|Alternative Title||Mechanism exploration of algae-induced endogenous release and in-situ restoration of arsenic in eutrophic lakes|
|Place of Conferral||北京|
|Keyword||水体富营养化，砷污染，纳米气泡，同步辐射，功能基因分析 Eutrophication, Arsenic Pollution, Oxygen Nanobubble, Synchrotron Radiation, Functional Genes Analysis|
砷（As )作为一种可 致畸致癌的 有毒环境污染物，在湖泊生态系统中广泛分布，并通过饮用水和食物链暴露对人体健康和生命安全产生潜在威胁。 近年来，由于外源 营养物质的持续输入，很多 As污染湖泊同时也面临着日益严重的 水体富营养化问题 。富营养化引起“蓝藻水华”频繁爆发，藻细胞腐烂分解“营造”的厌氧 /缺氧 沉积物 -水体微界面 环境是众多污染物质包括 As迁移转化的主要诱因之一。然而，人们对于藻华爆发后期 As在大气 -水体 -沉积物中的迁移转化规律和相关机理缺乏深入认识。另外，尽管厌氧 /缺氧修复是 As污染控制的有效途径之一，目前的修复 手段都面临着难以经济高效地将氧气输送到厌氧 /缺氧区域的技术难题。
1）滇池草海沉积物总 As浓度为 73~285 mg/kg，平均浓度为 161 mg/kg，呈现从北到南逐渐降低的 空间 分布规律。沉积物总 As以铁锰氧化物结态和有机/硫结合态为主，二者约占总 As含量的 70%。地累积指数法评估表明目草海表层沉积物 As污染处于重度污染的水平，富集指数法评估表明人为因素对草沉积物 As污染空间分布影响较强。另外，风险指数编码法和潜在生态风险指数法评估得出，尽管目前草海沉积物 As污染风险较小，但其潜在生态污染风险很强。积物 As释放动力学和释放潜力实验结果也证明了该结论。草海沉积物 As的污染平和潜在生态风险与水体富营养化程度密切相关，因此，系统研究富营养化湖泊 As的生物地球化学循环过程，具有重要的理论和现实意义。
2）富营养化程度的加深显著增加了 As 从污染沉积物向大气和水体释放的
3 ) O2-Ze覆盖能有效 逆转 藻源有机质分解 引起的 沉积物 -水界面厌氧环境 。在其作用下，沉积物 -水界面 形成了 约 1 cm的氧化层，界面附近的 DO浓度从 0升高到 4 mg/L Eh从 -220 mV升高到 150 mV。 与此同时 ，上覆水体的 溶解性总砷 TDAs 浓度 从 23 μg/L显著下降至 世界卫生组织规定的饮用水标准 10 μg/L以下 。 表层沉积物 同步辐射显微 X射线荧光 As和 Fe元素分布结果表明， TDAs浓度的降低主要是由于氧化条件下 大量的 As(Ⅴ)被 铁 氧化物吸附固定在表层沉积物 中 。 另外 O2-Ze作用下 上覆水体的 As(III)转化为 毒性相对较小的
Arsenic(As) is recongnized as a teratogenic and carcinogenic environmental pollutants, who is widespread in the lake ecosystem. It poses a potential threat to human health and life through drinking water and food chain exposure. In recent years, many As-contaminated lakes are suffering with eutrophication due to continutious exogenous nutrients inputs. Excessive production of algal biomass in these eutrophic lakes and the consequent hypoxia/anoxia in the sediment-water interface (SWI) was one of the main inducements of As mobilization and transformation. However, As biogeochemical cycling process and mechanism in eutrophic systems, especially during the last period of algea bloom is still not properly understood. Additionally, although hypoxia/anoxia restoration has been recongnized as an effective strategy for As pollution control, the existing restoration methods are facing with big challenges in efficiently delivering oxygen to the hypoxia/anoxia SWI.
In view of this, this paper firstly evaluated As pollution status and potential ecological risk of shallow sediments in an eutrophic lake—Dianchi Caohai, throngh field sampling survey and risk assessment methods. Sediments in Caohai were then choosed as research objects to investigate As spatial distribution in air-water-sediment during algal biomass decomposition through simulation experiments. Synchrotron radiation XANES technology, microbial functional genes (aioA, arrA, arsC and arsM) analysis and various chemical analysis methods were used to further reveal the mechanism of As mobilization and transformation in eutrophic lakes. Finally, oxygen-nanobubble modified zeolite (O2-Ze) was prepared and capped in hypoxia/anoxia SWI to study their effects on hypoxia/anoxia restoration and As release control, in order to provide a new insight into hypoxia/anoxia restoration and pollutants release control in relevant eutrophic waters. The main results and conclusions are as follow:
1) The total As concentration in shallow sediments of Caohai was 73~285 mg/kg, with an average concentration of 161 mg/kg, and As levels decreased gradually from north to south. Fe-Mn oxides fraction and organic/ sulphide fraction were the major As fractions, accounting for about 70% of the total As level in shallow sediments. The analysis of geoaccumulation index indicated that As pollution in Caohai was at the severe pollution level, and the analysis of accumulation index indicated that anthropogenic factors had a slight heavy influence on the spatial distribution of As pollution. Moreover, the analyses of potential ecological risk index and RAC risk index indicated that, although the current As pollution risk was low, the potential ecological pollution risk was very strong for sediments in Caohai. This conclusion was supported by experimental results from both the As release kinetics and release potential of the sediments. Arsenic pollution levels of surface sediments and their potential ecological risk were closely related to the lake eutrophication status. Therefore, studies involving As biogeochemical cycle in eutrophic lakes are of theoretical and realistic significance.
2) Severe eutrophication enhanced environmental risks of As by accelerating As release from sediments to both lake water and atmosphere. The maximum As levels in the overlying water and atmosphere during black bloom eruption (HAD groups) were 4 and 8 times higher than those in Control. During decomposition of the algal biomass, As reduction and methylation was observed in the overlying water and shallow sediments, this process was closely related to the inhibited As oxidative metabolism and enhanced As reductive and methylated metabolism of the indigenous microorganism. Fortunately, the produced NOM- and S- enriched sediments can mitigate the As pollution risks on a certain extent through the formation of As2S3 (43%-51%) and As(III)-Fe-NOM (28%-35%), based on the analysis of As, Fe and S k-edge XANES results. Therefore, this paper highlighted the great significance of long-term and in situ monitoring of As level in atmosphere and water in eutrophic waters.
3) Capping with O2-Ze can effectively reversed the anaerobic SWI induced by algae biomass decomposition. Oxygen-locking surface sediment layer ~1 cm was formed after capping with O2-Ze, near which the dissolve oxygen level increased from nearly 0 to 4 mg/L and redox potential values increased from -220 mV to 150 mV over the experimental period. The TDAs concentration in the overlying water decreased from 23 μg/L to below the WHO standard for drinking water (10 μg/L), owing to As sequestration by Fe-(hydr)oxides in solid phases under oxidizing condition, based on the analysis of Fe and As distribution in shallow sediments by SR-μXRF method. Moreover, the released As(Ⅲ) in the Control was transferred to As(Ⅴ) (75%) and methylated As (15%) with relatively lower toxicity in the overlying water. The As(III) methylation was induced by methylated metabolism of the indigenous microorganism. The As(III) oxidation was not only resulted from the enhanced As oxidative metabolism of indigenous microorganism, but also resulted from oxidation by •OH, who was formed during the oxidation of reduced iron and dissolve organic matter under oxygenation. Therefore, this paper provided a new insight into hypoxia/anoxia restoration and pollutants release control in eutrophic waters.
|唐颖. 藻源有机质诱发湖泊砷內源释放及其原位修复机理研究[D]. 北京. 中国科学院生态环境研究中心,2018.|
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