| A new procedure for recovering nematodes from soils in an efficient and non-destructive manner has been devised and applied to the development of a short-term soil toxicity test using nematodes as toxicity indicators. The procedure involves gentle centrifugation through a colloidal silica suspension which allows the soil to settle out while floating the nematodes on top of the suspension. The nematodes are recovered with great efficiency and are unharmed by the recovery process. Short-term lethality tests were performed with several metals in several different characterized soils, and replicable results were obtained, allowing concentration-response curves to be generated and LC{dollar}sb{lcub}50{rcub}{dollar}s estimated. It was found that the presence of soil generally decreased the toxicity of the metals to nematodes when compared to tests done without soil present. Comparison between nematode lethality results and data published for earthworms exposed to metals in soil revealed that, in most cases, the nematode is at least as sensitive as the earthworm, which is currently the standard animal soil toxicity test. Some correlations between soil or metal properties and the resulting toxic effects were obtained, while other properties showed no significant correlation with toxic effects. This suggests that, as other studies have indicated, the bioavailability of metals in soils cannot be reliably predicted by considering only a few sample conditions. It was found that most metal-soil combinations examined by the nematode toxicity test fit the Langmuir sorption model very well, while only a few did not. This may suggest a future direction for study which would involve matching toxicity data with chemical data to further understand processes which determine bioavailability of chemicals in soils. Preliminary results using field samples suggest that such applications are feasible and may be successfully incorporated into standard methods for regulatory and assessment purposes. |
