A multi-institute team headed by researchers at University of California, Santa Barbara's Bren School of Environmental Science & Management has studied the environmental impact of nanomaterials by growing soybeans in soil polluted by two manufactured nanomaterials (MNMs).
Soybean plants growing in a UCSB greenhouse (credit: Laurie C. Van De Werfhorst, UCSB)
According to the study, the soil contaminated with MNMs affects the yield and quality of soybean crops. The study findings have appeared in the Proceedings of the National Academy of Sciences. Senior author, Patricia Holden informed that the ultimate objective of the study, funded by the US Environmental Protection Agency and the National Science Foundation, is to help identify more eco-compatible substitutes.
The researchers analyzed the impact of zinc oxide and cerium oxide nanoparticles on the growth of soybeans in greenhouses. Biosolids, a solid material obtained at the last stage of wastewater treatment, are applied to soils in several parts of the United States. The soil is fertilized by this material as it brings back phosphorus and nitrogen that are captured in the wastewater treatment to the soil. This is also the stage where cerium oxide and zinc oxide nanoparticles enter the soil.
The researchers mentioned that the US Environmental Protection Agency demands pretreatment programs to restrict the direct release of industrial metals into publicly owned wastewater treatment facilities. Nevertheless, as per the research team, although it is possible to measure MNMs in the wastewater treatment plants, they are neither observed nor regulated. MNMs have a greater affinity towards activated sludge bacteria, and thus get concentrated in biosolids.
The researchers also noted that there is a possibility of soil deposition of MNMs through exhaust as soybean crops are planted with fossil fuel-powered equipment. The study demonstrated that zinc was bioaccumulated by soybean crops grown in soil containing zinc oxide and absorbed into the beans, leaves, and the stems. Holden stated although the absorption of zinc oxide nanoparticles by plants affects food quality, they may not cause any harm to humans if the zinc is in the form of salts or ions in the plants. However, cerium oxide was not bioaccumulated but affected the plant growth and made changes in the root nodules, which points out that it may be necessary to use more amount of synthetic fertilizers with the accumulation of MNMs in the soil.