Effect Of Aging On Arsenic And Lead Fractionation And Availability In Soils

We coupled the diffusive gradients in thin-films (DGT) technique, the physiologically based test (PBET) with two sequential extraction methods to investigate the influence of aging on As and Pb fractionation and availability in three soils spiked with As (40 or 400 mg kg-1), Pb (150 or 1500 mg kg-1) or As+Pb (40 mg kg-1 As and 150 mg kg-1 Pb). During aging, As moved from the more available (non-specifically and specifically sorbed) to less available (amorphous and crystallized Fe/Al) fractions while Pb moved from the first three fractions (exchangeable, carbonate and Fe/Mn hydroxide) to organic fraction. However, even after 33-week aging, much more As and Pb were in the least available residual fraction in native soils than spiked soils (11-59% vs.1.2-12%), and caution needs to be excised when using spiked soils for research. Relatively, As in spiked soils was much more available than Pb with 11-14% As and 46-59% Pb in the residual fraction. DGT and PBET data showed that prolonged aging in soils would result in a decrease in As/Pb availability, especially within the first month. And after 33-week aging, available As measured by DGT and PBET was 0.9-14.1 mg L-1 and 48-84%, much higher than the values for Pb (0.9-364 μg L-1 and 8-34%),which suggested the higher availability for As than Pb in soils, and this was consistent with sequential extraction result above. Moreover, availability data demonstrated that the alkaline soil was less effective in As sorption, while the acidic soil was less effective in Pb sorption, and these variations were largely explained by soil properties, including Fe hydroxide content. Correlation analysis indicates that As in the non-specifically and specifically sorbed fractions and Pb in the exchangeable fraction were likely sources of DGT-measured labile As and Pb; while for PBET measurement, the non-specifically As was likely to constitute the proportion of bioaccessible As, while Pb bound with carbonates and the exchangeable Pb fractions were probably the bioaccessible Pb sources in gastric and intestinal phases, respectively. Human risk assessment showed that hazard quotient values for As/Pb in low loading rate soils suggests no potential non-carcinogenic risk to children. But, in high loading rate soils, the hazard quotient values of As/Pb were above 1, while carcinogenic risk of As exceeded 1.39×10-4. which both were above acceptable level.