Researchers at Rice University discovered that when purified carbon nanotubes were introduced into strains of wheat grass, they had an advantageous impact on their early growth . However, it was discovered that the same nanotubes showed considerable damage when contaminants were present.
To investigate the possible toxicity of nanoparticles on wheatgrass, the plant was grown in chemist Andrew Barron's rice laboratory in a hydroponic garden. Surprisingly, the researchers discovered that a type of particle distributed in water helped faster and greater growth of wheat grass.
The researchers assume that the results are due to the natural hydrophobic or water-repellent nature of the nanotubes, which apparently helped in the increase of water intake by the plants in an experiment.
The study has been published in the Royal Society of Chemistry Environmental Science: Nano .
Small-scale research was conducted in the laboratory with the understanding that the industrial synthesis of nanotubes will naturally result in the widespread distribution of the particles in the environment. The research has indicated the rapid growth of nanoparticles in the market of fabrics, drugs, military weapons, cosmetics and water filters, where several thousand tons of products are manufactured per year.
Barron said that despite the extensive application of nanoparticles, very few scientists have analyzed the effect of natural or artificial environmental nanoparticles on the growth of plants.
The team planted wheat grass seeds in several cotton replicas and introduced dispersions comprising single-walled, untreated purified nanotubes, single-walled or multi-walled nanotubes, or iron oxide nanoparticles that were similar to the leftover catalyst normally attached to the nanotubes. Tetrahydrofuran (THF), an industrial solvent, or water was used to make the solutions. Some seeds were treated as controls and fed with THF or pure water.
At the end of the 8 days, it was discovered that wheatgrass plantations fed single wall purified nanotubes distributed in water had improved germination rate and shoot growth, which was almost 13% larger than the plants grown in pure water. The researchers also discovered that the nanotubes and the single-wall and multilayer particles distributed in one of the two solutions had a negligible impact on the growth of the plants.
Single-walled purified nanotubes dispersed in THF slowed the development of 45% plants versus single-walled nanotubes dispersed in water, indicating that the nanotubes function as transporters of the noxious substance.
According to Barron, the disturbing fact is that the fusion of simple wall nanotubes with organic pollutants such as industrial chemicals, pesticides or environmental solvents can lead to the concentration and immobilization of harmful substances and increase their intake in plants.
Barron said that this restricted research could not determine whether carbon nanotubes distributed in the environment – and possibly in plants – go into the food chain and cause harm to humans.
On the contrary, the team indicated that it would be an advantage to study whether hydrophobic substrates that mimic the positive impacts of single-walled nanotubes can be used for highly efficient channeling of water to the seeds.  " Our work confirms the importance of thinking about nanomaterials as part of a system in isolation ," Barron said. " It is the combination with other compounds that it is important to understand ."
The study's lead author is Seung Mook Lee, a former visiting student research assistant at Memorial High School in Houston who is presenting an undergraduate student at the University of California, Berkeley. Pavan Raja, Rice's research scientist, and Gibran Esquenazi, a graduate student, are the co-authors of the study. Barron is Charles W. Duncan Jr.-Welch Professor of Chemistry and professor of materials science and nanoengineering at Rice and the Sêr Cymru Chair of Low Energy Carbon and Environment at the University of Swansea, Wales (United Kingdom).
The study was supported by the S r r Cymru Program of the Welsh Government and the Robert A. Welch Foundation.