A comparison of metal-induced lethality and behavioral responses in the nematode Caenorhabditis elegans

Behavioral changes are believed to be a sensitive indicator of toxicant exposure but can be very difficult to quantify. Using the free‐living soil nematode Caenorhabditis elegans, a computer tracking system was used that measures several behavioral parameters for approximately 100 subjects on a real‐time basis. Toxicant exposures can be performed in soil, on agar plates, or in aquatic media. Following the exposure period, the worms are transferred to a thin‐layered agar slab for viewing in dark‐field illumination by a video camera interfaced directly to a computer. Information can be obtained on a number of behavioral parameters including number of subjects moving, their individual rates of locomotion, and the frequency of change in direction. Exposure to five metals (Pb, Cu, Cd, Al, and Zn) were tested in this study to evaluate behavioral changes in the worm. The nematodes were exposed for 24 h to concentrations of an individual metal in aquatic medium representing the interstitial pore water within the soil. Under identical conditions, concurrent LC50 and BC50 (concentration at which movement is reduced by 50% compared with controls) values were determined for each metal tested. The results from computer tracking revealed significant changes in rate of locomotion at concentrations of less than 10% of the respective LC50 value.