Age-specific differences in cadmium sensitivity and bioaccumulation in bivalve molluses

Abstract

Age-specific differences in sensitivity to and bioaccumulation of cadmium are demonstrated in a range of life-history stages of the bivalve Isognomon californicum. An acute-toxicity assay was used to document the relative sensitivities of embryos, young veligers, older veligers, pediveligers, juveniles, and adults. There was an inverse relationship between age and sensitivity, so the scale of relative sensitivity was embryos > veligers > pediveligers > juveniles > adults. The bioaccumulation of cadmium by the various life-history stages was measured over a 24-h period by using a radioactive isotope of cadmium. With embryos, there was an 8-h lag phase before accumulation of cadmium was observed. Onset of accumulation coincided with hatching, which supported the hypothesis that embryonic membranes are impermeable to metal ions. The relative rates of accumulation of the various life-history stages did not reflect the relative sensitivities. In these experiments, embryos did have the highest accumulation rates, and adults had the lowest. However, the rates of accumulation of pediveligers were greater than veliger rates. It is therefore interesting to realize that the stages with the highest rates of Cd accumulation were embryos and pediveligers. These two stages can be regarded as developmental hurdles, requiring profound morphological and physiological changes for transformation into the next stage. These results suggest that metal ions and perhaps metallothioneins may play important roles in gene expression and inductive processes and are the basis for continued research.