There are great concerns around current wide usage of copper-based agrochemicals. Nanotechnology may be used to design more performant copper formulations, but the environmental risks and benefits of the novel nanoformulations need to be critically compared to existing agrochemicals to support the development and authorisation of improved agrochemicals. A series of investigations were carried out to compare the fate on leaves and in soil of nine different nano- and conventional forms of copper, as well as their salt or bulk equivalents.
A new protocol was developed to characterise the resistance to wash-off by rain (rainfastness), from treated citrus leaves [1]. The proportion of Cu lost by wash off from citrus leaves ranged from <2% (Tribasic, nanoCuO or Cu(OH)2) up to 93% (CuSO4) of the initial amount of Cu applied. Intermediate Cu losses were observed for formulations with silica (nano)particles, Kocide, ChampDP, and a formulation with graphene oxide. Smaller particles generally resulted in lower wash off, possibly due to strong attachment to the leaf surface, but other factors such the particle shape and solubility also played an essential role. The retention of nano CuO to the leaves was particularly high and the exact mechanisms involved (e.g. foliar uptake) deserve further work.
The fate of the nine Cu formulations was also compared in three soils with contrasting properties by measuring the fraction of available Cu over one month of incubation. While short-term differences in Cu availability were observed among formulations, there did not seem to be nano-specific behaviours. Differences in available Cu mostly disappeared within a month, showing that the longer term availability of Cu is mainly determined by soil properties rather than the Cu formulation.
These results provide essential information to optimise agrochemical efficacy while minimising the environmental impact.
[1] Kah et al., 2019. Environmental Chemistry. https://doi.org/10.1071/EN18279