Integrated Assessment Of Pollution Of Effluent-seawater Mixture Based On The Sensitive Biomarkers In Meretrix Meretrix

As the discharge of municipal sewage treatment plants (MSTPs) effluents increasing, the threat of water ecosystem health has been becoming more and more serious. It is more practical to investigate the combined pollution of effluents to organisms to reflect the comprehensive toxicity of effluents directly, and assess the overall water quality using the biological methods, than detect the contents or concentration of containmants simply. Therefore, in this study, treated municipal effluent (TME) collected from the outfall of Tuandao MSTPs in Qingdao in autumn 2013 was selected as the experimental material and bivalves Meretrix meretrix as the model species. Effluent volume ratios (EVR) were set as 0%,1%,5%,10%,20%,30% and 40%, respectively, in which M. meretrix was exposed for 15 days. Meanwhile,8 biomarkers (lysosomal membrane stability (LMS) and micronucleus frequency (MF) of hemolymph; glutathione peroxidase (GPx), glutathione reductase (GR), glutathione (GSH), malondialdehyde (MDA), acetylcholinesterase (AChE) and metallothioneins (MTs) in gills and visceral) were determined. According to the sensitivity of biomarker response and correlation analysis with TME concentration and exposure time, a set of biomarkers were selected to be as good indicators of pollutants in seawater receiving TME, so as to establish a biochemical index system for the comprehensive evaluation of waterquality. Moreover, integrated biomarker response (IBRV2) index was calculated to distinguish the pollution level of seawater containing different concentrations of effluents. Finally, a classification scheme was developed using the IBRV2 index based on health status index (HSI) classification scale. Besides, the method was applied successfully to grade the water quality synthetically of different concentration of TME in the study. The main conclusions were as follows:(1)There were some biomarkers responding quite sensitively to the effluent after 3 days’exposure, including LMS(depressed between 39.28% and 55.62%), GPx activity in gills and digestive glands, GSH and MDA contents in viscera, concluding that those indicators could be set as sensitive biomarkers for the short-term exposure of the effluent; What’s more, MF (highest increased 316.50%) and MTs in both gills and digestive glands showed significant variations during the exposure period, which could be also considered as sensitive indicators for the effluent pollution; but GR and AChE did not show any obvious change in the present study.(2)Effluent exposure caused different levels of oxidative reaction in gills and digestive glands of M. meretrix, gills showed oxidative damage under EVR1%,30% and 40% groups, but digestive glands kept the same level as the control except EVR20%. GSH oxidation-reduction system, MTs and AChE allied to resist the complex stress of pollutants in effluent. There were no lipid peroxidation detected both in gills and digestive glands at the end of exposure.(3) Although multiphase biomarkers of the different exposure time have been analyzed during the period of the exposure to TME, sensitive responses to TME concentration were detected only at the 9th and 12th days, which could build an evaluation index system (EIS) of the pollution system in the light of biomarkers. So two EISs were established based on the two exposure time:LMS, GPx, MTs and AChE in viscera of 9d were selected and built EIS-Ⅰ. LMS, MF, GSH and AChE in gills of 12d were selected to build EIS-Ⅱ.(4) According to measured values of biomarkers from the evaluation index system mentioned above, IBRv2 index values were calculated corresponding to the different concentrations of TME (0%,1%,5%,10%,5%,30% and 40%) as follows:9 day-0.00,0.61,1.32,1.37,1.48,2.28,2.65; 12 day -0.00,0.79,0.80,1.45,1.72,1.76, 2.64. The pollution pressure increased with the value of IBRv2. Hence it was obvious that IBRv2 index can clearly distinguish the effluent pollution level of the mixed system.(5) Calculating the critical values of selected biomarkers in different levels of health states of organisms based on the alteration level of HSI and blank values of biomarkers in EISs, then IBRv2 index values were calculated as classification threshold to reflect pollution level of mixted system comprehensively.The results were 0.29,0.96 and 2.23, so the pollution level of mixed system could be classified into four categories, clean, lightly polluted, moderately polluted and seriously polluted. In the present study, the water quality of the EVR 40% or higher was serious pollution, whereas the pollution classification of EVR 5% or lower was light pollution, and when EVR between 5% and 40%, the water quality was moderate pollution.