Sorption of Volatile Organic Chemicals in Plant Surfaces

Sorption in the cuticles covering most of the above-ground surface of plants is the first step of the atmosphere-to-vegetation transfer of volatile organic compounds (VOCs). The partitioning of 50 reference VOCs of varying physical-chemical properties between the vapor and the cuticular matrix (MX, obtained by dewaxing isolated cuticles) or aqueous phase, respectively, was studied at 25 °C using static headspace gas chromatography. Linear sorption isotherms were obtained over a wide range of concentrations, indicating that Henry's law applies. Concentration-independent cuticular polymer matrix (MX)/air (K_MXa), air/water (K_aw), and MX/water (K_MXw) partition coefficients were derived from the slopes of the sorption isotherms. The experimentally determined values of K_MXa ranged from 39 (isoprene) to 33 000 (1-hexanol). K_MXas were linearly related to the corresponding partition coefficients for the native cuticular membrane. The values of K_aw of the reference compounds varied from 1.94 × 10^-4 (methanol) to 1.66 (limonene). MX/water (K_MXw) partition coefficients ranging from 0.090 (methanol) to 18 094 (limonene) were estimated from K_MXa and K_aw. For predictive purposes, a set of quantitative property/property and structure/property relationships between K_MXa and simple physical-chemical properties and structural descriptors was established.