Quantifying the Biomagnification Capability of Arctic Wolf and Domestic Dog by Equilibrium Sampling

Abstract

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 noninvasively derive the thermodynamic limit to an organism’s biomagnification capability (biomagnification limit 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, which 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 an 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. Besides the dietary lipid content that 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 food 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 (V D/V F ranging from 4 to 15) was comparable to the effect of the Z-value reduction (Z D/Z F from 3 to 20).

Probing the Thermodynamics of Biomagnification in Zoo-Housed Polar Bears by Equilibrium Sampling of Dietary and Fecal Samples

“…However, the ϕ NLOM in bear feces had a value (22%) similar to that of the previously measured ϕ NLOM in adult dog feces (20%), even though it was still much lower than that in juvenile dog (40%) and wolf feces (75%). 2 Obviously, the carbon content alone cannot fully explain the ϕ NLOM value in a fecal sample, and the characterization of NLOM is crucial. The low ϕ NLOM in both polar bear and adult dog feces might be due to a large portion of indigestible fibers with a low absorptive capacity for HOCs, e.g., from fresh fruit (e.g., apple) and vegetables (e.g., potato).…”

“…Our results showed that the BMF lim value is dependent on both the dietary composition (e.g., lipid content, P lipids ) and the digestion efficiency of a canine. 2 The actual BMF may exceed the BMF lim , if a chemical is more efficiently absorbed from the intestine than it is lost to the intestine: e.g., as a result of the “fat flush” 9 effect or micelle-mediated transport. 10 The BMF lim value can also exceed the BMF value, if processes other than fecal elimination notably contribute to the loss of a chemical from the organism.…”

“… 10 The BMF lim value can also exceed the BMF value, if processes other than fecal elimination notably contribute to the loss of a chemical from the organism. 2 …”

“…Another shortcoming of our earlier study was that the original contamination of the diet of the investigated canines was too low to determine the Z D and Z F values directly. 2 In order to meet the criteria of good equilibrium sampling, the fraction of chemicals extracted by the silicone should be lower than 5%, so that changes in the contaminant levels in the samples due to sampling are negligible. 6 This limits the amount of chemical in the silicone phase, which can cause C siliconeD and/or C siliconeF to be too low for reliable quantification, especially if the sample size is small and contaminant levels are low.…”

“…We circumvented this issue by spiking contaminants on diet and fecal samples in amounts that were high enough for reliable quantification in the silicone while working with sample to silicone ratios that ensured negligible sample depletion. 2 Relying on spiked compounds, however, meant that (i) we had to assume that the measured Z values of spiked contaminants ( Z spiked ) are similar to the Z values of contaminants already present in the samples ( Z native ) and (ii) the fugacity of the contaminants in the diet and feces ( f D and f F , respectively) could not be determined. The assumption that Z spiked = Z native is plausible as long as the spiked compounds are given sufficient time to achieve the same distribution within the samples as the native compound.…”