Extracting fossil fuels from underground reservoirs requires so much water a Chevron scientist once referred to its operations in California’s Kern River Oilfield “as a water company that skims oil.”

Fracking operations use roughly 1.5 million to 16 million gallons per well to release oil and gas from shale, according to the U.S. Geological Survey. All that water returns to the surface as wastewater called flowback and produced water, or FPW, contaminated by a complex jumble of hazardous substances in fluids injected to enhance production, salts, metals and other harmful elements once sequestered deep underground, along with their toxic breakdown products. 

Concerns that spills could damage sensitive ecosystems skyrocketed with the rapid expansion of fracking across the United States and Canada almost two decades ago, as technological advances allowed energy companies to exploit previously inaccessible shale oil and gas reserves. 

Those concerns are well founded, new research shows. Exposing animals that play a critical role in freshwater food webs to diluted samples of flowback and produced water from fracked wells causes lasting harm, scientists reported earlier this month in the peer-reviewed journal Environmental Science & Technology. 

The researchers investigated FPW’s effects on Daphnia magna, small crustaceans commonly called water fleas, that are the go-to lab organism for studying toxicity in aquatic ecosystems. They obtained the wastewater from a fracked well in the Montney formation, a vast reservoir of unconventional gas and oil that spans the border of British Columbia and Alberta in western Canada.

It’s well known that flowback and produced water harms many different aquatic species. Less clear is whether keystone species like water fleas, the primary link between plants and fish and other animals higher in the food chain, can bounce back after a transient exposure, as might occur during a spill.

No single U.S. agency collects oil spill data. But a 2017 study of four states found that up to 16 percent of fracked wells reported a spill each year between 2005 and 2014, totalling more than 6,600 spills. In Alberta, an estimated 2,500-plus spills of flowback and produced water occurred from 2005 to 2012, Tamzin Blewett, an ecotoxicologist at the University of Alberta and her colleagues reported in a 2020 review. More than 113 of those spills entered freshwater lakes and streams.

“With this experiment, we were trying to see if recovery was possible after an acute spill,” said Blewett, a senior author on the ES&T study. “We wanted to see how fracked fluids would affect reproduction and life span compared to controls, which had never been exposed.”

The scientists exposed water fleas to two different dilutions of fracked wastewater for 48 hours, simulating what the animals might encounter downstream of a spill, using untainted water as a control. They transferred the fleas to clean water for the remaining 19 days of the experiment, tracking their ability to grow, mature and reproduce.

The water fleas did not fare well. Close to 70 percent died in the more concentrated wastewater and half died in the less concentrated sample, with most of the deaths occurring after just five days. Those that survived took longer to mature and produced up to fivefold fewer offspring.

Blewett’s group had exposed the animals to fracking wastewater for 21 days in a previous study. With the new study, she said, “We saw that it didn’t matter if you were exposed for 21 days or 48 hours. Even a small, short-term exposure can have long-lasting effects.”

Daphnia is a popular study organism for ecotoxicologists because what happens in the lab has real-world implications.

“Daphnia live in freshwater bodies across a large part of the planet,” said Aaron Boyd, a Ph.D. candidate at the University of Alberta who led the study. “They’re actually in environments that we’re concerned about.”

Anything that imperils these water fleas in the environment could trigger detrimental effects that ripple through the ecosystem. Daphnia feed on algae and other tiny organisms, and are in turn food for larger organisms like fish. Even if a contaminant doesn’t directly affect fish, it can harm them by wiping out their main food source.

The Daphnia that survived were not in the best condition, Boyd said. That means fleas exposed to this wastewater in the environment are likely to be less resilient in the face of additional stressors like, say, a drought or another spill. “There are just so many factors to consider and we can’t test all of these things at once,” he said. “There are a lot of questions left to be answered.”

Boyd and Blewett investigated what the wastewater was doing to the fleas at a molecular level, by analyzing how it changed their protein levels. They saw that the wastewater basically shut down their metabolism. It shifts all the animals’ energy toward coping with this toxic assault until they have no energy left for living, Blewett said.

The results fall in line with the evidence that salts, a major constituent of flowback and produced water, can harm and kill Daphnia, said Sally Entrekin, an aquatic ecologist at Virginia Tech who was not involved in the study. 

“What is exciting about this study,” Entrekin said, “is seeing the differences across concentrations in the flowback water and the persistent effects on the Daphnia through reproduction that can be linked to their individual physiology.” 

Chemical surfactants, or surface-active agents, in the wastewater seem to immobilize the animals, which can’t break the surface tension of the water and get stuck, Blewett said. “What that’s going to do is dry them out, so they’re as good as dead.”

Surfactants, one of scores of different chemicals added to wells, help release hydrocarbons trapped in rocks. They may be primarily responsible for harming the fleas, given their inability to move. But salts are also quite toxic to freshwater organisms, and there are so many noxious substances in the wastewater, including some the researchers haven’t been able to identify, it’s hard to settle on one culprit.

Blewett is careful to note that the toxicity of flowback and produced water varies considerably from well to well. “But this particular well that we were using is pretty aggressive in terms of its toxicity,” she said.

A Growing Threat

Produced water is the largest wastestream of oil and gas extraction, whether companies deploy traditional methods like the steam flooding favored in Kern County, California, or unconventional methods like fracking of horizontal wells that extend 10,000 feet to reach hydrocarbons embedded in shale.

For years, scientists thought fracking used less water and produced less wastewater than conventional drilling techniques. But water used per fracked well jumped 770 percent between 2011 and 2016, as developers drilled longer horizontal wells, a 2017 study found. The amount of wastewater a well produced in its first year of operation increased by nearly seven times over that period. 

Eight U.S. states generated more than a billion barrels of wastewater from both conventional and unconventional wells in 2021, the latest figures show, with California surpassing 3 billion barrels and Texas leading the pack with more than 8 billion barrels.

In the Canadian Montney formation, the source of Boyd and Blewett’s FPW samples, fracking generates on average close to 160,000 barrels of wastewater each drilling stage in a well, or about 6.6 million gallons.

The composition and toxicity of that wastewater varies with the fluids operators inject into a well and the geology of the formation, which typically contains salts, metals, radioactive elements and toxic compounds like arsenic. 

Most states do not require companies to disclose what chemicals they inject into wells. That leaves scientists scrambling to figure out the best way to remediate a spill.

The type of analysis Blewett’s team did would not be possible in the field, Entrekin said. “It’s critical and valuable information for future field assessments that try to piece together relationships after an accident.”

The study’s FPW samples included compounds called polycyclic aromatic hydrocarbons, or PAHs, including most of the 16 that the Environmental Protection Agency has classified as “priority pollutants,” based on their toxicity and potential for human exposure among other factors. 

Nine of these priority pollutants were flagged by California water regulators as chemicals used in conventionally drilled wells that supply wastewater to grow crops in Kern County. Regulators assured consumers that the water posed no risks, but the evidence was insufficient to support safety claims, as Inside Climate News reported.

Crop irrigation is just one so-called beneficial use of the oil industry’s wastewater. It’s legal to use produced water as a dust suppressant on roads in 13 states, including Pennsylvania, New York and Ohio. The practice can leave a trail of cancer-causing radium in its wake, a 2018 study found, posing risks to both aquatic life and people.

Entrekin’s biggest concern is that unreported or undetected spills are affecting the health of aquatic invertebrates. Plus, the study likely underestimates what could be happening to invertebrate species that, unlike Daphnia, are too sensitive to rear in the lab, she said. Those more sensitive species could be wiped out where spills occur.

Flowback and produced water should never enter the environment, Blewett said. “I don’t want to be alarmist in any way, but it’s quite toxic,” she said. “I’d never want to be exposed to it.”

The wastewater has many different toxic compounds that interact with each other in multiple ways to increase toxicity. There are just too many unknowns about what these complex chemical mixtures in the wastewater do to say it’s safe to put on something, Blewett said, whether roads or crops.

Blewett used to study the effects of metals on fish and found that people in the metal industry voluntarily worked with scientists and regulators to help develop protective water quality guidelines. The oil and gas industry, by contrast, “doesn’t want anybody to know anything,” she said. “They won’t give you their flowback and produced water, because it’s proprietary.”

Scientists rarely talk about the difficulty of getting information on chemicals injected into wells or accessing companies’ wastewater, worried they’ll lose access. But their frustration grows when they’re left cleaning up spills and don’t know what they’re dealing with.

“If there was more transparency with fracking for the people who are trying to assess toxicity, that would go a long way,” Blewett said. “But that’s never going to happen because oil and gas won’t let it happen.”