Bioaccessibility of lead in urban soil of Broken Hill, Australia: A study based on in vitro digestion and the IEUBK model

Abstract

This study was conducted to investigate lead (Pb) bioaccessibility in urban soil and to assess health risk to children in the city of Broken Hill, Australia, which was established around one of the world's largest lead–zinc–silver mines. Fifty-three topsoil (0–0.1m) and 50 subsoil (0.3–0.5m) samples were collected from earthen footpaths, nature strips, parks or vacant land throughout the urban area. The soil samples were analysed for total Pb concentration, Pb bioaccessibility and Pb mineral phases, together with important soil physicochemical properties known to influence Pb bioaccessibility. Lead bioaccessibility ranged from 24% to 89% in topsoil and from 16% to 100% in subsoil, exhibiting a generally decreasing pattern with increasing distance from the orebody. Lead bioaccessibility was strongly positively related to total Pb concentration in both the topsoil and subsoil. In subsoil, a moderate negative correlation existed between Pb bioaccessibility and soil pH, while a moderate positive correlation existed between Pb bioaccessibility and soil organic matter (OM) content. In contrast, only a weak positive correlation existed between Pb bioaccessibility and OM content in topsoil. The presence of different Pb mineral phases also appeared to have caused variation in soil Pb bioaccessibility, with galena (PbS)-rich samples tending to exhibit lower Pb bioaccessibility. The prediction of blood lead (PbB) levels in Broken Hill children aged 1–4years using the IEUBK model well matched the measured data from a recent PbB screening, suggesting a high risk of childhood chronic low-level Pb exposure (PbB levels >5μg/dL) in Broken Hill, especially in the vicinity of the orebody. Future Pb abatement programs in Broken Hill should utilise the IEUBK model to establish target soil Pb values in an effort to achieve particular child PbB outcomes.