EcoImpact – unraveling the ecological impact of micropollutants in streams

The contamination of freshwater systems with micropollutants (MPs) is regarded as a key environmental problem, and a wealth of data on the impact of MPs on specific organisms exist, but we know little how these MPs impact the complex structure and function of entire natural aquatic ecosystems.

EcoImpact is an Eawag-wide interdisciplinary research effort aimed at filling this knowledge gap. The project that started in 2013 is strongly motivated by the coming upgrading of the Swiss wastewater treatment plant infrastructure. These modifications represent a unique opportunity to study the impact of MPs on natural aquatic ecosystems. To that end two complementary approaches are pursued: A field survey at selected wastewater treatment effluent sites and experimental approaches including a flume system (Maiandros) with controlled water chemistry. Maiandros was developed to experimentally investigate the effects of mixtures of MPs on biological endpoints.

In the survey approach established methods will be used to assess at a selection of sites the water quality parameters, various biological endpoints and species compositions (e.g. macroinvertebrates).
In the experimental approach, the effluent composition will be manipulated in a controlled way and the various organisms or combinations thereof will be exposed to the different effluents.
Experimental approach


Dr. Christian StammTel. +41 58 765 5565Send Mail

Project partner

Federal Office for the Environment (FOEN), Dept. Water

  • Aquabug, Sciences naturelles et environnement, Neuchatel

The partners are governmental and cantonal authorities as well as companies and the non-profit organizations.

Water Lecture (Video) at the University of Waterloo


Micropollutants are organic or inorganic chemical pollutants which occur in water bodies in very low concentrations. Despite such low concentration levels, micropollutants can have negative impacts on organisms or contaminate the drinking water resources. Micropollutants are derived from many products used in industry, agriculture, tourism and households and include personal care products, construction material, pharmaceuticals or biocides. They enter the water environment via various routes such as urban wastewater, or runoff from agricultural land or transportation areas.

Effects of micropollutants

Micropollutants may cause effects on organisms already at very low concentrations. Many compounds are developed to be biologically active (e.g. biocides, pharmaceuticals, plant protection products). Therefore it is to be expected that similar but undesired side-effects can be observed in the environment. Herbicides for example that inhibit photosynthesis in weeds also stop photosynthetic activity in algae and macrophytes. Vertebrates, such as fish, will also react on e.g. hormones, or insecticides will also have a negative impact on insects in an aquatic environment.

Incomplete removal of micropollutants in wastewater treatment plants

A major source for micropollutants in the aquatic environment are wastewater treatment plant (WWTPs) effluents. Current WWTPs have mainly been developed to remove nutrients. They successfully contributed to achieve water protection goals. In recent years it became clear that many micropollutants are not sufficiently removed by conventional treatment processes and additional treatment steps are needed. As part of the  “Strategy Micropoll” Swiss authorities have decided to implement additional treatment steps on about 100 out of the 700 Swiss WWTPs. These modifications represent a unique opportunity to study the impact of micropollutants on natural aquatic ecosystems in our project EcoImpact.

Hypothesis and Goals

In a combination of surveys and experimental approaches, EcoImpact will test the following two hypotheses:

  • The discharge of MPs from WWTPs leads to changes that go beyond the effects of other wastewater constituents like nutrients (e.g., the loss and reduction of sensitive species at downstream sites or induced tolerance against MPs).
  • There are indirect effects of MPs, mediated by biological interactions that go beyond the direct effects of MPs on key organisms and functions.

The EcoImpact project has three goals

  • Establishing causation
    We want to establish whether ecological differences between sites are caused by different exposure to (specific) groups of micropollutants. The impact of micropollutants and confounding factors needs to be separated.
  • Integration
    We will include a variety of molecular, physiological and ecological endpoints, and integrate the measurements, observations and patterns.
  • Establishing generality
    We want to make general statements rather than specific statements on individual study sites.

Survey and field sites

In the survey, established methods are used to assess the water quality parameters, various biological endpoints, biodiversity and functional traits at a selection of 24 river reaches up- and downstream from wastewater treatment plant discharges across the Swiss Plateau and the Jura mountains. The goals of this approach are to examine biological effects of treated wastewater in general and micropollutants in particular, and to have a baseline for monitoring subsequent changes caused by upgraded WWTPs.

Site selection was based on the following criteria and was aimed at obtaining scientifically significant results, which will allow to draw generalizable conclusions:

  • Only streams are considered as receiving waters, no lakes
  • No wastewater discharge upstream of the selected WWTPs  
  • At least 20% of total discharge consists of WWTP effluent during dry weather flow (Q347)
  • Settlement area in catchment < 21%
  • Less than 10% areal coverage with vineyards and/or orchards

Data source: © 2017 swisstopo (JD100041)

Experimental approaches

Experiments are needed to disentangle the effects of different factors on the structure and function of aquatic ecosystems. To study the specific role of micropollutants we have both performed laboratory-based, small scale experiments but also designed  a 16 channel flume system called Maiandros (from the Greek Μαίανδρος being the God of the River Maeander in modern Turkey). In the Maiandros system different organisms can be exposed to four different and controlled water qualities. Maiandros is currently located at the WWTP in Fällanden, Switzerland, and several experiments have been executed so far. Water quality was on the one hand varied by mixing river water and effluent from the WWTP in different ratios. On the other hand, river water was spiked with nutrients and/or artificial mixtures of micropollutants to disentangle the possibly opposing effects of nutrients and micropollutants.

the experimental flume system “Maiandros”


Findings so far demonstrate that MPs exert impact on stream ecosystems. At all field sites, wastewater discharge substantially increased the load and concentrations of MPs at the downstream locations. Bioassays clearly show that these concentrations increase the ecotoxicological effects at different endpoints like inhibition of photosynthesis. Periphyton communities downstream are more tolerant to these MPs, and induced gene expression of detoxification activities in brown trout has been demonstrated at selected sites. All of these results demonstrate that MPs exert stress on the organisms resulting in biological responses. Such effects are also seen with macroinvertebrates. In particular, species that are sensitive against pesticides are reduced at downstream sites, indicating the presence of these toxicants in the treated effluent. This effect gets larger the more wastewater is discharged in relation to the average stream flow. Interestingly, this effect was independent of how pristine the stream was upstream of the WWTP. Ecosystem functions like leaf decomposition were also affected by wastewater discharge and potentially by MPs. 

Using the Maiandros flume system, 4 experiments have been conducted so far that allowed to disentangle some of the intricate processes occurring in the field. For example, degradation assays using cotton strips showed that nutrients ‘mask’ the toxic effects of MPs on this functional endpoint.Comparative analysis of results from the field and in the flume will be used to obtain a better causal understanding of patterns observed in the field.


The following selection of publications are from or strongly related with the EcoImpact topic.

Tlili, A.; Hollender, J.; Kienle, C.; Behra, R. (2017) Micropollutant-induced tolerance of in situ periphyton: establishing causality in wastewater-impacted streams, Water Research, 111, 185-194, doi:10.1016/j.watres.2017.01.016, Institutional Repository
Stamm, C.; Räsänen, K.; Burdon, F. J.; Altermatt, F.; Jokela, J.; Joss, A.; Ackermann, M.; Eggen, R. I. L. (2016) Unravelling the impacts of micropollutants in aquatic ecosystems: interdisciplinary studies at the interface of large-scale ecology, In: Dumbrell, A. J.; Kordas, R. L.; Woodward, G. (Eds.), Large-Scale Ecology: Model Systems to Global Perspectives, 183-223, doi:10.1016/bs.aecr.2016.07.002, Institutional Repository
Burdon, F. J.; Reyes, M.; Alder, A. C.; Joss, A.; Ort, C.; Räsänen, K.; Jokela, J.; Eggen, R. I. L.; Stamm, C. (2016) Environmental context and magnitude of disturbance influence trait-mediated community responses to wastewater in streams, Ecology and Evolution, 6(12), 3923-3939, doi:10.1002/ece3.2165, Institutional Repository
Czekalski, N.; Díez, E. G.; Bürgmann, H. (2014) Wastewater as a point source of antibiotic-resistance genes in the sediment of a freshwater lake, ISME Journal, 8(7), 1381-1390, doi:10.1038/ismej.2014.8, Institutional Repository
Deiner, K.; Walser, J.-C.; Mächler, E.; Altermatt, F. (2015) Choice of capture and extraction methods affect detection of freshwater biodiversity from environmental DNA, Biological Conservation, 183, 53-63, doi:10.1016/j.biocon.2014.11.018, Institutional Repository
Eggen, R. I. L.; Hollender, J.; Joss, A.; Schärer, M.; Stamm, C. (2014) Reducing the discharge of micropollutants in the aquatic environment: the benefits of upgrading wastewater treatment plants, Environmental Science and Technology, 48(14), 7683-7689, doi:10.1021/es500907n, Institutional Repository
Fischer, S.; Klüver, N.; Burkhardt-Medicke, K.; Pietsch, M.; Schmidt, A.-M.; Wellner, P.; Schirmer, K.; Luckenbach, T. (2013) Abcb4 acts as multixenobiotic transporter and active barrier against chemical uptake in zebrafish (Danio rerio) embryos, BMC Biology, 11, 69 (16 pp.), doi:10.1186/1741-7007-11-69, Institutional Repository
Hollender, J.; Zimmermann, S. G.; Koepke, S.; Krauss, M.; McArdell, C. S.; Ort, C.; Singer, H.; von Gunten, U.; Siegrist, H. (2009) Elimination of organic micropollutants in a municipal wastewater treatment plant upgraded with a full-scale post-ozonation followed by sand filtration, Environmental Science and Technology, 43(20), 7862-7869, doi:10.1021/es9014629, Institutional Repository
Margot, J.; Kienle, C.; Magnet, A.; Weil, M.; Rossi, L.; de Alencastro, L. F.; Abegglen, C.; Thonney, D.; Chèvre, N.; Schärer, M.; Barry, D. A. (2013) Treatment of micropollutants in municipal wastewater: ozone or powdered activated carbon?, Science of the Total Environment, 461, 480-498, doi:10.1016/j.scitotenv.2013.05.034, Institutional Repository
Ort, C.; Hollender, J.; Schaerer, M.; Siegrist, H. (2009) Model-based evaluation of reduction strategies for micropollutants from wastewater treatment plants in complex river networks, Environmental Science and Technology, 43(9), 3214-3220, doi:10.1021/es802286v, Institutional Repository
Schymanski, E. L.; Singer, H. P.; Longrée, P.; Loos, M.; Ruff, M.; Stravs, M. A.; Ripollés Vidal, C.; Hollender, J. (2014) Strategies to characterize polar organic contamination in wastewater: exploring the capability of high resolution mass spectrometry, Environmental Science and Technology, 48(3), 1811-1818, doi:10.1021/es4044374, Institutional Repository
Schuwirth, N.; Kattwinkel, M.; Stamm, C. (2015) How stressor specific are trait-based ecological indices for ecosystem management?, Science of the Total Environment, 505, 565-572, doi:10.1016/j.scitotenv.2014.10.029, Institutional Repository
Tlili, A.; Berard, A.; Blanck, H.; Bouchez, A.; Cássio, F.; Eriksson, K. M.; Morin, S.; Montuelle, B.; Navarro, E.; Pascoal, C.; Pesce, S.; Schmitt-Jansen, M.; Behra, R. (2015) Pollution-induced community tolerance (PICT): towards an ecologically relevant risk assessment of chemicals in aquatic systems, Freshwater Biology, 61, 2141-2151, doi:10.1111/fwb.12558, Institutional Repository

Project team

Project Management

Project leader: Christan Stamm

Dr. Christian StammTel. +41 58 765 5565Send Mail
Prof. Dr. Rik EggenDeputy DirectorTel. +41 58 765 5320Send Mail
Dr. Katja RäsänenTel. +41 58 765 5186Send Mail

Project team

The project is carried out in close collaboration with members of the wider project team, which consists of representatives of different Eawag disciplines and the Ecotox Centre of the Eawag/EPFL.

Marta ReyesResearch TechnicianTel. +41 58 765 6725Send Mail
Dr. Adriano JossTel. +41 58 765 5408Send Mail
Dr. Christoph OrtGroup LeaderTel. +41 58 765 5277Send Mail
Dr. Jakob BrodersenTel. +41 58 765 2204Send Mail
Dr. Cornelia KienleTel. +41 58 765 5563Send Mail

The different project tasks will be carried out by task groups which consist of scientific and technical personnel of all levels and will be supervised by a task leader.

Research partners

Assoc. Prof. Scott D. Tiegs, Biological Sciences, Oakland University, Michigan, USA
Dr. Yaohui Bai, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China

Scientific Advisory Board

Prof. Dr. R. Brouwer
Professor in Environmental Economy, University of Waterloo, Canada

Prof. Dr.-Ing. Martin Jekel
Professor in Environmental Engineering, Technical University, Berlin, Germany

Dr Pim E.G. Leonards
Senior researcher department of Chemistry and Biology, Vrije Universiteit, Amsterdam, The Netherlands

Dr. Guy Woodward
Reader in ecology, Imperial College, London, England