Study: Nanotech Processing 'Greener' Than Oil Refining

The study is available online and slated for publication in the Nov.15 issue of Environmental Science and Technology. It compares theenvironmental and health risks associated with the production of fivenanomaterials -- single-walled carbon nanotubes, buckyballs, zincselenide quantum dots, alumoxane nanoparticles and titantium dioxidenanoparticles -- with the risks of making six commonplace products --silicon wafers, wine, high-density plastic, lead-acid car batteries,refined petroleum and aspirin.

"There are many unknowns about the impacts of nanomaterials onliving organisms and ecosystems, but a great deal is known about theproperties of the materials that are used to create nanomaterials,"said study co-author Mark Wiesner, professor of civil and environmentalengineering at Rice University. "Our goal was to produce an earlyestimate of the environmental 'footprint' for nanomaterialsfabrication.

"The jury is still out on whether some nanomaterials pose arisk, but it is not too early to consider how we might avoidenvironmental and health risks associated with making these newmaterials," Wiesner said. "We have a narrow window of opportunity toguide the emerging nanomaterial industry towards a green future. Withthis study, we hope to establish a baseline for the safe, responsibledevelopment of the nanomaterials manufacturing industry."

In developing their risk assessments, the research teamdeveloped a detailed account of the input materials, output materialsand waste streams for each process. Risk was qualitatively assessed foreach process, based on factors including toxicity, flammability andpersistence in the environment.

Using an actuarial protocol developed by the Zurich-basedinsurance company, XL Insurance, the researchers developed three riskscores for each of the 11 processes: incident risk, which refers toin-process accidents; normal operations risk, which refers to wastestreams and airborne emissions; and latent contamination, which refersto the potential for long-term contamination.

Wiesner said the incident risks for most of the nanomaterials were comparable or lower than those of non-nanoprocesses.

"That doesn't imply that the non-nano processes present anacceptable level of risk, or that there is no room for improvementacross the board, but the study does suggest that the risks of makingthese new materials will not be drastically different from those weencounter in current industries," he said.

For example, the incident risks associated with alumoxane andnanotube production fell near or below the scores for wine production.Buckyballs had the highest incident risk rating among nanomaterials andscored near the risks associated with producing polyolefins, a broadclass of polymers like polyethylene that are used in making plastics.

The normal operations risk scores for nanotubes and alumoxaneswere comparable to those of wine and aspirin making, while the scoresfor buckyballs, quantum dots and titanium dioxide were comparable tothe operations risks of making silicon wafers and car batteries. Thenormal operations risks associated with plastics and petroleum refiningwere greater than those for any nanomaterial.

For all of the nanomaterials except buckyballs, latent riskscores were comparable to those of silicon wafers, wine and aspirinproduction. Buckyballs had a latent score comparable to car battery andplastics production and considerably lower than the score for petroleumrefining.

"We can't anticipate all of the details of how nanomaterialsfabrication will evolve, but based on what we do know, the fabricationof the nanomaterials we considered appears to present lower risks thancurrent industrial activities like petrochemical refining, polyethyleneproduction and synthetic pharmaceutical production," said Wiesner.

Co-authors on the study include Rice doctoral student ChristineRobichaud; sustainability researcher Dicksen Tanzil of Bridges toSustainability; and Ulrich Weilenmann of XL Insurance.

The research was funded in part by the National Science Foundation, and by the Environmental Protection Agency.