页岩气压裂返排液的水生生态毒性效应研究

页岩气压裂作业过程产生大量压裂返排液,这类废液富含有毒且致癌的芳香烃、有毒金属和铀、钍、镭等放射性物质、石油类添加剂等,具有可生化性差和难处理的特点。这类废液若不经任何处理就进行排放,将给环境和人群健康带来潜在的危害和风险。目前尚不清楚它们的生态毒性效应。论文从涪陵页岩气开采基地采集了4口开采井(2号井、6号井-1、6号井-2和9号井)的压裂返排液,采用国家废水测试标准分析4种压裂返排液的水质理化指标,采用斜生栅藻(Scenedesmus obliquus)、大型溞(Daphnia magna)等标准毒性试验生物探究压裂返排液污染物体系的水生生态毒性效应,并研究水质理化指标与压裂返排液综合毒性的关系。结果表明,采集的所有压裂返排液样品均具备较大的水生生态毒性效应。以斜生栅藻的96 h的半数效应浓度(96 h-EC_(50))或大型溞的96 h的半数致死浓度(96 h-LC_(50))和毒性单位(TUa)为评价指标进行生态毒性分级,4个位点压裂返排液的生态毒性均为中毒及以上。压裂返排液的重金属、阴阳离子及有机物含量与其综合毒性的相关性结果表明,这些污染物成分与其藻类综合毒性无显著相关性。但Li、V、Cu、Ga、Rb、Ba等6种重金属及Na+、Cl-等2种阴阳离子对压裂返排液的溞类综合毒性有显著影响,影响程度依次为LiGaBaCl-VNa+RbCu。因此,在对压裂返排液进行处理时,这些与毒性相关的污染物是需要重点考虑的化学成分。

Study on the Aquatic Ecological Toxicity of Shale Gas Fracturing Fluids

A lot of fracturing fluids are generated in the process of shale gas fracturing. The fracturing fluids contain toxic and carcinogenic substances such as aromatic hydrocarbon, heavy metals, radioactive substances (U, Th, Ra), petroleum additives, et al, which are poorly biodegradable and difficult to be dealt with. These waste fluids may cause potential hazards and risks to the environment and human health if they are discharged without any treatment. However, there have been few researches about the ecological toxicity of the shale gas fracturing fluids up to now. In this paper, four types of fracturing fluids were collected from No.2 well, No.6-1 well, No.6-2 well and No.9 well in the Fuling Shale Gas Mining Base. The water quality physicochemical indices of these fracturing fluids were analyzed according to the national testing standards of wastewater; meanwhile their aquatic ecological toxicity was investigated by employing the standard toxicity test organisms Scenedesmus obliquus and Daphnia magna. Then the relationship between water quality physicochemical indices and the comprehensive toxicities was studied. The results showed that all the four fracturing fluids presented considerable aquatic ecological toxicity. The ecological toxicity of four fracturing fluids was medium-toxic and even more toxic, using 96 h-EC₅₀ of Scenedesmus obliquus, 96 h-LC₅₀ of Daphnia magna and toxicity units (TUa) as evaluation indexes. There was no significant correlation between the contents of heavy metals, anions, cations, and organic matters and the comprehensive algal toxicities of the fracturing fluids. However, six metals (Li, V, Cu, Ga, Rb, Ba) and Cl^- anion and Na⁺ cation in the fracturing fluids had a significant effect on the comprehensive daphnia toxicities, which followed the pattern Li > Ga > Ba > Cl^- > V > Na⁺ > Rb > Cu. It can be concluded that these chemicals related to the comprehensive toxicities should be considered when treating fracturing fluids.