The Levels Of Organochlorine Pesticides In Taihu Lake, Historical Trends And The Migration Of The Study

Organochlorine pesticides (OCPs) are important persistent organic pollutants (POPs), Because of their persistence, half-volatility and high toxicity in the environment and biological accumulation through the food web, OCPs have great harm to the environment and human health. China is the largest user and producer of OCPs in the world. Because they were used largely and are difficult to be degraded, OCPs are still the most widespread POPs in the environment despite ban or restricted use in developed countries and in china since1983.At present, the studies on OCPs are mainly paid attention to bays and estuaries, and very few studies on OCPs in Lake. Taihu Lake is a typical multifunctional Lake in southeast coast of China, However, no date of water-sediment exchange are available for OCPs in Taihu Lake. Through the discussion about the origin, tendency and release of OCPs, we can know the transferring and transforming pathways of OCPs in the water and sediments in Taihu Lake, which may provide theoretical foundation for controlling and treating organic pollution of Taihu Lake.This study systematically researched into the concentration of OCPs in sediments, water and core samples from Taihu Lake, distribution feature, possible sources, potential ecological risk and the water-sediment exchange flux.The results are following: It employed gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS) to analysis a total of69sediment samples. The total OCPs concentrations in sediments were0.55-11.66ng/g and the average levels of OCPs were4.13ng/g. Among the OCPs, the concentrations of DDTs (0.14-8.53ng/g dw), HCHs (0.12-4.75ng/g dw) and HCB (nd-6.24ng/g dw) were much higher than other pesticides. DDTs were the most dominant compounds in the sediments, accounting for about40%of the total levels. The dominant compound of DDTs was the residual metabolic products p,p'-DDE and the dominant compound of HCHs was?-HCH. According to component analysis, the ratios of a-HCH/γ-HCH and p,p'-DDT/p,p'-DDE suggested that residues of HCHs and DDTs in surface sediments from Taihu Lake were mainly due to long-term usage in past. But there was still new inpute of some OCPs in recent use. By comparing the concentration of OCPs in surface sediments from Taihu Lake with other regions, the concentration of OCPs in sediments from Taihu Lake were slightly lower than the median level around the world.Less than the ERL value of the content of all sampling points of the T-chlordane in Taihu Lake sediments, most of the sampling points of DDT, DDE and SDDTs, content is less than the ERL value content more than the ERL value of the region in more serious pollution ZhushanBay, Meilianghu Bay region, there is no content to exceed the ERM value of the sampling points. Overall, the organochlorine pesticides in Taihu Lake sediments there is a certain ecological risk, and may cause harm to the ecological environment of OCPs in the potential threat to the environment can not be ignored.Three column sediments were sampled from Taihu Lake, The contents of OCPs in these samples were tested. The results indicated that the total OCPs concentrations in sediments ranging from0.88to4.73ng/g dw (average2.17ng/g dw), Among the different OCPs, hexachlorobenzene(HCB), DDTs and HCHs presented the hightest detection rate and residual level, The average value of HCB, DDTs and HCHs in sediments sample was0.92ng/g,0.55ng/g,0.65ng/g respectively. Three bays of the sedimentary column surface DDTs content of the highest apparent surface enrichment, the composition analysis results showed that there was still new input of DDTs in recent years.It can be seen from the analysis data, among all the organochlorine pesticides in Taihu Lake water samples, the highest concentration of p,p'-DDT was426.26pg/L, followed by a-HCH and endosulfan which concentration were289.99pg/L and215.20pg/L. The concentration of hexachlorobenzene (HCB) and p,p'-DDE in the sediments were slightly higher. But the octanol-water partition coefficient (log Kow) of hexachlorobenzene (HCB) and p,p'-DDE were very high, with poor water solubility, so concentration of HCB and p,p'-DDE in the water were not high.According to ratio of a-HCH/γ-HCH and HCHs source analysis, it can be found that HCHs pollution in Taihu Lake came from the use of industrial lindane. We use exchange model to calculate the net exchange flux of HCHs, the derived release flux of HCHs from sediments to water bodies were about706.71kg throughout the year. The ratio of p,p'-DDT/p,p'-DDE in water bodies is much larger than1, indicating the new sources of input. The exchange model indicated that the net exchange flux of p,p'-DDT were deposition fluxes. The deposition fluxes of p,p'-DDT were about50.74kg throughout the year. Besides there were about25.63kg of endosulfan I from water bodies into sediments, reflecting the endosulfan I pollution in Taihu Lake was very serious and new input of DDTs products, resulting in the DDT pollution of water bodies.