Pesticides are widespread in the agriculture industry to minimise the effects of weeds, pests and diseases on crops. Debates
about costs to wildlife and their environmental impact are common, but
the health impact on the farmers using the pesticides is rarely
considered. This study delved into this issue, observing how surfactants responsible for the irritation interact with the eye.
Commercial pesticides are often formulated as emulsifiable concentrates with nonionic surfactants. Nonionic
surfactants consist of an uncharged hydrophilic head group and
hydrophobic tail. In pesticides, they re-disperse the formulation in the
spray tank, help reduce bouncing of spray droplets on leaf surfaces and
can improve pesticide uptake into the desired plant by influencing
solubility and mobility. However, when these nonionic surfactants come into contact with users' eyes, it can cause irritation. Thus, there is a need to understand how nonionic surfactants irritate corneal cells to help the agrochemical industry design safer pesticides while maintaining benefits on leaf dispersal.
The
focus of this study was the impact of surfactants on changes in the
membrane nanostructure and composition. Both natural and model cell
membranes were used in this study, the nanostructures of which were
analysed upon exposure to nonionic surfactants. Techniques included insertion of nonionic
surfactants into lipid membranes by quartz crystal microbalance with
dissipation (QCM-D), dual polarization interferometry (DPI), confocal
laser scanning microscopy (CLSM), and neutron reflection (NR) performed
on our OFFSPEC beamline.
The cartoon schematic shows different surfactant-lipid bilayer interactions observed.
Surfactants with well-balanced hydrophobicity accumulate in the lipid
bilayer of the cell. Highly hydrophobic surfactants cannot break the
lipid hydrophilic head boundary (resulting in weak structural impact)
and hydrophilic surfactants are only inserted into the membrane a small
amount.
The
surfactants tested varied in hydrophobicity and therefore have
differing interactions with the membrane (depicted in the schematic).
Hydrophobically balanced surfactants elicit large cytoplasm leakage by
damaging the membrane. When increasing or decreasing the hydrophobicity
of the surfactants, the researchers observed
reduced membrane disruptive ability. Surfactants that are highly
hydrophilic or hydrophobic elicit less structural changes and cell death
is not immediately caused by cytoplasm leakage, but rather occurs over a longer period due to membrane leakage.
The
researchers hope that these findings, and information on the
physiochemical properties such as membrane leakage and permeability will
provide a basis for reduction of the eye irritation potential of
pesticide industrial formulations.
