Reddy Christopher M, Drenzek Nicholas J, Eglinton Timothy I, Heraty Linnea J, Sturchio Neil C, Shiner Vernon J
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
Environ Sci Pollut Res Int. 2002;9(3):183-6. doi: 10.1007/BF02987486.
INTENTION, GOAL, SCOPE, BACKGROUND: Identifying different sources and following reaction pathways of chlorinated organic contaminants in the environment can be challenging, especially when only their concentrations are available. Compound-specific stable chlorine measurements of some contaminants have recently been shown to provide additional information and an increased understanding of their biogeochemistry. These studies, however, have been generally limited to volatile molecules.
Here, the stable chlorine isotope ratios of the semi-volatile pesticide, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) were investigated. Specifically, the intramolecular stable chlorine isotopic compositions of DDT and the kinetic isotope effect (KIE) for the abiotic dehydrochlorination of DDT to 2,2-bis(p-chlorophenyl)-1,1-dichloroethene (DDE) were determined.
Selective chemical oxidation of DDT to dichlorobenzophenone (DCBP) and analysis of each compound was used to calculate the stable chlorine isotope ratios of the alkyl and aromatic chlorines in DDT. To determine the KIE for dehydrochlorination, DDT was reacted in a basic solution to yield DDE at 52 degrees C, 60 degrees C, and 72 degrees C for 3, 5, and 5 days, respectively.
Significant intramolecular stable chlorine isotopic differences were observed in one sample of DDT where the alkyl and aromatic delta 37Cl values were -5.76 +/- 0.45 and -2.21 +/- 0.24%@1000, respectively. Dehydrochlorination of DDT to DDE in basic solutions at 52, 60, and 70 degrees C resulted in a substantial intramolecular KIE where the alkyl chlorines of DDE shifted by approximately 3%@1000 relative to the alkyl chlorines in DDT. However, no temperature dependence was observed. The KIE, calculated by an iterative program, was 1.009.
Intramolecular differences in the stable chlorine isotope ratios were observed in DDT and this is the first such finding. Dehydrochlorination of DDT yields a measurable and distinct intramolecular stable chlorine KIE.
The results of this study demonstrate the existence of significant intramolecular differences in chlorinated organic compounds. Many other chlorinated semi-volatile and volatile organic contaminants are synthesized from multiple sources of chlorine, and we recommend that similar studies be performed on many such molecules in order to attain a clear understanding of their intramolecular chlorine isotopic differences. The existence of a measurable KIE for the dehydrochlorination of DDT to DDE shows the potential strength of using isotopic measurements to investigate the biogeochemistry of these important compounds. For example, the isotopically depleted aqueous chloride produced by dehydrochlorination of DDT to DDE may be a useful tracer of these reactions in freshwater environments.
目的、目标、范围、背景：识别环境中氯化有机污染物的不同来源并追踪其反应途径可能具有挑战性，尤其是在仅知道其浓度的情况下。最近研究表明，对某些污染物进行化合物特异性稳定氯测量可提供更多信息，并增进对其生物地球化学的理解。然而，这些研究通常仅限于挥发性分子。
本文研究了半挥发性农药1,1,1-三氯-2,2-双（对氯苯基）乙烷（滴滴涕，DDT）的稳定氯同位素比值。具体而言，测定了滴滴涕分子内稳定氯同位素组成以及滴滴涕非生物脱氯化氢生成2,2-双（对氯苯基）-1,1-二氯乙烯（DDE）的动力学同位素效应（KIE）。
通过将滴滴涕选择性化学氧化为二氯二苯甲酮（DCBP）并分析每种化合物，计算滴滴涕中烷基氯和芳基氯的稳定氯同位素比值。为确定脱氯化氢的KIE，使滴滴涕在碱性溶液中分别于52℃、60℃和72℃反应3天、5天和5天以生成DDE。
在一个滴滴涕样品中观察到显著的分子内稳定氯同位素差异，其中烷基和芳基δ³⁷Cl值分别为-5.76±0.45‰和-2.21±0.24‰。在52℃、60℃和70℃的碱性溶液中，滴滴涕脱氯化氢生成DDE导致显著的分子内KIE，其中DDE的烷基氯相对于滴滴涕中的烷基氯偏移了约3‰。然而，未观察到温度依赖性。通过迭代程序计算得出的KIE为1.009。
在滴滴涕中观察到稳定氯同位素比值的分子内差异，这是首次有此类发现。滴滴涕脱氯化氢产生了可测量且明显的分子内稳定氯KIE。
本研究结果表明氯化有机化合物中存在显著的分子内差异。许多其他氯化半挥发性和挥发性有机污染物由多种氯源合成，我们建议对许多此类分子进行类似研究，以清楚了解其分子内氯同位素差异。滴滴涕脱氯化氢生成DDE存在可测量的KIE，这表明利用同位素测量研究这些重要化合物生物地球化学的潜在优势。例如，滴滴涕脱氯化氢生成DDE产生的同位素贫化水相氯化物可能是淡水环境中这些反应的有用示踪剂。
