The contribution of aliphatic-rich plant biopolymer to sorption of hydrophobic organic compounds is significantly important because of their preservation and accumulation in the soil environment, but sorption mechanism is still not fully understood. In this study, sorption of 1-naphthol by plant cuticular fractions was examined to better understand the contributions of respective fraction. Toward this end, cuticular materials were isolated from the fruits of tomato by chemical method. The tomato cuticle sheet consisted of waxes （6.5 wt%）, cuticular monomer （69.5 wt%）, and polysaccharide （24.0 wt%）. Isotherms of 1-naphthol to the cuticular fractions were nonlinear （N value （0.82 - 0.90）） at the whole tested concentration ranges. The K∞/Kow ratios for bulk cuticle （TC1）, dewaxed cuticle （TC2）, cutin （TC4）, and desugared cuticle （TC5） were larger than unity, suggested that tomato bulk cuticle and cutin are much powerful sorption medium. Sorption capability of cutin （TC4） was 2.4 times higher than the nonsaponifiable fraction （TC3）. The 1-naphthol interactions with tomato cuticular materials were governed by both hydrophobic-type interactions and polar （H-bonding） interactions. Removal of the wax and polysaccharide materials from the bulk tomato cuticle caused a significant increase in the sorption ability of the cuticular material. There was a linear negative trend between K∞ values and the amount of polysaccharides or fraction＇s polarities （（N＋O）/C）; while a linear positive relationship between K∞ values and the content ofcutin monomer （linear R^2 = 0.993） was observed for present in the cuticular fractions. Predominant sorbent of the hydrophobic organic compounds （HOCs） in the plant cuticular fraction was the cutin monomer, contributing to 91.7% of the total sorption of tomato bulk cuticle.
Black carbons （e.g., charcoal） have a great impact on the transport of organic contaminants in soil and water because of its strong affinity and ubiquity in the environment. To further elucidate their interaction mechanism, sorption of polar （p-nitrotoluene, m-dinitrobenzene and nitrobenzene） and nonpolar （naphthalene） aromatic contaminants to burned straw ash charcoal under different de-ashed treatments were investigated. The sorption isotherms fitted well with Freundlich equation, and the Freundlich N values were all around 0.31-0.38, being independent of the sorbate properties and sorbent types. After sequential removal of ashes by acid treatments （HCl and HCl-HF）, both adsorption and partition were enhanced due to the enrichment of charcoal component. The separated contribution of adsorption and partition to total sorption were quantified. The effective carbon content in ash charcoal functioned as adsorption sites, partition phases, and hybrid regions with adsorption and partition were conceptualized and calculated. The hybrid regions increased obviously after de-ashed treatment. The linear relationships of Freundlich N values with the charring-temperature of charcoal or biochar （the charred byproduct in biomass pyrolysis） were observed based on the current study and the cited publications which included 15 different temperatures （100-850℃）, 10 kinds of precursors of charcoal/biochar, and 10 organic sorbates.
Wenhai Huang,Baoliang Chen Department of Environmental Science,Zhejiang University,Hangzhou 310028,China
