【作者】 楼涛；

【导师】 陈国华； 谢会祥；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2005， 博士

【摘要】 本研究采用有代表性的溶解有机物（DOM）和天然河水样品,如国际标准的Suwannee河（美国）提取的腐植酸（SRHA）和黄腐酸（SRFA）、土壤腐植酸（德国）（FSHA）、Rimouski河水黄腐酸（加拿大魁北克省）（RRFA）和天然河水（Saguenay河,加拿大魁北克省）（SFW）的样品,研究和讨论了DOM在不同溶解氧浓度、总铁浓度以及不同的入射光波长条件下,模拟太阳光照射过程中溶解氧浓度、溶液pH、紫外可见吸收的变化和溶解无机碳（DIC）的产量;更重要的是定量测量了溶解有机物在各种光照条件下分子量及其分布的变化。另外,研究和讨论了溶解有机物在以上各种照射条件下对两种代表性的环境污染物（苯并芘和五氯苯酚）结合系数Koc的影响,并讨论了光化过程中溶液pH、溶解有机物分子量、芳环含量变化与结合系数Koc之间的相关关系。 研究结果表明,溶解有机物的光化学氧化过程受溶解氧浓度、总铁浓度和入射光波段范围的影响。溶解氧浓度的增加能够加速DOM的氧化,造成溶解氧消耗增加。UV-A+可见光的氧气消耗速率为全波长照射下的61±25%（4种DOM的平均值）,而可见光只有其20±19%（4种DOM的平均值）。加入甲磺酰基脱铁氧胺（deferoxamine mesylate, DFOM）有效地降低了SRHA的氧气消耗速率,约为20%（72小时照射数据）;总铁10μM条件下的照射,SFW、SRFA和FSHA使氧气消耗速率分别增加了22%,94%和45%。铁的浓度增加,并在溶液中含有足够的溶解氧的条件下,能加速光氧化过程。时间系列的各种照射表明,溶解氧随照射时间呈良好的指数下降关系。同样溶解氧浓度的增加能够加速pH的下降。SRHA、SRFA、FSHA在氮气饱和下照射72小时后,其pH上升约为0.1个单位（起始pH为5.0）。SFW在起始pH为8.18的氮气饱和条件下照射使其pH下降至7.18。UV部分对pH的下降起重要的作用。铁浓度的增加其pH的下降和氧气饱和条件下的照射非常接近。但在氧气浓度较低的情况下,其pH值有所升高,与氮气饱和条件下照射相似。溶解有机物经光照后,其紫外和可见光吸收都下降。时间系列的各种照射表明,紫外吸收a₃₂₀随照射时间呈良好的指数下降关系。 在同一个条件下照射,有足够的溶解氧的存在下,溶解无机碳（DIC）的生更多还原

【Abstract】 In this study, we investigated kinetics of O₂ consumption, pH changes, photobleaching, and more importantly, MW and distribution changes under simulated solar irradiation in different O₂ and Fe levels and the wavelength of incident light of the DOMs prepared from a German soil humic acid, Suwannee River humic and fulvic acids, and natural water from the Saguenay Fjord in Quebec, Canada. For the first time the impact of photo-oxidation of DOM on its affinity for binding organic pollutants （two model compounds, benzo（a）pyrene （BaP） and pentachlorophenol （PCP）） were investigated using above DOM samples plus Rimouski river fulvic acid. We also examined the effects of O₂ abundance and the wavelength of incident light on photo-alteration of bingding coefficient (K_oc) and discussed the effects of pH, molecular weight and aromaticity of DOM on K_oc.In generally, high dissolved oxygen and total iron concentration can accelerate the photooxidation of DOM and caused rapid decreases in the dissolved oxygen, absorptivity and pH. Adding 20 nM DFOM in SRHA decreased the oxygen consumption rate by 20%, while adding FeCl₃ to reach total 10 μ M iron accelerated the oxygen consumption rate by 22%, 94%, 45% for SFW, SRFA, FSHA respectively. The oxygen consumption of UV-A plus visible or only visible light irradiations were 61 ±25% and 20 ± 19% of that of full spectrum. The pH of SRHA, SRFA and FSHA increased 0.1 unit after 72-h N₂-saturated irradiations （initial pH5.0）, while SFW decreased to 7.18 from initial 8.18. UV-irradiation is the key factor to cause pH decreases during irradiation. Both dissolved oxygen and a₃₂₀ were found a good exponential correlation in the course of irradiation under different conditions.The production of DIC were linear with irradiation time and were found the quickest in the O₂-saturated and total Fe 10 μ M irradiations, followed by air-saturated,UV-A+visible and visible irradiations.MW decreased continuously in time-series irradiations in most cases, and found a well inversely correlated with E2/E3. Wavelength dependence irradiation showed that the each part of light region, UV-A, UV-B, and visible, played an important role to reduce the MW, their contributions were 32.2±19.4%, 31.4±23.2% and 36.5±10.6% respectively. Addition of Fe increased the initial MW of DOM, but also can accelerated MW decrease combined with dissolved O2; while addition of DFOM retarded the MW decline rate. The polydispersity also decreased during irradiations and the decrease well matched the decrease extent of MW.Solar-simulated irradiations substantially decreased the BaP and PCP binding affinity to DOM. After 24-h irradiations, KBap decreased 33%, 33%, 23%, 14 % for SFW, SRFA, SRHA, and FSHA respectively, RRFA incresed 6%; KPCP decrased 48% and 39% for SRHA and FSHA respectively. The decreases of KoC （corrected for photo-induced pH changes） were positively correlated with the decreases of the molecular weight and aromaticity of DOM in the time-course of irradiation. The binding capacity, R, defined as KoC * [DOC], is more useful to evaluate the relative importance of DOC loss and structural change of DOM. The contribution of ARdoc to AR was generally lower but significant compared to the contribution of ARk. Decreases in pH due to photo-production of acidic products often partly offset the reduction of the binding affinity （7%） caused by direct photo-alteration of DOM’s chemical structure, suggesting that the binding affinity of DOM in natural waters with high acid-neutralizing capacity is expected to be more severely affected than in natural waters with low acid-neutralizing capacity. Increasing O2 abundance accelerated the decreases of the binding affinities as a result of enhanced photo-degradation of DOM. Over a 72-h exposure period, full-spectrum irradiation reduced Kb3p of SRHA, among which UV-B （i.e. full spectrum minus （UV-A plus visible）） contributed 7%, UV-A （i.e. （UV-A plus visible） minus visible） 42% and visible 51%. UV-B, UV-A and visible wavelengths accounted for 8%, 38% and 54%, respectively, of the reduction of BaP binding by SRFA. For the decrease of Kpcp in SRHA, the relative contribution in ascending order was UV-B （18%）, visible （35%）,and UV-A （47%）. Visible light played a more important role in reducing the molecular weight and aromaticity of DOM （and hence its binding affinities） than in reducing the content of dissolved organic carbon （DOC） while vice versa for UV radiation, indicating that photochemical reduction of the binding affinities may occur in natural waters at depths deeper than UV radiation can reach.The decreases of the capacities of DOM for binding BaP and PCP, resulting from a combination of photo-remineralization （DOC loss） and photo-alteration of DOM’s chemical characteristics, will increase the freely dissolved fractions of the two compounds and thus their availability and toxicity to aquatic organisms. The results from this study may have similar implications for organic pollutants other than BaP and PCP.更多还原