An approach to incorporate soil lead bioavailability in ecological risk assessment by including diet in a novel avian in vitro gastrointestinal assay

When bioavailability data is not available for a chemical, it is often assumed to be 100% bioavailable, though many common contaminants of concern are in reality much less bioavailable. Overly conservative estimates of 100% bioavailability can thus result in overestimation of risk as well as unnecessarily cost- and time-intensive cleanups. Experimentally determining bioavailability directly is also unappealing as it necessitates in vivo studies which likewise raise cost and time concerns in addition to ethical ones. We report a novel in vitro simulated gut digestion method that can be used to accurately predict relative bioavailability of soil lead (Pb) to birds. When diet is included in the novel in vitro method, in vivo-in vitro correlations were strong (r2 = 0.92), showing potential for use in ecological risk assessment. Among six different avian diets, the in vitro bioaccessible Pb was strongly correlated with total phosphorus content (r2 = 0.78). By including a representative diet sample in the in vitro assay, relative bioaccessible Pb can be accurately estimated while avoiding the need for animal experimentation or diet-specific adjustments for toxicity calculations. This relative bioaccessible Pb estimation can be used in ecological risk assessment to yield more true-to-life estimated exposure doses for comparison to avian toxicity reference values.