Biotransfer and bioaccumulation of dioxins and furans from soil: chickens as a model for foraging animals

Chickens were used as a model for foraging animals to examine the bioavailability of all 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/PCDFs) from soil. Three groups of chickens were exposed through their diet to soil contaminated with PCDD/PCDFs at less than 0.5 pg/g I-TEQ (control group), 42 pg/g I-TEQ (low exposure group), and 460 pg/g I-TEQs (high exposure group). Eggs, tissues, feces and feed were analysed throughout the exposure and depuration period. Daily intake was estimated at 2.5 ng/kg-day for the high and 0.3 ng/kg-day for the low exposure groups. Bioavailability was chlorination-dependent ranging from 80% for tetrachlorinated to less than 10% for octachlorinated congeners. During exposure, tissue distribution was congener-dependent with 5-30% of the intake excreted in the eggs, 7-54% deposited in the adipose and less than 1% present in the liver. On a fat weight basis, the highest concentrations were observed in the liver, implying that mechanisms other than lipid solubility operate in that tissue. Bioconcentration factors and elimination half-lives were also congener- and tissue-dependent. Results from this study indicate that animals foraging on soil contaminated at low ppt PCDD/PCDF levels may bioaccumulate these compounds to unacceptable levels.