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 radiata 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 Cr(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.
Microbial Utilization of Pinus radiata Bark
