Interclonal variation in the acute and delayed toxicity of cadmium to the European prosobranch gastropod Potamopyrgus antipodarum (Gray)

The lethal responses of three European clones-A, B, and C-of the prosobranc h snail Potamopyrgus antipodarum to acute cadmium exposure were examined by the use of a conventional LC50 test and a delayed toxicity test. The quest ions addressed were: (1) Are there differences in susceptibility (LC50 valu es and uniformity of response) among the three European clones of P. antipo darum? (2) Are the patterns of differences in susceptibility among clones o bserved in the LC50 test also observed for the delayed toxicity test? (3) I s there concordance in the ranking of susceptibility among clones under acu te cadmium exposure and under chronic cadmium exposure? The results showed that the widths of the tolerance distribution differed among clones. Clones A and B had a steeper slope than clone C (for clone A the difference was m arginally significant), which indicates that individuals from clones A and B showed a more uniform response to acute lethal cadmium stress than indivi duals from clone C. On the basis of the measured differences in LC50 values , clone A individuals showed the highest tolerance to acute cadmium (LC50 v alue: 1.92 mg Cd L-1) followed by clone B (LC50 value: 1.29 mg Cd L-1) and clone C (LC50 value: 0.56 mg Cd L-1). Clone C was significantly less tolera nt than clones A and B. The delayed toxicity test showed a similar pattern to the LC50 test with regard to tolerance differences among clones: however , mortality continued following transfer to clean water, indicating that ca dmium was lethal at much lower concentrations than indicated by the convent ional LC50 test. Results of the LC50 test and the delayed toxicity test in the present study were in general agreement with results from chronic cadmi um exposure experiments (Jensen et al. [2000] Ecol Appl [submitted]), i.e., the least susceptible clone A in the acute cadmium exposure test was also the least susceptible clone in the chronic cadmium exposure test. Based on the dramatic differences between the LC50 and the cadmium exposure concentr ations causing delayed toxicity, we suggest that the potential for delayed toxicity should be given greater consideration in ecotoxicity testing.