Integrated whole-cell ecotoxicity assessment of urban wetweather discharges on Chlorella vulgaris: interest of whole-cell biomarkers for fast toxicity monitoring
Résumé
Urban wet weather discharges (UWWDs) are designed as all the water discharged by sewerage installations (mixture of treated wastewater and rainwater), by combined sewer overflows (CSO) (mixture of non-treated wastewater and rainwater), and stormwater outfalls (non treated rainwater), during rain events. These events can lead to a rejection of a high number of micropollutants in aquatics ecosystems, as pesticides, polycyclic aromatic hydrocarbons, heavy metals, poly-chloro-biphenyls, or pharmaceutics, due to the currently low number and efficiency methods to treat them. Consequently, there is strong issue to monitor them and prevent any degradation of suburban aquatic ecosystems. Many pollutants detected in UWWDs can impact aquatic organisms, as microalgae. These micro-organisms represent very sensitive bio-indicators, at the base of aquatics food webs. Numerous publications highlight the sensitivity and rapidity of response of these organism’s biomarkers to UWWDs pollutants as heavy metals and pesticides; more sensitives than classical bioassays as algal growth inhibition. Then, the aim of the study was to develop and apply a set of biomarkers on Chlorella vulgaris, a very common algae in potentially impacted aquatic suburban ecosystems as rivers and lakes, on UWWDs samples from a high diversity of watershed. Thus, this study’s aim is to the interest of using these biomarkers for the fast monitoring of UWWDs pollution and toxicity. UWWDs samples were obtained in a high urbanized region of France, Lyon agglomeration. Multiple campaigns were performed to obtain 14 samples collected on auto-sampled samples. A set of 4 biomarkers was developed to the ecotoxicity assessment of UWWDs. Among them, membrane permeability (linked to cell viability), esterase, phosphatase and photosynthetic activity were assessed after short (2 and 24 hours) UWWDs exposure. In parallel, physico-chemical analyses were carried out analyzing classical parameter (pH, conductivity, nitrates, etc.), 8 inorganic pollutants (heavy metals) and 112 organics pollutants to correlate ecotoxic effects to the presence of pollutants. Results showed a significant impact of UWWDs on algal metabolism. Among these algal biomarkers, photosynthetic activity disturbance was the more sensitive, with high inhibitions observed after 24 h (until 85.6% of inhibition). Phosphatase and esterase activities were subjected to inhibitions or stimulations. No toxicity was observed with membrane permeability. The results can be explained by the fact that photosynthesis activity is a less specific biomarker, which respond to many families of micropollutants while phosphatase and esterase activities are linked to specific families of pollutants (heavy metals and pesticides), present in low concentrations in UWWDs. Moreover, stimulation can be linked to the presence of large concentrations of stimulant nutrients (phosphates and nitrates). Consequently, biomarkers can be classed in terms of sensitivity for UWWDs as following: Photosynthetic activity>Phosphatase activity=Esterase activity>Membrane permeability. In conclusion, these fast-response biomarkers were validated to be used for UWWDs fast monitoring.