Soil toxicity assessment of 2,4-DCP using lux microbial biosensors
Lux-marked E. coli was responsive to a wide variety of chlorophenols with differing degrees of toxicity depending on number and position of chlorine substitution. The pH robustness of lux-marked E. coli was exploited in investigating the effect of pH on the sorption of 2,4-DCP to the bacterium. As the pH decreased, the accumulation of 2,4-DCP increased correlating with the amount of non-dissociated 2,4-DCP present, indicating that non-dissociated 2,4-DCP was preferentially sorbed. It was also shown that the toxicity of 2,4-DCP was increased at low pH values correlating with the increased sorption previously observed. The effect of an environmentally relevant matrix (soil pore water) on the toxicity of 2,4-DCP was investigated. The toxicity of 2,4-DCP was found to be enhanced in soil pore water, which questions the use of toxicity tests performed in pure aqueous systems. The effect of soil pH on the adsorption of 2,4-DCP was investigated using pH plots maintained at different pH values for 30 years. The pH had very little effect on the adsorption and desorption of 2,4-DCP but it does have a high affinity and is not easily desorbed. A solid phase toxicity assay was developed to measure the toxicity of 2,4-DCP sorbed to soil. It was found that 2,4-DCP was not toxic to lux-marked E. coli, demonstrating the ameliorative effect of sorption of pollutants to soil. This has major implications for the field of soil toxicity testing as soil toxicity testing is commonly performed using soil extracts or elutriates.