No No to Nano?

By Susan Littlefield

Perhaps you've heard of concerns about the potential human health impacts associated with nanoparticles. These tiny manufactured particles, found now in everything from cosmetics and sunscreen to the exhaust of diesel fuel, are about 10,000 times smaller than the diameter of a human hair, so small that they are measured in billionths of a meter. Because of their size, they behave differently than larger particles of the same material, a characteristic that makes them valuable to manufacturers of various products, but one that also causes concern about their effects on the environment and living organisms.

Some recent studies reinforce these concerns as they relate to plants. The research suggests that these manufactured nanomaterials pose a risk to some crops when they are present in the soil in which crops are grown, causing stunting, increasing the absorption of pollutants from the soil, and interfering with the ability of legumes to "fix" nitrogen from the air, resulting in an increased need for added fertilizers.

How do nanoparticles get into the soil in the first place? Cerium oxide is a widely used as a catalyst in diesel fuel. The particles enter the soil as exhaust from diesel farm tractors settles on the ground. Nanoparticles of zinc oxide, widely used in products like sunscreens and cosmetics, accumulate in the solids that are separated out of sewage and wastewater and used as fertilizer on many crops. Researcher Patricia Holden, quoted in an online Science News article on the crop risks posed by nanosized pollutants, notes that the studies "forewarn of agriculturally associated human and environmental risks from the accelerating use of manufactured nanomaterials."

One study led by scientists at UC Santa Barbara's Bren School of Environmental Science & Management showed that when soybeans were grown in soil containing zinc oxide, the zinc accumulated in the stems, leaves, and beans of the plants, causing stunting. Nanoparticles of cerium oxide from the soil did not accumulate inside the soybeans, but caused changes in their root nodules, interfering with the ability of symbiotic bacteria to convert nitrogen in the atmosphere into a form usable to the plants. Another study done at the Connecticut Agricultural Experiment Station showed that when the roots of tomatoes, zucchini and soybeans were exposed to a type of nanoparticles called fullerenes, they took up more toxic pesticide residues from the growing medium than control plants not exposed to the nanomaterials.

These studies point to the need for continued research into the risk to crops posed by exposure to nanoparticles and the potential for environmental harm as their use increases.

To read more about the research into the effects of nanoparticles on crops, go to Science News and Science Daily.

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