Using the SBRC Assay to Predict Lead Relative Bioavailability in Urban Soils: Contaminant Source and Correlation Model

Using in vitro bioaccessibility assays to predict Pb relative bioavailability (RBA) in contaminated soils has been demonstrated, however, limited research was performed on urban soils having lower Pb levels. In this study, 162 soils from urban parks in 27 capital cities in China were measured for Pb bioaccessibility using the SBRC assay, with Pb-RBA in 38 subsamples being measured using a mouse-kidney assay. Total Pb concentrations in soils were 9.3–1198 mg kg–1, with 92% of the soils having Pb concentrations <100 mg kg–1. Lead bioaccessibility in soils was 20–94%, increasing with Pb concentration up to 100 mg kg–1 (r = 0.44), however, limited variability in Pb bioaccessibility (60–80%) was observed for soils with Pb > 100 mg kg–1. On the basis of a stable isotope fingerprinting technique, coal combustion ash was identified as the major Pb source, contributing to the increased Pb bioaccessibility with increasing soil Pb concentration. Lead-RBA in soils was 17–87%, showing a strong linear correlation with Pb bioaccessibility (r2 = 0.61), with cross validation of the correlation based on random subsampling and leave-one-out approaches yielding low prediction errors. On the basis of the large sample size of 38 soils, this study demonstrated that the Pb-RBA predictive capability of the SBRC assay can be extended from mining/smelting impacted soils to urban soils with lower Pb levels.