Impact of (nano)formulations on the distribution and wash-off of copper pesticides and fertilisers applied on citrus leaves

Abstract

Environmental contextThere are great concerns around current wide usage of copper-based agrochemicals. We compare the fate of nano- and conventional forms of copper, in particular their resistance to wash-off by rain (rainfastness), following their application to citrus leaves. Results showing large differences between the formulations in the amount and forms of copper washed from the leaves provide essential information to optimise agrochemical efficacy while minimising the environmental impact. AbstractThis study compares the rainfastness of nine forms of Cu, including nano and conventional Cu-based fungicide formulations, as well as their salt or bulk equivalents. Rainfastness is the ability to resist wash-off; it is a key property for improving pesticide formulations and for assessing the potential transfer of pesticides to the soil. A new protocol was developed to characterise losses of Cu from treated leaves. It consisted of dipping the leaves in rainwater and then in an acid/ethanol mixture followed by size fractionation. The proportion of Cu lost by wash-off from citrus leaves ranged from <2% (Tribasic, nCuO 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 (9–14% of applied Cu), Kocide (22%), ChampDP (31%), and a formulation with graphene oxide (47%). Smaller particles generally resulted in less wash-off, possibly due to stronger attachment to the leaf surface, but other factors such as the particle shape and solubility also played an essential role. The retention of nCuO to the leaves was particularly high, and the exact mechanisms involved (e.g. foliar uptake) deserve further work. Most of the Cu was washed off in its ionic form (>74%). Two Cu formulations (one commercial formulation and the formulation with graphene oxide) also showed wash off in significant proportions of Cu (~17%) in the nano-sized fraction. This study provides essential information on the amounts and forms of Cu that may reach the soil after the application of Cu-based agrochemicals. The great diversity in behaviour across the range of formulations considered highlights the need for more systematic research to fully exploit the potential improvements of current agrochemicals through (nano)formulation technologies.

Differential Reactivity of Copper- and Gold-Based Nanomaterials Controls Their Seasonal Biogeochemical Cycling and Fate in a Freshwater Wetland Mesocosm

“…Previous size fractionation studies of Cu from Kocide in water found that 100% of Cu species were below 0.45 μm, with 20% passing through a 0.1 μm filter. 29 Kocide also contains 1−5% of (undefined) clays, 5−10% 2-propenoic acid, and 38.9− 47.9% of "other proprietary ingredients". 28 These organic phases may influence ENM fate once released in the environment.…”

Copper-fixed quat: a hybrid nanoparticle for application as a locally systemic pesticide (LSP) to manage bacterial spot disease of tomato

“…Simulated wash of LSP particles on leaves. The release of Cu upon wetting of LSP previously dried on the leaves was evaluated following the protocol described by Kah et al 38 with minor modications. Newly emerged citrus leaves were collected, gently washed with DI water, and air dried.…”

Fate of copper in soil: effect of agrochemical (nano)formulations and soil properties

“…In a previous study, 29 we considered a series of nine wellcharacterised formulations of Cu, including nano and conventional Cu-based formulations, as well as their salt or bulk equivalents. A wash off study carried out on citrus leaves highlighted a wide range of behaviour in terms of rainfastness among the nine formulations (i.e.…”