LAUSR

The mechanism underlying contaminant biomagnification is a decrease in the volume (V) and the fugacity capacity (Z) of food during digestion in the gastrointestinal tract. Traditionally biomagnification is quantified by measuring contaminant concentrations in animal tissues. Here we present a proof-of-concept study to non-invasively derive the thermodynamic limit to an organism's biomagnification capability (BMFlim) by determining the ratio of the V.Z-products of undigested and digested food. We quantify Z-values by equilibrating food and feces samples, that have been homogenized and spiked with polychlorinated biphenyls (PCBs), with silicone films of variable thickness coated on the inside of glass vials. We demonstrate the feasibility of this method for wolf (Canis lupus hudsonicus) and domestic dog (Canis lupus familiaris). For adult wolf eating a relatively lean meat diet, a BMFlim (averaged over several PCB congeners) of approximately 41 was observed, whereas the BMFlim reached 81 for an adult domestic dog eating a lipid-rich diet. Beside the dietary lipid content which strongly affects the Z-value of the diet, the capability of an animal to digest its diet also influences the BMFlim by controlling the Z-values of their feces and the volume reduction of the foods in the gastrointestinal tract. Less efficient digestion leads to a lower BMFlim in a juvenile dog (approximately 35) compared to its older self, even though their diets had similar lipid contents. The effect of the volume reduction (VD/VF ranging from 4 to 15) was comparable to the effect of the Z-value reduction (ZD/ZF from 3 to 20).