Review of more than a thousand articles seeks to understand how nanomaterials affect plants

Researchers from the Center for Nuclear Energy in Agriculture at the University of São Paulo (Cena-USP) reviewed 1.154 original scientific articles, published between 2009 and 2022, which deal with the effect of nanomaterials on 1.374 plants from 253 species. The objective was to capture (quantitatively) and organize the experimental parameters used by the scientific community, in addition to the results obtained over the last decade.

With metadata – data generated from others already published in the literature – the group of authors systematized which nanomaterials are most used, what type of environment plants are exposed to, which plant organs are most exposed to treatments and how long the treatments last. studies. Furthermore, they showed the percentages of nanomaterial-based treatments that caused positive, negative or both effects – in addition to those that did not affect the plants.

The work received funding from FAPESP through eight projects (20/07721-9, 20/11178-9, 20/11546-8, 17/16375-4, 15/05942-0, 16/50014-6, 22/03399-0 e 17/21004-5). The conclusions were published in the magazine Environmental Science: Nano, from the Royal Society of Chemistry.

“If we really want to explore the properties of nanomaterials to increase crop productivity, or access the potential risk they can pose to the environment, we need to properly plan and execute the studies”, explains Hudson Wallace Pereira de Carvalho, main author of the work . “The results obtained in a given experiment depend on how it was conducted”, adds Carvalho, who received his doctorate in chemistry from USP and Paris XI University.

The research found, for example, that 71% of studies did not use positive controls. But when evaluating the effect of a given nanoparticle, one should also try to include micrometric particles or soluble compounds with similar chemical composition. “The decoupling of effects arising from nanometric properties from those caused by ions or microparticles could be facilitated by this strategy”, explains Carvalho.

Another issue addressed was the concentration of nanomaterials to which plants are exposed. “We noticed that for a given chemical element the concentrations are, in general, higher than those to which plants are naturally exposed in the environment or those to which they are exposed in agricultural production environments”, says the researcher. This leads to another question: do the effects obtained, especially the negative ones, derive from high concentrations or actually from properties of the nanometric world?

Furthermore, it was found that the studies are short when comparing their duration and the life cycle of crops. The median duration of most experiments was 49 days for plants grown in soil, which is very little compared to annual crop cycles, of 90 to 120 days. In other words, the minority of studies evaluate the impact of nanomaterial-based treatments on productivity and production quality. And few experiments (6%) were carried out under field conditions (which require great effort). In a field experiment, climate, pathogens and soil variables change from one location to another. Therefore, to be valid, it must be installed in different locations and even for more than one harvest, points out the article. On the other hand, before applying nanoparticles to crops, great care must be taken with well-established experiments in greenhouses, so as not to spread potentially toxic substances into the environment.

Impacts

The group also found that only 19% of studies in which nanoparticles were applied to soil assessed whether they had any impact on microorganisms. “The latter are essential components for maintaining soil fertility”, warns Carvalho.

“It is difficult to draw conclusions as to why the experiments were conducted in this way. On the other hand, our meta-analysis points out opportunities and directions that may be interesting to follow”, says the researcher. “Clearly, this is a relatively recent area of ​​multidisciplinary knowledge and there is still a lot to be studied.”

For example, it is known that some properties are more pronounced in particles smaller than 29 nanometers. The study reveals that around half of the treatments were above this threshold. “This may signal that we are still trying to understand how particle size affects plants.”

The observations point to the intricate relationship between the ability to infer conclusions and the experimental design used, the study concludes.

The comprehensive and updated view of the effects of nanomaterials on plant systems raises the question of whether they will lead to incremental yield gains by replacing current inputs with nanotechnology-based ones, such as the controlled release of fertilizers and pesticides, or whether they could revolutionize agriculture by attacking problems that have not yet been addressed in practice, such as “dodging” stress and plant defense mechanisms, or modulating their metabolism.

The article Are nanomaterials leading to more efficient agriculture? Outputs from 2009 to 2022 research metadata analysis, signed by 14 other researchers from six different institutions, can be read by accessing here.