Arsenic mobility in the amended mine tailings and its impact on soil enzyme activity

The objectives of this study were to elucidate the effects of soil amendments [Ferrous sulfate (Fe-II), red mud, Fe-II with calcium carbonate (Fe-II/L) or red mud (RM/F), zero-valent iron (ZVI), furnace slag, spent mushroom waste and by-product fertilizer] on arsenic (As) stabilization and to establish relationships between soil properties, As fractions and soil enzyme activities in amended As-rich gold mine tailings (Kangwon and Keumkey). Following the application of amendments, a sequential extraction test and evaluation of the soil enzyme activities (dehydrogenase and beta-glucosidase) were conducted. Weak and negative relationships were observed between water-soluble As fractions (As-WS) and oxalate extractable iron, while As-WS was mainly affected by dissolved organic carbon in alkaline tailings sample (Kangwon) and by soil pH in acidic tailings sample (Keumkey). The soil enzyme activities in both tailings were mainly associated with As-WS. Principal component and multiple regression analyses confirmed that As-WS was the most important factor to soil enzyme activities. However, with some of the treatments in Keumkey, contrary results were observed due to increased water-soluble heavy metals and carbon sources. In conclusion, our results suggest that to simultaneously achieve decreased As-WS and increased soil enzyme activities, Kangwon tailings should be amended with Fe-II, Fe-II/L or ZVI, while only ZVI or RM/F would be suitable for Keumkey tailings. Despite the limitations of specific soil samples, this result can be expected to provide useful information on developing a successful remediation strategy of As-contaminated soils.