Reduction of as Mobility Using Soil Amendments, and Its Impact On Soil Enzyme Activity and Phytotoxicity of the Former Au Mine Tailings.

To examine the efficiency of amendments for reduction of As mobility, several iron Fe bearing- and organic- amendments (at a rate of 1%, w:w) were applied to three mine tailings (Kangwon Au mine, KW; Keumkey Au mine, KK; Chungryong Au mine, CR). The amendments applied included FeSO₄·7H₂O [Fe(II)]; FeSO₄·7H₂O + lime [Fe(II)/L]; iron powder, [Fe(P)]; Fe(OH)₃ [Fe(III)]; goethite (Goe); redmud (RM); redmud coated with iron (RM/F), furnace slag (F-slag), spent mushroom waste (MW), by-product fertilizer (BPF) and acidified humic acid extracted from MW (HA). Following the application of amendments sequential extraction and selective single extraction tests were conducted to determine As distribution, leachability, bioaccessibility and also soil enzyme (dehydrogenase, β-glucosidase, acid phosphatase and urease) activities were determined. For KW, Fe(II) and Fe(II)/L treatment significantly reduced mobile As fraction, whereas these amendments treated in KK and CR showed significantly increased mobile As due to increases in other heavy metal mobilities and pH. Reduction of mobile As in KK was observed with treatment of Fe(P), Fe(III) and RM. However, significant decreases in mobile As were not observed with treatments of organic amendments in all mine tailings examined. As leachability and bioaccessibility in amended mine tailings showed similar trends with their changes in mobile As fractions. Also, the enzymes activities showed significantly negative correlation with mobile As fractions, indicating that the elevated mobile As exerted a strong inhibitory effect on the soil enzyme activities. Finally, phytotoxcitiy assay using lettuce and Chinese cabbage also showed enhanced root elongations as the mobile As reduced due to soil amendments treatments. In conclusion, iron-bearing amendments can be applicable as the effective amendments to reduce As mobility in mine tailings, however, careful consideration regarding their adverse effects on soil pH and other toxic metal mobility should be required.