Regional Geochemistry Of Organochlorine Pesticides In The Pearl River Delta

Organochlorine pesticides (OCPs) are one group of persistent organic pollutants (POPs) which are going to be eliminated or reduced on the release into the environment under the Stockholm Convention on Persistent Organic Pollutants adopted by many countries. Because of their persistence in the environment, and biological accumulation through the food web, OCPs can cause environmental damage, and affect human health, After prohibition of the use of many POPs, including PCBs and organochlorine pesticides in the developed countries, emission sources of a number of POPs (such as DDTs and HCHs) in last 20 years have been shifted from industrialized countries of the Northern Hemisphere to the developing countries in the tropical and sub-tropical regions, including India and China, owing to the late production ban and present legal and illegal application in agriculture and for the control of certain diseases, such as malaria, typhus and cholera. Due to their physiochemical properties, organochlorine pesticides (OCPs) are subject to long-range atmospheric transport (LRAT). Therefore, OCPs released in the tropical and subtropical environments could be dispersed rapidly through air and water, and tend to be redistributed at a global scale. Recently many studies showed that the atmospheric transportation from these regions across the Pacific Ocean was one of the major contributing sources for OCPs in Canadian west coast and Arctic regions. The Asia monsoon has played an important role in this process.The Pearl River Delta (PRD) is located on the South China and under strong influence of the Asia monsoon system due to its geographic location. In an effort to better characterize environmental chemistry behaviors of OCPs, and to study theinfluence of the Asia monsoon on the OCPs transport over this tropical-subtropical, monsoonal and coastal region, the distribution and characteristic of OCPs in air, soil, and atmospheric deposition in the PRD were studied and the gaseous OCPs exchanges across the air-soil and air-water were calculated.In the first part of the thesis, the atmospheric OCPs characteristic in Peal River Delta was studied. Sampling was conducted at the same time at four sampling sites for a consecutive 24 h period during the whole day and night every half-monthly base from December 2003 to December 2004. 92 particle samples and 92 PUF samples were collected. The results showed higher levels of OCPs found in the PRD in comparison with other places in the world, and the predominant compounds were DDTs and chlordane. The average concentrations of p,p'-DDT, trans-chlordane(TC), and cis-chlordane(CC) in Guangzhou air were 789, 871 and 1340 pg/m3, respectively; in Hong Kong air were 358, 389, and 380 pg/m3, respectively. In general, the concentrations of OCPs increased from the winter to the summer except for a-HCH which had no clear seasonal pattern. The results of 5 and 10 days back trajectory indicated that the unusual high p,p '-DDT levels in summer in PRD could be caused by the summer Asia monsoon originated from the South Asia where large quantities of technical p,p '-DDT was used. The high concentration of endosulfan in winter in the study area was influenced by the winter monsoon from the East China where large amounts of endosulfan were used as insecticide in cotton fields. The results demonstrated that Asia monsoons can play an important role in the long-range atmospheric transport of POPs at a global scale.In the second part of the thesis, OCPs values in 74 soil samples, which included paddy soil, crop soil, and primary soil, in Pearl River Delta were determined. The predominant compounds in soils were DDTs, which contributed about 87 percent of the total OCPs in soil. The average concentrations of DDTs in the three kinds of the soils were 56.32, 46.71, and 3.26 ng/g, the concentrations of HCH were 4.94, 3.65, and 0.8 ng/g. Combined the composition changes of OCPs and the enantiomer fraction of chiral compounds, the high concentration of DDT in soils could be attributed to the present usage of dicofon in the Pearl River Delta Region. The relativehigh levels of a-HCH in soils might be transformed from y-HCH newly used in this region. Cis-chlordane might have the lower values of half-life than that of trans-chlordane in the sub-tropic region.In the third part of the study, the atmospheric deposition of OCPs in PRD was determined and the preliminary study on OCPs exchange across the interface of air-soil and air-water was performed. Total 15 sample sites were selected in PRD. Both dry deposition and precipitation were collected continuously by an open apparatus for a 2-month period from December 2003 to February 2005. 105 particle deposition samples and 74 dissolved samples were collected in one year. Same as the characteristic of OCPs in the atmosphere, the predominant compounds in atmospheric deposition were DDTs and chlordane. Significant spatial and seasonal variations of the OCPs deposition fluxes were observed, the higher deposition flux of DDTs and chlordane was observed in the centre of the PRD with the average of 22.1 and 6.98 ng/m2/day, respectively, and the lower deposition flux was at the offshore sites with the average of 3.7 and 3.1 ng/m2/day, respectively. The deposition fluxes of DDTs, which positively correlated with the particle phase concentration of DDTs in atmosphere, decreased from the winter to the summer. This suggested that both highly variable atmospheric OCPs concentrations and complex scavenging processes, which due to the typical monsoon-controlled climate, wet and hot in summer, and dry and cool in winter, controlled the result. The balance statues of OCPs between the air and earth surface suggested the global re-cycling of persistent organic pollutants, especially OCPs, was strongly retarded by soils and water in the South China.