Vertical Profiles and Seasonal Variations of Linear Alkylbenzenesulfonates in Lake Sediments

Abstract

Linear alkylbenzenesulfonates (LAS) were detected in a, 0-30cm-deep sediment column at the upperstream point in Lake Teganuma. The range of the LAS concentration in sediments was between 0.1 and 500 ppm (C₁₁C₁₄ LAS per dry solid), and its vertical profile demonstrated the seasonal variation. A mathematical model with a diffusion term and the biodegradation term was applied to simulate the seasonal variation of LAS in the sediment column and to calculate the diffusive flux rate of LAS across the sediment-water interface.
An averaged value 2.4×10^-5 cm²·s^-1 for the diffusion coefficient in the sediment column was obtained from the experiments using the sediment core samples in Lake Teganuma. The biodegradation rate constant of LAS in the sediments was obtained from both the experiments and the model analysis. The obtained rate constant between 0.001 and 0.01 d^-1 was less than the reported value of biodegradation rate constant of LAS in the water on anaerobic condition.
It was suspected that the model which described diffusive transport and biodegradation of LAS could have simulated the seasonal variation of LAS in near surface sediments. The calculated diffusive flux rate across the sediment-water interface was between -0.20 and 0.52 (C₁₁C₁₄ LAS) mg·m^-2·h^-1, and the annual net flux rate from water to sediment was 0.7 g·m^-2·y^-1.