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.
Index
Micropollutants in municipal wastewater (Summary)
Processes for advanced removal in wastewater treatment plants
Mikroverunreinigungen in Fliessgewässern aus diffusen Einträgen
Situationsanalyse
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:
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.
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.
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.
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.
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.
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.
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.
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.