Sorption of phenanthrene and atrazine by plant cuticular fractions

Several studies have shown selective preservation of plant cuticular materials in soils. However, very little is known about their function as sorbents for the hydrophobic organic contaminants (HOCs) in the soil. In this study, we investigated the sorption and desorption of phenanthrene and atrazine by cuticular fractions of pepper (bulk, dewaxed, nonsaponifiable, and non-hydrolyzable) to better understand the sorptive activity of cuticular matter in soils. The bulk and dewaxed cuticles exhibited carbon-normalized distribution coefficients (K_oc) for phenanthrene and atrazine in the range of that reported for soil humic substances, although both samples were rich in aliphatic structures. No hysteresis was observed in the desorption isotherms of either solute. The nonhydrolyzable residue exhibited a very high K_oc value for atrazine, whereas the nonsaponifiable sample exhibited the lowest K_oc value for both sorbates. Based on solubility parameter data, it is suggested that the nonsaponifiable sample be considered an intermediate between the physical and chemical mixture of pectin and cutan/lignin-like fractions, whereas the dewaxed cuticle is a chemical blending of cutin and pectin. The n-hexane-normalized sorption data suggest that the pepper cuticle can interact specifically with atrazine. This study leads to the conclusion that the contribution of aliphatic-rich plant biopolymers to the sorption of HOCs can be significant because of their preservation and accumulation in soils.