Abstract
There is public and scientific concern about air, soil and water contamination and possible adverse environmental and human health effects as a result of hydraulic fracturing activities. The use of greener chemicals in fracturing fluid aims to mitigate these effects.This study compares fracturing fluids marketed as either ‘conventional’ or ‘green’, as assessed by their chemical composition and their toxicity in bioassays. Chemical composition was analysed via non-target screening using liquid chromatography - high resolution mass spectrometry, while toxicity was evaluated by the Ames fluctuation test to assess mutagenicity and CALUX reporter gene assays to determine specific toxicity.Overall, the results do not indicate that the ‘green’ fluids are less harmful than the ‘conventional’ ones. First, there is no clear indication that the selected green fluids contain chemicals present at lower concentrations than the selected conventional fluids. Second, the predicted environmental fate of the identified compounds does not seem to be clearly distinct between the ‘green’ and ‘conventional’ fluids, based on the available data for the top five chemicals based on signal intensity that were tentatively identified. Furthermore, Ames fluctuation test results indicate that the green fluids have a similar genotoxic potential than the conventional fluids. Results of the CALUX reporter gene assays add to the evidence that there is no clear difference between the green and conventional fluids.These results do not support the claim that currently available and tested green-labeled fracturing fluids are environmentally more friendly alternatives to conventional fracturing fluids.
Highlights
Chemical composition was analysed via non-target screening using liquid chromatography - high resolution mass spectrometry, while toxicity was evaluated by the Ames fluctuation test to assess mutagenicity and CALUX reporter gene assays to determine specific toxicity
All controls and fracturing samples or their water accommodated fraction (WAF) were analysed for their chemical composition using liquid chromatography-high resolution mass spectrometry (LC-HRMS) suspect screening and non-target screening (Sjerps et al, 2016; Hollender et al, 2017), and for their toxicity as assessed with a selection of in vitro bioassays
The results show that the environmental fate parameters do not strongly differ between the green and conventional products, based on available data for a selection of the top five chemicals that were identifiable to a confidence level of at least 3
Summary
There is public and scientific concern about air, soil and water contamination and possible adverse environmental and human health effects as a result of hydraulic fracturing activities. Results of the CALUX reporter gene assays add to the evidence that there is no clear difference between the green and conventional fluids. Hydraulic fracturing is a well stimulation technique which is used for oil and gas production from relatively impermeable rock formations, such as shale, sandstone or limestone. During this process fracturing fluid, made up of water (~90%), proppants such as sand (~9%), and chemical additives (~1%), is injected into the targeted earth formations (Vidic et al, 2013). Chemical additives are used in relatively low concentrations in the fracturing fluid, due to the large total volumes of fluid needed during a hydraulic fracturing event total loads to the environment can still be high
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