Environmental Geochemistry Laboratory, University of Texas at San Antonio, San Antonio, TX, USA.
Environ Sci Pollut Res Int. 2010 Jun;17(5):1167-73. doi: 10.1007/s11356-009-0281-7. Epub 2010 Jan 23.
BACKGROUND, AIM, AND SCOPE: Organoarsenical-containing animal feeds that promote growth and resistance to parasites are mostly excreted unchanged, ending up in nearby wastewater storage lagoons. Earlier work documented the partial transformation of organoarsenicals, such as, 3-nitro-4-hydroxyphenylarsonic acid (roxarsone) to the more toxic inorganic arsenate [As(V)] and 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA). Unidentified roxarsone metabolites using liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC/ICP-MS) were also inferred from the corresponding As mass balance. Earlier batch experiments in our laboratory suggested the presence of organometallic (Cu) complexes during relevant roxarsone degradation experiments. We hypothesized that organocopper compounds were complexed to roxarsone, mediating its degradation in field-collected swine wastewater samples from storage lagoons. The objective of this study was to investigate the role of organometallic (Cu) complexes during roxarsone degradation under aerobic conditions in swine wastewater suspensions, using electrospray ionization mass spectrometry (ES-MS).
Two swine wastewater samples differing in % solids content and total recoverable Cu concentrations were reacted with 500 ppb of roxarsone under aerobic conditions for 16 days. LC/ICP-MS and ES-MS were used for As speciation analyses, and characterization of metal-organoarsenical complexes in swine wastewater subsamples, respectively.
An organocopper roxarsone metabolite was found only in the high-Cu wastewater sample, suggesting the role of Cu in roxarsone degradation under aerobic conditions. The organocopper metabolite was not found in the low-Cu wastewater sample, because roxarsone did not undergo degradation under aerobic conditions even after 16 days.
Aerobic degradation of organoarsenicals (roxarsone) has not been documented before. Preliminary dataset from this study illustrates the direct and/or indirect association of particulate Cu in catalyzing roxarsone degradation under aerobic conditions in samples with high % solids content.
Concerns regarding the degradation of roxarsone in wastewater to the more toxic inorganic As may be partially linked to the presence of particulate Cu. The presence of Cu in wastewater-suspended particle surfaces has never been coupled before to organoarsenicals degradation reactions, thus, further studies are needed to elucidate the related reaction mechanisms and pathways. Water depth-dependent solid particle distribution profiles in wastewater storage lagoons could provide empirical evidence towards the design of effective degradation practices for nitrophenol-containing compounds, such as, organoarsenical-containing antibiotics, or explosive munitions compounds.
背景、目的和范围：含有有机胂的动物饲料能促进生长和抵抗寄生虫，大部分饲料会以原样排出，进入附近的废水储存池。早期的工作记录了有机胂的部分转化，例如 3-硝基-4-羟基苯胂酸（洛克沙胂）转化为更有毒的无机砷酸盐[As(V)]和 3-氨基-4-羟基苯胂酸（3-AHPAA）。使用液相色谱-电感耦合等离子体质谱（LC/ICP-MS）检测到未识别的洛克沙胂代谢物，这是相应砷质量平衡的推断结果。我们实验室之前的批处理实验表明，在相关的洛克沙胂降解实验中存在有机金属（铜）配合物。我们假设有机铜化合物与洛克沙胂结合，介导其在来自储存池的现场采集的猪废水中降解。本研究的目的是使用电喷雾电离质谱（ES-MS）研究有氧条件下猪废水中洛克沙胂降解过程中有机金属（铜）配合物的作用。
将两份猪废水样品（%固体含量和总可回收铜浓度不同）与 500 ppb 的洛克沙胂在有氧条件下反应 16 天。使用 LC/ICP-MS 和 ES-MS 分别对砷形态分析和猪废水中金属-有机胂配合物进行了特征分析。
仅在高铜废水样品中发现了一种有机铜洛克沙胂代谢物，这表明铜在有氧条件下洛克沙胂降解中的作用。在低铜废水样品中未发现有机铜代谢物，因为即使在 16 天后，洛克沙胂在有氧条件下也未发生降解。
以前没有记录过有机胂（洛克沙胂）的有氧降解。本研究的初步数据集说明了在高固体含量样品中，颗粒状 Cu 的直接和/或间接作用与有氧条件下洛克沙胂的降解有关。对废水降解为更有毒的无机砷的担忧可能部分与颗粒状 Cu 的存在有关。在废水悬浮颗粒表面上 Cu 的存在以前从未与有机胂降解反应联系在一起，因此需要进一步的研究来阐明相关的反应机制和途径。废水储存池中的水深相关固体颗粒分布剖面可以为设计有效的含硝基酚化合物（如含有机胂的抗生素或爆炸弹药化合物）降解实践提供经验证据。
