A soil toxicity test using the nematode Caenorhabditis elegans and an effective method of recovery

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Abstract

A new method for recovering nematodes from soils in an efficient, reproducible, and non-destructive manner has been developed. It was used to conduct short-term soil toxicity tests using the soil-dwelling nematode Caenorhabditis elegans and several different soil types spiked with copper chloride. The recovery method, which involves centrifugation through a colloidal silica suspension, allows the nematodes to be extracted from the soil matrix so that lethality can be assessed. The nematodes are unharmed by the recovery procedure, and both live and dead individuals are recovered with high efficiency (well over 80%), allowing reproducible concentration-response curves to be made after a 24-h exposure. The LC50s for copper were increased about tenfold by the presence of soil, and different soils had significantly different effects on toxicity. Toxicity of copper ion was also influenced by the concentration of sodium chloride and potassium chloride in the test solution, and the presence of bacteria increased the toxicity of copper ion in some soils. The LC50s in soil were close to the LC50 for the 2-week earthworm soil toxicity test, suggesting that a 24-h nematode toxicity test may be comparable to the 2-week earthworm test in terms of sensitivity.