MOBILITIES OF ORGANIC-COMPOUNDS IN RECONSTITUTED CUTICULAR WAX OF BARLEY LEAVES - EFFECTS OF MONODISPERSE ALCOHOL ETHOXYLATES ON DIFFUSION OF PENTACHLOROPHENOL AND TETRACOSANOIC ACID

Effects of monodisperse alcohol ethoxylates on mobilities of C-14-labe lled pentachlorophenol (PCP) and tetracosanoic acid (C(24)AC) in recon stituted cuticular wax of barley leaves were measured. Depending on th e respective alcohol ethoxylate investigated, the diffusion coefficien t (D) of PCP in barley wax was increased by factors ranging from 3 . 3 to 19 . 6, whereas D of C(24)AC, was increased by factors varying bet ween 22 and 315. In order to analyse the relationship between the conc entration of surfactants in the wax and their effects on D, the amount s of alcohol ethoxylates dissolved in the wax at equilibrium with exte rnal concentrations well above the critical micelle concentration (CMC ) were determined. Wax/water partition coefficients (K-ww) of the alco hol ethoxylates were about one order of magnitude lower than cuticle/w ater partition coefficients (K-cw), which is a consequence of the semi -crystalline structure of the wax compared with amorphous cutin. Corre lations between effects on D and maximum amounts of alcohol ethoxylate s dissolved in the wax were obtained indicating an unspecific wax/surf actant interaction. This was solely dependent on the amount of surfact ant sorbed to the wax, leading to increased mobilities of pesticides i n the wax. Applying ESR-spectroscopy, which gave an insight into the m olecular structure of the wax, supported this interpretation of an uns pecific plasticising effect of the alcohol ethoxylates on the molecula r structure of the wax. The results obtained in this study are in good accordance with the results obtained in a recent study investigating the effects of the same group of alcohol ethoxylates on mobilities of pesticides in isolated, but intact, cuticular membranes of Citrus. Thi s demonstrates that the investigation of isolated and subsequently rec onstituted cuticular wax is a useful model system analysing the mechan isms of the surfactant interaction with the transport-limiting barrier of plant cuticles.