Polychlorinated biphenyls from dairy farms: consequences in market milk.

Samples of milk from bulk tanks of individual farms were collected from 198 producers and analyzed for polychlorinated biphenyl residues. During the first year of the study these producers represented the entire milk supply for one processor. Detectable concentrations were in milk from nine farms, which contributed 5% of the milk delivered to the processor. The daily amount of polychlorinated biphenyl entering this milk market was 212 mg. During the second year, samples again were collected from the same producers. The compound was quantified in samples from ten herds, two of which were undetectable the previous year. Concentrations in milk from the other farms had declined significantly from the previous year, contributing less than one-third the calculated amount to market milk.