Sorption interactions of plant cuticular matter with organic compounds are not yet fully understood. The objective of this study was to examine the competitive sorption-desorption interactions of the triazine herbicides (atrazine and ametryn) with cuticular fractions isolated from tomato fruits and leaves of Agave americana. The 13C NMR data suggest a rubber-like nature for the cutin. This biopolymer exhibited reversible and noncompetitive sorption. Enhanced desorption of atrazine was recorded in the bi-solute system with bulk and dewaxed A. americana cuticles. 13C NMR analyses of these samples suggested that the sorbed competitor ametryn facilitated a physical phase transition of rigid paraffinic sorption domain to mobile and flexible domain during sorption process. We suggest that the different sorption-desorption behavior obtained for the two cuticles is related to the higher content of waxes (14% vs 2.6%) and lower content of cutin (46% vs 75%) in the A. americana versus tomato fruit cuticle.

Plant cuticles have been reported as highly efficient sorbents for organic compounds. The objective of this study was to elucidate the sorption and desorption behavior of polar and nonpolar organic compounds with the major structural components of the plant cuticle: the biopolymers cutin and cutan. The sorption affinity values of the studied compounds followed the order: phenanthrene > atrazine > chlorotoluron > carbamazepine. A higher sorption affinity of phenanthrene and atrazine to cutin was probably due to the higher level of amorphous paraffinic carbon in this biopolymer. Phenanthrene exhibited reversible sorption behavior and a high ratio of organic-carbon-normalized distribution coefficient (Koc) to carbon-normalized octanol-water partitioning coefficients (Kowc) with both biopolymers. This suggests that both biopolymers provide phenanthrene with a partition medium for hydrophobic interactions with the flexible long alkyl-chain moieties of the biopolymers. The low Koc/Kowc ratios obtained for the polar sorbates suggest that the polar sites in the biopolymers are not accessible for sorption interactions. Atrazine and carbamazepine exhibited sorption-desorption hysteresis with both sorbents, indicating that both sorbates interact with cutin and cutan via both hydrophobic and specific interactions. In general, the sorptive properties of the studied biopolymers were similar, signifying that the active sorption sites are similar even though the biopolymers exhibit different properties.

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The aliphatic biopolymers cutin and cutan are important precursors of soil organic matter. In this study, we examined the effects of these biopolymers' decomposition and transformation in the soil on their sorptive properties. The levels of cutin and cutan decreased by 35 and 30%, respectively, after 20 mo of incubation. Carbon‐13 nuclear magnetic resonance and differential scanning calorimeter analyses suggested that the rigid (crystalline) polymethylene moieties of cutan decompose with time. This observation is in contrast to previous reports, which suggested that this alkyl‐C moiety is resistant to biodegradation. Cutin, however, exhibited mainly decomposition of the mobile (amorphous) polymethylene moieties. Moreover, some of its degraded materials were transformed into humic materials. The phenanthrene sorption coefficient decreased by 80 and 37% with incubation time of the cutin and cutan samples, respectively. For 1‐naphthol, the sorption capacity decreased by 90% due to cutin decomposition. With cutan, this parameter did not show any changes correlated with incubation time. Phenanthrene exhibited linear and reversible sorption isotherms. In contrast, pronounced desorption hysteresis was obtained for 1‐naphthol with the 20‐mo‐incubated cutin sample and with all cutan samples. With all cutan samples, desorption hysteresis increased with decomposition. Our data suggest that the sorptive nature of both biopolymers was affected by soil decomposition. With degradation, the role of cutin as a natural sorbent decreases while cutan acts as a natural highly efficient sorbent for organic compounds in the soil.