New data raise questions about asbestos containment strategy

By the 1970s, mass production of asbestos-containing material was starting to wind down as people realized that the mineral is carcinogenic. But former dumping sites and areas where asbestos disposal was mismanaged remain in communities across the US.

For example, Ambler, Pennsylvania, home to former asbestos manufacturing giant Keasbey & Mattison, piled snowy asbestos-containing waste so high the site became known as “the White Mountains.” In a residential area of Klamath Falls, Oregon, improper demolition of military barracks from the 1940s led to the release of hundreds of thousands of cubic yards of asbestos-containing materials and contaminated soils. According to the US Environmental Protection Agency, there are 51 active Superfund sites involving asbestos waste management.

Though now widely regulated, asbestos was once widely used in insulation, roofing, and automotive parts because of its resistance to heat and fire. Asbestos is a family of silicate minerals, the most common member of which is chrysotile, also known as white asbestos. These minerals occur naturally in bundles of thin fibers. When someone inhales these fibers, which are too small to see individually, the minerals can cause tissue scarring, lung cancer, and an asbestos-specific membrane tumor known as mesothelioma.

When dealing with asbestos waste, digging up and removing large amounts of contaminated soil can be risky, as it can send asbestos fibers into the air. So, rather than remove all the contaminated dirt, the EPA often caps a site with more soil. Scientists thought that these soil caps would trap the long, thin fibers and prevent them from escaping.

But a new peer-reviewed laboratory study shows a potential escape route for these fibers. The findings, first presented as preliminary data in 2016, demonstrate that the presence of certain organic material in soil can actually enhance the mobility of asbestos fibers (J. Hazard. Mater. 2021, DOI: 10.1016/j.hazl.2021.100015). The researchers are concerned that if the fibers can reach groundwater, they could make it to nearby communities via irrigation, or become airborne after washing up and drying out on riverbanks. Experts think more research on this exposure route is needed, including official monitoring of groundwater asbestos, and some say the communities around asbestos waste sites should be notified of this possible risk.

Doug Jerolmack, a geophysicist at the University of Pennsylvania, doesn’t think the assumption that soil would trap asbestos fibers was unreasonable. Asbestos moving through soil is like threading a strand of hair through soil—it may be long and thin, but eventually it will get caught, says Jerolmack, who was not an author of the study but participated in previous work on asbestos mobility presented at the American Chemical Society Fall 2016 meeting. “So even just from a physical perspective, I would have thought that these particles might not be able to make it through soil in groundwater, simply because they might get caught up,” he says.

Scientists also thought that chemical interactions between asbestos fibers and soil would help trap the waste. Chrysotile asbestos fibers have a net positive surface charge in water around neutral pH, while natural soil has a net negative surface charge. Scientists believed the attraction between the asbestos fibers and the soil should limit the fibers’ mobility.

But dissolved organic matter (DOM), commonly found in soil, might be throwing a wrench into that trap. DOM is a broad term referring to organic compounds dissolved in water. Research has shown that DOM can change the surface charge of some particles, such as iron oxide or aluminum oxide, effectively forming a negatively charged coating around them. If asbestos fibers got such a coating, they potentially could slip through a negatively charged medium like soil more easily than they would be able to otherwise because of the resulting repulsive interactions. This effect of DOM had never been examined on asbestos fibers, however.

Around 2014, geologist Jane Willenbring; environmental engineer Sanjay Mohanty, then a postdoctoral researcher; and their colleagues at the University of Pennsylvania were working on a series of asbestos-related studies on behalf of the residents of Ambler—one of the communities with asbestos-containing waste covered by soil caps. Willenbring’s group was interested in researching potential methods of phytoremediation, the process of using living organisms, like plants, to remediate waste. But first, the researchers wanted to understand the factors that could affect how the fibers move in soil. Because DOM had been shown to alter the surface charges of particles before, they decided to examine how DOM might affect the mobility of asbestos fibers.

The researchers put soil from one of the Superfund sites in Ambler into columns in their lab. Then they added suspensions of chrysotile asbestos, some with DOM and some without, and flushed the soil with a salt solution to mimic the movement of groundwater through soil. The team monitored the liquid coming off the soil columns for asbestos content.

In the columns that didn’t contain DOM, almost no asbestos moved out of the soil. But in the presence of fulvic acid—one type of DOM—about 10% of the fibers passed through the soil column. Two other types of DOM—humic acid and natural organic matter—also enhanced asbestos mobility, but not as much, with only about 4% and less than 1% of fibers, respectively, transported through the columns containing those materials.

“We knew that there may be a role, but we are surprised that [DOM] actually has that much impact,” says Mohanty, now an assistant professor at the University of California, Los Angeles.

The findings could have implications for people living near sites containing asbestos waste. “This work clearly shows that it can migrate,” says Arthur Frank, an expert in asbestos-related diseases at Drexel University who was not involved with the study. “It clearly presents another potential source of exposure to individuals.”

Asbestos fibers could move from groundwater to the air in these communities in a few ways, according to Mohanty. Groundwater drawn up for irrigation or that flows to nearby riverbanks could lead to asbestos fibers sitting on the soil surface after evaporation, and contaminated groundwater that becomes part of a community’s water supply could result in asbestos fibers becoming airborne via showers and indoor humidifiers.

Brenda Buck, a geologist at the University of Nevada, Las Vegas, who was not involved with the study, supports research into whether or not soil caps can effectively contain asbestos, but says much more work needs to be done to determine whether the increased fiber mobility with DOM seen in the lab would be significant in a real-world setting.

“Extrapolating these results to say that we need policy changes,—I don’t think we’re there yet,” Buck says. “I don’t think there’s enough data to support that.”

Scientists need to determine what types of DOM actually reach buried asbestos and in what quantities, Buck says. They also need to find out if mobility increases occur in different soil textures and compositions and whether enough asbestos moves quickly enough to present an exposure risk, she adds. Buck also thinks the mobility effects will vary by site.

Researchers do plan to study DOM’s impact on asbestos mobility further in a field setting. Mohanty and Jerolmack intend to go to Superfund sites containing asbestos, sample nearby groundwater, and test the soil for DOM. Such data could give them a better idea of whether DOM is causing asbestos fibers at these sites to escape into groundwater, and could provide insight into whether nearby communities are at risk of exposure.

The scientists also think that the EPA should start testing groundwater near Superfund sites for asbestos content. “Not taking [a] groundwater sample is a mistake,” Mohanty says. “What we saw here, there is a possibility that it might be in the groundwater, so at least there should be monitoring.”

EPA spokesperson Tim Carroll says that the EPA doesn’t test groundwater near these sites for asbestos. A policy change doesn’t seem to be on the horizon.

“EPA is committed to ensuring all cleanup actions are guided by the best available science and data,” Carroll says via email. “We don’t normally test water for asbestos fibers near Superfund sites because the weight of evidence generally does not indicate ingestion of asbestos fibers presents significant risk at Superfund sites. We will continue to review new science to inform our future risk assessment and management decisions.”

After Willenbring, Mohanty, Jerolmack, and other researchers presented data from this study and related work at ACS Fall 2016, the EPA requested that a consulting group evaluate the impacts of the research on the asbestos-containing Raymark Superfund Site in Connecticut. The firm concluded that, based on the abstracts, parts of the site had potential for asbestos migration, but that there wasn’t enough information to draw further conclusions. The firm also highlighted that it was unclear whether the same mobility would occur in a real-world setting and suggested that the agency should review the full, peer-reviewed papers once released.

Mikayla Rumph, an EPA spokesperson for the New England region, said in an email, “We have not yet reviewed the recent publication so we cannot comment on it. The Agency will review new relevant information and determine whether any additional follow-up relative to the Raymark remedy or long-term groundwater monitoring plan at the site is appropriate.”

Sean Marchese, a registered nurse and oncology medical writer with the advocacy organization the Mesothelioma Center, still thinks soil caps are a relatively safe method of asbestos remediation, but says the EPA should ensure that people are made aware of the potential risks this study identifies.

“It comes down to people being able to make their own decisions based on the information that’s out there,” Marchese says. “And right now, they just don’t have that information.”