Transformation of plant cuticles in soil: Effect on their sorptive capabilities

Plant cuticular materials play an important role in sorption of polar and nonpolar pollutants in soils. The objective of this study was to examine the effect of decomposition and transformation of plant cuticles on their sorption behavior with triazine herbicides and polycyclic aromatic hydrocarbons (PAHs). Sorption-desorption behavior was studied during 12 mo of incubation of cuticles isolated from tomato (Lycopersicon esculentum Mill.) fruits and pummelo [Citrus maxima (Burm.) Merr.] leaves in sandy soil. Sorption and desorption experiments and spectroscopic and chemical analyses were performed on the samples after 0, 1, 3, 6, and 12 mo of incubation. The decomposition of the cuticles (46-49% after 12 mo) did not affect the organic-C-normalized Freundlich capacity coefficient (K_FOC) for the PAHs. In addition, throughout the incubation period, the two PAHs exhibited linear and reversible sorption isotherms with both cuticles. The isotherms of the triazines were significantly affected by the decomposition of the cuticles from pummelo leaves, whereas only minor changes were recorded for the tomato cuticle samples. For the microcosm with cuticles from the pummelo leaves, the K_FOC values of the triazines increased with increasing decomposition. Preferential degradation of pectin and cutin probably facilitated the interaction between the triazines and the residual cutan and more condensed cutin moieties. Our data suggest that both cutin and cutan play important roles in the sorption of polar and highly nonpolar and aromatic compounds in soils; however, with decomposition, the more condensed structure of the cutin and mainly the cutan biopolymer govern sorption of the cuticle residues.