Effects of linear alkylbenzene sulphonates (LASs) on exogenous organic matter content and evolution in sewage sludge-amended soils

Linear alkylbenzene sulphonates (LASs) are anionic surfactants commonly used in commercial detergents. A potential risk associated with the recycling of sewage waste materials is the presence of LASs and their primary degradation products, which could accumulate in sludge, especially during anaerobic processing. The long-term accumulation of these contaminants in soils and especially the potential disturbance of soil functions need to be studied in more detail. In our study, the influence of the amendment added to an agricultural soil with different organic wastes containing LASs on organic matter content and nitrogen (N) content evolution and mineralization was studied in field conditions. A completely randomized 3 x 3 factorial arrangement, representing two sewage sludge types (composted and uncomposted) and three levels of LAS presence (0, 15, and 30 g/m(-2)) in treated soils, was established using field plots (7 x 2 m); the results are compared with untreated plots. Statistical models based on covariance analysis were used to understand the dynamics of and the main factors influencing carbon (C) and N mineralization in sewage sludge amended-soils in the presence of LAS. LAS seemed to alter nitrogen mineralization, especially the nitrate dynamics.