Mineralization of linear alkylbenzene sulfonate (las) and linear alcohol ethoxylate (lae) in 11 contrasting soils

The microbial mineralization of [U-14C-ring] linear alkylbenzene sulfonate (LAS) and [U-14C-ethoxylate] linear alcohol ethoxylate (LAE) was examined in 11 soils. These soils differed in their physical-chemical properties and were obtained from geographically distinct locations. With one exception, they had no previous exposure to synthetic surfactants. Soil samples were amended with trace levels (50 ng/g soil) of each 14C surfactant, and evolution of 14CO2 was measured over time. When appropriate, the data were fitted to a first-order production equation, and first order rate constants and asymptotic yields of 14CO2 were estimated using nonlinear regression. Both surfactants were mineralized without a lag period in every soil tested. Yields ranged from 16 to 71% and 30 to 69% for LAS and LAE respectively. First-order rate constants ranged from 0.14 to 0.63 for LAS and 0.07 to 0.62 for LAE. Mean half-life (across all soils) was 2 d for both surfactants. Community microbial activity, measured as the rate of acetate incorporation into lipids, did not correlate with either the rate or extent of surfactant mineralization. Subjecting these soils to cycles of wetting and drying in the laboratory prior to testing in most cases resulted in more rapid and extensive mineralization. These results indicate that microbial communities in soils have an indigenous ability to degrade low concentrations of LAS and LAE. This ability appears to be ubiquitous since it is present in a wide array of soil types from various locations. In addition, laboratory experiments involving wetting and drying of soils indicated that both the rate and extent of mineralization may be affected by climatological events.