Study on the abiotic halogenation of dissolved organic matter in aqueous environment by using Fourier transform ion cyclotron resonance mass spectrometry

天然卤代有机物（OHCs）是卤素在环境中的重要存在形态，并对卤素在全球地球化学的循环中起着重要作用。近年来，随着分析技术的不断进步和相关科学的不断发展，越来越多的天然OHCs在环境中被发现，由于部分OHCs具有强毒性，引起了人们的广泛重视。但是，目前在环境中识别的天然OHCs主要来源于生物途径，而对非生物来源的天然OHCs研究较少。 环境中广泛存在的溶解性有机质（DOM）的非生物卤化被认为是天然OHCs最重要而广谱的非生物来源。由于DOM的高度复杂性和异质性，其卤化产物的组成和结构也必然极其复杂。因此，研究 DOM在环境中的非生物卤化并从分子水平上分析产物的组成和分布具有重要的环境学意义。本论文利用傅里叶变换离子回旋共振质谱（FT-ICR MS）分析研究了光照，以及Fe(II)/Fe(III)、二氧化锰（δ-MnO2）和纳米二氧化钛（TiO2 NPs）共存条件下DOM的溴化和碘化产物的数量、分子组成和分布，并探讨了其可能的分子反应机制，主要包括以下四个部分： (1）以富里酸（SRFA）和天然有机质（NOM）作为研究对象，研究了DOM在模拟和自然光照条件下的光化学碘化，并利用 FT-ICR MS从分子水平上分析了其产物组成和分布。结果发现：DOM在水体中的光化学碘化容易发生，光照7d后检测到了大量的碘化有机物（OICs）。由于海水中存在的大量ClDOM的碘化反应，海水中生成的OICs比淡水中多。I的浓度对OICs的生成也有重要影响，10 μmol L条件下生成的OICs数量是1 μmol L的3−6倍。自然光由于具有更强的光强以及含有更多的紫外线成分，容易导致生成 OICs的降解。生成的 OICs主要以一碘化合物（OICs-I）为主，多为富含羧基的酚类或者多酚类物质，通过取代反应（SR）和加成反应（AR）生成，分子质量在 200−600Da之间，包含-CH2、-C2H2O、-C2H4O等多种同系物。 （2）研究了DOM在含Fe(II)/Fe(III)的水体中的光化学溴化和碘化，利用FT-ICR MS从分子水平上分析了其组成和分布。结果表明，在pH 4.0的条件下，初始浓度为 5μmol L-1I-的 Fe(II)和 Fe(III)能够促进 DOM的光化学溴化，经光照 4d后可分别检测到 158种和 122种溴化有机物（OBCs）。OBCs主要通过 SR和AR之外的其他反应（SAOR）和 SR生成，主要属于高度不饱和类、酚类和脂质类物质。与 DOM的溴化相比，Fe(II)和 Fe(III)能够更显著地促进 DOM的碘化，在 pH 4.0、5.0和 6.0的水体中都检测到了大量的 OICs，产物主要是一碘化合物（OICs-I）。不含 Fe(II)/Fe(III)的水体中可检测到 OICs的生成，但远少于对应的含铁水体中生成的 OICs，且随着 pH的升高而减少。OICs主要通过 SR和 AR生成，属于木质素和单宁酸类物质，含有较多的酚羟基和羧基。 （3）研究了水环境中普遍存在的δ-MnO2颗粒对 DOM碘化的作用，基于FT-ICR MS技术分析了碘化产物分子的组成和分布。结果表明，在0.01g L -1 δ-MnO2和不同 pH条件下反应 24 h后，当 I-浓度为 0.2 μmol L-1时，只在 pH 5.5时可检测到 OICs（58种）；当 I-浓度为1 μmol L-1时，在 pH 5.5和 7.0反应条件下分别检测出了 321种和 20种 OICs。，当I-浓度为 0.2 μmol L-1 111种和 15种 OICs；当 I-浓度为1 μmol L-1的反应条件下，分别检测到了 563种、263种和 127种 OICs。OICs主要以 OICs-I为主，属于不饱和度高的多酚类和酚类物质，主要通过 SR和 AR生成。与其它体系中生成的 OICs类似，OICs的分子质量主要分布于 300−600 Da，包含-CH2、-C2H2O、-C2H4O等多种同系物。以上结果说明：水体 pH、I和 δ-MnO2浓度能显著影响 DOM的碘化。本研究结果可为暗环境中碘代有机物的来源研究提供参考。 （4）研究了人工纳米材料 TiO2 NPs对 DOM光化学溴化和碘化的影响，并利用 FT-ICR MS从分子水平上分析了其产物组成和分布。结果表明，TiO2 NPs在光照下能够显著促进 DOM的溴化和碘化。OBCs和 OICs的生成和 TiO2 NPs的浓度有关，含有 1 mg L TiO2 NPs的淡水水体反应 24 h后，没能检测到 OBCs-1和 OIC的生成，但在海水中检测到 236种 OBCs和 346种 OICs，说明海水中的参与了 DOM的光化学卤化过程。高浓度的 TiO2 NPs（10 mg L淡水和海水中 OBCs和 OICs的生成，反应 24 h后分别在淡水中检测到 607种OBCs和 169种 OICs，在海水中检测到 623种 OBCs和 247种 OICs。OBCs主要以 OBCs-Br为主，所占比例约为（54.7%−99.6%），高浓度 TiO2 NPs条件下也有大量的OBCs-2Br生成。OBCs含有的元素以 C、H、O和 Br为主（40.4%−69.9%），部分物质也含有 S（16.9%−55.4%）；OICs主要以 OICs-I为主（88.1%−99.8%），所含元素绝大多数为 C、H、O和 I（82.4%−99.4%）。TiO2 NPs存在下，海水与淡水中生成的 OBCs的组成有着明显差异。海水中生成的 OBCs主要属于酚类和高度不饱和类物质，淡水中生成的 OBCs主要属于酚类和高度不饱和类物质，这种差异可能与海水中 TiO2 NPs吸附的组分以及海水的高盐不利于脂肪类物质的溶解有关；但是两种水体中 OICs的组成和分布基本相同。水体中 OBCs主要通过 SAOR和 SR生成，OICs主要是通过 SR和 AR生成。OBCs和 OICs的分子质量主要分布在 300−600 Da，包含-CH2、-C2H2O、-C2H4O等多种同系物，并富含-COOH，-OH和-CO-等多种官能团。本研究结果可为 TiO2 NPs环境效应的评价提供参考。Naturally occurring organohalogen compounds (OHCs) is a class of substances in natural environments that makes an important contribution to the biogeochemical cycle of halogen. Recently, an increasing number of OHCs were found in natural environments with the continuous improvement of analytical technologies and development of the relevant disciplines. As many OHCs were regard as highly toxic chemicals, OHCs has attracted wide public concerns. However, the currently identified OHCs were mainly formed through biotic pathway, and only a few studies focus on the OHCs produced through abiotic pathway. A variety of natural OHCs may stem from the non-biological halogenation of dissolved organic matter (DOM), and the composition and structure of the halogenated products should be very complex due to the tremendous complexity and heterogeneity of DOM. Therefore, it is of great importance to study on the OHCs from non-biological halogenation of DOM, and analyze the compositon and distribution of halogenated products at molecule level. This dissertation focuses on the non-bioligcal bromination and iodination of DOM by using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) under sunlight irradiation, and in the presence of Fe(II)/Fe(III), manganese oxide (δ-MnO2) and engineered titanium dioxide nanoparticals (TiO2 NPs). The number, molecular composition and distribution of brominated and iodinated products has been investigated, and molecular mechanism of halogenation processes has been discussed. The following four parts are included in the dissertation: First, Suwannee River fulvicacid (SRFA) and natural organic matter (SRNOM) were selected as model DOM to explore the DOM photoiodinaion under the simulated and natural sunlight irradiation, and FT-ICR MS was used to analyze the composition and distribution of halogneated products. The results showed that DOM photoiodination was favorable. After 7 d of irradiation, many orgnoiodine compounds (OICs) were identified. Due to the high level of chloride ion, the OICs formed in seawater were more than in freshwater. The concentration of iodide has significant effects on the formation of OICs, as the OICs produced at 10 μmol L iodide were 3−6 times more than at 10 μmol L-1iodide. The natural sunlight can lead to the photodegradation of the newly formed OICs largely because of the strong light intensity and more UV radiation of solarlight. The formed OICs primarily contained one iodine atom (OICs-I), and were typical of polyphenol, phenolic and highly unsaturated compounds with carboxylic-rich groups. The OICs formed mainy through substitution reacation (SR) and addition reaction (AR), and were composed of multitudinous -CH2, -C2H2O and -C2H4O homologous series. Secondly, DOM photobromination and photoiodination were studied in the presence of Fe(II)/Fe(III) by using FT-ICR MS. The results showed that DOM could be photobrominated only in the presence of Fe(II) or Fe(III) with the initial concentrations of 5 μmol L-1 at pH 4.0, and 158 and 122 OBCs were identifed after 4 d of light irradiation. The newly formed OBCs were mainly phenolic, highly unsaturated-like and aliphatic compounds, and the primary formation pathway were SR and AR but accompanied with other reactions (SAOR) and SR. Unlike the DOM photobromination, Fe(II) and Fe(III) played a more significant role in enhancing the photoiodination of DOM with a large number of OICs detected at pH 4.0, 5.0 and 6.0. The primary components were OICs-I. OICs were also detected in the absence of Fe(II) and Fe(III), and the number of OICs decreased with the increase of pH. OICs were mainly produced via SR and AR, and typical lignin-like and tannin-like compounds with a great number of carboxylic and phenolic groups. Thirdly, the role of δ-MnO2, which extensively exists in water environments, on the DOM photoiodination has been investigated, and the molecular composition and distribution of OICs was analyzed using FT-ICR MS. The results showed that at a concentration of 0.01 g L detected at pH 5.5 in the presence of 0.2 μmol L detected at pH 5.5 and 7.0, respectively, in the presence of 1 μmol L concentration of 0.1 g L δ-MnO2 and a reaction time of 24 h, 111 and 15 OICs were identified at pH 5.5 and 7.0 in the presence of 0.2 μmol L , while 563, 263 and 127 OICs were measured in the presence of 1 μmol L -1 . Like the OICs formed in other δ-MnO2 and a reaction time of 24 h, OICs could only be, and 321 and 20 OICs were . At a systems, the vast majority of OICs were OICs-I, and typical of highly unsaturated polyphenol, phenolic and highly unsaturated compounds. The OICs had a mass range of 200−700 Da, and several -CH2, -C2H2O and -C2H4O homologous series were revealed. These results suggested that water pH, the concentration of I and δ-MnO2 can greatly influenced the DOM iodination. Our results evidenced the source of OICs in the dark environments. Finally, DOM photobromination and photoiodination induced by manufactured nanomaterial TiO2 NPs were explored using FT-ICR MS. We found that, TiO2 NPs can significantly promote DOM photohalogenation. The number of formed organohologenated products were associated with the concentration of TiO2 NPs. Specifically, in the presence of 1 mg L TiO2 NPs and after 24 h of light irradiation, no OBCs and OICs were detected in freshwater, while 236 OBCs and 346 OICs were measured in seawater, in which the high level of chloride in seawater might contributed to the photohalogenation. The number of OBCs and OICs increased in the presence of 10 mg L TiO2 NPs in both freshwater and seawater. After 24-h photocatalical halogenation of DOM, 607 OBCs and 169 OICs were found in freshwater, and 623 OBCs and 247 OICs were found in seawater. The composition and distribution of OBCs were quite different from OICs. OBCs were primarily one-bromine-containing compounds(OBCs-Br,54.7%−99.6%),and many TiO2 two-bromine-containing compounds were identified in the presence of 10 mg L-1 NPs. The majority of OBCs consisted of four elements including C, H, O and Br (40.4%−69.9%), while some OBCs contained S (16.9%−55.4%). OICs were mainly OICs-I (88.1%−99.8%) and primarily composed of C, H, O and I (82.4%−99.4%). The OBCs formed in freshwater and seawater in the presence of TiO2 NPs showed remarkable differences in their composition and distribution. OBCs produced in freshwater were typical of phenolic and highly unsaturated compounds, while in seawater were typical of phenolic and highly unsaturated, and aliphatic compounds. However, the OICs formed in freshwater and seawater were both phenolic and highly unsaturated-like compounds. The OBCs were formed mainly through SAOR and SR, while OICs mainly through SR and AR. Both OBCs and OICs were molecules in the mass range of 200−700 Da, and composed of multitudinous -CH2, -C2H2O and -C2H4O homologous series with a great number of carboxylic, phenolic and ketone groups. The results of this study may offer a reference to the assessment of environmental effects of TiO2 NPs