Worm Breeder's Gazette 13(1): 89 (October 1, 1993)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

C. elegans as a Soil Toxicity Test Organism

Steven G. Donkin, David B. Dusenbery

School of Biology
Georgia Institute of Technology, Atlanta, GA 30332-0230

We have developed a new procedure for recovering nematodes from soils in an efficient and non-destructive manner, which has permitted the development of a short-term soil toxicity test using nematodes as toxicity indicators. The procedure involves gentle centrifugation through a colloidal silica suspension (Ludox AM or Ludox HS-40, both available from E. I. Du Pont de Nemours & Co., Wilmington, DE), which allows the soil to settle out while floating the nematodes on top of the suspension. The nematodes are recovered with great efficiency (~90%) and are unharmed by the recovery process. Short-term lethality tests (24-hour exposure) were performed with several metals (Cd, Cu, Hg, Ni, Pb, and Zn) in several different characterized soils, and replicable results were obtained, allowing concentration-response curves to be generated and LC(50)s to be 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. This is presumably due to the sorption of the metal ions to the soil particles, which lowered their availability to the nematodes. 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 in terms of its response to toxic metals in soil. The earthworm test, which is currently the standard animal soil toxicity test, has the disadvantage of taking two weeks to perform, while the nematode test can be done in 24 hours.

Some correlations between soil or metal properties and the resulting lethal 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. Soils are complex and heterogeneous systems, and there are many physico-chemical processes that may occur within them and which may influence the resulting bioavailability of a contaminant. The C. elegans soil toxicity test may provide the means to identify some of the more important environmental characteristics that influence contaminant bioavailability.