Fate and migration of arsenic in large-scale anaerobic landfill

The fate and migration of arsenic in a large-scale anaerobic landfill site was investigated by characterization of the total As content and its speciation using a sequential extraction procedure. The total As content in the anaerobic landfill varied greatly with age of the deposited refuse, ranging from 15.26 ± 4.18 mg kg^-1 to 38.41 ± 10.41 mg kg^-1. There was an increasing trend from the upper layer to a depth of 18-19 m, followed by a decrease in the lower layer. Sequential extraction results showed that As present in exchangeable and weak-acid soluble forms (F1) varied from 0.08 ± 0.01 mg kg^-1 to 12.61 ± 0.92 mg kg^-1, but from 1.28 ± 0.11 mg kg^-1 to 8.40 ± 0.23 mg kg^-1 in reducible forms (F2). Oxidizable (F3) and residual (F4) forms of As, which were much more stable and for which the environmental risk correspondingly decreased, accounted for 24.21%-58.70% and 10.11%-30.90% of the total As content, respectively. Nitrate and carbonate had a strong influence on the distribution of As in F1 species; ferric ion affected As distribution in F2; both ferrous ion and dissolved oxygen content contributed to F3 distribution; As in F4 was associated with crystalline minerals structures and was only weakly affected by environmental factors. The deposition process could be divided into six phases to interpret As migration and distribution within the anaerobic landfill after closure.