Posted in | Nanomaterials

Study Reveals Burning of Coal Produces Potentially Harmful Airborne Nanoparticles

Environmental Researchers led by the Virginia Tech College of Science revealed that the burning of coal creates extremely small particles of a highly uncommon form of titanium oxide.

Michael F. Hochella Jr. is a University Distinguished Professor of Geosciences with the Virginia Tech College of Science.

When inhaled, these nanoparticles will enter the lungs and potentially the bloodstream.

The particulates — known as titanium suboxide nanoparticles — are involuntarily produced as coal is burned, generating these smallest of particles, as small as 100 millionths of a meter, said the Virginia Tech-led team. When the particles are emitted into the air — unless captured by high-tech particle traps — they can drift away from power plant stacks due to air currents and travel locally, regionally and even globally.

As an example of this, these nanoparticles were found on city streets, sidewalks and in standing water in Shanghai, China.

The research findings have been published in the recent issue of Nature Communications under team leader Michael F. Hochella Jr., University Distinguished Professor of Geosciences with the College of Science and Yi Yang, a Professor at East China Normal University in Shanghai. Other study participants include Duke University, the University of Kentucky and Laurentian University in Canada.

“The problem with these nanoparticles is that there is no easy or practical way to prevent their formation during coal burning,” Hochella said, adding that in countries with robust environmental regulations, such as the United States, most of the nanoparticles would be caught by particle traps. Not so in China, Africa or India, where regulations are negligent or nonexistent, with coal ash and smoke released into the open air.

Due to advanced technology used at U.S.-based coal burning power plants, mandated by the Clean Air Act and the Environmental Protection Agency, most of these nanoparticles and other tiny particles are removed before the final emission of the plant’s exhaust gases. But in countries where the particles from the coal burning are not nearly so efficiently removed, or removed at all, these titanium suboxide nanoparticles and many other particle types are emitted into the atmosphere, in part resulting in hazy skies that plague many countries, especially in China and India.

Michael F. Hochella Jr., Distinguished Professor of Geosciences, Virginia Tech

Hochella and his team found these formerly unknown nanoparticles not only in coal ash from around the world and in the gaseous waste emissions of coal plants, but in storm water ponds and soils, on city streets and at wastewater treatment plants.

“I could not believe what I have found at the beginning, because they had been reported so extremely rarely in the natural environment,” said Yang, who once worked as a Visiting Professor in Virginia Tech’s Department of Geosciences with Hochella. “It took me several months to confirm their occurrence in coal ash samples.”

The newly found titanium suboxide — called Magnéli phases — was formerly thought of as rare, found only sparingly on Earth in a few meteorites, from a small area of rock formations in western Greenland, and sporadically in moon rocks. The findings by Hochella and his team reveal that these nanoparticles are actually extensively spread across the globe. They are only currently being investigated for the first time in natural environments using robust electron microscopes.

Why did the discovery happen now? According to the report, almost all coal contains hints of the minerals rutile and/or anatase, both “normal,” naturally occurring, and comparatively inert titanium oxides, particularly in the absence of light. When those minerals are burned in the presence of coal, research discovered that they are easily and rapidly converted to these uncommon titanium suboxide nanoparticles. The nanoparticles then become entrained in the gases that escape the power plant.

When inhaled, the nanoparticles go right into the lungs, potentially into the air sacs that move oxygen into the bloodstream during the regular breathing process. Although its toxicity to humans is not yet known, a primary biotoxicity test by Hochella and Richard Di Giulio, Professor of Environmental Toxicology, and Jessica Brandt, a Doctoral Candidate, both at Duke University, reveals that the particles certainly have toxicity potential.

According to the team, additional study is evidently needed, especially biotoxicity testing directly applicable to the human lung. Collaborating with coal-power plants either in the United States or China would be ultimate, said Yang.

More troubling, the research reveals that titanium suboxide nanoparticles are biologically active in the dark, making the particles extremely suspect. Precise human health effects are still unidentified.

Future studies will need to very carefully investigate and access the toxicity of titanium suboxide nanoparticles in the human lung, and this could take years, a sobering thought considering its potential danger.

Michael F. Hochella Jr., Distinguished Professor of Geosciences, Virginia Tech

As the titanium suboxide nanoparticle itself is created incidentally, Hochella and his team noticed the nanoparticle only by accident while studying a 2014 coal ash spill in the Dan River, North Carolina. During the study of the downstream movement of contaminated metals in the ash in the Dan River, the team discovered and detected the presence of small quantities of the extremely unusual titanium suboxide.

The team later made the titanium suboxide nanoparticles when burning coal in a lab simulation.

This new potential air pollution health threat builds on already proven findings from the World Health Organization. It estimates that 3.3 million premature deaths occur globally per year because of polluted air, Hochella said. In China, 1.6 million premature deaths are estimated per year as a result of cardiovascular and respiratory injury from air pollution. Most Chinese megacities top 100 severely hazy days each year with particle concentrations two to four times higher than WHO recommendations, Yang said.

Direct health effects on humans are just one factor. Findings of thousands of Researchers have established that the chief driver of warming of the planet and the resultant climate change is industrial-scale coal burning. The impact of titanium suboxide nanoparticles found in the atmosphere, besides greenhouse gases, on animals, plants and water is not yet identified.

The research received funding from many sources, including Virginia Tech’s Institute for Critical Technology and Applied Science, two National Science Foundation grants, the U.S. Department of Energy, and several China-based research foundations, Hochella said.

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