| Organochlorine pesticides (OCPs) are a kind of the persistent organic pollutants (POPs), which have the role of endocrine disruption. Owing to its characteristics, such as the long-time residue, biological accumulation, semi volatile and highly toxic, OCPs can migrate for long distance in atmospheric environment, and then return to the earth. Because of its serious harm to the health of human beings and ecological environment, OCPs has attracted the attention of environmental chemists.The karst area in southwestern China is about 600000 km2 including Yunnan, Guizhou, Guangxi, Chongqing, Sichuan, Hunan, Hubei and Guangdong. The unique distribution pattern of water and soil has made the karst environment as vulnerable as the edge of the desert. Once destroyed, it is hard to recover. In recent years, the impact of human activities on resources and environment in karst area has become serious. Especially the organic fertilizer and pesticide used in agricultural production can directly go into the underground river system by direct leaking or with farmland water. Hence, the karst ecological environment and human health faced the serious threat.In this article the hydrogeology system of Xueyu Cave which located at Chongqing has been taken as a study case, OCPs as the aim compounds. Through explored the composition, seasonal change, migration rule and influence factors of OCPs in the hydrogeology system of Xueyu Cave, and then reveal its environmental behavior, so as to provide the theory basis and the reference for OCPs pollution prevention and control in southwest karst region.This research mainly contains three aspects:Firstly, through collecting the overlying soil samples of Xueyu Cave, investigating the horizontal and vertical distribution, composition and then concluding the possible sources of OCPs, analyzing the soil organic carbon, and discussing its influence on the distribution of OCPs. Secondly, through collecting the water samples from doline, underground river and drip waters in different months, discussing the composition and seasonal distribution characteristic of OCPs. Lastly, through comparing with the migration characteristic of OCPs in non-karst areas, discussing the rule of OCPs’s migration in karst hydrogeology system. 10 typical surface soil samples were taken on the top of Xueyu Cave, in which 18 OCPs were analyzed by gas chromatography equipped with miro-63Ni electron capture detector. The results showe that (1) Most OCPs except for o,p’-DDD,ε-HCH, aldrin and dieldrin are detected in the soil samples. Moreover,4 OCPs including HCH, DDT, heptachlor and methoxychlor are detected in all samples, which compose the predominant contaminations. The OCPs concentrations of surface soils range from 1.24 to 750.56 ng·g-1 with a mean value of 79.57 ng·g-1, and the concentration of OCPs in the depression is higher than on its slope. (2)The ratio of OCPs isomers imply that the unlawful using of lindane and industrial DDTs cause HCHs and DDTs pollution, and a new contamination source can be observed. As for HCB, heptachlor, methoxychlor, isodrin and endrin, the possible source is regional atmospheric deposition or regional diffusion. Correlation analysis between 10 samples indicated that OCPs in study area generally have the same source, and soil organic carbon is an important factor in the distribution of OCPs. (3)Compared with the Environmental Quality Standard for Soils of China GB15618-95, the concentrations of HCHs and DDTs in these samples stay in a low pollution level. Compared to the similar researches in China and abroad, HCHs and DDTs residues in the soil belonged to low levels.Two typical profile of abandoned and agriculture land, which were taken on the top of Xueyu Cave, in which 18 OCPs were analyzed by gas chromatography equipped with miro-63Ni electron capture detector. The results showe that (1) The HCHs concentrations of abandoned range from 0.06 to 2.23 ng·g-1,γ-HCH is detwoected in all samples, which composes the predominant component of HCH. The DDTs concentrations of abandoned range from 0.14 to 18.58 ng·g-1, p,p’-DDT is detected in all samples, which composes the predominant component of DDT. The concentrations of HCB, methoxychlor, heptachlor, isodrin and endrin in abandoned profiles are N.D～0.93ng·g-1 N.D～2.6ng·g-1, N.D～0.28ng·g-1,0.1～0.41 ng·g-1, N.D～0.42ng·g-1. (2) The HCHs concentrations of agriculture land range from 0.08 to 0.33 ng·g-1,γ-HCH is detected in all samples, which composes the predominant component of HCH. The DDTs concentrations of abandoned range from N.D to 5.68 ng·g-1, p,p’-DDT is detected in all samples, which composes the predominant component of DDT. The concentrations of HCB, methoxychlor, heptachlor, isodrin and endrin in agriculture land profiles were N.D～0.07 ng-·g-1, N.D～2.04ng·g-1,0.05～0.23ng·g-1, N.D～0.18ng·g-1, N.D～0.33 ng·g-1 respectively. (3)By comparing the percentage between the concentration of OCPs in soil layers and surface soil, we find that vertical migration ability of isodrin is strongest, HCH, heptachlor, methoxychlor’s vertical migration ability are weaker than isodrin, and DDT,HCB, endrin are the weakest ones.The soil organic carbon is an important factor in the distribution of OCPs. The different land uses which cause different tillage degree, permeability and microbial activities may affect the concentration of OCPs in the soil.The water samples of Hongmiao well, doline, underground water and two drip waters of Xueyu Cave were analyzed. The results show that (1) The HCHs concentrations of water samples range from 0.75 to 4.72 ng·L-1,α-HCH andδ-HCH are detected in all samples, which compose the predominant component of HCH. The DDTs concentrations range from 0.83 to 18.93 ng·L-1, p,p’-DDT and p,p’-DDE are the predominant component of DDT in surface waters. p,p’-DDD and o,p’-DDD are the predominant component of DDT in underground water and drip waters. The concentrations of HCB, heptachlor, methoxychlor, isodrin. dieldrin and endrin in water samples are N.D～0.16ng·L-1,1.32～10.30 ng·L-1,0.69～5.05 ng·L-1,0.42～2.42 ng·L-1.0.10～3.60 ng·L-1. N.D～5.27 ng·L-1, N.D～19.09ng·L-1 respectively. (2)The concentration of OCPs in surface water samples is higher than underground water and drip waters. Compared to the similar researches in China and abroad, HCHs and DDTs residues in water samples belonged to low levels. (3)The concentrations of OCPs in winter is higher than that in summer which is the obvious seasonal change among water samples.By comparing the variety and concentration of OCPs in soil samples overlying Xueyu Cave and water samples of Hongmiao well, doline, underground water and two drip waters of Xueyu Cave, we find that the high concentration compounds in overlying soil and water samples also appear in underground water and two drip waters. The compounds which have stronger transfer ability are detected high concentration in underground water and two drip waters. What’s more, DDT exits in the form of p,p’-DDT in surface waters and in the form of p,p’-DDD in underground water and two drip waters. The results show that owing to the special hydrogeological structure in karst area, OCPs that come into the soil, river and doline through the agricultural activity or rainfall will migrate to underground water and drip water through the pipe or fissure finally, which should be a potential threat to the local ecological environment and residents whose living water are underground waters. |
PDF Full Text Request