Reina Rachel G, Leri Alessandra C, Myneni Satish C B
Department of Civil & Environmental Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Environ Sci Technol. 2004 Feb 1;38(3):783-9. doi: 10.1021/es0347336.
The contribution of halocarbons from plant weathering to the total organohalogen budget of terrestrial systems is gaining recognition. To evaluate the formation of such halocarbons, speciation of chlorine in Sequoia sempervirens (redwood) needles was examined in the presence of an external chloroperoxidase (CPO) enzyme using Cl K-edge X-ray absorption spectroscopy. The Cl forms in fresh and naturally weathered needles and in model laboratory reactions were compared. To provide a straightforward analogue to the enzymatic chlorination in plants, chlorination reactions were conducted for phenol, a common moiety of plant macromolecules. Plant material chlorination was also examined in the presence of hypochlorite in an ancillary mechanistic investigation. The dominant form of Cl in fresh, unreacted plant material was found to be inorganic Cl-, which was partially converted to organochlorine in the presence of CPO. Chlorination is affected by the nature of reactant (CPO, H2O2) addition, reaction time, and temperature. The organochlorines produced in these laboratory investigations closely resemble those produced during the natural weathering of redwood needles. A striking consistency in chlorine speciation observed among the various sample types suggests that (i) CPO produced by terrestrial organisms could play a vital role in the generation of organochlorines associated with the degradation of plant material and (ii) initial targets of enzymatic chlorination might include lignin-like macromolecules rich in aromatic character and hydroxyl groups. These findings lend further credibility to a significant biogenic contribution to the global organohalogen burden by elucidating a probable route of enzymatic chlorination of natural organic matter in terrestrial systems.
植物风化产生的卤代烃对陆地系统总有机卤素预算的贡献正逐渐得到认可。为了评估此类卤代烃的形成，利用Cl K边X射线吸收光谱，在外部氯过氧化物酶（CPO）存在的情况下，对红杉针叶中的氯形态进行了研究。比较了新鲜和自然风化针叶以及实验室模型反应中的氯形态。为了提供与植物中酶促氯化作用直接类似的情况，对植物大分子的常见部分苯酚进行了氯化反应。在辅助机理研究中，还研究了在次氯酸盐存在下的植物材料氯化作用。发现新鲜未反应植物材料中氯的主要形态是无机Cl-，在CPO存在下部分转化为有机氯。氯化作用受反应物（CPO、H2O2）添加性质、反应时间和温度的影响。这些实验室研究中产生的有机氯与红杉针叶自然风化过程中产生的有机氯非常相似。在各种样品类型中观察到的氯形态的显著一致性表明：（i）陆地生物产生的CPO可能在与植物材料降解相关的有机氯生成中起关键作用；（ii）酶促氯化的初始目标可能包括富含芳香特征和羟基的类木质素大分子。这些发现通过阐明陆地系统中天然有机物酶促氯化的可能途径，进一步证明了生物源对全球有机卤素负担有重大贡献这一观点的可信度。
