Single And Combined Effects Of Mercury And Cadmium On Mussel Mytilus Edulis

Biotoxicity of individual metals is well investigated but that of metal mixture, an environmental reality, in the developing metal mixture is relatively obscure. Experimental evidences had shown that this mixture could give rise to combined effects that were different from the effect of metals one by one. The present study is conducted to evaluate the single and combined effects of heavy metals-Hg and Cd on mussel Mytilus edulis under the controlled laboratory conditions. The main research contents include:Contrastive analysis the physiological and biochemical effects of the long-time sub-lethal stress of the mercury and cadmium exposure in the different tissues of the mussels (gills and digestive glands); Studying the difference in sensitivity to antioxidant responses in both tissues and discussing the different effects of the studied heavy metals on the activities of CAT, SOD and GST in the gill and digestive gland tissue of the mussel Mytilus edulis, and then we also have discussed the possible mechanism preliminarily.The research indicated that generally the activities of the three antioxidant enzymes increased significantly at first (2d or 4d) and then decreased (6d-8d) whether under the single or combined exposure of the mercury and cadmium (p< 0.05 or p<0.01). CAT activity reached a peak on the second day after exposure while the peak of SOD activity was observed on the 4th or the 6th day, this might be due to the different detoxification mechanisms. The GST activity reached a peak on the second day after the mixture exposure while the sole exposure was postponed.CAT activity in digestive gland was higher than that in the gill, but SOD and GST activity in the gill revealed a much higher sensitivity to heavy metals than in the digestive gland. This might be due to the different detoxification mechanisms in the different tissues of the mussels. The influence of the effects on the M. edulis by the single exposure of the Hg or Cd was depended on the different tissues and the three different antioxidant enzymes in the mussel. The activities of SOD and GST in the gills under the exposure of the single Hg were higher than the single Cd, however, there was no significant difference on the CAT activities; As for the GST activities in the digestive gland, the exposure of the single Cd2+ were higher than the single Hg, and for the activities of the CAT and SOD in the digestive gland, the exposure of the single Cd were lower than the exposure of single Hg.When compared the single and combined effects of Hg and Cd on the gill and digestive gland tissue of M. edulis, the mixture exposure of Hg2+ and Cd2+ showed antagonistic effects on the metal-induced oxidative stress in the gills, but in the digestive gland, it was showed the synergistic effect except for the activities of the SOD.