土壤中两种手性有机氯农药的选择性降解研究

为了更深入的了解和阐释手性有机氯农药在土壤中的转化和环境归趋，采用实验室室内避光培养方法，研究了o,p＇-DDT及o,p＇-DDD 2种手性有机氯农药的外消旋体在水稻土厌氧培养体系和菜园土好氧培养体系中的选择性降解情况。为了更好的利用土壤中土著微生物的活性，我们选择了厌氧微生物比较丰富的水稻土和好氧微生物丰度比较高的菜园土来做培养实验。结果表明实验体系中o,p＇-DDT及o,p＇-DDD在水稻土和菜园土中的降解均没有明显的对映体选择性。这一结果与2种手性化合物不同对映体在自然环境中的含量普遍具有差异性有所不同，说明野外环境条件和室内模拟实验条件的差异会影响手性化合物的降解选择性。在2种体系中，o,p＇-DDT的降解速率均高于o,p＇-DDD的降解速率。这与以前的研究报道一致，DDD比DDT更难降解。通过2个体系的比较，发现DDT的降解速率在厌氧体系中高于好氧体系，而DDD的降解速率与之相反，好氧体系高于厌氧体系。这应该与DDT和DDD 2种化合物的化学结构及2种土壤中微生物群落的差异有关。对于厌氧体系中的2种水稻土，采自中山的水稻土中DDT的降解速率高于江门的水稻土，这应该与中山水稻土有机质含量高于江门的水稻土有关。有机质含量的高低直接反映了土壤中微生物的多少，进而会影响污染物的降解速率。研究发现本实验所用水稻土和菜园土总有机碳含量偏低可能是影响2种化合物的对映体无降解选择性的因素之一。此外，由于本研究采用缓冲溶液将pH 调控在中性，因此本文的土壤 pH 对降解选择性的影响仍有待进一步研究。本研究中好氧体系和厌氧体系对目标物的降解选择性无明显差异。

Enantioselective Degradation of Two Types of Chiral Organochlorine Pesticides in Soils

Our research examined the degradation of racemic mixture of o,p＇-DDT and o,p＇-DDD in paddy soil under anaerobic culture condition and in vegetable soil under aerobic culture condition, respectively with the objective of understanding and＆amp;nbsp;elucidating the transformation and environmental fate of chiral organochlorine pesticides in soil. In order to biostimulate the activities of indigenous microbial communities in soil being capable of degrading o,p＇-DDT or o,p＇-DDD, paddy soil with high abundance of anaerobic microorganism and vegetable garden soil consisting of abundant aerobic microorganism were chosen as experimental matrices. Results showed that there is no significantly enantioselective degradation in anaerobic culture system or aerobic culture system for o,p＇-DDT and o,p＇-DDD. Enantiomeric shifts are very common in field environment, different with our results, indicating that the differences between laboratory experimental and natural conditions can result in the difference of enantioselective degradation of chiral compounds. In both anaerobic and aerobic systems, the degradation rates of o,p＇-DDT are higher than those of o,p＇-DDD, which is consistent with the previous report that DDD is more difficult to be degraded than DDT. Comparing the two culture systems, the degradation rate of o,p＇-DDT in anaerobic system is higher than that in aerobic system, while contrary to DDT, the degradation rate of o,p＇-DDD in aerobic system is higher than that in anaerobic system. This may be related to the difference between the chemical structure of DDT and DDD and the difference between the microbial communities in paddy soil and vegetable garden soil. For the two paddy soils in anaerobic system, the degradation rate of DDT in the paddy soil from Zhongshan （ZS） is higher than that in Jiangmen （JM）. This may be attributable to the contents of organic matters in ZS soil is higher than that in JM soil. The content of organic matters can reflect the quantity of microorganism in soil dir