Challenges with soils contaminated by mixed contaminants: bioavailavility, bioremediation and ecotoxicity considerations

Full text: Global industrialisation coupled with modern agriculture has resulted in the production and emissions of various xenobiotic compounds into the environment. Soil, the ultimate repository/sink for most contaminants is generally encountered not with single pollutant, but with mixtures of several contaminants [organic-organic (pesticides plus their metabolites), organic-inorganic (DDT-As; PAH-metals), inorganic-inorganic (sewage sludge containing several heavy metals). Often the parent chemicals exist simultaneously with their degradation products. Contaminated sites are widespread and are of common occurrence in most countries, industrial countries in particular. Adverse impacts of contaminants on biological systems are primarily governed by their bioavailability which is often a major factor determining the success or failure of bioremediation. However, its success depends on several factors related to the biological agent used, soil, environmental and contaminant characteristics. Risk based remediation is currently gaining importance as an attractive option for remediation of contaminated environments. Bioavailability and toxicity are the key parameters that need to be adequately understood prior to estimating the risk posed by the contamination or any remedial activity to be undertaken. GCER and CRC CARE are therefore conducting research to examine the factors affecting bioavailability of contaminants in relation to ecotoxicity and bioremediation. A few case studies from our research on the toxicity of mixed contaminants (eg. DDT and its metabolites, petroleum hydrocarbons, Copper, cadmium - atrazine, arsenic-DDT etc) in long-term contaminated sites and the associated challenges to remediation will be discussed. (author)