Biocides are chemicals that are added to hydraulic fracturing fluid to kill bacteria that can corrode well casings, reduce efficiency of oil and gas extraction, and produce (highly toxic) hydrogen sulfide gas. University researchers haves completed "the most comprehensive review to date of the environmental fate and toxicity of the biocides most commonly used in hydraulic fracturing fluids" and found that they are "largely unknown."
Biocides in Hydraulic Fracturing Fluids: A Critical Review of Their Usage, Mobility, Degradation, and Toxicity was published in the journal Environmental Science & Technology. According to a University of Colorado press release, the review of "more than 200 research papers, studies, and other literature" found that:
- [L]ittle is known about what happens to these biocides if they are accidentally spilled on agricultural soil, enter surface or groundwater, or are exposed to the high temperature and pressure conditions in well boreholes...
Additional research is surely needed. As is a drive to waterless, chemical-free fracking. Industry innovation can get us there; for example, according to this publicity piece (caveat emptor), new technologies are being developed to replace water and chemicals for enhanced oil recovery from existing wells. That innovation can be driven by better accounting and coupled with next-gen regulations to get us there faster.
- None of the 16 major biocides used in hydraulic fracturing are specific to the oil and natural gas industry. All of them are used in other industrial processes and/or commercial products...
- Of the 16 major biocides used in fracking, nine have been reported to have chronic toxicity effects (such as developmental, reproductive, mutagenic, carcinogenic, or neurological effects). Of the seven that have not shown any evidence of chronic toxicity, three may transform into intermediate products with toxic potential.
- Based on currently available data, surface spills appear to be the most likely cause for environmental contamination by fracking fluids...
- If inadvertently released into the environment, some biocides will primarily contaminate water and will thus be more mobile but also break down faster. Others will stick to soil and be less mobile and thus take longer to break down.
- Many biocides degrade naturally in the environment, but some may transform into more toxic or persistent compounds.
- Hardly anything is known about transformation, sorption and transport of fracking chemicals once injected into these deep formations, which have high temperature, pressure, salt and organic matter concentrations. Consequently, little is known about the type and toxicity of the compounds that return to the surface with produced/flowback water. More research is critically needed to understand these processes.
- Several biocide alternatives exist but are rarely used because of higher costs and high energy demands or potential formation of toxic disinfection byproducts such as chloroform.
- Environmental and human health risks associated with the use and disposal of hydraulic fracturing fluids are not well understood due to lack of research.