Determinants of human exposure to fipronil following use as a topical flea and tick treatment of companion animals

Use of FrontlineRTM topical pet products on dogs and cats introduces low fipronil (5-amino-3-cyano-1-(2, 6-dichloro-4-trifluoromethylphenyl)-4-trifluoromethylsulfinylpyrazole1)-1H-pyrazole-3-carbonitrile; CAS 120068-37-3) levels into residences. Characterization of the human exposure potential to pet pest products is lacking. Four distribution and fate studies of fipronil on pets and in the environment were performed to evaluate potential determinants of human exposure.;Cotton fabric and pet hair fortified with fipronil or Frontline RTM were exposed to sunlight. Fipronil decay was first-order. Desulfinyl fipronil, fipronil sulfone and fipronil sulfide were formed. The formation of fipronil derivatives was low (<10% of fipronil applied). Pet owners wearing cotton gloves over impervious nitrile gloves petted treated companion animals for 2 min. Transferable Pet Residues declined from 17,000 to 0.23 mug/pair gloves during the 4 weeks following application. Total Hair Residues were measured on hair brushed from companion animals. Fipronil levels were time-dependent and followed first-order decay over a four week period. Fipronil on pet hair declined from 6,100 to 0.13 mug/g hair. Desulfinyl fipronil, fipronil sulfone and sulfide were low relative to fipronil. The distribution and fate of fipronil on dogs was measured using two separate procedures based upon hair clippings and a TinopaleRTM CBS-X (CAS;Analysis of urine specimens of 12 human volunteers who collected either convenience morning or 24 h specimens did not reveal a fipronil metabolite. Fipronil in acid hydrolysates of pre- and post-application urine specimens in nanogram per mL levels was an artifact of trace level analysis. The human exposure potential of FrontlineRTM is low relative to levels of health concern.