Mechanistic insight into the release behavior of arsenic (As) based on its geochemical fractions in the contaminated soils around lead/zinc (Pb/Zn) smelters

Arsenic (As) was known as human carcinogen. It was therefore of great importance to better understanding the release behavior of arsenic in soils for managing and controlling the potential risks of smelter contaminated sites. The present work evaluated arsenic bioavailability and bioaccessibility, in combination with geochemical fractionation and valence analysis by X–ray photoelectron spectroscopy (XPS), and also investigated the release patterns of bioavailable and bioaccessible arsenic in soils. The present results showed that there was a significant variation in the bioavailable and bioaccessible fractions of arsenic, due to the great difference in soil properties, extractants types, and in vitro assays. Moreover, it was found that KH2PO4 presented the relatively higher arsenic bioavailability with wide range of 9.89–25.5 %, which might better predict the arsenic bioavailability in soils than the other extractants. In addition, the relatively higher arsenic bioaccesibility was found in Solubility Bioaccessibility Research Consortium (SBRC) assay, ranging from 5.50 to 67.4 % for gastric phase (GP) and 3.85–18.8 % for gastrointestinal phase (GIP), respectively. In addition, the time–dependent release of bioavailable arsenic was controlled by the competitive desorption between phosphate and As (V) ions, while the time–dependent release of bioaccessible arsenic was dominated by the stable complexation of organic ligands and the strong affinity of Al, Mn and Fe–(hydr) oxides. According to the study results, a new insight into the arsenic behavior was provided to more scientifically evaluate its contamination risks.