[Investigation of the residue of the fasciolicide nitroxynil in milk and dairy products].

A sensitive gas chromatographic method with electron capture detection of the fasciolicide, nitroxynil, in milk and dairy products was developed and was applied to assess nitroxynil concentration in cow's milk after subcutaneous injection of three lactating cows. The level of nitroxynil in cow's milk reached a maximum (0.25-0.26 micrograms/ml) in 6-30 hours, and was undetectable within 8 weeks. Analysis of nitroxynil concentrations in cream, skimmed milk, curd and whey prepared from nitroxynil excreting cow's milk showed that the chemical became concentrated in cream and curd. Nitroxynil appeared to be stable at temperature used in LTLT and HTST pasteurization with the rate of degradation in milk being less than 10%. Investigation of nitroxynil residues in milk (raw, liquid whole, processed) and dairy products (processed cheese, natural cheese, butter, sweetened condensed milk, evaporated skimmed milk, skimmed milk powder, formulated milk powder) was performed during 1976-1979. Nitroxynil was detected in 20% of milk samples at a maximum level of 39 ng/ml, with one formulated milk powder at level of 0.34 ng/g. Confirmation of nitroxynil was performed by GCMS. The results of this investigation were promptly reported to the government. Since then administrative guidance was provided leading to appropriated use of nitroxynil thereafter. The ordinance controlling dairy production amended in 1979 revised the withdrawal time for medicines administrated to cows from "three days" to "the period when medicine remains in the milk". There was no mutagenicity of nitroxynil evident by the Ames test.