Micropollutants in watercourses

Many micropollutants can be detected in Swiss watercourses. Pesticides exceed their ecotoxicological limits primarily in streams and small watercourses, whereas in large rivers there are excessive levels of some medicinal products. In the affected watercourses in densely populated and intensively farmed regions, sensitive animal and plant species are exposed to a high risk of harm from these substances.

Micropollutants include pesticides, medicinal products and other chemicals that occur in very low concentrations in watercourses. In Switzerland, over 30,000 chemicals in numerous different products are in daily use. They enter watercourses from wastewater treatment plants (WWTPs), agriculture, residential areas and traffic. Micropollutants are toxic to aquatic life in a number of different ways. Many substances that enter rivers and streams in large quantities via wastewater treatment plants are not a cause for concern from an ecotoxicological point of view; artificial sweeteners are one example. However, there are other micropollutants, such as many pesticides and some medicinal products, that are toxic to sensitive aquatic organisms even at very low concentrations.

Micropollutants in the national monitoring programme

Water is being tested for 80 or more micropollutants at 38 monitoring sites in the TREND continuous monitoring programme, which is part of the National Surface Water Quality Monitoring Programme (NAWA). Specific issues are investigated in time-limited specialised monitoring programmes (NAWA SPEZ).

The micropollution NAWA SPEZ has been gradually built up since 2018, in conjunction with the cantons. Further information:

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

NAWA TREND monitoring stations with studies on micropollutants operating in 2020 (33) and new additional stations set up in 2022 (5).
NAWA TREND monitoring stations with studies on micropollutants operating in 2020 (33) and new additional stations set up in 2022 (5).

Concentrations of micropollutants vary according to substance and watercourse

Measurements taken in 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 micropollutant concentrations (98) at 33 NAWA TREND monitoring sites. 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 (included in the boxplot) is shown. Data: NAWA 2018–2020.

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 2020, 20 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 the limit values. Only 5 of the 33 watercourses examined so far have always complied with the limit values.

Anzahl Messstellen, an denen Überschreitungen der Grenzwerte festgestellt wurden
Number of monitoring sites where limit values were violated (red), per size category. The number of substances (# substances) detected above the limits is listed under each bar. Data: NAWA 2020.

Small and medium-sized watercourses particularly affected by pesticide contamination

Pesticide contamination is most marked in small and medium-sized watercourses. Pesticides exceed the ecotoxicological limits set in almost all of the watercourses studied in NAWA TREND. In these watercourses, the risk of harm from these substances is too high for sensitive animal and plant species. The pesiticde load is significantly less in large rivers, in the majority of which the limit values are not exceeded.

The use of plant protection products (PPPs) in agriculture is the main reason for pesticide contamination observed in streams. More than half of all limit violations 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, isoproturon, thiacloprid) in the future.

Insecticides that already have a harmful effect on aquatic life in minute concentrations (picogram-per-litre range – millionths 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?

Aqua&Gas Nr. 11/2019: Geringe Konzentrationen mit grosser Wirkung (PDF, 1 MB, 18.08.2022)Nachweis von Prythroid- und Organophosphat-Insektiziden in Schweizer Bächen im pg l-1-Bereich

Mikroverunreinigungen mit ökotoxikologischen Grenzwerten
The 22 micropollutants with ecotoxicological limit values differ in terms of the maximum limit violation (ratio of maximum concentration to limit value), the number of detections above the limit values and the number rivers in which they were detected above their limit value. The limit violations for persistent and non-persistent loads 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.d. = not determinable, as there is no ecotoxicological limit value for non-persistent exposure for diclofenac. Data: NAWA 2020.

Medicinal products violate limits in many medium-sized and large rivers

The three medicinal products regulated in the WPO (azithromycin, clarithromycin, diclofenac) violate the limits in the majority of medium to large rivers. The painkiller diclofenac is responsible for the majority of violations of the ecotoxicological limit value.

Medicinal products generally enter rivers and lakes via treated wastewater. Industrial wastewater is also discharged either directly via the companies' own wastewater treatment plants or indirectly via municipal wastewater treatment plants. Most wastewater treatment plants still primarily remove nutrients from wastewater. Micropollutants are only removed in part or not at all, and so end up in lakes and rivers. Wastewater treatment plants are currently being upgraded by an additional purification stage; 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. These micropollutants are both pesticide and medicinal product residues.

Violations of ecotoxicological limit values of medicinal products over the course of a year
Violations of ecotoxicological limit values of medicinal products at 33 sites over the course of a year. Land use information: % Agr. = Share of agricultural land with high PPP use (arable land, fruit, vines) in the catchment area, % WW = Percentage of treated wastewater at low water discharge (Q347) in the watercourses monitored. Data: NAWA 2018–2020.
Violations of ecotoxicological limit values of pesticides over the course of a year
Violations of ecotoxicological limit values of pesticides at 33 sites over the course of a year. Land use information: % Agr. = Share of agricultural land with high PPP use (arable land, fruit, vines) in the catchment area, % WW = Percentage of treated wastewater at low water discharge (Q347) in the watercourses monitored. Data: NAWA 2018–2020.

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, 19.08.2022)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

Further information

Last modification 23.08.2022

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