A survey of PCB congeners in U.K. cows' milk

Samples of unpasteurised bulked milk, taken directly from ten herds of dairy cattle on rural and urban farms in the north west of England on five separate sampling occasions, were analysed for a range of PCB congeners. Sigma PCB concentrations (sum of 37 congeners) ranged from 3.4-16.4 ng/g milk fat with a mean sigma PCB concentration of 8.4 ng/g milk fat. The dominating congeners were 118, 153, 138 and 180, which contributed 15%, 20%, 17% and 9% of the sigma PCB load respectively. The chlorine pattern of the congeners which made moderate or major contributions to the sigma PCB concentration were typically substituted at both para positions (4,4'), while the PCB congeners not detected in the milk had at least one ring that was not 4-substituted. These results indicate the 4,4' substitution pattern as being the key to PCB persistence in cows. It is estimated that consumption of typical daily intakes of milk with the PCB concentrations measured in this study would contribute 11% of the average daily sigma PCB intake for individuals in the UK. This contribution would increase to 30% when exposure through the consumption of dairy products prepared from such milk (e.g. cheese, butter) is taken into account. It is estimated that the inclusion of the TEF assigned PCBs would typically increase the TEQ rating of cows' milk by approximately 40% over that attributed to PCDD/Fs alone.