WEST LAFAYETTE, Ind. — Some types of carbon nanotubes used
for strengthening plastics and other materials may have an adverse effect on
soil microbiology and soil microbial processes, a Purdue University study
Specifically, these raw, non-functionalized single-walled
carbon nanotubes were shown to damage the active microbiology in low-organic
Ron Turco, a professor of agronomy, said many of the
bacteria affected could be involved in carbon and nitrogen cycling, which are
critical processes to ensure a fully functional soil.
“There appears to be more negative potential on the active
microbial population than we thought,” said Turco, whose findings were published
in the journal Environmental Science & Technology.
“The as-produced materials could be a negative environmental
situation if they are released into low-organic soils that could not absorb
Functionalized carbon nanotubes have modifications that
create chemical or biological changes to the nanotubes.
They’re often used in medicines, and Turco’s research showed
they had no effect in high-organic or low-organic soils.
Non-functionalized single-walled nanotubes — those lacking
intentional surface alterations — are being added to a variety of products
during manufacturing because they can strengthen the material without adding
Nanotubes contained in manufacturing waste products may find
their way into wastewater treatment plants and biosolids that result from water
purification. Those biosolids cannot be released into water, so they are often
discarded by spreading on land, adding critically needed plant nutrients to
“Land application of biosolids is standard procedure now,”
Turco said. “If any of that contains nanotubes, that could be a problem.”
Single-walled nanotubes also didn’t affect microbes in
high-organic soils, Turco said, likely because organic materials are highly
reactive. Organic materials may have reacted with the nanotubes, leaving them
unable to affect microbes.
“We want to alert people to the fact that if you’re going to
apply these as part of a land-treatment program, you may want to focus on
high-organic matter soils,” the professor said.
It’s also possible, though much less likely, that nanotubes
could contaminate soil through accidental spills during a delivery, Turco
Next, Turco said he would look at the effects on plants and
soils from other nanomaterials and nanometals that are being more widely used in
products for different properties they convey, such as nanosilver for its
disinfecting properties and nanoindium, which is used in electronics.
The National Science Foundation and the U.S. Environmental
Protection Agency funded the research.