Assessment of sublethal endpoints for toxicity testing with the nematode Caenorhabditis elegans

Toxicity tests in invertebrates often use sublethal endpoints, which may ex hibit different sensitivity for various toxicants. Our objective was to cha racterize the sensitivity of movement, feeding, growth, and reproduction as endpoints for heavy metal toxicity testing with Caenorhabditis elegans. Gr owth and feeding were assessed in the same nematode samples used to assess movement and reproduction. Median effective concentrations (EC50s) for 24-h exposures to Pb, Cu, and Cd were determined for movement, feeding, and gro wth and a 72-h EC50 was derived for reproduction. The order of toxicity was Cu > Pb > Cd for each endpoint, including lethality and movement. There we re no differences in sensitivity among endpoints for any metal. When expose d for 4 h at (sublethal) concentrations that were 14 times the 24-h EC50 va lue, Pb and Cu reduced feeding to the same extent while movement was reduce d significantly more by Pb than by Cu. Thus, a difference in sensitivity of endpoints was apparent at 4 h, which was not evident at 24 h. These observ ations suggest potentially different mechanisms of toxicity for 24- and 4-h tests.