INFLUENCE OF SOME NONIONIC SURFACTANTS ON WATER SORPTION BY ISOLATED TOMATO FRUIT CUTICLES IN RELATION TO CUTICULAR PENETRATION OF GLYPHOSATE

The effects of several nonionic surfactants on [C-14]glyphosate-mono(isopropylammonium) diffusion across isolated tomato fruit cuticles (Lycopersicon esculentum Mill.) were compared under controlled atmospheric conditions (25-degrees-C; 65% R.H.) using a model system consisting of 1-mul droplets applied to isolated cuticles on agar blocks. Rates of diffusion for glyphosate (10 g acid equivalent litre-1 in the applied solution) and overall amounts recovered in underlying agar blocks were influenced by the ethylene oxide (EO) chain length for a homologous nonylphenol surfactant series (10 g litre-1). Glyphosate uptake increased with EO content, reaching an optimum at a mean of 17 EO, then decreasing below control values for surfactants with 40 EO. There was a strong influence of the hydrophobe on glyphosate penetration for different surfactants with similar mean EO content (10 EO). The primary aliphatic amine enhanced penetration the most, followed by the nonylphenol while the aliphatic alcohol showed no improvement on glyphosate transfer across cuticles. Water sorption was greatly enhanced by a primary aliphatic amine (10 EO) and by a nonylphenol (17 EO). The aliphatic alcohol (10 EO) and a shorter-chained nonylphenol (4 EO) did not significantly enhance water sorption. Comparison of water sorption with glyphosate diffusion across cuticles suggests a strong relationship between the two. Change in solution pH over a limited range had no significant effect. Promotion of cuticular hydration by surfactants may thus play an important role in the enhancement of foliar uptake of water-soluble herbicides such as glyphosate.