Bioaccessibility and dynamic dissolution of arsenic in contaminated soils from Hunan, China

Purpose Bioaccessibility is always a factor in human health risk assessment; the accurate determination of arsenic (As) dynamic dissolution in the gastric and small intestinal phases can provide a better understanding of its potential impact on human health. Materials and methods Eighteen soil samples were collected from different sites in Hunan, China, and the factors controlling the bioaccessibility and dynamic dissolution of soil As were investigated. The bioaccessibility of soil As was determined by the physiologically based extraction test (PBET). Results and discussion The results indicated that the bioaccessibility ranged from 6.9 to 59.5 % and 5.9 to 83.2 % in the gastric and small intestinal phases. Among all the soil properties, the concentrations of oxalate-extractable Fe, Mn, and total As were important for controlling bioaccessible As. In the gastric phase, the bioaccessible As concentrations increased rapidly in the first 20 min and kept steady state after 1 h. In the small intestinal phase, the bioaccessible As concentrations kept steady state rapidly after 2 h. Moreover, the more soluble fraction of As-bearing metal minerals had enhanced solubility in the gastric phase under acidic conditions, and most of the metal oxyhydroxides formed were usually unstable in the small intestinal phase under neutral conditions. By the interaction between kinetic laws and simple linear correlation, the dissolution rate of As for soils with lower pH was faster in the gastric phase; thus, the soil pH and dissolution of Fe, Mn, and Al minerals may be the main factors controlling the As dissolution rate. Conclusions The As bioaccessibility in the small intestinal phase was higher, and the prescribed 4 h duration of the PBET method can meet As complete dissolution. The dynamic dissolution of As from soil in the gastric and small intestinal phases was strongly controlled by the concentrations of dissolved Fe, Mn, and Al.