Quantitative assessment of the toxic effects of heavy metals on 1,2-dichloroethane biodegradation in co-contaminated soil under aerobic condition

1,2-Dichloroethane (1,2-DCA) is one of the most hazardous pollutant of soil and groundwater, and is produced in excess of 5.44 x 10(9) kg annually. Owing to their toxicity, persistence and potential for bioaccumulation, there is a growing interest in technologies for their removal. Heavy metals are known to be toxic to soil microorganisms at high concentrations and can hinder the biodegradation of organic contaminants. In this study, the inhibitory effect of heavy metals, namely; arsenic, cadmium, mercury and lead, on the aerobic biodegradation of 1,2-DCA by autochthonous microorganisms was evaluated in soil microcosm setting. The presence of heavy metals was observed to have a negative impact on the biodegradation of 1,2-DCA in both soil samples tested, with the toxic effect being more pronounced in loam soil, than in clay soil. Generally, 75 ppm As3+, 840 ppm Hg2+, and 420 ppm Pb2+ resulted in 34.24%, 40.64%, and 45.94% increase in the half live (t(1/2)) of 1,2-DCA, respectively, in loam soil, while concentrations above 127.5 ppm Cd2+, 840 ppm Hg2+ and 420 ppm of Pb2+ and less than 75 ppm As3+ was required to cause a >10% increase in the t(1/2), of 1,2-DCA in clay soil. A dose-dependent relationship between degradation rate constant (k(1)) of 1,2-DCA and metal ion concentrations was observed for all the heavy metals tested, except for Hg2+. This study demonstrated that different heavy metals have different impacts on the degree of 1,2-DCA degradation. Results also suggest that the degree of inhibition is metal specific and is also dependent on several factors including; soil type, pH, moisture content and available nutrients. (C) 2011 Elsevier Ltd. All rights reserved.