Micropollutants in watercourses

Many micropollutants are detected in Swiss watercourses. In small and medium-sized watercourses, pesticides in particular exceed their ecotoxicological limits , whereas in large watercourses this is the case for some medicinal products. In the affected watercourses, sensitive animal and plant species are at excessive risk of harm from these substances. These watercourses are mainly located in the densely populated and intensively farmed regions of Switzerland.

Micropollutants are pesticides, medicinal products and other chemicals that occur in very low concentrations in water bodies. In Switzerland, over 30,000 chemicals in numerous different products are in daily use. They enter water bodies from wastewater treatment plants (WWTPs), agriculture, residential areas and traffic. Micropollutants vary in their level of toxicity to aquatic organisms. Many substances entering rivers and streams in large quantities via WWTPs are no problem from an ecotoxicological point of view, e.g. artificial sweeteners. However, other micropollutants, such as many pesticides and some medicinal products are toxic to sensitive aquatic organisms even at very low concentrations.

Micropollutants in the national monitoring programme

Within the National Surface Water Quality Monitoring Programme (NAWA), 38 monitoring sites are being tested for no less than 72 micropollutants as part of the TREND continuous monitoring programme. In addition, specific research questions are addressed with short-term monitoring programmes (NAWA SPEZ).

The monitoring programme NAWA TREND has been gradually built up since 2018, in conjunction with the cantons. Further information:

Mikroverunreinigungen im Gewässermonitoring (PDF, 11 MB, 06.07.2020)Artikel Aqua & Gas 7/8 2020 - Ausbau von NAWA TREND und erste Resultate 2018.

This publication does not exist in English and is only available in other languages.

NAWA TREND monitoring stations with studies on micropollutants operating in 2021 (33) and new additional stations set up in 2022 (5).
NAWA TREND monitoring stations with studies on micropollutants.

Concentrations of micropollutants vary according to substance and watercourse

Measurements from the NAWA TREND programme show that concentrations of micropollutants in watercourses vary greatly depending on the substance and the type of watercourse. They are detected over a wide concentration range, from nanogram-per-litre to microgram-per-litre. In large rivers, concentrations particularly of pesticides and medicinal products are usually lower than in smaller watercourses, as they are highly diluted. Seasonal fluctuations can also be observed: while some substances are present all year round, others are only detected during the periods in which they are in use.

Micropollutant concentrations at NAWA TREND monitoring sites
Boxplots of 122 micropollutant concentrations at 46 NAWA TREND monitoring sites (incl. monitoring stations with irregular analyses of micropollutants). Concentrations of the 14-day composite samples (or at some sites 3.5- or 7-day composite samples) are shown on a logarithmic scale, per substance group and size of watercourse. Measured values below the limit of quantification are not shown. Below each boxplot the total number of readings (N) and the percentage of readings above the limit of quantification is shown. Data: NAWA TREND 2018–2022.

Many watercourses are polluted with micropollutants

The NAWA TREND studies show that many watercourses in the Swiss Plateau and valley plains are contaminated with micropollutants. In 2022, 18 of the 22 micropollutants (19 pesticides and 3 medicinal products) for which ecotoxicological limit values are set in the Waters Protection Ordinance (WPO) were shown to exceed those limit values. In 2022, only 6 of the 38 examined watercourses were found to be in compliance with the ecotoxicologicallimit values.

Number of monitoring sites where limit values were exceeded
Number of monitoring sites where limit values were exceeded (red), per size category. The number of substances (# substances) detected above the limits is listed under each bar. Data: NAWA TREND 2022.

Small and medium-sized watercourses particularly affected by pesticide contamination

Pesticide contamination is most pronounced in small and medium-sized watercourses. Pesticides exceed the ecotoxicological limits set in most of these watercourses studied in NAWA TREND. In the affected watercourses, sensitive animal and plant species are exposed to excessive risk of harm from these substances.

The use of plant protection products (PPPs) in agriculture is the main reason for pesticide contamination observed in streams. Almost half of all limit exceedances are currently caused by pesticides that are exclusively approved for use as PPPs. Some of these substances are now no longer approved or their use is restricted. It is thus expected that there will be less exposure to these substances (e.g. chlorpyrifos, thiacloprid) in the future.

Insecticides that already have a harmful effect on aquatic life in minute concentrations (picogram-per-litre range – billionths of a gram) pose a particularly high risk.

Aqua&Gas Nr. 4/2022: Insektizide in Schweizer Fliessgewässern (PDF, 2 MB, 18.08.2022)Welche Risiken gehen von Pyrethroiden und Organophosphaten aus?

This publication does not exist in English and is only available in other languages.

Aqua&Gas Nr. 11/2019: Geringe Konzentrationen mit grosser Wirkung (PDF, 1 MB, 21.03.2023)Nachweis von Pyrethroid- und Organophosphat-Insektiziden in Schweizer Bächen im pg l-1-Bereich.

This publication does not exist in English and is only available in other languages.

Micropollutants with ecotoxicological limit values
Overview of the 22 micropollutants with ecotoxicological limit values. The micropollutants differ in terms of the maximum limit exceedances (ratio of maximum concentration to limit value), the number of detections above the limit values and the number of rivers in which they were detected above their limit value. The limit exceedances for persistent and short-term exposure are shown. It is indicated for each substance whether it was approved for use as a biocide (B), plant protection product (PPP), veterinary medicinal product (VMP) or medicinal product for human use (HU) at the time of the study; n.a. = not approved, n.d. = not determinable, as there is no ecotoxicological limit value for short-term exposure for diclofenac. Data: NAWA TREND 2022.

Medicinal products exceed limits in many medium-sized and large watercourses

The three medicinal products regulated in the WPO (azithromycin, clarithromycin, diclofenac) exceed the limits in the majority of medium and large watercourses. The analgesic  diclofenac is responsible for the majority of ecotoxicological limit value exceedances.

Medicinal products generally enter rivers and lakes via treated wastewater. Industrial wastewater is also discharged either directly via the companies' own WWTPs or indirectly via municipal WWTPs. Currently, most WWTPs remove various types of contaminationsfrom wastewater, micropollutants are only removed in part or not at all. WWTP are currently being upgraded by an additional stage for the treatment of micropollutants; this will bring improvements in the coming years.

Micropollutants permanently above the limit value

The investigations show that the water quality in watercourses does not meet the legal minimum requirements in many places, in some cases persistently. Many watercourses are almost permanently polluted by micropollutants above the limit values and are thus contaminated. While exceedances due to medicinal product residues persist in many cases throughout the year, exceedances due to pesticides occur mainly during the application period of plant protection products.

Violations of ecotoxicological limit values of medicinal products over the course of a year
Exceedances of ecotoxicological limit values of medicinal products at 33 sites over the course of a year. Data: NAWA 2018–2022.
Violations of ecotoxicological limit values of pesticides over the course of a year
Exceedances of ecotoxicological limit values of pesticides at 38 sites over the course of a year. Data: NAWA 2018–2022.

Main findings of the special studies carried out so far (NAWA SPEZ)

NAWA SPEZ 2012: NAWA SPEZ 2012 focused on obtaining as complete a picture as possible of pesticide levels (PPPs and biocides) in medium-sized rivers. The results clearly indicated that PPPs play a significant role in polluting watercourses.

Über 100 Pestizide in Schweizer Fliessgewässern (PDF, 5 MB, 01.03.2014)Programm NAWA Spez zeigt die hohe Pestizidbelastung der Schweizer Fliessgewässer auf. Artikel aus Aqua & Gas 3/2014

NAWA SPEZ 2015: The NAWA SPEZ 2015 study focused on small watercourses. High concentration peaks of PPPs were found in the five intensively farmed areas investigated. These have a harmful effect on aquatic organisms.

Aqua&Gas 4/2017: Hohe PSM-Belastung in Schweizer Bächen (PDF, 3 MB, 21.03.2023)NAWA-SPEZ-Kampagne untersucht Bäche in Gebieten intensiver landwirtschaftlicher Nutzung

NAWA SPEZ 2017: As in 2015, NAWA SPEZ 2017 focused on PPP contamination of small watercourses in intensively farmed areas. This was the first time that a comparison was made over two consecutive years at two locations. The study also showed that individual pesticides are present in excessive concentrations over a long period of time, continuing into the autumn, and pose a considerable risk for aquatic life.

Aqua&Gas 4/2019: Anhaltend hohe PSM-Belastung in Bächen (PDF, 1 MB, 18.08.2022)NAWA SPEZ 2017: Kleine Gewässer in Gebieten mit intensiver Landwirtschaft verbreitet betroffen

NAWA SPEZ 2023: The special campaign comprehensively recorded the pollution of medium-sized watercourses with pesticides from residential areas and agriculture. The focus was on insecticides that are highly toxic to aquatic organisms. To this end, measurements were carried out in five watercourses downstream of wastewater treatment plants. In addition, the WWTP effluents were also sampled. This provides indications of the proportion of insecticides originating from agriculture or from residential areas. The data is currently being analysed.

Further information

Last modification 30.04.2024

Top of page