Use of fly ash in reducing heavy metal toxicity to plants

An alkaline fly ash was used to reduce the metal toxicity of contaminated soil through immobilization of heavy metals. Pot culture studies were carried out with maize ( Zea mays) crop grown in acidic sandy loam (pH 4.9) and calcareous silty clay (pH 7.9) soils treated with known concentrations of heavy metals (viz. cadmium, copper, nickel and zinc). Fly ash was mixed in metal-treated soil at the rate of 0%, 2%, 5%, 10%, 15%, 20%. The possible variation in metal toxicity to the plants due to fly ash treatment was ascertained through changes in growth patterns. Application of 2% and 5% of fly ash to the calcareous soil shows better growth response as compared to control soil. However, when the fly ash application exceeds 5%, the crop growth was significantly reduced. On the contrary, acidic soil shows positive response with a fly ash addition up to 20% but the resultant crop growth was lesser as compared to growth of plants in the virgin soil (i.e. soil as such, without fly ash and metal treatment). Fly ash addition effectively raised the pH of acidic soil and thus helped to reduce the metal solubility and availability to plants.