广西百朗地下河水和沉积物中有机氯农药的分布特征

为了解典型岩溶地区广西乐业百朗地下河表层水和沉积物中有机氯农药的分布特征,采集地下河不同断面的水和沉积物样品,利用气相色谱仪测定了19种有机氯农药。结果表明:(1)百朗地下河表层水中19种有机氯农药总量(∑OCPs)浓度为1.95~71.45ng/L,HCHs和DDTs浓度分别为未检出至58.40ng/L和未检出至0.44ng/L;(2)沉积物中∑OCPs浓度为0.75~14.85ng/g,HCHs和DDTs浓度分别为0.11~3.52ng/g和0.03~2.90ng/g;(3)地下河表层水和沉积物中有机氯农药的分布与吸附作用、环境温度以及和地下河连通的天坑的底部的土壤侵蚀有关,即因温差作用,大气沉降的有机氯农药易富集在天坑底部("冷陷阱效应"),并在土壤侵蚀作用下向水体移动,使地下河沉积物中有机氯农药浓度升高;(4)百朗地下河出口沉积物吸附系数最低,但水中有机氯农药浓度较高且种类最多,推测可能是地下河沉积物中因有机氯农药被释放而引起二次污染;(5)表层沉积物中大多数断面的异狄氏剂浓度及乐业县城附近断面的DDTs和DDD浓度在风险评估低值与风险评估中值之间,表明百朗地下河处于较低的生态风险水平;(6)目前,流域部分断面尚有新的-γHCH(林丹)和DDTs农药输入。由于有机氯农药长期累积,可能对地下河生态系统造成危害,应采取防治措施。

Distribution of organichlorine pesticide in the water and sediment of the Bailang Subterranean Stream in Guangxi

In order to understand distribution of organochlorine pesticide in the water and sediments of the Bailang Subterranean Stream in typical karst area in Leye, Guangxi, the water and sediment samples on different sections are collected and 19 kinds of OCPs are detected with GC-ECD. The results show that, （1） The total organochlorine pesticides concentration（∑ OCPs） in the surface water of the Bailang subterranean stream ranges from 1.95 to 71.45ng/L, the concentration of HCHs ranges from undetectable to 58.40ng/L, and DDTs undetectable to 0.44ng/L respectively. （2） The concentration of ∑OCPs in the sediment ranges from 0.75 to 14.85ng/L, HCHs from 0.11 to 3.52ng/L, and DDTs from 0.03 to 2.90ng/L. （3） Distributions of OCPs in water and sediment from the Bailang Subterranean Stream are related with adsorption, temperature and the soil erosion at the bottom of Tiankeng where connected with subterranean stream. Namely, OCPs of atmospheric sedimentation is easily gathered in soil at the bottom of Tiankeng for temperature difference effect（this is＂cool trap effect＂）, and then, OCPs moves toward the water body so that concentration of ∑OCPs in sediment of the subterranean stream increases. （4） It is inferred that the OCPs in the sediment of the subterranean stream could be released to cause secondary pollution for the value of the sediment adsorption coefficient being lowest at the exit of the stream, but higher in concentration and kinds of OCPs in the stream water. （5） The ecological risk is at the low risk due to concentrations of the endrin on most sections and both DDTs and DDD on the section of the Leye County surrounding areas range between effects range to low （ERL） and effects range to median（ERM）. （6） There are both newly HCHs and DDTs inputs recently on some sections. Organochlorine pesticide has accumulated for a long time, which may be cause harm to the underground river ecosystem. Therefore, local government should take preventive measure.