An ecotoxicological assessment of the impacts of chronic exposure to metals and radionuclides on marine mussels: relating genotoxicity to molecular and organism-level eﬀects
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Metals and radionuclides are environmentally relevant contaminants, yet their potential impacts on marine organisms have not been adequately evaluated. This is especially true for exposures of longer duration and/or lower contaminant concentration (i.e. chronic) which are often more representative of real world scenarios. In this context, a suite of biomarkers at diﬀerent levels of biological organisation were investigated in an ecologically relevant bivalve species, Mytilus galloprovin- cialis after exposure to nickel (a metal), zinc pyrithione (an organometal) and tritiated water (a radionuclide). These contaminants were chosen based on their diﬀering properties, and hence, mechanisms of action. All three contaminants produced genotoxicity (DNA strand breaks, as measured by the comet assay, and induction of micronuclei [MN]). For nickel (> 1800 µg L −1 ) and tritiated water (15 MBq L−1 ), biomarkers at lower levels of biological organisation (i.e. DNA strand breaks, MN, changes in the expression of key stress response genes) were more sensitive than those at higher levels (i.e. clearance rate, attachment, tolerance of anoxia). In particular, exposure to tritiated water for 14 days resulted in DNA damage and molecular alterations without aﬀecting higher level responses. As environmental contaminants could interact with other physical or chemical stressors in a complex environment, further exploration of biological responses revealed modulation by hyperthermia with concomitant changes in the transcriptional ex- pression of key defence genes (hsp70, hsp90, mt20, p53 and rad51). In contrast to nickel and tritiated water, exposure to both 0.2 and 2.0 µM zinc pyrithione caused signiﬁcant deviation from concurrent controls for every biomarker examined, suggesting that further investigation of the environmental impacts of this contaminant is particularly necessary. Variation in biological responses induced by diﬀerent contaminants suggests that potential links between levels of organisa- tion should be evaluated on a contaminant-speciﬁc basis. The integrated, multiple biomarker approach used in the current study provides a robust methodology for such studies, which could be translated to other ecologically relevant species for proper evaluation of risks to both environmental and human health.
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