A critical evaluation of the use and ‘misuse’ of As and Pb bioaccessibility data in human health risk assessments

With the now widescale reporting of oral bioaccessibility data at contaminated sites, following our investigation of three sites (one public open space and two residential) for As and Pb contamination, a critical evaluation of the application and utility of such bioaccessibility testing was undertaken to better inform future use. Mean As and Pb soil levels across the sites varied between 12.5 and 24,900 mg/kg and 149–5930 mg/kg, respectively. Using the Unified Bioaccessibility Method (UBM) for in vitro bioaccessibility testing the highest bioaccessible concentrations were identified in the gastric phase. At site 1, a residential urban garden site the maximum bioaccessible As was 50.2% while the maximum bioaccessible Pb was 64.8%; similarly in site 2, also a residential urban garden site the maximum bioaccessible As was 38.72% while the maximum bioaccessible Pb was 66.0%. However, at site 3, a public open space site, the maximum bioaccessible As was 29.7% while the maximum bioaccessible Pb was 38.4%. Using the appropriate soil screening values and recommended statistical testing, we highlight that the use of bioaccessibility testing was unnecessary at sites 1 and 2 (residential urban garden sites), while at site 3 the value of oral bioaccessibility testing is highlighted as part of a ‘lines of evidence approach’ to support the site's specific risk assessment. We need to move away from the uncritical, blanket application of oral bioacessibility testing and strategically target where the results of these data add real value to site determination.