Co-occurrence of veterinary antibiotics and fecal source markers in Brittany superficial waters: an experimental study
Résumé
Background and objectives
After absorption by human or animals, pharmaceuticals compounds are excreted either in their free, conjugated or metabolized form in soil and water. The dissemination of those compounds through water resources can lead to antibiotic resistance and could have health effects on living organisms. Numerous studies attest the contamination of various aquatic environments by pharmaceutical compounds, including water resources. The two major contaminations sources are : i) the localized release by industrial and municipal wastewater treatment plants ; ii) non-point dispersion through soil amendment using animal manure or release from animal pastures or by individual septic tanks (Sarmah et al. 2006 ; Ruhoya et Daughton, 2008). Prerequisite of any assessment of the health risks induced by these emerging contaminants requires identification of the contamination sources, close quantification of the input to the water environmental compartment, while developing knowledge on the chemical speciation and fate of the residues once released in the environment. Some residues found in waters may have a mixed origin (human and animal), such as some hormones or antibiotics that can be used indifferently (Kemper, 2008). Identification of the source relies then on co-tracers specifics to humans or animals (Murata et al., 2011). This is particularly important in area of intensive livestock activities such as Brittany, region in the North-West part of France, with mixed watershed. We propose to evaluate by experimentation in laboratory the co-persistence of veterinary pharmaceuticals and fecal markers (fecal stanols) in water from agricultural watershed. Fecal stanols associated with usual bacterial indicators of fecal contamination are microbial source tracking markers used to distinguish among human, bovine and porcine fecal contamination in water (Jardé et al., 2007 ; Gourmelon et al., 2010 ; Jeanneau et al., 2011 ; Derrien et al., 2012).
Methods and results
Experimental study has been carried out at the laboratory scale to evaluate the persistence of veterinary antibiotics and fecal indicators and markers (E.coli and fecal stanols) during 21 days. Microcosms of freshwater have been inoculated with pig slurry contaminated by sulfadiazine, sulfamethazine and oxytetracycline. The microcosms were maintained under aerobic conditions with constant mixing and at constant temperature (20°C ± 1 °C). These experiments were conducted in darkness to avoid heterogeneous lighting due to the turbidity of the system. Antibiotics concentration, E.coli and fecal stanols were quantified in microcosms at the starting day and on days 1, 2, 3, 8, 15 and 21.
Discussion and conclusion
Decay rates and the length of time to obtain a reduction of 50% of the initial inoculums (T1/2) were calculated for E.coli, fecal stanols and antibiotics in the microcosms inoculated with pig slurry. T1/2 was lower for E.coli (1.2 days) than for fecal stanols (between 3.4 to 4.6 days depending on the stanol) and antibiotics (between 2.2 days for oxytetracycline to 7 days for sulfamides). Among antibiotics, the persistence of oxytetracycline is similar to that of fecal stanols and lower than persistence of sulfamides. These differences might be linked to different sorption properties of tetracycline and sulfamides. Fecal stanols seem to co-occur with tetracycline in water samples and might be useful to track sources of pharmaceuticals contamination at the watershed scale. al., 2007 ; Gourmelon et al., 2010 ; Jeanneau et al., 2011 ; Derrien et al., 2012).