In vitro digestion and DGT techniques for estimating cadmium and lead bioavailability in contaminated soils: Influence of gastric juice pH

Abstract

A sensitivity analysis was conducted on an in vitro gastrointestinal digestion test (i) to investigate the influence of a low variation of gastric juice pH on the bioaccessibility of Cd and Pb in smelter-contaminated soils ( F B , using the unified bioaccessibility method UBM) and fractions of metals that may be transported across the intestinal epithelium ( F A , using the diffusive gradient in thin film technique), and (ii) to provide a better understanding of the significance of pH in health risk assessment through ingestion of soil by children. The risk of metal exposure to children (hazard quotient, HQ) was determined for conditions that represent a worst-case scenario (i.e., ingestion rate of 200 mg day − 1 ) using three separate calculations of metal daily intake: estimated daily intake ( EDI), bioaccessible EDI ( EDI- F B ), and oral bioavailable EDI ( EDI- F A ). The increasing pH from 1.2 to 1.7 resulted in: (i) no significant variation in Cd- F B in the gastric phase but a decrease in the gastrointestinal phase; (ii) a decrease in soluble Pb in the gastric phase and a significant variation in Pb- F B in the gastrointestinal phase; (iii) a significant decrease in Cd- F A and no variation in Pb- F A ; (iv) no change in EDI- F B and EDI- F A HQs for Cd; (v) a significant decrease in EDI- F B HQs and no significant variation in EDI- F A HQ for Pb. In the analytical conditions, these results show that risk to children decreases when the bioavailability of Pb in soils is taken into account and that the studied pH values do not affect the EDI- F A HQs. The present results provide evidence that the inclusion of bioavailability analysis during health risk assessment could provide a more realistic estimate of Cd and Pb exposure, and opens a wide field of practical research on this topic (e.g., in contaminated site management).