Steroids: markers of faecal contamination
Résumé
The faecal pollutions contribute to the degradation of aquatic ecosystems, affect water quality and thus generate public health problems. In a context of intensive agriculture, animal faeces or sludge from wastewater are applied to fields in the place of traditional mineral fertilizers. According to the implementation of the Water Framework Directive [DCE 52006/7/CE], the level of faecal contamination is based on the analysis of microbiological markers (E.coli, enterococci). However, they are not suitable for monitoring faecal pollution and are not able to distinguish the different sources of pollution. Therefore, it is necessary to develop tools to discriminate the origin of faecal contamination. Molecular markers, such as steroids can be used as indicators of faecal contamination. This study aims to propose an absolute tool that is able to differentiate a set of animal manures (cow and pig faeces) and different types from the same origin (cowpat, fresh and old cow manures, fresh and treated pig slurries and separated pig solids). The results show that cow and pig faeces have different steroids fingerprints. For cow faeces, there is an increase phytosterols amount from cowpat to cow manure. For pig faeces, there is an important heterogeneity in pig slurry sub-group. But on the diagram %C27 versus %(C28+C29), the two types of animal manures are well separated one from the other. Coupled with statistical analysis and after identification and selection of principal components, we have arrived at a model able to distinguish easily the origin of faecal contamination in agro-hydro-systems.