Toxic effect of fracturing flow-back fluid on Vibrio fischeri, Daphnia, and specific industry microorganisms Aspergillus niger and S. cerevisiae.

Previous studies have shown that the soil microbial population and soil enzyme activity are seriously affected by fracturing flow-back fluid (FFBF) from the shale gas mining process. However, the toxic effect of FFBF on specific bacteria, fungi, and plankton has not been systematically confirmed in detail. In this paper, a toxic effect evaluation of FFBF was conducted using the representative toxicity test organisms Vibrio fischeri, Daphnia, Aspergillus niger, and S. cerevisiae, indicating that FFBF can significantly decrease the survival rate of these species. The results also showed that there was a significant negative correlation between the concentration of some inorganic toxicity factors and the survival rate when Daphnia was used as the test organism, indicating that the toxicity degree order for these inorganic toxicity factors is Ba > Li > As > Cl > Cu > Rb > Ga > V > Na. In addition, other toxic factors, including polycyclic aromatic hydrocarbons (PAHs), were also determined, and the order of toxic effects with a negative correlation to the Daphnia survival rate was confirmed. These results showed that the biological toxicity of FFBF was caused not only by inorganic toxicity factors such as heavy metals but also by organic compounds such as PAHs. The results not only provide a significant reference value for the systematic assessment of biological toxicity by FFBF, but they also have great significance for developing approaches to appropriate FFBF treatment.