Toxicity of linear alkylbenzene sulfonates and nonylphenol in sludge-amended soil

The application of sewage sludge to agricultural land brings several chemicals to the soil ecosystem. Linear alkylbenzene sulfonates (LAS) and nonylphenol (NP) are frequently found in sludge at relatively high concentrations. The toxic effects of LAS and NP to two soil invertebrates (Folsomia candida and Enchytraeus albidus) and five different microbial processes (aerobic respiration, nitrification, denitrification, anaerobic CH4 production, and anaerobic CO2 production) were investigated in sludge–soil mixtures. Median lethal concentrations (LC50 values) and median effective concentrations (EC50 values) were quite similar and calculated to be in the range of 1,143 to 1,437 and 71 to 437 mg/kg (dry wt) for LAS and NP, respectively. The EC50 values for nitrification and CH4 production were 431 and 277 mg/kg, respectively, for LAS and 343 and 754 mg/kg, respectively, for NP. Aerobic respiration and denitrification were not inhibited at the tested concentrations. The results show that NP was more toxic than LAS to both F. candida and E. albidus, whereas LAS was more toxic than NP to the anaerobic CH4 production. The safety margins between the lowest 10% effective concentration (EC10) and the estimated environmental concentration were a factor of 11 for LAS and 510 for NP when the concentrations of the contaminants corresponded to the current Danish cutoff values of 1,300 mg/kg for LAS and 30 mg/kg for NP.