Effect of steel-making slag as a soil amendment on arsenic uptake by radish (Raphanus sativa L.) in an upland soil

The steel-making slag (SMS), a by-product of steel manufacturing process with an alkaline pH (11–12) and high amount of iron (Fe) and calcium (Ca) oxides, was used to reduce arsenic (As) phytoextractability. The by-product was selected as an alternative to commercial Fe oxides, which can decrease plant uptake, but they are expensive if used as amendments of contaminated arable soils. SMS was applied at rates 0, 2, 4, and 8 Mg ha⁻¹ to an As (1 N HCl-extractable As 25 mg kg⁻¹) contaminated soil prepared by mixing non-contaminated soil and mine tailings and cropped to radish (Raphanus sativa L.) seeding. Calcium hydroxide (Ca(OH)₂), a common liming material in Korea, was applied at the same rates for comparison. Steel-making slag more effectively suppressed radish As uptake and increased yield than Ca(OH)₂ due to stronger As immobilization because it significantly increased extractable Fe concentration and decreased extractable As. The SMS-treated soil showed an apparent increase in As chemisorbed by Fe and Al oxides and hydroxides of surface soil, As associated at the Fe and Al oxides and hydroxides of internal surfaces of soil aggregates, and Ca-associated As. The steel-making slag can be a good soil amendment to suppress As phytoextractability and improve nutrient balance in As-contaminated soil.