Nathalie Chèvre

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

Many organic micropollutants present in wastewater, such as pharmaceuticals and pesticides, are poorly removed in conventional wastewater treatment plants (WWTPs). To reduce the release of these substances into the aquatic environment, advanced wastewater treatments are necessary. In this context, two large-scale pilot advanced treatments were tested in parallel over more than one year at the municipal WWTP of Lausanne, Switzerland. The treatments were: i) oxidation by ozone followed by sand filtration (SF) and ii) powdered activated carbon (PAC) adsorption followed by either ultrafiltration (UF) or sand filtration. More than 70 potentially problematic substances (pharmaceuticals, pesticides, endocrine disruptors, drug metabolites and other common chemicals) were regularly measured at different stages of treatment. Additionally, several ecotoxicological tests such as the Yeast Estrogen Screen, a combined algae bioassay and a fish early life stage test were performed to evaluate effluent toxicity. Both treatments significantly improved the effluent quality. Micropollutants were removed on average over 80% compared with raw wastewater, with an average ozone dose of 5.7 mg O3 l(-1) or a PAC dose between 10 and 20 mg l(-1). Depending on the chemical properties of the substances (presence of electron-rich moieties, charge and hydrophobicity), either ozone or PAC performed better. Both advanced treatments led to a clear reduction in toxicity of the effluents, with PAC-UF performing slightly better overall. As both treatments had, on average, relatively similar efficiency, further criteria relevant to their implementation were considered, including local constraints (e.g., safety, sludge disposal, disinfection), operational feasibility and cost. For sensitive receiving waters (drinking water resources or recreational waters), the PAC-UF treatment, despite its current higher cost, was considered to be the most suitable option, enabling good removal of most micropollutants and macropollutants without forming problematic by-products, the strongest decrease in toxicity and a total disinfection of the effluent.

Occurrence and fate of micropollutants in the Vidy Bay of Lake Geneva, Switzerland. Part II: Micropollutant removal between wastewater and raw drinking water.

The occurrence and removal of 58 pharmaceuticals, endocrine disruptors, corrosion inhibitors, biocides, and pesticides, were assessed in the wastewater treatment plant (WWTP) of the city of Lausanne, Switzerland, as well as in the effluent-receiving water body, the Vidy Bay of Lake Geneva. An analytical screening method to simultaneously measure all of the 58 micropollutants was developed based on ultra performance liquid chromatography coupled to a tandem mass spectrometer (UPLC-MS/MS). The selection of pharmaceuticals was primarily based on a prioritization study, which designated them as environmentally relevant for the Lake Geneva region. Except for the endocrine disruptor 17alpha-ethinylestradiol, all substances were detected in 24-h composite samples of wastewater entering the WWTP or in the treated effluent. Of these compounds, 40% were also detected in raw drinking water, pumped from the lake 3 km downstream of the WWTP. The contributions of dilution and degradation to micropollutant elimination between the WWTP outlet and the raw drinking water intake were established in different model scenarios using hypothetical residence times of the wastewater in Vidy Bay of 1, 4, or 90 d. Concentration decrease due to processes other than dilution was observed for diclofenac, beta-blockers, several antibiotics, corrosion inhibitors, and pesticides. Measured environmental concentrations (MECs) of pharmaceuticals were compared to the predicted environmental concentrations (PECs) determined in the prioritization study and agreed within one order of magnitude, but MECs were typically greater than the corresponding PECs. Predicted no-effect concentrations of the analgesic paracetamol, and the two antibiotics ciprofloxacin and sulfamethoxazole, were exceeded in raw drinking water samples and therefore present a potential risk to the ecosystem.

Effect of pulse herbicidal exposure on Scenedesmus vacuolatus: A comparison of two photosystem II inhibitors

Herbicide concentrations fluctuate in rivers following crop application and can reach high levels after rain events, yet the duration of these pulses is short. In the present study, we assessed the effect of atrazine and isoproturon pulse exposure on Scenedesmus vacuolatus (Chlorophyceae; strain 211-8b, Kessler) as well as the recovery in the postexposure period. We further explored whether the time-dependent toxicity is similar for herbicides inhibiting the photosystem II (PSII). The growth rate was assessed for different exposure durations, and in addition the inhibition of the effective quantum yield of PSII was measured to monitor the response at the target site. Atrazine and isoproturon did not have similar time-dependent effects on growth rate, despite their same primary mode of action on PSII. Atrazine was less toxic than isoproturon after 10 h of exposure, but the toxicity of both herbicides was similar after 48 h of exposure. However, both compounds inhibited the PSII effective quantum yield within 1 h following exposure. Similarly, the effective quantum yield recovered completely within 4 h after removal of the toxicants, leading to rapid recovery of algal growth. The rapid onset of effects of isoproturon on the growth of the alga during exposure suggests that a single pulse to this herbicide is likely to induce greater effects than an atrazine pulse at the same concentration, even if these effects are reversible. The information gained in the present study should support the effect assessment of sequential exposures as well as the risk evaluation of fluctuating herbicidal exposure.

Spatial and Temporal Presence of a Wastewater-Derived Micropollutant Plume in Lake Geneva

This study discusses the occurrence and environmental risk associated with a micropollutant plume originating from the direct discharge of treated wastewater into the Vidy Bay of Lake Geneva, Switzerland. The temporal variations and spatial extent of the plume and its effect on the presence of 39 pharmaceuticals and other micropollutants in the Vidy Bay were assessed over a 10 month period. A pronounced plume was observed from April to October, leading to locally elevated (up to 70-fold) pharmaceutical concentrations compared to the surrounding water column. For three of the measured substances, these plume-associated concentrations were sufficiently high to pose an ecotoxicological risk. The plume depth followed the thermal lake stratification, which moved to lower depths over the course of the warm seasons. Pharmaceutical hotspots associated with the plume were detected as far as 1.5 km downstream of the effluent wastewater outfall, but concentrations typically decreased with increasing distance from the wastewater outfall as a result of dilution and photodegradation. From November to January, when uniform temperature prevailed throughout the water column, no micropollutant plumes were detected. In contrast to pharmaceuticals, most pesticides showed homogeneous concentrations throughout the Vidy Bay during the whole study period, indicating that the effluent wastewater was not their dominant source. A strong linear correlation between electrical conductivity and concentrations of wastewater-derived micropollutants was identified. This relation will allow future estimates of wastewater-derived micropollutant concentrations via simple conductivity measurements.

Application of rough sets analysis to identify polluted aquatic sites based on a battery of biomarkers: a comparison with classical methods.

The evaluation of toxicological effects at the cellular and molecular levels in organisms are often used to determine sites subjected to contamination problems that pose a threat to the long-term survival of organisms. However, the integration of multiple measurements on the health status of organisms into a model for site discrimination is challenging. This study compares two discrimination methods which are based on rule inference: rough sets (RS) analysis and classification trees (CT) with classical multivariate discriminant analysis (DA). Site classification was attempted with six biomarkers of effects: metallothionein levels, lipid peroxidation, DNA damage, levels of lipophosphoproteins (i.e., vitellins), phagocytosis activity and haemocyte cell viability on clam (Mya arenaria) populations from the Saguenay River fjord (Quebec, Canada). Rule based methods have the advantage of complete independence from data distribution constraints in contrast to the classification methods from multivariate analysis that are more commonly used in ecotoxicology. Results show that RS and CT gave better classifications than DA because they do not require strong distributional assumptions. Moreover, RS provided classification rules that could identify the most important biomarker(s) for site discrimination. RS and CT were shown to be simple and efficient methods for classifying multivariable ecotoxicological data. This methodology would be especially useful when freedom from distributional assumptions is required.

Occurrence and fate of micropollutants in the Vidy Bay of Lake Geneva, Switzerland. Part I: Priority list for environmental risk assessment of pharmaceuticals

Pharmaceuticals are substances designed to have a biological effect in humans. Their presence in the environment, especially in surface waters, is of increasing concern because of their potential risk to non-target species. A large number of pharmaceuticals are on the market; for example, approximately 2,000 active ingredients are approved in Europe, and many of them have already been detected in surface water. It is therefore crucial to select the substances that may do the most harm to the environment prior to performing measurements and extensive risk assessment. In the present study, a method to determine a list of pharmaceuticals to survey in surface water is proposed. Inclusion of substances on the list was based on a screening procedure, the analytical feasibility, and previous knowledge of pharmaceuticals detected in water. The screening procedure proposed here is an improvement on the standard procedure of the European Medicine Evaluation Agency (EMEA). It is designed to decrease the number of pharmaceuticals to be evaluated in a stepwise manner, thus decreasing the number of data necessary for the evaluation. We applied our approach to determine a list of 37 pharmaceuticals and four hormones to survey in a specific region of Switzerland, the Lake Geneva area, and discussed the advantages and weak points of the method.

S-metolachlor pulse exposure on the alga Scenedesmus vacuolatus: Effects during exposure and the subsequent recovery

In streams and creeks, the aquatic flora is exposed to fluctuating concentrations of herbicides during and following their application. Peak concentrations of herbicides, like the chloroacetanilide S-metolachlor, are usually detected following rain events. In this study, we assessed the effect of S-metolachlor pulse exposure on the algae Scenedesmus vacuolatus. We measured the time-dependency of effects during exposure on algae population and identified the algae development stage most sensitive to S-metolachlor. Furthermore, we assessed the time-to-recovery of the algae following exposure. A 6h pulse exposure at 598microgl(-1) was sufficient to inhibit cell reproduction by 50%. However, the exposure period had to coincide with the cell development stage specifically inhibited by S-metolachlor, which is the end of the cell growth phase. In algae populations composed of cells at all development stages, we initially observed an increase in the size of some algal cells, ultimately leading to an inhibition of the growth rate. In these experimental conditions, effects were observed after 18h of exposure and greatly increased with time. The recovery of algae following exposure to strongly inhibiting S-metolachlor concentrations was delayed and only occurred after 29h. These findings suggest that peak exposure to S-metolachlor may affect the growth of sensitive alga in surface waters, considering that the effects extend beyond the period of exposure.

Development of a biomarker-based index for assessing the ecotoxic potential of aquatic sites.

The use of biochemical or physiological measurements as indicators of ecotoxicity is under constant development and has the advantage of delineating effects before the appearance of disease. However, these biomarkers are often part of a battery of tests, and it is difficult to integrate them together to gain an overall view of an organisms health. The aim of this study was to develop an index that could integrate the data derived from a battery of biomarkers for application to both spatial and temporal studies. Mya arenaria clams were collected at different sites along the Saguenay Fjord (Quebec, Canada). Six biomarkers were measured: metallothioneins, DNA strand breakage, lipid peroxidation, vitellin-like proteins, phagocytosis, and non-specific esterase activity in haemocytes. A biomarker index was obtained by summing the biomarker values expressed in term of classes. Classes were determined by a distribution-free approach derived from the theory of rough sets. The results of the spatial study show that the index values discriminated well between contaminated and uncontaminated sites. The highly polluted sites had the highest index values (18 compared with a reference value of 14). In the temporal study, the index was also able to highlight possible contamination-induced alterations, even though the interpretation of temporal variation is complicated by natural variations occurring throughout the year. A control chart approach is proposed for determining contaminated sites in both spatial and temporal surveys.

Effect of Sequential Isoproturon Pulse Exposure on Scenedesmus vacuolatus

Aquatic organisms are typically exposed to fluctuating concentrations of herbicides in streams. To assess the effects on algae of repeated peak exposure to the herbicide isoproturon, we subjected the alga Scenedesmus vacuolatus to two sequential pulse exposure scenarios. Effects on growth and on the inhibition of the effective quantum yield of photosystem II (PSII) were measured. In the first scenario, algae were exposed to short, 5-h pulses at high isoproturon concentrations (400 and 1000 μg/l), each followed by a recovery period of 18 h, while the second scenario consisted of 22.5-h pulses at lower concentrations (60 and 120 μg/l), alternating with short recovery periods (1.5 h). In addition, any changes in the sensitivity of the algae to isoproturon following sequential pulses were examined by determining the growth rate-EC50 prior to and following exposure. In both exposure scenarios, we found that algal growth and its effective quantum yield were systematically inhibited during the exposures and that these effects were reversible. Sequential pulses to isoproturon could be considered a sequence of independent events. Nevertheless, a consequence of inhibited growth during the repeated exposures is the cumulative decrease in biomass production. Furthermore, in the second scenario, when the sequence of long pulses began to approach a scenario of continuous exposure, a slight increase in the tolerance of the algae to isoproturon was observed. These findings indicated that sequential pulses do affect algae during each pulse exposure, even if algae recover between the exposures. These observations could support an improved risk assessment of fluctuating exposures to reversibly acting herbicides.

Degradation in soil and water and ecotoxicity of rimsulfuron and its metabolites

The degradation and ecotoxicity of sulfonylurea herbicide rimsulfuron and its major metabolites were examined in batch samples of an alluvial sandy loam and in freshwater. An HPLC-DAD method was adapted to simultaneously identify and quantify rimsulfuron and its metabolites, which was successfully validated by GC-MS analysis. In aqueous solutions, pure rimsulfuron was rapidly hydrolyzed into metabolite 1 (N-(4,6-dimethoxypyrimidin-2-yl)-N-(3-(ethylsulfonyl)-2-pyridinylurea)), which itself was transformed into the more stable metabolite 2 (N-((3-(ethylsulfonyl)-2-pyridinyl)-4,6-dimethoxy-2-pyrimidineamine)), with half-life (t(1/2)) values of 2 and 2.5 days, respectively. Hydrolysis was instantaneous under alkaline conditions (pH = 10). In aqueous suspensions of the alluvial soil (pH = 8), formulated rimsulfuron had a half-life of 7 days, whereas that of metabolite 1 was similar to that in water (about 3.5 days). The degradation of the two major metabolites was also studied in soil suspensions with the pure compounds at concentrations ranging from 1 to 10 mg l(-1). The half-life of metabolite 1 ranged from 3.9 to 5 days, close to the previous values. Metabolite 2 was more persistent and its degradation is strongly dependent on the initial concentration (C0): half-life values ranged from 8.1 to 55 days at 2-10 mg l(-1), respectively. These values are higher than those determined from the kinetics of metabolite 1 transformation into metabolite 2 (t(1/2) = 8-19 days). The ecotoxicity of the three chemicals was evaluated through their effect on Daphnia magna and Vibrio fischeri (Microtox bioassay). No effect was observed on D. magna with 24 and 48 h acute toxicity tests. Similarly, no toxic effect was observed with the Microtox test for the three chemicals in the range of concentrations tested that included the field application dose. Thus, being of low persistence and lacking acute toxicity, these chemicals present a low environmental risk. However, chronic effects should be studied in order to confirm the safety of rimsulfuron and its major metabolites.