14 de agosto de 2016
Study raises questions about measuring radioactivity in fracking wastewater - Apr. 9, 2015
Commonly used testing methods may underestimate the total radioactivity of wastewater produced by gas wells that use hydraulic fracturing, or fracking, to tap the Marcellus Shale, a geological formation in the northeastern United States, concludes a new study. The findings suggest government agencies should consider retooling some testing recommendations and take a fresh look at possible worker exposure to potentially harmful waste, the authors say. But some outside researchers are skeptical that the laboratory study reflects real-world conditions.
Fracking, which involves injecting water mixed with chemicals and sand deep underground in order to fracture rock and release oil and gas, generates large amounts of wastewater. Some of the waste is simply injected water that flows back to the surface. But in the Marcellus and other formations, a major waste component is salty, mineral rich water found naturally underground. Researchers have long known that this natural brine can carry radioactive components, including radon gas, radium, and other isotopes of uranium and thorium. And the waste’s radioactivity has gotten increased attention as a fracking boom in the Marcellus has resulted in the recovery of millions of liters of wastewater, which is typically stored, treated, or recycled for use in other fracking wells. In some cases, improper handling has resulted in the release of radioactive fracking waste that has contaminated streams and rivers.
Last year, Andrew Nelson, a doctoral candidate in human toxicology at the University of Iowa in Iowa City, helped the U.S. Environmental Protection Agency (EPA) write an analysis that concluded that agency-recommended testing methods may understate some measures of radioactivity. Although EPA does not regulate most oil and gas activities, laboratories that test water for state regulators, oil and gas producers, and wastewater treatment plants often rely on the agency’s recommended methods. One problem with current EPA techniques, the report found, is that they focus on levels of radium in fresh water used for drinking, and so do not work well with fracking waste. In part, that’s because Marcellus Shale wastewater is saltier than seawater; it also holds other potentially problematic radionuclides in addition to radium.
Now, in a paper published online on 2 April in Environmental Health Perspectives, a team led by Nelson shows that radium-focused tests can significantly underestimate the total radioactivity of wastewater that is stored in closed containers, such as tanks. The researchers found the testing methods don’t fully measure radium’s daughter decay products, which can build up in the days and years after the briny waste reaches the surface. Radioactivity levels in stored wastewater can rise fivefold within 15 days, for example, and continue to rise for decades.
To undertake their study, the researchers obtained a sealed sample of Marcellus wastewater and then measured selected radioactive isotopes that appeared as radium decayed into daughter products. The half-lives, radioactivity, and chemistry of radium isotopes and their decay products vary considerably, the researchers note. For example, the half-life of radium-226 is 1600 years (meaning it takes that long for 50% of the total to decay). In contrast, lead-210’s half-life is 22.2 years, while polonium-210’s is 138.4 days. To calculate the total radioactivity of a sample over time, researchers must account for all of these daughter products.
At first, the researchers could barely detect the presence of many daughter isotopes, including polonium-210 and lead-210. Over time, however, the levels rose as the decay reactions took place and continued to rise for months.
Just how much risk these radioactive isotopes might pose to people exposed to the waste is unclear. One issue is that the researchers used a sealed sample, which meant that radon gas that gives birth to daughter isotopes could not escape into the air. At real-world fracking sites, however, the radon may escape from the wastewater as it emerges from the wellhead, sits in collecting ponds, or is transferred between containers, notes environmental engineer Radisav Vidic of the University of Pittsburgh in Pennsylvania, who was not involved in the study. “If radon gas leaves the solution you stop the subsequent creation of the daughter products,” he says.
One of the study’s authors, however, notes that the half-lives of some of the radioactive products are so short that they could still pose problems in the days after the waste surfaces, before radon has a chance to escape. Radon-220, for instance, has a half-life of just 55.6 seconds. “That means that it’s unlikely to escape before the other daughters are formed,” says co-author Michael Schultz, a radiochemist at the University of Iowa. And even if some radon gas does escape, more can be generated in closed containers as any remaining radium decays, Nelson adds.
Another issue is uncertainty about the health risks posed by the different isotopes. Some are considered to pose a greater risk because they emit radiation that can penetrate the body, while others are considered less risky because they must be inhaled or ingested to do damage. And some can accumulate in the food chain, with long-lived isotopes potentially posing a threat for decades.
Given such unknowns, “we have yet another reason to be concerned about understanding exposure related to the hydraulic fracturing procedures,” says environmental toxicologist Bernard Goldstein, a professor emeritus at the University of Pittsburgh Graduate School of Public Health, who was not involved in the study. “They’ve made a very good case that we need a much more thorough evaluation of worker exposure at different places at different times,” he says.
David Allard, director of Pennsylvania’s Bureau of Radiation Protection in Harrisburg, says the new study’s findings agree with those of a recent state analysis of radioactive fracking wastewater, particularly regarding radon decay in sealed containers. But Allard believes there is little risk to the public or workers of exposures exceeding international radiation standards during normal fracking procedures. But he adds that spills of fracking wastewater may pose some additional risk because it can carry radium-226 into ground water.
Allard agrees that tests tailored to waste from oil and gas operations are needed. Although EPA has recognized potential problems with current testing methods for use on fracking wastewater, it is not clear whether the agency is contemplating new recommendations. “EPA does not have authority to regulate [hydraulic fracturing] wastewaters as they are generated,” said an EPA representative in a statement. Its “non-regulatory” testing methods, the statement noted, are available only “as a tool for hydraulic fracturing.”
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