A multiple biomarker approach to investigate the effects of copper on the marine bivalve mollusc, Mytilus edulis.

While copper (Cu) is considered to be an essential trace element for many organisms, overexposure to this metal can induce a wide spectrum of effects including DNA damage. Given that Cu is a highly relevant contaminant in the marine environment, we aimed to evaluate the induction of DNA strand breaks (using the comet assay) in haemocytes and concurrently also determined biological responses at higher levels of biological organisation in bivalve molluscs, Mytilus edulis, following exposure for 5 days to a range of environmentally realistic levels of Cu (18-56 μg l(-1)). Prior to evaluation of genetic damage, the maximum tolerated concentration (MTC) was also determined, which was found to be (100 μg l(-1)) above which complete mortality over the exposure period was observed. In addition to DNA damage, levels of glutathione in adductor muscle extracts, histopathological examination of various organs (viz., adductor muscle, gills and digestive glands) and clearance rates as a physiological measure at individual level were also determined. Furthermore, tissue-specific accumulation and levels of Cu in water samples were also determined using ICP-MS. There was a strong concentration-dependant induction for DNA damage and total glutathione levels increased by 1.8-fold at 56 μg l(-1) Cu. Histological examination of the organs showed qualitatively distinct abnormalities. Clearance rate also showed a significant decrease compared to controls even at the lowest concentration (i.e. 18 μg l(-1); P=0.003). Cu levels in adductor muscle (P=0.012), digestive gland (P=0.008) and gills (P=0.002) were significantly higher than in the control. The multi-biomarker approach used here suggests that in some cases clear relationships exist between genotoxic and higher level effects, which could be adopted as an integrated tool to evaluate different short and long-term toxic effects of pollutants.