Study On Biochemical Responses Characteristics Of Bivalves Meretrix Meretrix Exposed To Effluent From Municipal Sewage Treatment Plants

Effluents from municipal sewage treatment plants (STPs) are the major sourcesof aquatic ecosystem pollution by a variety of trace pollutants such as heavy metals,surfactant, chlorinated hydrocarbons, polycyclic aromatic hydrocarbons (PAHs),certain medications and endocrine disruptors. Due to the variety of contaminants inreceiving waters, there are coordination or antagonist effects among them. Accordingto the existing environmental quality assessment methods, it is difficult to assess thecomprehensive environmental effects. Biomarkers, which are characteristic of highspecificity and sensitivity, are suitable for the instruction of trace pollutants. Furthermore, Multi-biomarker response can reflect the contamination conditions integrally.Mussels Meretrix meretrix as the indicator were exposed to effluent from theLicunhe STP in Qingdao City at5effluent volume ratio (EVR,0%,1%,5%,10%and20%v/v), diluted in seawater, for15days. The following12biochemical responseswere measured: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase(GPx) and glutathione reductase (GR), glutathione (GSH), malondialdehyde (MDA),acetylcholinesterase (AChE), metallothionein(MTs),7-ethoxyresorufin-O-deethylase(EROD), glutathione S-transferase(GST) in both gills and viscera, vitellogenin(Vtg)in haemolymph and lysosomal membrane stability(LMS) of blood cells.The abovedetermination results were integrated in order to screen a set of biomarkers sensitiveto the effects of effluent from the Licunhe STP by response sensitivity and correlationanalysis. The main conclusions obtained were as follows:(1) Inductive effect was dominant in SOD activities response of gills and viscera;CAT activities of gills had poor response regularity of3period: inalterability at theinitial stage, inhibition in the mid and recovery even induction in the late. CATactivities of viscera were inhibited by the effluent with the serious inhibition, and the degree of inhibition increased with the extension of exposure time; GPx activities ofgills were significantly inhibited in the late and GPx a activities ctivity of viscera weregenerally inhibited during the exposure time. Correlation analysis results showed thatGPx and CAT activities of viscera both were inhibited synchronously; Significantinhibition-pick up-significant inhibition-induced drastically of “two drop two rise”process taken place in GR activity of gills. On the opposite, GR activities of viscerawere generally inhibited during the exposure time; GSH of gills brought down in themiddle and later periods and GSH of viscera were significantly induced in most of thetime; During the whole time MDA of gills were not induced by the effluent, but MDAof viscera appeared significantly induction in the mid and late.(2) AChE activities of gills and viscera showed inductive effect at the day3, day6, day9and day15, they were inhibited at day12; Vtg of EVR10%and EVR20%treatment groups were significantly induced at day15, and it showed that endocrinedisruptors in the effluent had estrogenic effect on Meretrix meretrix. But Vtg was notsensitively enough, relatively, and which limited its application compared to otherbiomarkers (such as GPx).(3) The effluent concentrations, especially those high EVR, declined thelysosome stability of blood cells significantly. LMS had sensitive response to theeffluent and it could be used as warning biomarker applicated in marineenvironmental monitoring; MTs of of gills and viscera were mainly induced. EVR10%treatment group of gills was significantly induced all the time. Compared to viscera,MTs of of gills were more sensitive to effluent pollutants.(4) EROD activities of gills were all inhibited except day9. For viscera, ERODwere all inhibited except day12; At day3, day9and day15, GST activities of gillswere all induced. GST activities of viscera exhibited a parabolic curve shape from day3to day12. GST activities of two kinds of organization were mostly inhibited at day12.(5) Under the screening principles, which includes high frequency of significantchange and clear dose-effect relationship with EVR, GSH、GPx、MTs、GR in gills, CAT、GPx、MDA in viscera and LMS of blood cells were all suitable for instructingthe toxicity effect of effluent.(6) Oxidative damage didn’t appear in gills of mussels among EVR1%~20%,there was oxidative damage in viscera of EVR5%and EVR10%groups. EVR10%、20%had endocrine disruptors on the mussels. All treatment groups could decline the LMS.(7) Biomarkers in gills and viscera connected with each other to resist to effluentpollutants mutually.There were not lipid peroxidation in gills, in this issue, GSHconsumption and joint detoxification of SOD、MTs and AChE played important partsin resist with ROS, while EROD had relatively low contribution; Lipid peroxidationappeared in viscera, it might caused by low utilization of GSH, the accumulation ofH2O2and MTs、EROD had relatively low contribution. On the other hand, jointdetoxification of SOD、GST and AChE played an important role in controlling lowlipid peroxidation level of viscera.