Last updated May 17, 2018 at 12:01 pm
Study calls for more research into nano-fertilisers and nano-pesticides.
There is “a crucial lack of knowledge” regarding the impact of nano-fertilisers and nano-pesticides used in agriculture, researchers have found, meaning that claims of greater efficiency and safer outcomes for the materials cannot be verified.
In a meta-analysis of 78 studies into nano-agrochemicals, published in the journal Nature Nanotechnology, researchers led by Melanie Kah of the University of Vienna in Austria, report that almost all studies into their efficacy and environmental impact are missing essential information.
“There is currently not a single comprehensive study that has evaluated the relative environmental footprint of nano-agrochemicals compared with conventional formulations,” the researchers write.
Nano-agrochemicals – fertilisers and pesticides delivered in tiny capsules about 100 to 200 nanometres in diameter – have been touted as offering multiple benefits for farmers, the environment and the public.
Reducing chemical load
Nano delivery systems have the potential to reduce the overall amount of chemicals deployed by enabling highly targeted applications and controlled slow release. Present delivery systems – by spraying or large particle dispersion, for instance – result in significant amounts of the active ingredients being lost through evaporation and leaching.
In the matter of nano-pesticides, Kah and colleagues identify 19 studies that compare their release efficiency with standard agro-pesticide systems.
In general, the nano-materials delivered a fourfold increase in release efficiency – particularly in slowing release of ingredients – and in a couple of instances the active life of nano-system ingredients was “several hundredfold” longer than the same ingredients delivered by conventional means.
So far, so promising, but the researchers identified wide and concerning gaps in the available data. They were unable, for instance, to find a single study comparing nano slow-release pesticides with those delivered using existing larger-scale slow-release systems based on organoclays or zeolites.
Several of the studies, too, were conducted in laboratory conditions, and over short periods, rather than in the field, raising doubts about how the delivery systems perform in real-world scenarios.
Nano-fertilisers in the spotlight
“Comparisons under more realistic conditions are thus lacking to evaluate how slow-release nano-formulations would perform in the field,” the researchers note.
Similar problems were identified when they turned their attention to nano-fertilisers.
Kah and her team found 29 studies that compared the efficacy of nano-fertilisers to conventional applications. Most, although not all, showed an increase in efficiency, but problems with study design and reporting mean their usefulness is severely limited.
The researchers noted that the relative quantities of chemicals used were often not specified, meaning dosage could not be deduced. Many studies were staged using only seeds and seedlings as targets, and several were conducted in Petri dishes, once again excluding real-world field trials.
Others examined speciality crops, such as tomatoes and fennel, meaning the results could not be meaningfully transferred to broad-acre cereal models.
Nano-materials risk assessments
When it came to assessing the environmental effects of nano-fertilisers, the researchers found just four studies that addressed the issue. Information regarding how, or if, the chemicals deployed impacted on non-target species or accumulated in soils was, they note, “rather scant”.
Such information, they note with a distinct tone of criticism, is considered essential for formal nano-materials risk assessments “but it seems it is not a common standard in other disciplines”.
Quantifying the results from all 78 selected studies, the scientists found that nano-pesticides and nano-fertilisers were overall 20-to-30% more efficient than conventionally applied agents. However, the paucity of data and the multiple design issues associated with most of the studies mean than the finding is not indicative of true efficacy.
The researchers conclude that a lot more work will be “necessary for a sound evaluation of the benefits and new risks that nano-agrochemicals represent relative to existing products”.