EFFECT OF SOME ETHOXYLATED ALKYLPHENOLS AND ETHOXYLATED ALCOHOLS ON THE TRANSFER OF [C-14] CHLOROTOLURON ACROSS ISOLATED PLANT CUTICLES

The effect of several ethoxylated octylphenols (OF), nonylphenols (NP) and alcohols (AA) on the penetration of [C-14]chlorotoluron through i solated box-tree (Buxus sempervirens L.) leaf cuticles was investigate d. The herbicide solution was deposited as droplets onto cuticle discs maintained on agar blocks acting as receivers. The effects on chlorot oluron transfer across the cuticles depended on the degree of ethoxyla tion of the surfactant, For each series, the chlorotoluron transfer wa s considerably increased by surfactants with low ethylene oxide (EO) c ontent (3 to 6 EO). This effect appeared 24 h after droplet applicatio n, then increased with time. It decreased with further increase in the ethoxylation number, and surfactants with a long ethylene oxide chain (OP16, NP20, NP40 and AA20) had no effect. Surfactant concentration ( OP5) had a large influence on chlorotoluron transfer; penetration incr eased sevenfold when OP5 concentration was raised from 0.01 to 10 g l( -1). Diffusion of the two tritiated octylphenols, [H-3]OP5 and [H-3] O P16, was measured simultaneously during chlorotoluron transfer. The di ffusion rate of the two surfactants across the cuticles was similar, b ut a higher amount of OP5 was retained within the cuticle during trans fer. Study of the effect of surfactants on the cuticular waxes using d ifferential scanning calorimetry showed that wax begins to melt at a l ower temperature in the presence of the nonylphenols NP9 and NP4. Fusi on enthalpy was close to -30 J g(-1).