| Popis: |
The concentrations of HCHs and DDTs in soil and air of urban/rural/forestry centre locations in the Hami region of Xinjiang were monitored for a year by passive atmospheric sampling in order to study the residual levels and air-soil exchange and evaluate ecological risk. The study results showed that the annual average concentrations of HCHs and DDTs in the air of Hami were 107.1 pg x m(-3) and 43.9 pg x m(-3), respectively, and the concentrations of HCHs and DDTs in summer and autumn were generally higher than those in winter and spring. It was deduced that the HCHs and DDTs tended to evaporate into the air because of the higher temperatures in summer and autumn. For OCPs in the air of study area, HCHs were dominanted the main pollution compared with DDTs. Meanwhile, alpha-HCH contributed the largest portion among all HCHs isomers, and p,p'-DDE dominated the residual levels of DDTs. Moreover, the values of alpha-HCH/gamma-HCH were in the range of 3 to 7, which indicated that the use of technical HCHs or the long distance atmosphere transport of HCHs may play a significant role for HCHs in the air of Hami region. Furthermore, ratios of (DDD + DDE)/DDTs were in the range of 0.4-0.9, 71.4% of which were higher than 0.5, indicating that DDTs in the air were mainly from historical usage and no new DDTs sources emerged in Hami recently. The concentrations of HCHs and DDTs in soil were between 0.344-6.954 ng x g(-1) and 0.104-26.397 ng x g(-1), respectively, which did not exceed the National Soil Quality Standard Level I. In addition, DDTs predominated in soil OCPs, in which beta-HCH accounting for a huge percentage in HCHs isomers, while o,p'-DDT predominated in pollution caused by DDTs isomers. From study results, it was also suggested that the important cause of DDTs residues in soil of Hami area could be the recent inputs of new sources since the value of (DDD + DDE)/DDTs were lower than 0.5. The sources of HCHs and DDTs in soil and atmosphere were not consistent, which was mainly caused by the different characteristics of soil and atmosphere and the complex geographical environment and climatic conditions in Hami region. The study on air-soil exchange showed that the escaping tendency of the various isomers of HCHs and p, p'-DDE was mainly from the soil to the air, on the contrary, the escaping tendency of o,p'-DDE,o,p'-DDD,p,p'-DDD,o,p'-DDT,p,p'-DDT was mainly from the air to the soil in Hami, which indicated that the soil was the sink of most of DDTs, and the air was the source of most of DDTs; while the air was the sink of HCHs and p,p'-DDE, and the soil was the source of HCHs and p,p'-DDE. There were potential risks of DDTs to birds and soil organisms in urban soil and forestry centre soil of Hami region, while the ecological risk of HCHs was light in Hami surface soil. |
