Studies On Toxicological Effects Of Waterborne Cadmium In Sinonovacula Constricta

Recently, environmental pollution along coastal areas in China is serious increasing, especially the heavy metal contamination which will disturb the normal vital activity of aquatic animals seriously and then can lead to the negative effects on the development of aquaculture industry in China. Furthermore, the transfer of heavy metal through food chains also endanger the human health. This paper studied the effect of Cd²⁺-a common heavy metal ion, on the biochemical index of the Sinonovacula constricta- a kind of economic bivalvia in China, including the rule of cadmium bioaccumulation in the organism, the biochemical responses of antioxidant and detoxification systems as well as the effects on the DNA damage in the digestive glands and gills of S. constricta, meanwhile discussed the toxic and detoxified courses of Cd²⁺in S. constricta in order to provide scientific data for nuisanceless aquaculture and monitoring the heavy metal contamination in coastal areas.1. The rule of accumulation of Cd²⁺in S. constrictaThe effect of Cd bioaccumulation and distribution in S. constricta at different concentrations (0.005mg/L, 0.025mg/L, 0.05mg/L, 0.1mg/L) was investigated using microwave digestion-graphite furnace atomic absorption spectrometry. The result showed that during the 168h exposure time, Cd accumulation in S. constricta increased with the increase of Cd²⁺concentration in seawater and exposure time. Furthermore the Cd accumulation in gills is more serious than in muscle, but less then in the digestive glands.2. The effects of Cd²⁺on the SOD, CAT, GSH-Px activities of digestive glands and gills in S. constrictaAn exposure experiment was conducted to study the effects of cadmium (Cd²⁺) at different concentrations on antioxidant enzyme activities (SOD,CAT,GSH-Px) for up to 168h in the digestive glands and gills of S. constricta. The results showed that the activation of Cd²⁺on SOD and CAT activities in the two tissues increased with its concentration increasing during the short exposure time(<24h). The highest dose-group (0.1mg/L) reached the peak value earlier than other dose-groups, then decreased constantly until be inhibited significantly at 96h, meanwhile the increase-decrease law also could be seen in other treatments, the SOD and CAT activities of gills in the 0.005mg/L dose-group were stimulated significantly on 144h; GSH-Px activities in digestive glands showed the obvious fluctuations during 168 hours, while there was no significant variation in gills during 48 hours (P>0.05). The changes in the activities of antioxidant enzymes SOD, CAT, GSH-Px suggested that S. constricta suffered oxidative stress which might be involved in the toxicity mechanism of Cd²⁺in S. constricta.3. The effects of Cd²⁺on the GST, ACP, AKP activities of digestive glands and gills in S. constrictaEffects of waterborne Cd²⁺at different concentrations (0.005mg/L, 0.025mg/L, 0.05mg/L, 0.1mg/L) and different time on activites of GST, ACP and AKP in digestive glands and gills of S. constricta were studied. The result showed that the GST activities of the two tissues could be stimulated in all treatments during the exposure time, however, those in higher dose-groups(0.05 mg/L,0.1 mg/L) which increased earlier decreased with the prolonged exposure. The activation of Cd²⁺on ACP activities in the two tissues increased with its concentration increasing on the 6h, the higher dose-group reached the peak value earlier than lower dose-group, then decreased constantly until be inhibited significantly after 72h. The AKP activities in the two tissues showed the"decrease-increase-decrease"law during the exposure time in all treatments, and those in higher dose-groups were stimulated earlier than that in lower ones. AKP activities in each treatments all decreased constantly after reaching the peack value respectively, then to be inhibited again. The fluctuations in GST, ACP, AKP activities in experiment suggested that Cd²⁺could have the influence on the process of metabolism and detoxification system of the organism.4. The effects of Cd²⁺on DNA damage of digestive glands and gills cells in in S. constrictaAn exposure experiment was conducted to study the effects of cadmium (Cd²⁺) at different concentrations on DNA damage in the digestive glands and gills of S. constricta for up to 96h using single cell gel electrophoresis(SCGE). The extent of DNA lesion represented by the DNA tail moment, tail length and tail DNA% value in digestive glands and gills of S. constricta increased significantly, meanwhile represented a dose-time response relationship in certain time. However, the three values decreased which indicated that there were some recovering of the breaking DNA. Under the same dose-group, the extent of DNA damage in gills was higher than digestive glands.