; those results are extended to humans through multiplication.  In this case, the Agency’s target MOE was 1,000; this means that if the MOE for toddlers exposed to the nanosilver through oral plus dermal exposure is less than or equal to 1,000, the risk is a concern and mitigation is required.  The EPA reported that the oral-plus-dermal MOE for surface-coated textiles was 1,000.  The Agency then stated that “all MOEs are greater than the target MOE of 1,000, indicating that the risk for short- and intermediate-term exposure to toddlers that chew on AGS-20 is not a concern.”  The Agency contended that it had rounded off numbers used in the calculation and the actual MOE was 1,006.  The panel stated that EPA’s explanation was acceptable in practical terms but failed the legal test.  “Having established a rule of decision of less than or equal to 1,000, EPA cannot unmake it because its actual MOE is in the neighborhood,” stated the court.  NRDC’s petition on this matter was therefore granted. 

One member of the panel agreed with these three views, but stated that NRDC’s petition should be granted in full and not in part as the majority held.

NRDC v. EPA