Effect of bile type on the bioaccessibility of soil contaminants in an in vitro digestion model.

Soil ingestion is an important pathway of exposure for many nonvolatile contaminants for man and in particular for children. A fraction of the ingested contaminant may not dissociate from the soil particles during digestion in the gastrointestinal tract, and is thus not available for transport across the intestinal epithelium. In order to estimate the contaminant fraction that is mobilized from soil, i.e., the bioaccessible fraction, several in vitro digestion models have been developed. The currently existing digestion models display many differences. One aspect that may affect bioaccessibility and may induce differences between digestion models is the bile that is used. Often freeze-dried bile of animal origin is preferred to purified bile salts. However, also the animal origin of bile may give rise to differences in bioaccessibility because bile composition appears to be species dependent. In the present study, we compared the bioaccessibility of benzo[a]pyrene, arsenic, cadmium, and lead of four different soils after digestion with ox bile from two different suppliers, pig bile, and chicken bile. Bioaccessibility appeared to vary amongst the different soils and contaminants. Only chicken bile increased the bioaccessibility of lead and cadmium significantly and relevantly for one of four soils. For chicken bile, the bioaccessibility of lead was 3-5.5 times greater than for the other bile types and the bioaccessibility of cadmium was 1.5 times greater. In all other cases, the bioaccessibility differences were less than 10%, which is considered irrelevant for risk assessment purposes.