Do human individuals differ in their potential for lipophilic contaminant biomagnification?

Biomagnification is the process that leads to the chemical potential of organic contaminants in an organism exceeding that in its diet. Despite its obvious importance, studies on biomagnification in humans are rare, in particular those that seek to quantify and characterize interindividual differences in biomagnification potential. Applying a method based on equilibrium sampling and chemical analysis of paired dietary and fecal samples we determined the thermodynamic limit to biomagnification (BMF_lim) as well as a feces-based biomagnification factor (BMF_F) for a selection of polychlorinated biphenyls in five human volunteers sharing the same diet over a period of five days. Four younger participants displayed similar BMF_lim and BMF_F, while an older participant's BMF_lim and BMF_F were higher by factors of up to 5 and 7, respectively. These differences were due to divergent dietary digestion efficiencies, with lipid assimilation efficiency ranging from 93 to 99%. Small sample size prevented us from confirming whether lipid assimilation efficiency is influenced by the participants' gut microbiomes. Fugacities in blood and feces, were highly correlated for each participant, but the relationships were different between participants. Only the younger participants had contaminant fugacities in blood that greatly exceeded those in feces, consistent with a fat flush effect, whereas contaminants were close to chemical equilibrium between blood and feces in the older participant. Differences in biomagnification are likely to contribute to the variability in contaminant levels within a population that is typically observed in biomonitoring.