Bioassay-Based and Parameter-Optimized Bioaccessibility Assay to Predict Chromium Oral Bioavailability from Contaminated Soils

Oral exposure to toxic chromium from incidental ingestion of contaminated soil is of concern due to its adverse effects on human health. We developed a mouse urine bioassay to measure the Cr relative bioavailability (Cr-RBA) in contaminated soils. We used Cr-RBA data (5.12–50.0%; n = 16) to evaluate the predictive capability of three in vitro bioaccessibility assays, including Solubility Bioaccessibility Research Consortium (SBRC), PBET, and IVG. The Cr bioaccessibility depended on both soils and assays, being 0.80–15% (averaging 4.2%), 1.1–19% (6.3%), and 0.47–7.7% (2.3%), respectively. Based on in vivo-in vitro correlations, strong relationships were observed for their gastric phase (GP; acceptable R 2 at 0.62–0.73; slope at 3.1–7.3), with SBRC-GP being the best. To address the high slopes of low prediction accuracy issue, parameters including pH, solid/liquid ratio, and extraction time were optimized via response surface methodology using Box-Behnken Design. The modified SBRC-GP assay (pH = 1.2; solid/liquid ratio = 1/150; extraction time = 2 h) increased Cr bioaccessibility by 2.3–4.2 fold, which can better predict soil Cr-RBA ( R 2 = 0.66, slope = 1.0). This bioassay-based and parameter-optimized bioaccessibility assay can be used to predict Cr bioavailability in soils, which is important to assess the health risk associated with human exposure to soil Cr via incidental ingestion and help to refine the remediation goal in Cr-contaminated soils.