Relative disposition of PCDD/Fs and PCBs in paired liver and muscle tissues from different species of farm animals and different contamination scenarios

Polychlorinated dibenzo-p-dioxins, furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) are preferentially retained in animal liver and adipose but exact distribution is difficult to ascertain because of a limited number of studies which often use tissues from different animals. These limitation were mitigated by using paired liver/muscle tissues from the same animals and combining data from seven independent studies in the UK and Italy on three species. Additionally, the effects of variable (low, moderate, high) levels of pasture/housing contamination were also investigated. Combined PCDD/F and PCB toxic equivalents (TEQs) (range: 0.11-219 pg/g fat) occurred to a significantly (P < 0.001) higher level in livers of sheep and pigs (>15:1, liver:muscle), reducing to 4:1 for cattle, but supplementary data on chickens showed similar distribution. Occurrence levels in tissues were consistent with pasture contamination - highlighting the food safety and regulatory importance of pasture/housing locations for animals used in food production. Congener patterns in muscle and liver tissues were similar for chickens and pigs but notably different in sheep. Remarkably, across all 189 animals investigated, PCDD/Fs consistently dominated the combined TEQ in UK cattle, sheep and chickens showing highest contributions in pig tissues. Conversely, PCB-TEQ dominated in the tissues of Italian animals. This divergence may arise from feed, husbandry, geographical differences but elevated PCB contamination has been reported in Southern Italian locations. The higher liver contamination corresponds to the ability of PCDD/Fs and DL-PCBs to induce and bind to the hepatic CYP1A2 enzyme, restricting CYP-mediated metabolism and resulting in liver retention or sequestration.