Toxic organic compounds, such as the surfactants linear alkylbenzene sulfonates (LAS) and nonylphenol polyethoxylates (NPE), Polycyclic aromatic hydrocarbons (PAH) and residues derived from plastics (PAE-phthalates) end up in sewage sludge. In order to evaluate and quantify the potential environmental risks associated with the xenobiotic introduction into biological life cycle, the EU BIOWASTE project (QLK5-CT-2002-01138) devotes one task to the study of the fate of xenobiotic in a sandy soil after sludge spreading on a 30-year field-scale record experiment. Experimental maize crop fields from Bordeaux (France) have been amended with 100 tons per hectare each 2 years from 1974 to 1992. From 1992 to 2004, the fields were maintained and cropped with maize. This experiment shows that the concentration fluctuations in the sludge amended soil follow the same pattern of those in the sewage sludge showing that there is a real impact of the present xenobiotics in the sewage sludge on the concentration of the xenobiotics in the soil. Nonetheless, 12 years after the last addition of sewage sludge, the residual concentrations remain from 2 to 10 times higher than the content of the control soil, even though these levels are inferior to the Predicted Non Effect Concentration (PNEC). Only LAS level went back to the level in the control soil. However, only the LAS concentration is above the PNEC during all the experiment due to the very high level of LAS in the sludge (20 g/kg dry weight). These results show that even though this compound is much more degradable than NPE and PAE, it may have a long term effect in soil if high quantities are spread. To conclude, this study underlines the importance to fix maximum level for xenobiotic compounds for sewage sludge spreading on agricultural land, and also the central role of the sewage sludge processes in reducing the xenobiotic concentrations before spreading.

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