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From Products Liability Law Daily, November 8, 2013

EPA ignored its exposure threshold rule when conditionally registering pesticide

By John W. Scanlan, J.D.

The U.S. Environmental Protection Agency’s (EPA) decision to conditionally register a nanosilver-containing pesticide for use in treating textiles was vacated and remanded in part by the U.S. Court of Appeals for the Ninth Circuit. The agency’s finding that there was no risk concern for short- and medium-term exposure to textiles that were treated with the pesticide was not supported by substantial evidence, the court held. However, the court upheld the agency’s use of three-year olds rather than infants for its risk assessments along with the agency’s decision not to consider other sources of nanosilver in weighing exposure (National Resources Defense Council v. U.S. Environmental Protection Agency, November 7, 2013, Bybee, J.).

Background. HeiQ Materials AG sought approval from the EPA under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) to apply two pesticides called AGS-20 and AGS-20 U (referred together as AGS-20) to manufactured textiles. AGS-20 contains nanosilver, which would be used to prevent the growth of microbes that cause odors, stains, discoloration, and degradation in the textiles. After the EPA granted HeiQ’s application for conditional registration of AGS-20, the National Resources Defense Council (NRDC) petitioned the Ninth Circuit to vacate the conditional registration.

Risk assessment. The EPA’s decision to use the characteristics of three-year old children rather than infants in its risk assessment was supported by substantial evidence. EPA routinely uses the body weight of three-year olds when evaluating oral and dermal exposure to pesticides because it has previously determined that they were the subpopulation that was most vulnerable to pesticide exposure. A study used by the EPA that examined the extent that treated textiles shed nanoparticles when laundered provided a reasonable estimate of how they would perform under aggressive conditions, such as being worn or chewed on by a child. While infants are more vulnerable because of lower body weight, three-year old children are more vulnerable because they chew fabric aggressively and they move around more and make contact with more textiles. While the environmental group asserted that these observations were not supported in the record, the court found them to be common-sense statements about distinctions between children of different ages. The agency’s decision to base the risk assessment on three-year olds rather than infants created tradeoffs in the formula used by the agency to calculate exposure, and while the environmental group demonstrated that there was a reasonable basis for disagreement as to which group was more vulnerable, a court will not second-guess an agency determination in that situation.

Margin of exposure. The EPA’s determination that there was no risk concern for three-year old children exposed to the pesticide was not supported by substantial evidence. The agency established a rule stating that there was a risk concern requiring mitigation when there was a calculated margin of exposure (MOE) less than or equal to 1,000 for short- and medium-term exposure. Target MOE was based on a formula that included several uncertainty factors, and represented the level of exposure that might cause an adverse effect. It then calculated the actual MOE (toxicological point of departure divided by the daily dose) under a number of scenarios involving dermal contact, oral contact, and inhalation, along with an actual MOE for aggregate dermal and oral contact to estimate the exposure for a three-year old who chews on clothing while wearing it.

Although the agency found aggregate MOEs that equaled the target MOE of 1,000, which according to the agency’s rule represented a risk, the agency ignored its standard when concluding that there was no risk concern. Although it asserted in a supplemental briefing that the figures were equal only due to rounding of the figures in calculating the actual MOEs, the court noted that the agency had rounded the numbers to two significant digits repeatedly throughout the document, and that the end result was not precise enough to “unround” the final number.

Furthermore, the agency asserted that its calculations were based on very conservative assumptions, and that a three-year old’s exposure to an actual MOE of 1,000 was exposure to no more than 1/1000th of the amount necessary to produce no harmful results in mice in lab testing. Nevertheless, the court noted that the EPA had created the rule itself, listed its assumptions that resulted in its setting a target MOE at 1,000, and specified that a risk existed if the MOE was less than or equal to 1,000. Therefore, the EPA was not permitted to ignore its rule of decision when the actual MOE equaled 1,000.

Other sources of exposure. The EPA’s decision not to conduct an aggregate risk assessment that included sources of potential nanosilver exposure other than in the pesticides at issue was supported by substantial evidence. There was no data available as to whether other nanosilver in the marketplace was chemically similar to the nanosilver in this pesticide or how consumers might be exposed to other sources of nanosilver. The agency was not required by statute to calculate an aggregate risk assessment when conditionally registering a non-food-use pesticide, and its decision not to do so in this case was consistent with its regulations. EPA’s Scientific Advisory Panel had recommended a case-by-case approach to risk assessment because it determined that the nanosilver ingredient in the pesticide differed from that in currently-registered silver-based antimicrobial products, and in the absence of data indicating that it was similar, it was reasonable for the agency to assume that other types of nanosilver might not be chemically silver similar to the nanosilver in the pesticide.

The case number is 12-70268.

Attorneys: Catherine Marlantes Rahm for Natural Resources Defense Council. Matthew Brian Henjum for U.S. Department of Justice, Environment and Natural Resources Division, Environmental Defense Section. Ignacia S. Moreno, Assistant Attorney General, Environmental and Natural Resources Division. Amber Aranda, of Counsel, U.S. Environmental Protection Agency.

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