Cadmium-induced production of a metallothioneinlike protein in Tubifex tubifex (Oligochaeta) and Chironomus riparius (Diptera): correlation with reproduction and growth.

Laboratory-cultured Chironomus riparius and Tubifex tubifex were exposed to sediments artificially enriched with a range of cadmium (Cd) concentrations. Both species accumulated Cd in a concentration-dependent manner. The concentration of a metallothioneinlike protein (MTLP), as measured by a mercury saturation assay, increased with increasing Cd exposure. After reaching a threshold of Cd exposure, the whole-body endpoints of reproductive output in T. tubifex and growth in C. riparius declined significantly. The threshold effect concentrations for T. tubifex and C. riparius were 2.68 and 0.134 micromol Cd/g dry sediment, respectively. Metallothioneinlike protein and Cd tissue concentrations were more sensitive indicators of exposure than the whole-body endpoints. For T. tubifex, the concentrations of MTLP and tissue Cd were significantly elevated above control levels after exposure to the 0.67 micromol Cd/g dry sediment treatment. In C. riparius, MTLP concentration and tissue Cd concentration were both significantly elevated above control levels after exposure to the 3.8 x 10(-3) micromol Cd/g dry sediment treatment. Analysis of these data suggests that MTLP and tissue Cd concentrations are sensitive subcellular endpoints, which can be used to predict exposure to and the effects of metals at the individual or population level.