August 20, 2012

expert reaction to new research into nanoparticles and crops

A study in PNAS found that two commonplace nanoparticles — zinc oxide and cerium oxide — may have deleterious effects on plant growth and soil fertility.

Professor Steve McGrath, Senior Principal Scientist at Rothamsted Research, Hertfordshire, said:

“As the authors state, there is in fact a dearth of data on environmental impacts of nanoparticles (NPs). Many of the small number of reports in the first wave of NP research focussed on artificial systems such as hydroponics, and used unrealistically high concentrations. But it is important to remember that even water can be toxic if exposure is great enough.

“It is laudable that the study uses soil, as too few studies to date do this. What is missing is a consideration of pathways and actual levels of exposure. NPs are not added “neat” to soils. If they do transfer in quantities to municipal sewage treatment plants, as seems likely for ZnO (not CeO2) then they are likely to enter agricultural soils. ZnO may dissolve and release Zn, but other processes are also likely along this particularly intense pathway – formation of insoluble sulphide or phosphates crusts on NPs of Zn during processing may make the Zn less bioavailable. This needs further investigation. However, the build-up towards any maximum allowed concentration (MAC) is very slow, and in the case of ZnO, subject to legislative controls in the EU and USA. Thus, total Zn (and therefore automatically ZnO) is monitored in UK soils that receive biosolids, and addition must stop when 0.2 g Zn/kg is reached. It is already well known that plants take up and translocate more Zn around the plant when presented with up to 0.2 g/kg, but this level is not toxic and does not affect yields.

“CeO2 is used in catalysers, but it seems unlikely that the amount deposited on agricultural land would ever be a great as 1 g/kg used by Priester et al. What is therefore needed is a proper assessment of the pathways as CeO2 movement to the environment and the worst case concentrations that are likely to occur. Although it important to be vigilant and protect agricultural production and ecosystem functions, it is premature to say that deleterious effects such as those the authors suggest will actually occur.”

‘Soybean susceptibility to manufactured nanomaterials with evidence for food quality and soil fertility interruption’ by Priester et al., published in PNAS on Monday 20 August.