Abstract}It is hypothesised that the experimental sorption coefficient normalised to the organic carbon fraction of sediment (K exp oc ) for non-ionic, hydrophobic, organic pollutant depends upon the molecular properties as well as background ionic strength of the aquatic system. The utility of this concept has been demonstrated by incorporating ionic strength as a parameter in the three quantitative structure activity relationships (QSARs) namely octanol-water partitioning coefficient model (Kow model), the linear solvation energy model (LSE model), and molecular connectivity indices theory (MCI model). Four chlorinated benzenes and two chlorinated phenols were employed in the present study. Sorption experiments using sediment from the Patalganga River were conducted in laboratory (bottle point method) at different ionic strengths (viz. 0.01, 0.05, and 0.10 M). The K cal oc values predicted using Kow model incorporating ionic strength compare reasonably well with the K exp oc values (r 2 ¼ 0:60 and standard error of estimator i.e. SEE=0.35). The LSE model incorporating ionic strength too, was found to be equally good (r 2 ¼ 0:67, SEE=0.33). An attempt has also been made to validate the QSARs developed in the present study utilising the sorption parameters experimentally measured by Dewulf et al. (1996)
This study addresses the issues related to decontamination of marine beach sand accidentally contaminated by petroleum products. Sorption and desorption of BTEX (i.e., benzene, toluene, ethylbenzene, and xylene) onto the sand from Uran Beach, located near the city of Mumbai, India, were studied, and isotherms were determined using the bottle point method to estimate sorption coefficients. Alternatively, QSARs (i.e., quantitative structure activity relationships) were developed and used to estimate the sorption coefficients. Experiments for kinetics of volatilization as well as for kinetics of sorption and desorption in the presence of volatilization were conducted in a fabricated laboratory batch reactor. A mathematical model describing the fate of volatile hydrophobic organic pollutants like BTEX (via sorption and desorption in presence of volatilization) in a batch sediment-washing reactor was proposed. The experimental kinetic data were compared with the values predicted using the proposed models for sorption and desorption, and the optimum values of overall mass transfer coefficients for sorption (K s a s ) and desorption (K d a d ) were estimated. This was achieved by minimization of errors while using the sorption coefficients (K p ) obtained from either laboratory isotherm studies or the QSARs developed in the present study. Independent experimental data were also collected and used for calibration of the model for volatilization, and the values of the overall mass transfer coefficient for volatilization (K g a g ) were estimated for BTEX. In these exercises of minimization of errors, comparable cumulative errors were obtained from the use of K p values derived from experimental isotherms and QSARs.
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