Research into the environmental and health risks associated with nanotechnology tends to focus on end product toxicology, and until now there have been no detailed studies of toxic by-products from nanomaterial synthesis. New research at the Woods Hole Oceanographic Institution and Massachusetts Institute of Technology aims to help the nanotechnology industry avoid the kind of unanticipated problems that have adversely affected other technologies.
Doctoral student Desirée Plata, along with her Woods Hole PhD supervisor Christopher Reddy and MIT environmental engineer Philip Gschwend, used a laboratory-scale carbon vapour source to analyse the chemical by-products of the carbon vapour deposition reaction. The researchers found that the CVD process can produce a number of toxic by-products, and recently reported their findings at a meeting of the American Chemical Society.
More than 15 aromatic hydrocarbons were identified, including four different kinds of toxic polycyclic aromatic hydrocarbons similar to those found in cigarette smoke and vehicle exhaust emissions. The most harmful substance found was benzo[a]pyrene, a known human carcinogen. Other reaction products can contribute to smog formation, and trigger the formation of ozone in the lower atmosphere. Ground-level ozone contributes to respiratory problems in humans.
“If nanotube production expands as predicted, then it will be necessary to understand CVD’s potential environmental impact in a quantitative and qualitative sense so that problems may be mitigated in advance,” says Plata. “In our study, we focus on quantifying carbonaceous by-products of CVD synthesis so that we may estimate the industry’s potential impact on environmental health, and make necessary changes to minimise undesirable effects.”
Some might question the significance of the problem when relatively small amounts of nanotubes are made by whatever process. Plata acknowledges this, but insists that if these same methods are used to produce nanotubes on a large scale, it could well become a significant issue. She adds: “It might not have surprised chemists to know that dioxins were co-formed and released during PVC synthesis or paper bleaching, but few predicted it would become a problem that necessitated new industrial methods and/or clean up procedures.”
Plata hopes that her work will in the future lead to environmental chemists collaborating closely with manufacturers to ensure the safety of processes and products during the design phase of new materials. “In this way we hope to prevent future environmental catastrophes,” she says.
Plata and her colleagues are currently working with a number of nanomaterial manufacturers, and a dozen initial contacts have resulted in four ongoing collaborations. “Many companies are afraid that sharing information will ultimately lead to profit loss,” says Plata. “Those who have invited us to work with them have been quite accommodating, although they are careful not to give too much detailed financial information (e.g., we are allowed to know production capacity, but not actual production or sales).”
Duke University’s Mark Wiesner is another scientist looking at nanomaterial toxicology and environmental impact. He comments: “Our own work first called attention to this issue, and suggested that the handling and disposal of feedstocks and wastes associated with carbon nanotube production may produce risks comparable to other industrial processes like plastics manufacturing and petroleum refining.
“Plata and her co-workers have taken this assessment a step further by directly measuring compounds likely to be present in the waste streams resulting from CNT fabrication. They have found compounds that we did not consider in our analysis, that are known to be environmental hazards. This is an important step forward in providing the information needed to ensure that the nanomaterials industry emerges without inflicting the environmental damage that we observed in the early trajectories of industries such as microelectronics or petrochemicals.”
Further reading: Relative Risk Analysis of Several Manufactured Nanomaterials: An Insurance Industry Context, Robichaud et al., Env. Sci. Technol. 39, 8985 (2005).
Figure: Chemical vapour deposition apparatus used by Desirée Plata and her colleagues to sample the by-products of single-walled carbon nanotube synthesis. The ‘QFF’ collects particles greater than 1 μm in size, while the ‘PUF’ traps smaller particles and hydrophobic compounds in the vapour phase. Stainless steel canisters collect gaseous compounds (source; Desirée Plata/Woods Hole Oceanographic Institution).
Article first published in Nanomaterials News.