Biodegradation kinetics of linear alkylbenzene sulfonate in sludge-amended agricultural soils

The kinetics of ultimate biodegradation (mineralization to CO2) of linear alkylbenzene sulfonate (LAS) were studied in sludge-amended agricultural soils for a series of pure chain length LAS homologs containing 10 to 14 carbon atoms in the alkyl chain. Degradation rates were measured by following the production of 14CO2 from uniformly 14C-ring-labeled material. In general, degradation of LAS was rapid in soil over a broad concentration range (0.1 to 10 times the expected environmental concentration) and demonstrated little variation among different homologs. Half-lives for mineralization of the benzene ring ranged from 18 to 26 days and were not significantly different for any homolog over the range of alkyl chain lengths tested. Half-lives measured for LAS degradation in these studies were comparable to values reported in the literature and also to values obtained for naturally occurring materials (stearic acid, cellulose) typically present in soil environments. On the basis of the results of the present studies and those of other investigators, it is concluded that soil environments exposed to LAS in sewage sludges contain microbial communities which can actively metabolize this material. Rates of biodegradation of the benzene ring, the final step in the LAS biodegradation pathway prior to complete mineralization, are also sufficient to prevent LAS from accumulating in soil environments.