Gardea-Torresdey, Ph.D., center, and his students study the effects of nanoparticles on plants. (Photo courtesy of UTEP)
University of Texas at El Paso
Experiments led by Jorge Gardea-Torresdey, Ph.D., of the University of Texas at El Paso have shown that certain man-made nanoparticles that land in soil can be transferred from the roots of plants to the grains, thus entering the food supply via crops grown for human consumption.
“A growing number of products containing engineered nanoparticles are in the market and eventually they will get into the soil, water and air,” said Gardea-Torresdey, Dudley Professor of Chemistry and Environmental Science and Engineering at UTEP and chair of the Department of Chemistry. “This is why it is very important to study the interactions of crops with nanoparticles, as their possible translocation into the food chain starts here.”
The study, published online on Jan. 15 in the American Chemical Society journal ACS Nano, was selected as one of the best papers in 2013 out of all 40 ACS journals. The study tested two of the most common man-made nanoparticles – zinc oxide and cerium dioxide – and laced the soil of soybean plants with them.
The nanoparticles, used in cosmetics, lotions, sunscreens and other products, eventually go down the drain, through municipal sewage treatment plants, and end up in the sewage sludge that some farmers apply to crops as fertilizer.
One key question was whether or not the nanomaterials would break down once the plants absorbed them, or if they would remain a metal oxide nanoparticle, which could potentially have effects on humans if consumed.
“Once engineered nanoparticles enter the food chain, this is an accumulative process. Tolerable levels today can become dangerous tomorrow,” Gardea-Torresdey said. “This is why it is important to study not only whether man-made nanoparticles can be taken up from soil, but also how they are biotransformed in the plants.”
Cerium dioxide, which is commonly used in sunscreens and oil refining, remained intact when it was absorbed by the plant, and was transferred all the way into the edible soybean grains.
On the other hand, zinc oxide – commonly used in sunscreens and cosmetics – was transferred to the grain, but had broken down to a nontoxic form.
To track the nanoparticles’ route within the plants, the researchers used the intense beams of X-rays from the SLAC National Accelerator Laboratory’s Stanford Synchrotron Radiation Lightsource (SSRL) and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The X-rays also helped reveal whether or not the nanoparticles were chemically transformed in the process.
While studies are under way, Gardea-Torresdey says there is currently little information on the potential health implications of nanoparticles.
Earlier studies by the professor have shown that cerium oxide nanoparticles in soybeans stunted their growth, reduced yield, and affected their nitrogen fixation rate.
Additional contributors to the findings were UTEP doctoral chemistry students Jose Hernandez-Viezcas and Cyren Rico; Jose Peralta-Videa, Ph.D., a research specialist in chemistry; and scientists from the University of California, Santa Barbara.
Gardea-Torresdey now plans to study the effects of various sizes and types of nanoparticles on different food crops.
The National Science Foundation, Environmental Protection Agency, and U.S. Department of Agriculture funded the study.