Metal LC50s of a Soil Nematode Compared to Published Earthworm Data

摘要

A comparison of the acute LC50s for five metals between the standard test organism Eisenia fetida and the soil nematode Caenorhabditis elegans was made. Although the test with C. elegans is shorter (24 h vs. 2 wks) and uses less soil or testing medium (2.33 g vs. 200 g dry weight) than that for E. fetida, LC50s were comparable for the earthworm and nematode. The current study further investigated similarities by extending the exposure time to 48 h. Comparisons were made to 24-h C. elegans data, published E. fetida data, and U.S. Environmental Protection Agency (EPA) allowable concentrations. The nitrate salts of Pb, Ni, Cd, Zn, and Cu were used to generate LC50s. Two naturally occurring soils in Georgia were chosen to compare different soil properties on the metals' toxicity. Tifton soil was sampled from the southern region of Georgia and is characterized by relatively high sand and low clay and soil organic matter (SOM) contents. Cecil soil, in contrast, is found in the Piedmont region of Georgia and is characterized by relatively high amounts of clay and SOM. As anticipated, extending the exposure time to 48 h significantly increased the toxicity (i.e. decreased the LC50s) of the metals compared to published 24-h C. elegans data. Physical-chemical properties of soils are known to affect the binding of polyvalent metals and thus the bioavailability and toxicity of these metals. Increasing clay and SOM contents allow for an increased capacity to bind metals. For this reason, LC50s were higher in Cecil than in Tifton soil. Because tests using C. elegans are rapid, reliable, and generate data comparable to that of the earthworm, we suggest further studies that may lead to the standardization of the nematode for use as a soil toxicity-testing organism.