PENETRATION OF AN ETHOXYLATED FATTY ALCOHOL SURFACTANT ACROSS LEAF CUTICLES AS AFFECTED BY CONCENTRATION, ADDITIVES, AND HUMIDITY

The penetration of radiolabelled octaethylene glycol dodecyl ether (C1 2E8) across astomatous leaf cuticles from five plant species with spec ial regard to pear (Pyrus communis L.) was studied. Velocity of penetr ation across Fear cuticles was highest during the first 2 h and it inc reased with concentration. Fifty to 80 % of the applied dose penetrate d within 2 h with concentrations ranging from 0.04 g/l to 2.0) g/l C12 E8, respectively. Velocity of penetration was also increased by adding the polydisperse surfactant, Genapol C-100, which has a similar avera ge formula and ethylene oxide content (C12.5E8.4). In contrast, Genapo l C-200, wit h an average ethylene oxide content of 17 had no effect ( at. 2 g/l on C12E8 penetration. It is suggested that C12E8 and other h omologues of polydisperse surfactants diffuse independently and rates of penetration can be increased by those homologues which increase dif fusivity in the cuticles. Homologues having this property are termed a ccelerators as they increase their own rates of diffusion but also rat es of penetration of active ingredients which cross cuticles by follow ing the accelerator front. They are useful additives if rapid penetrat ion is desired, as with systemic active ingredients. Velocity of penet ration of C12E8 in presence of Genapol surfactants did nor. depend on relative humidity (11-93%) and only slightly so if applied alone. Howe ver, surfactant penetration rates were greatly slowed in presence of C aCl2 (greater than or equal to 0.2 g/l) and other salts. This effect w as largest at low (11%) humidity and diminished at higher (93 %) humid ities. Combining systemic fungicides with CaCl2 as foliar nutrient or the use of hard water is likely to reduce rates of uptake of active in gredients if accelerator adjuvants are used as ingredients of the form ulation.