Metallic nanoparticles are key ingredients in products such as sunscreen, cosmetics, diesel fuel, as well as odor-eating socks. This in turn causes them to end up in the soil, with somewhat troubling consequences.
Researchers published their findings in the journal Proceedings of the National Academy of Sciences. The study examines soybeans growing in soil mixed with two common nanoparticles, nano-zinc oxide, and nano-cerium oxide. It suggests that they can accumulate in crops and stunt bacteria that naturally fertilize soil.
Other studies have shown that plants can absorb nanoparticles in hydroponic greenhouses, but real soil is quite different. Environmental microbiologist Patricia Holden of the University of California in Santa Barbara states that most nanoparticles would get stuck in clays in soil, so it came as a surprise that they were biologically available to bacteria and plants.
This could in turn affect the food supply. Zinc oxide (ZnO) and cerium oxide (CeO2) are two materials used to fabricate nanoparticles. Nano-zinc uses oxide particles, as small as an HIV virus, to absorb ultraviolet light without leaving a white residue. The particles end up in drains and then transferred into sewage sludge, which is sold to farmers to use as fertilizer.
Holden and her team grew soybeans in greenhouses. Nano-cerium accumulated around the soybeans’ roots and stunted plant growth while nano-zinc allowed crops to absorb much more zinc than plants grown in regular soil.
The nodules weren’t functional because of the cerium oxide. Holden has yet to determine whether nano-zinc was absorbed whole or dissolved into an edible state.
The concentrations of nano-particles were high, so high that they couldn’t occur yet in the environment. Also, the research team obtained their nanoparticles directly from the manufacturers. More realistic conditions are required to state something useful about the overall environmental threat of manufactured nanoparticles.
Nano-zinc oxide changes when it enters sewage sludge. The same can be said of cerium oxide. The implications of absorption and blocking nitrogen fixation may have been overstated.
Whatever their effect, it’s clear that these kinds of nanomaterials need to be regulated.
Reference: “Soybean susceptibility to manufactured nanomaterials with evidence for food quality and soil fertility interruption” by John H. Priester, Yuan Ge, Randall E. Mielke, Allison M. Horst, Shelly Cole Moritz, Katherine Espinosa, Jeff Gelb, Sharon L. Walker, Roger M. Nisbet, Youn-Joo An, Joshua P. Schimel, Reid G. Palmer, Jose A. Hernandez-Viezcas, Lijuan Zhao, Jorge L. Gardea-Torresdey and Patricia A. Holden, 20 August 2012, Proceedings of the National Academy of Sciences.