Security Risk Assessment About Water Quality Of Water Source In Gonghu Bay-based On Improved Fuzzy-AHP

In recent years,the pollution of Taihu Lake has received increasing public attention.As the important drinking water source of Wu Xi and SuZhou,the water quality safety of Gonghu bay is critical to the health of the residents around.In this study,the water quality of 11 regions in Gonghu bay was investigated from December 2015 to November 2016.The water quality grade,eutrophication status,health risk assessment of dissolved heavy metals,and the ecological risk assessment of microcystin and antibiotics were chosen as the endpoints.Based on the model of improved analytic hierarchy process and fuzzy comprehensive evaluation(AHP-FCE),the endpoints were endowed with reasonable weights.In the end,a comprehensive value,representative of the water quality safety of Gonghu Bay was calculated by summing the weighted endpoints.The results of this study are expected to provide scientific basis for future water management and decision-making process.(1)The water quality grade of the Gonghu Bay was estimated using the single factorprincipal component analysis.The results indicated that the major pollutants in Gonghu bay included total nitrogen,total phosphorus,chlorophyll a and total organic carbon.During the entire period of monitoring,only 50% of the time in Gonghu Bay could be categorized as Class ? or better,whereas during the blue-algae blooming period,the water quality was still categorized as Class V or worse.The trophic level of the Gonghu Bay was evaluated using the comprehensive trophic level index(TLI).Throughout the period of monitoring,the Gonghu Bay was classified as mesotropher or worse.Specifically,the northern part was classified as eutropher during 75% of the monitoring period,while the southern part was eutropher during the entire monitoring period.Moreover,in May,2016,when the blue algae bloomed,the Gonghu Bay was classified as hyper eutropher.These results indicate that the Gonghu Bay is still faced with severe eutrophication issues,which deserves intensive concerns.(2)During the wet season,five heavy metals were detected in the surface water,and Zn was detected at the maximum concentration at every sampling site.During the dry season,only a small amount of heavy metals were detected at Site #1(Nanquan water intake)and #7(Wangyu river).The health risk model assessment showed that during the dry period,the water quality was good given that heavy metals occurred at a negligible level.During the wet period,the risk index of As ranked as the highest among the elements detected.The total risk index at Site #5(Xiaoxigang river)was the highest among the sampling sites,but still belonged to a low risk level.In general,the total risk index of the northern part was obviously higher than that of the southern part.According to the background values of soil elements,the percentages of the area where the heavy metal pollution exceeded the standard of surface sediments was calculated.The area percentages of Mn,Zn,Cu,As,and Pb were 33.3%,66.7%,33.3%,22.2%,and 11.1%,respectively.The Potential Ecological Risk Index of each detected metal in surface sediments was below 40,indicating a low risk level.The Cumulative Ecological Risk Index of each metal in Gonghu bay was also low and indicated low risk.(3)The risk of microcystic toxins was estimated using the model of hazard index(HI),and the results showed that the highest risk index of MCs during the monitoring period was about 0.15 indicating a potential risk.The pollution condition of antibiotics on the whole situation tends turn for the better.During the wet season,only norfloxacin(NOR)was detected at a level of 19.9 ng/L at Site #1,and ofloxacin(OFL)was detected at 2.3 ng/L at Site #6(Xidong water intake).In dry period,the concentration of antibiotics at Site #1 is the highest among the sampling sites.In general,the antibiotics concentration in the northern part is higher than that in the southern part.According to Risk Quotients(RQs),the Gonghu Bay was at a low risk level in the wet season,while there were 3 middle-high risks in the dry season.According to the accumulative RQs of the detected antibiotics,sulfamethoxazole(SMZ)was the main species at each sampling site,and 90.9% of the area was at middle-high risk.In general,there is still a high risk of antibiotics in Gonghu Bay during the dry period.(4)Based on the model of AHP-FCE,this study estimated a comprehensive risk index for Gonghu Bay water quality from the five endpoints,and the weights were determined as followed: W=[0.053,0.413,0.158,0.345,0.031].The results showed that 54.5% of the Gonghu Bay area was at a level of good but close to medium,and the risk index of the rest area was above 40 indicating a level of hyper-medium.The northern and the southern parts were categorized as hyper medium(40.02)and medium-to-good(39.85),respectively.In general,the comprehensive evaluation value of Gonghu bay was 39.99,and it was in good state,close to middle level.