Researchers from Patricia Holden‘s lab at UC Santa Barbara decided to take a look at soybeans grown to maturity in soil contaminated with two common “manufactured nanomaterials” zinc oxide or cesium oxide, additives commonly found in make up and diesel fuel respectively. The results from growing soybeans in this contaminated soils were disturbing. Plants grown in the presence of zinc oxide show widespread distribution through edible plant tissues, this has implications for bioaccumulation and toxicity (the effects of zinc oxide buildup are detrimental in animal models but largely untested in humans). Also unnerving is how cesium oxide reduced plant yields, most like because it entered the roots and interfered with nitrogen fixing bacteria present in root nodules.
While the results of this study are indeed pretty scary, the distribution and concentration of these synthetic nanomaterial byproducts is hard to predict. High concentrations of both zinc oxide and cesium oxide could indeed be detrimental to crop production and human health, but chances are most soils have very low levels of these compounds. Certain places where waste waters accumulate, or where there is alot of diesel traffic could certainly see elevated levels of these compounds. Regulation and detection of these compounds may well be important for the health and future of humanity, but don’t freak out yet. Buying produce locally from growers you know and trust should help to alleviate any fears you may have after learning about these nanomaterials. Further work definitely needs to be done.
Published in PNAS
Soybean susceptibility to manufactured nanomaterials with evidence for food quality and soil fertility interruption
Priester, J.H. et al. 2012
Based on previously published hydroponic plant, planktonic bacterial, and soil microbial community research, manufactured nanomaterial (MNM) environmental buildup could profoundly alter soil-based food crop quality and yield. However, thus far, no single study has at once examined the full implications, as no studies have involved growing plants to full maturity in MNM-contaminated field soil. We have done so for soybean, a major global commodity crop, using farm soil amended with two high-production metal oxide MNMs (nano-CeO2 and -ZnO). The results provide a clear, but unfortunate, view of what could arise over the long term: (i) for nano-ZnO, component metal was taken up and distributed throughout edible plant tissues; (ii) for nano-CeO2, plant growth and yield diminished, but also (iii) nitrogen fixation—a major ecosystem service of leguminous crops—was shut down at high nano-CeO2 concentration. Juxtaposed against widespread land application of wastewater treatment biosolids to food crops, these findings forewarn of agriculturally associated human and environmental risks from the accelerating use of MNMs.
Nanoparticle ‘risk’ to food crops by By Jonathan Ball of BBC News
Whilst many of their effects have been well documented, some of their mechanisms of action are not fully understood. Concern has arisen that widespread long-term nanoparticle use may “trickle down” into the environment, sparking unforeseen effects on plant or animal, or even human, health.
They grew soybeans in a greenhouse in the presence of increasing amounts of the nanoparticles, monitoring the plants’ growth. In addition, the accumulation of the nanoparticles in different parts of the plant was also scrutinised.
The plants grown in the presence of zinc oxide nanoparticles actually grew slightly better than control plants grown in the absence of nanoparticles. However, zinc built up in the edible parts of the plants, which included the leaves and the beans.
Zinc oxide nanoparticles have been shown to be toxic to mammalian cells grown in the laboratory, but effects in humans remain to be examined fully.
Soybean growth was significantly stunted when the plants were cultivated in the presence of high levels of cerium oxide nanoparticles.
The cerium was able to enter the plants’ roots. Soybeans are members of a group of plants called legumes. The roots of these plants host bacteria that turn atmospheric nitrogen into a form that the plant can use for growth – so-called nitrogen fixation.
The cerium nanoparticles seemed to completely inhibit the bacteria’s ability to fix nitrogen.
Commenting on the wider toxicity of nanoparticles, Prof Vicki Stone from the Heriot-Watt University, Scotland, said: “Nanomaterials are equally hazardous or conversely equally safe. Effects seem to depend upon their physical and chemical characteristics – this is what scientists are aiming at better understanding, so that in future they can predict toxicity or safety based on these characteristics.”