Study On Pollution Status And Health Risk Assessment Of Molluscicides And Byproduct In Dongting Lake

Dongting Lake, The second freshwater lake of China,located in the north of Hunan province and south of Jingjiang bank(middle reaches of the Yangtze River). The three outfalls(Songzi,Ouchi,Taiping)are the tie which connects the Dongting Lake and Yangtze River together;in the meantime,The Xiangjiang, the Zijiang, the Yuanjiang and the Li River converge on Dongting Lake,forming a complex river and lake relationship. Heavy silting raised the riverbed of Dongting Lake,and it became a serious area of schistosomiasis because of its appropriate climate and geographical conditions for snails flourish.Habitants there suffured a lot because of the the considerable economic and health effects of schistosomiasis. Molluscicides were widely used to kill oncomelania, which played an important role in preventing and controlling the disease.This paper takes molluscicides-contaminated Dongting Lake as research area, pollution status and health risk of pentachlorophenol(PCP) and byproduct polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans(PCDD/Fs), niclosamide(NIC)were investigated in the sediments and fish samples from Dongting Lake.An ultra performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS) method was developed for concentrations determination of niclosamide and PCP in sediments and fish tissues,since there were not any related studies before. A series of optimizations were done to find the most effective pre-treatment and suitable analytical parameters of UPLC-MS /MS for niclosamide and PCP. Strict measures of quality assurance/quality control were done to make sure that the results of analysis met the performance characteristics of the method. The results demonstrated that the limits of detection(LOD, S/N=3)were 0.003 ng·g-1 and 0.005 ng·g-1 for NIC in sediments and fish samples respectively.The recoveries of NIC in sediments were within the range of 77.6-84.2%(2 ng·g-1), 76.2-93.4%(10 ng·g-1), 72.4- 75.2%(50 ng·g-1),with relative standard deviation(RSD)less than 10%(n=4). The recoveries of NIC in fish muscle were in the range of 83-92.5%(2 ng·g-1), 82.6-91.4%(10 ng·g-1),with RSD less than 5%(n=4). The limit of detection(LOD, S/N=3) were 0.01 ng·g-1 and 0.005 ng·g-1 for PCP in sediment and fish muscle,respectively. The recoveries of PCP in sediments and fish muscle were in the range of 75-91%(50 ng·g-1) and 72-85%(50 ng·g-1)with RSD%<10%(n=4).And on this basis,NIC,PCP were analyzed with UPLC-MS/MS,PCDD/Fs were analyzed with isotope dilution HRGC/HRMS in sediments collected from the west, east and south Dongting Lake and the estuaries on Sep 2013,in order to explore the contamination status and the hydrodynamic effects on their distribution in Donting Lake.The concentrations of NIC in sediment samples ranged from 20 pg·g-1 to1213 pg·g-1dry weight(dw),PCP concentrations ranged from 170 pg·g-1 to 3320 pg·g-1 dw,total concentrations of seventeen 2378-PCDD/Fs ranged from 153 pg·g-1 to 7144 pg·g-1 dw.The PCDD/Fs concentrations was statistically correlated with PCP concentrations(correlation=0.906),which indicate that PCP’s usage was the source of PCDD/Fs contamination in sediment.NIC,PCP, PCDD/Fs concentrations diversed in the same order of magnitude, which meant that NIC and PCP were degradated easily in ecological environment.Such low concentrations may indicate less environmental hazard. The PCDD/Fs were hard to degrade and easy to absorb in sediments,which may become a potential risk to the environment.Six of fourteen sediment samples’ TEQ valves were crossed the lowest threshold of USEPA(2.5 pg TEQ·g-1),while were far below the higher threshold of USEPA(25 pg TEQ·g-1). Concentration of sediments collected from Dongting Lake outlet was in the middle level of all the sediments, suggesting that PCDD/Fs probably flushed into the Yangtze River.Ten species of commercial fish(Elopichthys bambusa, Mandarin fish, Erythroculter ilishaeformis, snakehead, catfish,carp, bream, spotted silver carp, silver carp, Grass Carp, respectively)were collected in Dongting Lake on Sep 2014.Concentrations of niclosamide, PCP and PCDD/Fs in fish tissue were analyzed in order to explore The rule of the distribution and enrichment of molluscicides and PCDD/Fs in fish mussles.Concentrations of niclosamide in fish tissue samples ranged from 20 to 2244 pg·g-1dw, concentrations of PCP ranged from 10.5 to748 pg·g-1dw, total concentrations of seventeen 2,3,7,8-PCDD/Fs ranged from under detect limit to 8.87 pg·g-1 dw.The fingerprint of each congener in fish mussle was different from which in sediments, The predominant congener in fish mussle was 2,3,7,8-TCDF,while The predominant congener in sediments was OCDD.The trophic level of Donting fish were constructed via stable nitrogen isotope values and the enrichment regularity of NIC,PCP,PCDD/Fs in different fish species were analyzed. There was no increase in the concentration of pollutants in organisms at the higher trophic levels. Subsequently, dietary exposure of habitants to NIC,PCP and PCDD/Fs was calculated in Dongting Lake, and potential health risk was also evaluated. The average dietary exposure of residents(urban residents) was within the range of 101-14429 pg/kg bw /month for NIC, within the range of 53-2860 pg/kg bw/month for PCP,within the range of 0-4.7 pg/kg bw/month for PCDD/Fs.PCP, PCDD/Fs dietary exposure values were all below the threshold recommended by NAS and JECFA,respectively,which indicated relatively low health risk caused by dietary exposure.No risk assessment was conducted for niclosamide by any country or organization because of the low volume of use and low toxicity.Dietary exposure for NIC may be too low to cause health problem for Dongting habitants.