Study On Organic Pollutants Sources And Their Distribution Characteristics In Daya Bay Waters

Based on the testing and analyzing the organochlorine insecticides (such as HCHs, DDTs and dieldrin) and PCBs contents in the sediment and water body covered the sediment, this paper plots and describes the various organic pollutants distribution, simultaneously analyzes the organic pollutants sources according to the main pollution sources along the coastwise of Daya Bay. The field survey was conducted in May, 2003, and there were 12 location points arranged for the survey. The sediment and water body covered the sediment were sampled by means of the sediment coring sampler (Patent No: 200420044691), which was developed by Professor Xu Jirong and Wang Youshao of the South China Sea Institute of Sinica Academy. This sampler can collect the sediment and water covered the sediment at the same time, the outstanding advantage of the sampler is to assure submarine sampling without any disturbing. Thereinto, the columnar sampling of sediment is divided into four stratums: (0-2) cm, (4~6)cm, (8~12)cm and (18~22)cm. The pretreatment and testing methods are all based on the methods specified in the Specification for Marine Monitoring (GB 17378.4-5-1998). The testing instrument is GC-2010 gas chromatographer made in Shimadzu Corporation, Japan. By means of Angelun capillary column DB-1 and AOC-20i automatic injection system, the organic pollutants, such as HCHs, DDTs, dieldrin and PCBs can be detected qualitatively and quantitatively.The survey results indicate: certain HCHs and DDTs have been detained in the water body (mainly refers to the water body covered the sediment) in Daya Bay, dieldrin level has been under the detection limit and PCBs content has been found to be high. In the water covered the sediment, HCHs level varied from 1.5 to 11.8 ng/L with an average of 7.0 ng/L, mainly composing of α -BHC 和 γ -BHC, β -BHC accounting for certain ratio. δ -BHC were seldom detected; DDTs level ranged between undetection and 48.0 ng/L with a level of 21.6 ng/L on average, mainly composing of PP'-DDE while OP'-DDT and PP'-DDD were seldom detected, PP'-DDT was found to be under the detection limit; PCBs level ranged from 742.1 to 2443.4 ng/L with an average of 1,306.3 ng/L. HCHs mainly distributed alongshore in the northern part of Daya Bay and the mouth of the Bay, so did DDTs. PCBs level was found to be higher in the entire water body, the highest level was detected in the central part of Daya Bay, that is the waters around Mabianzhou. The various organic pollutants source is greatly related to petrochemicals project, industry wasted water and sewage effluent from vessels.In the sediment of Daya Bay, the main organic pollutants refers to PCBs, and HCHs and DDTs remains have been found too while dieldrin has detected lower. In the sediment, HCHs content varied from undetection to 16.0×10-9 with an average of 2.2× 10-9, mainly distributed in the sediment in (4-6)cm and (18-22)cm stratum while lower in (0-2)cm stratum; DDTs content ranged between undetection to 1.7×10-9 with an average of 0.2× 10-9; in each stratum, dieldrin content was detected lower; PCBs content ranged from 0.7 to 14.1 × 10-9 with a content of 4.2 × 10-9 on average, while that in (0-2)cm stratum was the highest, the lowest in (18-22) cm stratum, in(4-6)cm stratum and (8-12)cm stratum was close.In accordance with various organic pollutants content in the sediment in each stratum, from the superficial sediment to the deep sediment HCHs content increased approximately, the other way round, PCBs content dropped down. Lower HCHs content in the superficial sediment clearly indicates HCHs level is lower in the water body than the previous. Higher PCBs content in the superficial sediment shows PCBs level in the water body at present is still higher, and this survey results makes out this point. Nowadays, DDTs and dieldrin content in the sediment of Daya Bay are lower.