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自2019年底新型冠状病毒肺炎(COVID-19,简称“新冠肺炎”)疫情暴发以来,许多场所(医院、污水处理厂、市政)均存在含氯消毒剂的大规模、大剂量使用[1-2],例如武汉市仅1个月就投放了1963.58 t消毒药剂[3],其他地区污水处理厂也将氯消毒剂使用量提升到平时的2.5—3.5倍,出现过度消毒现象[1]。大量余氯会与水体的有机物反应形成有害的氯化消毒副产物(DBPs),而后进入自然水体中[4]。其中大多数DBPs具有生物毒性[5-6],可能会对水生生物产生危害。
目前,国内外对于DBPs的风险评估主要侧重于在饮用水中DBPs对人体健康的影响[7-10]。已有研究表明DBPs对细菌[11]、大鼠[12]以及人类[8-9]的生长发育均会有负面影响。卤乙酸(HAAs)作为最常见的DBPs之一[13],存在于饮用水和通过采用次氯酸盐消毒的废水中[8],与三卤甲烷(THMs)相比,HAAs的毒性更高,在环境中存在的时间更长[11]。目前关于HAAs的毒理学研究多集中于鱼类[14-15]和大型溞[16-17],而有关藻类的毒理学研究较少。
藻类作为初级生产者,是水生生态系统的重要组成部分,通过水生食物链之间的能量传递,从而影响整个水生态系统[18],然而,关于DBPs对浮游植物的毒理学研究成果较为缺乏,需要进一步的研究来评估DBPs对水生态环境的影响。本文以我国淡水水域中常见的浮游植物小球藻作为模式生物[18],通过分析污水厂全年加氯消毒后出水的的DBPs检测情况,选择加氯消毒后出水中占比最高的一氯乙酸(CAA)为目标污染物,探究其对小球藻的毒性效应,可以为水环境中CAA的生态风险评估和环境污染控制提供理论支持。
污水厂尾水中消毒副产物对小球藻的生长生理影响
Effects of disinfection by-products in sewage treatment plant effluent on the growth and physiology of Chlorella vulgaris
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摘要: 通过检测无锡某污水厂疫情期间排放尾水中消毒副产物的种类和浓度,发现一氯乙酸(CAA)占全年总检出量的30.22%。采用毒性标准实验方法研究CAA对小球藻生长和抗氧化系统的影响。结果表明在CAA胁迫下,小球藻生长速率减慢,最大光化学量子产量(Fv/Fm)较空白组出现明显下降,96 h叶绿素 a 浓度明显降低。CAA对小球藻的96 h半数效应浓度(EC50)为14.734 mg·L-1。中、低浓度CAA胁迫会诱导超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性和还原型谷胱甘肽(GSH)含量的上升,减少丙二醛(MDA)含量的积累;而高浓度胁迫下,SOD、CAT活性和GSH含量持续下降,MDA含量先升高再下降。Abstract: This study investigated the species and concentration of disinfection by-products in a sewage treatment plant effluent in Wuxi during the COVID-19 pandemic. It was found that chloroacetic acid (CAA) accounted for 30.22% of the total amount of disinfection by-products detected in the whole year. The effects of CAA on the growth and antioxidant system of Chlorella vulgaris were studied via standard toxicity tests. The results showed that upon the exposure of CAA, the growth rate of Chlorella vulgaris was slowed down, the maximum photochemical quantum yield (Fv/Fm) decreased significantly compared to the control group, and the concentration of chlorophyll-a was significantly decreased at 96 h. The EC50 for 96 h-exposure of CAA was found to be 14.734 mg·L-1. The activities of superoxide dismutase (SOD) and catalase (CAT) and the content of reduced glutathione (GSH) were increased while the accumulation of MDA was reduced upon the exposure of medium and low concentrations of CAA. However, high concentration exposure could lead to a decreasing trend in SOD and CAT activities as well as GSH content, while the content of MDA was first increased and then decreased.
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表 1 藻类生长抑制毒性分级标准
Table 1. Toxicity grading standard of algae growth inhibition
96h-EC50/(mg·L−1) <1 1—10 10—100 >100 毒性分级 极高毒 高毒 中毒 低毒 表 2 不同CAA胁迫浓度对小球藻的比生长速率( μ )的影响
Table 2. Growth rate ( μ ) of Chlorella vulgaris under CAA exposure
暴露浓度 Exposure concentration CK 50 μg·L−1 500 μg·L−1 5 mg·L−1 10 mg·L−1 25 mg·L−1 50 mg·L−1 500 mg·L−1 比生长速率(μ)/ d−1 0.54 0.45 0.41 0.35 0.32 0.26 −0.83 −1.08 -
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