Jm. Coret et Ar. Chamel, INFLUENCE OF SOME NONIONIC SURFACTANTS ON WATER SORPTION BY ISOLATED TOMATO FRUIT CUTICLES IN RELATION TO CUTICULAR PENETRATION OF GLYPHOSATE, Pesticide science, 38(1), 1993, pp. 27-32
The effects of several nonionic surfactants on [C-14]glyphosate-mono(i
sopropylammonium) diffusion across isolated tomato fruit cuticles (Lyc
opersicon esculentum Mill.) were compared under controlled atmospheric
conditions (25-degrees-C; 65% R.H.) using a model system consisting o
f 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 wer
e influenced by the ethylene oxide (EO) chain length for a homologous
nonylphenol surfactant series (10 g litre-1). Glyphosate uptake increa
sed with EO content, reaching an optimum at a mean of 17 EO, then decr
easing below control values for surfactants with 40 EO. There was a st
rong influence of the hydrophobe on glyphosate penetration for differe
nt surfactants with similar mean EO content (10 EO). The primary aliph
atic amine enhanced penetration the most, followed by the nonylphenol
while the aliphatic alcohol showed no improvement on glyphosate transf
er across cuticles. Water sorption was greatly enhanced by a primary a
liphatic amine (10 EO) and by a nonylphenol (17 EO). The aliphatic alc
ohol (10 EO) and a shorter-chained nonylphenol (4 EO) did not signific
antly enhance water sorption. Comparison of water sorption with glypho
sate 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-solubl
e herbicides such as glyphosate.