Asbestos materials, a group of naturally occurring minerals once widely used in a range of industries for their strength and heat resistance, are notorious for being a health hazard. Though their use has declined substantially, asbestos isn’t banned in the United States, meaning exposure is still possible when renovation or demolition disturbs an asbestos-containing building. Better remediation options are needed for dealing with the minerals.
Recently, researchers from the Department of Earth and Environmental Science have shown that bacteria from extreme marine environments have the potential to detoxify asbestos. Their study, published in the journal Applied and Environmental Microbiology, suggests that the marine microbes may be better candidates for asbestos bioremediation than previously tested fungi and soil bacteria.
“We wanted to explore ways to lower the toxicity of these minerals for safer disposal or reuse as secondary raw materials,” says Assistant Professor Ileana Pérez-Rodríguez, lead study author.
To do this, Pérez-Rodríguez, who specializes in studying extremophilic deep-sea microbes, teamed with Professor Reto Gieré, who has a long history characterizing asbestos minerals. They thought that these extremophilic microbes might be good candidates for asbestos bioremediation because they use inorganic compounds and interact with a variety of minerals in their natural environments.
Specifically, the team focused on a pair of bacteria, Deferrisoma palaeochoriense and Thermovibrio ammonificans, to target two aspects of asbestos minerals that make them dangerous when inhaled: their iron content, largely responsible for the material’s carcinogenic effects, and their fibrous structure, which causes inflammation.
To test the microbes’ ability to detoxify asbestos, the researchers incubated them for seven days at 60 or 75 degrees Celsius—the microbes’ preferred temperatures—in small liquid-filled bottles that also contained asbestos minerals. Across this period, the researchers took samples of the liquid media to track cell growth and changes in chemical composition and used electron microscopy to look for changes in mineral structure.
They found that D. palaeochoriense, which uses iron as part of its metabolism, could effectively remove some iron from asbestos while using it to grow. However, this did not change the mineral’s overall fibrous structure, which is partially responsible for its toxicity.
“This is a gradual process of taking a highly hazardous mineral and making it less hazardous,” Pérez-Rodríguez says. “You can make the mineral less toxic by eliminating the chemical reactivity that comes with the iron, but you still have that fibrous structure, so the next question is, ‘How do we break down the shape?’”
Asbestos minerals are composed of a silicate backbone, and previous studies have shown that removing silicon and magnesium ions from this can disrupt its fibrous structure. This is where the second bacteria, T. ammonificans, came in.
“We can see through microscopy that these microbes incorporate silicon into their biofilms,” Pérez-Rodríguez says. “Usually when we think about biofilms, we think about a sort of slimy goo, but in this case the biofilms are actually quite rigid; they’re basically creating little houses made out of rocks.”
Microbial-based asbestos treatments are a desirable alternative to current asbestos treatment methods, which involve either heating it to very high temperatures and pressures or by treating it with strong acids or bases. However, more research is needed to test how these methodologies could be used to remediate asbestos on a large scale.
“This was just a first lab test, and of course there are still questions,” Gieré says. “We would have to do much more research, but hopefully we can take it to the next level.”