Transfer assessment of fipronil residues from feed to cow milk

Fipronil, a phenylpyrazole insecticide introduced for pest control on a broad range of crops, can also affect non-target insects such as honeybees. More widely, non-target environment such as milk produced by dairy cows fed with maize silage from treated seeds (=silage T) can be affected. To assess the potential transfer of fipronil residues (sulfone, sulfide, fipronil, desulfinyl and amide), a methodology including gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) analysis was developed and validated according to the 2002/657/EC decision, in order to reach a level of quantification below 0.1mugL(-1) in milk and 0.1mugkg(-1) in plants. Twelve dairy cows were fed with silage T during 4 months. Concentration of fipronil in treated seeds was estimated at 1gkg(-1), whereas silage from these seeds contained 0.30+/-0.05mugkg(-1) of dry material of fipronil, 0.13+/-0.03mugkg(-1) of dry material of sulfone. Sulfide residues were below the limit of quantification. Silage from untreated seeds (=silage U) presented traces of fipronil and sulfone, respectively at 0.04+/-0.06 and 0.02+/-0.03mugkg(-1) of dry material. Contribution of fipronil residues from supplies was insignificant. During administration of silage T, only sulfone residues were quantified in milk. The average concentration was 0.14+/-0.05mugL(-1). Before and after administration, sulfone residues were detected but not quantifiable (<0.025mugL(-1)). Our results suggest a transfer of fipronil from feed to milk under its sulfone form. Moreover, traces of fipronil residues in maize U, soya, wheat and straw show a diffuse contamination of this pesticide in the environment.