Retention and plant availability of chromium in soils as affected by lime and organic matter amendments

Chromium is used as Cr(III) in the tannery industry and as Cr(VI) in the timber treatment industry. In this experiment, the effect of 2 liming materials [fluidised bed boiler ash (FBA) and lime] and an organic amendment (Pinus radiata bark) on the retention of Cr by 2 soils (Egmont and Tokomaru) was examined using both 'batch' and 'column' experiments. The effect of these amendments on the uptake of Cr from the Egmont soil, treated with various levels of Cr (0-3200 mg Cr/kg soil), was examined using sunflower (Helianthus annuus) plants. The transformation of Cr was examined by fractionation of Cr in soils. Addition of FBA and lime increased the retention of Cr(III), but had the opposite effect on the retention of Cr(VI). Addition of bark did not affect the retention of Cr(III), but it increased the retention of Cr(VI). Increasing additions of Cr increased Cr concentration in plants, resulting in decreased plant growth. The liming materials were found to be effective in reducing the phytotoxicity of Cr(III) and the Pinus radiate bark was effective for Cr(VI). In both Cr(III)- and Cr(VI)-contaminated soils, the concentrations of Cr were higher in the organic-bound, oxide-bound, and residual fractions than in the soluble and the exchangeable fractions. The concentrations of Cr in the soluble and the exchangeable fractions were higher in the Ct(VI)-contaminated than the Cr(III)-contaminated soil. Addition of the liming materials decreased the concentration of the soluble Cr(III) and bark decreased soluble Cr(VI) in soil. There was evidence for the reduction of Cr(VI) to Cr(III) in the bark-treated soils.