Linear alkylbenzenesulfonate (LAS) was detected in a 0-30 cm deep sediment column collected in Lake Teganuma (one of the most polluted lakes in Japan) . The range of the LAS concentration in sediments was between 0 .1 and 500 µg g -1 (C11-C14 homologs per dry solid) and its vertical profile showed a seasonal variation . A mathematical model, which includes a diffusion term and a biodegradation term, was used to simulate the temporal variation of LAS in the sediment column and to calculate the diffusive flux rate of LAS across the sediment/water interface . An averaged diffusion coefficient of 2.4 x 10 -5 cm2 s -1 for the sediment interstitial water was obtained from sediment core samples located in Lake Teganuma . The biodegradation rate constant (0 .002 d -1 ) of LAS in the sediment obtained from the model analysis was considerably less than that reported for LAS in anaerobic waters . These results confirm that a model describing diffusive transport and biodegradation of LAS in the sediments can simulate the temporal variation of LAS in near surface sediments . The diffusive flux rate from overlying water to bottom sediment was calculated to be between -0 .20 and 0 .52 (C 11 -C14 LAS) mg m -2 h -1 and the annual net flux rate was 0.7 g m-2 y -1 .