In Natural Resources Defense Council v. U.S. EPA the U. S. Court of Appeals for the 9th Circuit ruled that EPA had arbitrarily denied NRDC’s petition to cancel the registration of tetrachlorvinphos, an insecticide contained in numerous prominent pet flea collars.

NRDC had filed a Petition to Cancel the registration of tetrachlorvinphos on April 23, 2009. The petition asserted that EPA had ignored serious risks, particularly to children, having concluded that the risk from such exposures was negligible and need not be assessed. NRDC conducted its own exposure studies and a risk assessment in which the estimated residues to a child exceeded safe levels. 

The petition had languished for years before NRDC brought a mandamus action seeking to compel the issuance of a response to the petition. EPA denied the petition, which NRDC challenged. The Court remanded the matter to EPA for the issuance of a revised risk assessment. EPA then compelled Hartz Mountain, the primary registrant of tetrachlorvinphos pet collars, to develop additional exposure data. When another year passed without a decision, NRDC filed a second mandamus action, based upon which the Court gave EPA ninety days to issue the revised risk assessment. EPA issued the revised risk assessment and promptly denied the Petition, following which NRDC filed a challenge to the denial.

            In reversing EPA’s denial, the Court stated:

We conclude that EPA’s denial of NRDC’s petition is not supported by substantial evidence. EPA failed to provide a reasoned explanation for its denial of NRDC’s petition and made several arbitrary calculations. EPA’s errors primarily impact two calculations central to its denial of NRDC’s petition: (1) the amount of TCVP dust released by the collars, and (2) the assumption that pet owners will trim the collars by at least 20%. Further, we cannot consider EPA’s post-hoc rationalizations, which themselves suffer from numerous flaws.

The Court found that EPA had unreasonably rejected the finding of the Hartz mountain data that significant exposure could occur, thus irrationally concluding that no risk of concern was presented by the exposure. The Court also rejected EPA’s contention that users would trim the size of the collars, thus reducing exposure.  Finally the Court rejected EPA’s additional reasons justifying the denial that were presented in the denial of the Petition.

The Court gave EPA 120 days in which to again respond to the Petition, which would put the approximate due date as August 20, 2022.  Stay tuned.