The Sorption Behavior Of Different Polarity Contaminant To Lettuce

Investigating plant uptake of organic contaminants is meaningful for ecological risk assessment, the crop safety and the development of phytoremediation. Previous works focused on the nonpolar organic compounds, and demonstrated that the capacity of plant uptake has a positive correlation with the hydrophobicity of the pollutants. However, the above conclusion may not be applied completely for the polar chemicals.The objective of this work is to investigate the influence of polarity on sorption behavior. Sorption of34compounds on lettuce was studied, as compared with the control sorbent (standard cellulose). The result showed that the sorption isotherm of all the experimental chemicals was highly linear with the correlation coefficient (R2) greater than0.97, which indicated that hydrophobic distribution was the main process for all the probe solutes. Plotting the octanol/water partition coefficient (logKow) against with the plant/water partition coefficient (logKp1), we found the R2was less than0.85for polar compound, and0.996for nonpolar compounds (PAHs). It implied that hydrophobic distribution was the sole sorption mechanism for PAHs, while for polar chemicals, the sorption was influenced by specific interaction besides hydrophobic effect.Linear solvation energy relationship (LSER) was taken to elucidate the special interaction between organic solutes and lettuce through intermolecular forces. Using SPSS16.0software, the LSER equation was given as follows:log Kp1=-0.519+0.98R2-0.87(?)2H+0.925Σα2H-2.0381Σβ2H+2.715VVx The related terms demonstrated that factors influencing the sorption are π-/n-electron interaction, dipolarity/polarity interactions, hydrogen-bond acidity interactions, hydrogen-bond basicity interaction and dispersion interaction. Moreover, the relative contribution of each interaction was calculated. The data suggested dispersion interaction and π-/n-electron interaction were the dominant factors. Hydrogen-bond basicity interaction depends on whether the solute has hydrogen-bond donor (HBD) or hydrogen-bond acceptor (HBA). However, dipolarity/polarity interactions and hydrogen-bond acidity interactions had a negative effect. For the isomeride, all the forces performed almost the same contribution.The comparison of sorption between lettuce and cellulose performed that the partition coefficients of all the probe compounds were followed with this order:logKow> logKp1>logKch (carbohydrate/water partition coefficient), owing to the composition of sorbent. Meanwhile, for the solute with identical hydrophobicity, the sorption difference caused by polarity is independent of sorbent.