Toxicity of cadmium to six species in two genera of crayfish and the effect of cadmium on molting success.

Nine acute (96-h) toxicity tests were conducted on six species of crayfish (Cambaridae). Six tests focused on adults, and three tests examined juveniles. Lethal concentration to 50% of a population (LC50) and lethal concentration to 10% of a population (LC10) values, respectively, for the adults of individual test species were as follows: Orconectes juvenilis, 2.44 and 0.623 mg Cd/L; Orconectes placidus, 0.487 and 0.092 mg Cd/L; Orconectes virilis, 3.30 and 0.947 mg Cd/L; Procambarus acutus, 0.368 and 0.048 mg Cd/L; Procambarus alleni, 3.07 and 0.386 mg Cd/L; and Procambarus clarkii, 2.66 and 0.486 mg Cd/L. The Orconectes LC50 genus mean acute value (GMAV) was 1.57 mg Cd/L, whereas the LC50 GMAV for Procambarus was 1.44 mg Cd/L. The LC10 GMAVs were 0.379 and 0.208 mg Cd/L, respectively. Family mean acute values (FMAVs) also were calculated for the Cambaridae using all species data (LC50, 1.51 mg Cd/L; LC10, 0.281 mg Cd/L). For tests with juvenile crayfish, the LC50 and LC10 values, respectively, were as follows: O. juvenilis, 0.060 and 0.014 mg Cd/L; O. placidus, 0.037 and 0.002 mg Cd/L; and P. clarkii, 0.624 and 0.283 mg Cd/L. The GMAVs were calculated for juvenile Orconectes (LC50, 0.047 mg Cd/L; LC10, 0.005 mg Cd/L). Additionally, FMAVs were calculated for juvenile crayfish (LC50, 0.111 mg Cd/L; LC10, 0.020 mg Cd/L). Crayfish sensitivity to Cd varied by a factor of nine among species tested as adults and by a factor of 17 among species tested as juveniles. Molting was a sensitive life stage for crayfish. Most individuals that molted shortly before or during exposure to Cd died, whereas all controls that molted in the adult assays survived. Because molting is a sensitive, recurring life-cycle event, molting individuals should be included in toxicological analysis despite some contrary recommendations.