Comparison of different sequential extraction procedures to identify and estimate bioavailability of arsenic fractions in soil

For the sake of risk assessment for arsenic-contaminated sites, the purpose of this study is to estimate the bioavailable arsenic fractions in soil by using the three arsenic-specific sequential extraction procedures (SEPs) and distinguish which SEP can reliably identify and estimate the bioavailable arsenic, so as to screen the most suitable SEP for the risk assessment of arsenic-contaminated sites. The arsenic uptake by spinach and amaranth was used to evaluate bioavailability of arsenic fractions defined by the SEPs proposed by Shiowatana, Larios, and Wenzel, respectively, as well as the ability of these three SEPs to identify and estimate bioavailable arsenic. The results showed that besides the highly mobile arsenic fractions defined by each SEP, the less mobile HCl-extractable arsenic (mainly carbonate-bound arsenic) in Shiowatana SEP was also the source of bioavailable arsenic, and their contribution to bioavailable arsenic depended not only on their mobility but also on their content, suggesting that the independent extraction of carbonate-bound arsenic should be considered in the design of arsenic-specific SEPs. All three SEPs could provide approximate estimation of bioavailable arsenic fractions. Although Wenzel SEP performed slightly worse than Larios SEP and Shiowatana SEP, all three SEPs had acceptable accuracy and reproducibility in arsenic fractionation. However, the Shiowatana SEP performed more comprehensive in extracting potential bioavailable arsenic fractions and identifying the source of bioavailable arsenic, indicating that it might be more suitable for the risk assessment of arsenic-polluted sites based on arsenic fractionation.