Manufactured Nanoparticles Could Pose a Hazard to Crops, But Are They a Risk?

Once again, here come the headlines, across both the trade and mainstream press, warning us that manufactured nanoparticles are a danger to our health and environment. This time it's that nanoparticles stunt soybean crop growth.

The warnings are based on research at the University of California Santa Barbara's Bren School for Environmental Science & Management. The language of the research, however, falls somewhat short of making such unconditional claims.

Instead the research, which was published the Proceedings of the National Academy of Sciences (PNAS),  claims to demonstrate “what could arise over the long term” if plants were grown in soil that had been contaminated with manufactured nanomaterials (MNMs), zinc oxide and cerium oxide.

Even the research that inspired the UC Santa Barbara team to put metal oxides in farming soil only suggested that MNMs “could” alter food crop quality and yield. Of course, if the researchers were to take ordinary household bleach from under the kitchen sink and pour it onto farming soil, they would surely conclude that it "could" alter the quality of the crop.

The real issue—and indeed as with any issue related to chemicals and Environmental, Health and Safety (EHS) concerns—is what is the real risk of these nanoparticles finding themselves in soil concentrations equal to those that were used in the experiments. The relevant formula is Hazard x Exposure = Risk. If we say that MNMs are a hazard, but have no figures on the level of exposure, how are we supposed to determine risk?

In other words, what concentrations of metal oxides did the researchers use in the soil? The answer is not explicit in either the news stories covering the research, nor the abstract that we have access to in the PNAS journal reference. While the researchers do say in at least one of the articles covering the research that “"MNMs…have a high affinity for activated sludge bacteria, and thus concentrate in biosolids," it’s still not clear in what kind of concentrations these nanoparticles exist in the environment, or what that might mean in terms of risk.

In one of the stories covering the research, Patricia Holden, one of the scientists in the research and a professor at the Bren School, has this to say about the risk of these nanoparticles getting into our plant soil: "There could be hotspots, places where you have accumulation, including near manufacturing sites where the materials are being made, or if there are spills."

Could we say then that if you grow your soybeans far from manufacturing sites and far from where there may likely be spills—which is largely the case now, as I understand—that we would mitigate the risk? 

Another troubling aspect of this research is that it has as its "ultimate goal" to help find more environmentally compatible substitutes, according to Holden. Shouldn't the research be to determine if nanoparticles pose a real risk? Instead, that seems to be a given, despite the limited, at best, evidence being provided to prove it.

And what are we substituting in this case? Zinc oxide nanoparticles are found in sunscreens and cosmetics and cerium oxide is used in catalytic converters to reduce carbon monoxide from automobiles. Where is the research to determine how much of these materials are produced, followed by measurements of how much of them are found in random water and soil samples? From there we could determine the key variable of exposure: how much of these nanoparticles in our environment pose a risk. That seems to be an essential line of research if our goal is protecting our environment from substances that are otherwise pretty useful. I am not so sure that setting out to replace them as your ultimate goal really satisfies that aim.

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
Editor
Dexter Johnson
Madrid, Spain
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
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