The relative contribution of individual PCBs, PCDDs and PCDFs to toxic equivalent values derived for bulked human breast milk samples from the UK.

Six pooled human milk samples were analysed for 50 individual PCB congeners, of which 24 were identified in all the samples. Mean total PCB (ΣPCB) concentrations were 10 ng/g of whole milk (equivalent to an average of 0.39 μg/g lipid). The milk samples were pooled into groups to comprise rural, semi-rural and urban areas. However, no clear differences were observed between PCB concentrations or congener patterns between the different pooled samples. The contribution of individual PCDDs, PCDFs and mono-ortho- (mono-o) and di-o-substituted PCB congeners to the total calculated toxic equivalent values (ΣTEQ) in the UK population were determined based on results from the present study and data from Startin et al. (1989). Using the toxic equivalent factors (TEFs) proposed by Safe (1990) for PCBs and by the NATO/CCMS (1988) for PCDD/Fs, the TEQs calculated for the monitored PCBs made a greater contribution towards the ΣTEQs than PCDD/Fs. The main contributors to the ΣTEQ (data reported as TEQ in pg/g lipid) were the mono-o-substituted PCB congeners # 118 (17.7), # 156 (15.3) and # 105 (9.95), 2,3,4,7,8-P5CDF (11), 1,2,3,7,8-P5CDD (6.5), 1,2,3,4,7,8-HxCDD/1,2,3,6,7,8-HxCDD (6.2) and 2,3,7,8-T4CDD (5.6). Collectively these compounds accounted for 90 % of the ΣTEQ values