Toxicological effects of fipronil on laying hens and its residue elimination in eggs

Eighty 24-week-old laying hens were divided into eight groups, seven given a single oral dose per chicken with 7 dosing levels from 13.6 to 137 mg/kg body weight (bw) and one serving as sham control. The hens were observed for 28 days for clinical abnormalities, egg yield, and body weight. Egg samples from groups of low-to-medium doses were analyzed for residues of fipronil and its metabolites by LC-MS/MS. Blood and organ samples from hens of the group receiving 63.3 mg/kg bw were collected for hematochemical and histopathological analysis. We found that the median lethal dose (LD50) of fipronil was 74 mg/kg bw for laying hens. No death occurred, and there were no obvious changes in body weight and egg production in the hens receiving doses at or below 20 mg/kg bw. In the hens that survived exposure to the dose at 63.3 mg/kg bw, there was significant reduction in body weight and egg yield; histopathological changes in the liver and kidney; and increased levels of creatine, urea, glutamate oxaloacetate transferase, and glutamate pyruvic transaminase. Fipronil-sulfone was the residual marker in eggs with significantly higher concentrations and longer withdrawal periods than its maternal compound. We conclude that fipronil is efficiently transformed into fipronil-sulfone in the body with subsequent excretion into eggs. More attention should be paid to the potential food safety risk of fipronil-sulfone because of its persistence in eggs.