This Oct. 1, 2014 news item on ScienceDaily about carbon nanotubes accumulating in the wetlands is carefully worded,
A Duke University team has found that nanoparticles called single-walled carbon nanotubes accumulate quickly in the bottom sediments of an experimental wetland setting, an action they say could indirectly damage the aquatic food chain. [emphasis mine]
The results indicate little risk to humans ingesting the particles through drinking water, say scientists at Duke’s Center for the Environmental Implications of Nanotechnology (CEINT). But the researchers warn that, based on their previous research, the tendency for the nanotubes to accumulate in sediment could indirectly damage the aquatic food chain in the long term if the nanoparticles provide “Trojan horse” piggyback rides to other harmful molecules. [emphases mine]
There’s a lot of hedging (could, if) in the way this research is being described. I imagine the researchers are indicating they have concerns but have no wish to stimulate panic and worry.
Carbon nanotubes are rapidly becoming more common because of their usefulness in nanoelectric devices, composite materials and biomedicine.
The Duke study was done using small-scale replications of a wetland environment, called “mesocosms,” that include soil, sediments, microbes, insects, plants and fish. These ecosystems-in-a-box are “semi-closed,” meaning they get fresh air and rainwater but don’t drain to their surroundings. While not perfect representations of a natural environment, mesocosms provide a reasonable compromise between the laboratory and the real world.
“The wetland mesocosms we used are a much closer approximation of the natural processes constantly churning in the environment,” said Lee Ferguson, associate professor of civil and environmental engineering at Duke. “Although it’s impossible to know if our results are fully accurate to natural ecosystems, it is clear that the processes we’ve seen should be considered by regulators and manufacturers.”
Ferguson and his colleagues dosed the mesocosms with single-walled carbon nanotubes and measured their concentrations in the water, soil and living organisms during the course of a year. They found that the vast majority of the nanoparticles quickly accumulated in the sediment on the “pond” floor. However, they found no sign of nanoparticle buildup in any plants, insects or fish living in the mesocosms.
That sounds marvelous and then the researchers provide a few facts about carbon nanotubes,
While this is good news for humans or other animals drinking water after a potential spill or other contamination event, the accumulation in sediment does pose concerns for both sediment-dwelling organisms and the animals that eat them. Previous research has shown that carbon nanotubes take a long time to degrade through natural processes — if they do at all — and any chemical that binds to them cannot easily be degraded either.
“These nanoparticles are really good at latching onto other molecules, including many known organic contaminants,” said Ferguson. “Coupled with their quick accumulation in sediment, this may allow problematic chemicals to linger instead of degrading. The nanoparticle-pollutant package could then be eaten by sediment-dwelling organisms in a sort of ‘Trojan horse’ effect, allowing the adsorbed contaminants to accumulate up the food chain.
“The big question is whether or not these pollutants can be stripped away from the carbon nanotubes by these animals’ digestive systems after being ingested,” continued Ferguson. “That’s a question we’re working to answer now.”
It’s good to see this research is being followed up so quickly. I will keep an eye out for it and, in the meantime, wonder how the followup research will be conducted and what animals will be used for the tests.
Here’s a link to and a citation for the researchers’ most recent paper on possible ‘Trojan’ carbon nanotubes,
Fate of single walled carbon nanotubes in wetland ecosystems by Ariette Schierz, Benjamin Espinasse, Mark R. Wiesner, Joseph H. Bisesi, Tara Sabo-Attwood, and P. Lee Ferguson. Environ. Sci.: Nano, 2014, Advance Article DOI: 10.1039/C4EN00063C First published online 03 Sep 2014
This is an open access paper.
I have written about Duke University and its nanoparticle research in mesocosms before. Most recently, there was a Feb. 28, 2013 posting about work on silver nanoparticles which mentions research in the ‘mesocosm’ (scroll down about 50% of the way). There’s also an Aug. 15, 2011 posting which describes the ‘mesocosm’ project at some length.
For anyone unfamiliar with the Trojan horse story (from its Wikipedia entry; Note: Links have been removed),
The Trojan Horse is a tale from the Trojan War about the subterfuge that the Greeks used to enter the city of Troy and win the war. In the canonical version, after a fruitless 10-year siege, the Greeks constructed a huge wooden horse, and hid a select force of men inside. The Greeks pretended to sail away, and the Trojans pulled the horse into their city as a victory trophy. That night the Greek force crept out of the horse and opened the gates for the rest of the Greek army, which had sailed back under cover of night. The Greeks entered and destroyed the city of Troy, decisively ending the war.