Leri Alessandra C, Ravel Bruce
Department of Natural Sciences, Marymount Manhattan College , 221 E 71st St., New York, New York 10021, United States.
National Institute of Standards and Technology , 100 Bureau Drive MS 8520, Gaithersburg, Maryland 20899, United States.
Environ Sci Technol. 2015 Nov 17;49(22):13350-9. doi: 10.1021/acs.est.5b03937. Epub 2015 Oct 27.
Biogeochemical transformations of plant-derived soil organic matter (SOM) involve complex abiotic and microbially mediated reactions. One such reaction is halogenation, which occurs naturally in the soil environment and has been associated with enzymatic activity of decomposer organisms. Building on a recent finding that naturally produced organobromine is ubiquitous in SOM, we hypothesized that inorganic bromide could be subject to abiotic oxidations resulting in bromination of SOM. Through lab-based degradation treatments of plant material and soil humus, we have shown that abiotic bromination of particulate organic matter occurs in the presence of a range of inorganic oxidants, including hydrogen peroxide and assorted forms of ferric iron, producing both aliphatic and aromatic forms of organobromine. Bromination of oak and pine litter is limited primarily by bromide concentration. Fresh plant material is more susceptible to bromination than decayed litter and soil humus, due to a labile pool of mainly aliphatic compounds that break down during early stages of SOM formation. As the first evidence of abiotic bromination of particulate SOM, this study identifies a mechanistic source of the natural organobromine in humic substances and the soil organic horizon. Formation of organobromine through oxidative treatments of plant material also provides insights into the relative stability of aromatic and aliphatic components of SOM.
植物源土壤有机质（SOM）的生物地球化学转化涉及复杂的非生物和微生物介导反应。其中一种反应是卤化作用，它在土壤环境中自然发生，并且与分解生物的酶活性有关。基于最近一项发现，即天然产生的有机溴在土壤有机质中普遍存在，我们推测无机溴化物可能会发生非生物氧化，从而导致土壤有机质的溴化。通过对植物材料和土壤腐殖质进行基于实验室的降解处理，我们发现，在一系列无机氧化剂（包括过氧化氢和各种形式的铁离子）存在的情况下，颗粒有机物会发生非生物溴化，生成脂肪族和芳香族形式的有机溴。橡木和松树凋落物的溴化主要受溴化物浓度限制。新鲜植物材料比腐烂的凋落物和土壤腐殖质更容易发生溴化，这是因为在土壤有机质形成的早期阶段，主要由脂肪族化合物组成的不稳定库会分解。作为颗粒状土壤有机质非生物溴化的首个证据，本研究确定了腐殖质和土壤有机层中天然有机溴的一个机制来源。通过对植物材料进行氧化处理形成有机溴，也为了解土壤有机质中芳香族和脂肪族成分的相对稳定性提供了思路。
