Suspected Poison Screening During Shale Gas Production And Toxicity Assessment In Extraction Sites

Objective: As a new type of unconventional natural gas,shale gas energy has the characteristics of large resource potential,long production cycle,long mining life and stable gas production.In the process of shale gas exploitation,especially hydraulic fracturing,a large number of chemicals are used,which not only facilitate energy exploitation,but also bring high risks to human health and ecological environment.In light of the potential environmental problems caused by fracturing fluids during shale gas production,our risk assessment started late,the systematic study of toxic pollutants screening in shale gas exploitation has not been carried out,and the site contamination and health risks caused by shale gas can not be effectively controlled.Based on the poison screening in shale gas extraction sites,this paper evaluates the comprehensive toxicity of polluted media and environmental media samples in shale gas extraction sites by Vibrioqinghaiensis sp.Q67 biological toxicity test,and determine the overall pollution situation.Based on this study,it can provide basic data support for environmental impact assessment and ecological environment restoration in the later stage,and provide scientific basis for environmental governance of shale gas extraction sites.Methods: Based on the actual situation of shale gas extraction sites,the typical toxic pollutants were selected by using Hasse diagram method on the basis of potential hazard index;evaluated the acute toxicity of contaminated media and environmental media samples from shale gas extraction sites by Vibrio-qinghaiensis sp.Q67,and using Q67 time microplate toxicity analysis to evaluate the dynamic changes of environmental water samples at different time nodes.Results: 1.The results showed that,as the results of Hasse diagram method,the toxic pollutants in shale gas extraction sites were determined to be dibutyl phthalate,diethylhexyl phthalate(2-ethylhexyl)ester,phenanthrene,m-cresol.2.The results of Q67 acute toxicity showed that polluted medium produced water in the shale gas extraction site is highly toxic.By comparing the biological toxicity of the water samples from the inlet and outlet of sewage treatment plant,the outlet toxicity was significantly reduced,indicating that the sewage treatment process has a significant effect on reducing the biological toxicity.The water samples in the surrounding rivers need to be concentrated100 times to reach the median lethal dose,so the acute toxic effects in the surrounding basins of shale gas exploitation sites are not obvious.Similarly,most of the soil and sediment around shale gas sites showed low toxicity,which indicates that the overall pollution of shale gas extraction sites is low.3.The results of time microplate toxicity showed that the toxicity of the samples increased with the extension of exposure time,showing a typical time-dependent characteristic.This indicates that changes of toxicity effects over time should be considered when studying acute toxicity.Toxicity results obtained from acute toxicity tests only may be deviated from the real toxicity,the effects of time on toxicity should be considered.Conclusion: 1.The potential toxic pollutants in shale gas exploitation are dibutyl phthalate,di-ethylhexyl phthalate(2-ethylhexyl)ester,phenanthrene,m-cresol.2.The toxicity of the polluted medium produced water is high,and the overall pollution of shale gas extraction sites is low.3.The toxicity of water samples in the surrounding rivers increased with the extension of exposure time,showing a typical time-dependent characteristic.