PCDD/F congener profiles have been used to determine the source of elevated TEQ concentrations in cows' milk collected in the vicinity of several industrial sites. Principal components analysis and modelling of the air-to-milk transfer of individual PCDD/F congeners have shown that the milk fingerprint was related to that of sediment taken from the River Rother adjacent to the farm where the cows had grazed. It is suggested that sediment from the river had been washed onto the grazing land during periods of flooding, and this had been ingested by the grazing cows. This pathway could represent an important route of contaminant intake for livestock grazing on the regularly inundated floodplains of rivers containing contaminated sediments.