Researchers at University of California, Riverside have measured the mobility of graphene oxide (GO) in water and have determined that it could move around easily if it were released into lakes and streams.
While the UC Riverside did not look at the toxicity of GO in their study, researchers at the Hersam group from Northwestern University did report in a paper published in the journal Nano Letters (“Minimizing Oxidation and Stable Nanoscale Dispersion Improves the Biocompatibility of Graphene in the Lung”) that GO was the most toxic form of graphene-based materials that were tested in mice lungs. In other research published in the Journal of Hazardous Materials (“Investigation of acute effects of graphene oxide on wastewater microbial community: A case study”), investigators determined that the toxicity of GO was dose dependent and was toxic in the range of 50 to 300 mg/L. So, below 50 mg/L there appear to be no toxic effects to GO. To give you some context, arsenic is considered toxic at 0.01 mg/L.
Graphene oxide is synthesized under extreme conditions (exposure to highly concentrated sulfuric acid, high temperatures, ultra sonication). This results in oxygen functional groups being present on the surface of the graphene oxide flakes. These oxygen functional groups make the material more stable than graphene and also more toxic, according to the researchers.
While GO is quite different from graphene in terms of its properties (GO is an insulator while graphene is a conductor), there are many applications that are similar for both GO and graphene. This is the result of GO’s functional groups allowing for different derivatives to be made on the surface of GO, which in turn allows for additional chemical modification. Some have suggested that GO would make a great material to be deposited on additional substrates for thin conductive films where the surface could be tuned for use in optical data storage, sensors, or even biomedical applications.
In addition to being a conductor before it is functionalized, GO is also known to be easily dispersed in water and other organic solvents, which begs the question of how does this research add to the understanding of GO’s known fundamental properties.
As Jake Lanphere, a UC Riverside graduate student who co-authored the paper, which was published in the journal Environmental Engineering Science (“Stability and Transport of Graphene Oxide Nanoparticles in Groundwater and Surface Water”), explained to Nanoclast in an email interview: “Other studies have looked at ideal lab conditions that do not necessarily reflect the conditions one might find in aquatic environments. Our study investigated the effects of environmentally relevant parameters and different water types that would be found in groundwater and surface waters. Our study is the first to look at the effects of these environmentally relevant parameters on the fate and transport in porous media.”
While Lanphere believes that this information will be critical for the Environmental Protection Agency (EPA) to understand the risk posed by GO, he doesn’t see that the EPA has to make any changes to its current approach for dealing with graphene in its various forms.
“I believe the EPA is doing a great job making sure that we maximize the benefits of nanotechnology while reducing the negative impacts it might have on society,” said Lanphere. “I do not have any specific suggestions.”
Ultimately, the question of danger of any material or chemical comes down to the simple equation: Hazard x Exposure=Risk. To determine what the real risk is of GO reaching concentrations equal to those that have been found to be toxic (50-300 mg/L) is the key question.
The results of this latest study don’t really answer that question, but only offer a tool by which to measure the level of exposure to groundwater if there was a sudden spill of GO at a manufacturing facility.
“As a result of our transport studies, you could determine the distance GO will travel in a specific environment as a function of the soil matrix conditions,” said Lanphere. “This information could help you understand, for example, if your well water would be at risk if there was a contaminant spill with GO nearby.”
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.