Nanoparticles could reduce wheat yield

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[BEIJING] Nanoparticles that escape during the manufacture and use of consumer products would substantially reduce the growth of wheat were they to end up in soil, according to Chinese scientists.

The production, use and disposal of nanomaterials from sectors such as cosmetics and electronics can lead to their release into air, water and soil. Their presence in wastewater, and their direct use in agricultural technologies, can bring them into contact with crops.

Once in soil, nanoparticles can transform crops and the soil ecosystem, say the researchers, from the Chinese Academy of Sciences, but so far these effects have been little studied.

They investigated the effect of titanium dioxide (TiO₂₎ and zinc oxide (ZnO) nanoparticles,  widely used in sunscreen and electronics, on wheat growth and soil enzyme activities, at the Changshu Agro-ecological Experimental Station.

Both of the nanoparticles reduced the biomass of wheat — TiO₂ by more than 13 per cent and ZnO by more than seven per cent. When wheat was grown with ZnO the adult plant also ended up harbouring the nanoparticles. TiO₂ adhered directly to the cell wall of wheat, while ZnO enhanced the crop's uptake of toxic zinc.

The nanoparticles were also "clearly toxic for the soil environment", changing the activity of some soil enzymes.

But the researchers said that their results do not warrant banning the use of nanoparticles.

"We can't say nanoparticles are a big threat to the world's crops because at present there are only a few studies on the impact of nanomaterials on the soil environment," Hongyan Guo, a co-author and professor at the State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, told SciDev.Net.

He said more research into the behaviour and ecological effects of nanoparticles in soil is needed to inform environmental policy.

Meanwhile, he suggested cutting the emissions of nanoparticles.

Li Daguang, a science policy expert at the Graduate University of the Chinese Academy of Sciences, agreed with calls for more research. He told SciDev.Net that "developing countries don't consider the potential risks of nanotechnology because they prioritise the economical benefits".

Graeme Batley, chief research scientist at Commonwealth Scientific and Industrial Research Organisation (CSIRO) Land and Water, Australia, said the paper could help regulators and environmental managers "put into perspective the risks posed by metal nanoparticles".

He added that such nanoparticles can damage cell walls and inhibit some enzyme activities, but exactly how this translates into environmental risk is still not clear — although it has been shown that the number of particles is a factor.

He noted that the only way for nanoparticles to reach the soil concentrations tested in this study would be from an environmental spill or if they were used in high doses for delivering herbicides or nutrients to plant roots.

The study was published last month (1 April) in the Journal of Environmental Monitoring.

Link to article abstract in Journal of Environmental Monitoring