Contamination, oral bioaccessibility and human health risk assessment of thallium and other metal(loid)s in farmland soils around a historic TlHg mining area

Highlights: • Elevated concentrations of Tl, Hg, As and Sb were determined in soils • Bioaccessibility of Tl, Hg, As and Sb were relatively low and varied greatly among metal(loid)s and sampling sites. • Bioaccessibility values of Tl, Hg, As and Sb by SBET were usually lower that those by PBET • Health risk to children exceeded adults through oral ingestion • Considering oral bioaccessibility was proposed as a more appropriate approach to assess human health risks of metal(loid)s. In this study, tweenty-nine soil samples were collected from a historic TlHg mining area, located in southwest Guizhou, China. Total concentrations of metal(loid)s in soils and in vitro extracts were analysed by ICP-MS, and the bioaccessibility of metal(loid)s was conducted by two often used in vitro extraction methods, Simplified bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). The health risk assessment based on total concentrations of metal(loid)s, bioaccessibility of SBET and PBET through soil ingestion were investigated. Results indicated that the collected cultivated soils contained elevated concentrations of Tl (44.8 ± 67.7 mg kg⁻¹), Hg (110 ± 193 mg kg⁻¹), As (84.4 ± 89.2 mg kg⁻¹) and Sb (14.8 ± 24.8 mg kg⁻¹), exceeding the regional background values of Guizhou province, China and the Chinese farmland risk screening values. However, the bioaccessibility of Tl, Hg, As and Sb were relatively low, usually less than 30% for most samples and varied greatly among metal(loid)s and sampling sites. The average bioaccessibility values of Tl, Hg, As and Sb by SBET were lower than those by PBET. The non-carsinogenic risk (HQ and HI) and Carcinogenic Risk (CR) values were significantly reduced when incorporating the bioaccessibiltiy of metal(loid)s into health risk assessment. It is worth noting that the health risk to children exceeded adults. Moreover, Tl and As contributed the most to the risk, indicating that more attention should be paid on Tl and As during the daily environmental regulation and management of contaminated soils in Lanmuchang.