Streams polluted with pesticides
The canton of St. Gallen has investigated the water quality of selected streams. The measurement campaigns show that the waters do not meet the legal requirements and that there is often a high risk for aquatic organisms. Pesticides and an industrial chemical are primarily responsible for the limit values being exceeded.
From 2018 to 2020, the Office for Water and Energy (AWE) of the Canton of St. Gallen took a close look at 14 streams in used areas and examined them for organic trace substances, so-called micropollutants. Even at very low concentrations, such substances can harm aquatic life. The evaluation of the measurement results would show for each of the 14 streams an increased or very high risk of damage to aquatic organisms due to chronic pollution with individual substances, writes the AWE.
Pesticides and industrial chemical in focus
The investigations also showed that the exceedances of the quality criteria and requirements were caused by a total of 27 substances: These were 14 herbicides, seven insecticides, two fungicides, three pharmaceuticals and the industrial chemical PFOS (perfluorooctane sulfonic acid). According to the data, the risk of chronic damage to aquatic organisms was elevated in 12 of the 14 streams during more than two-thirds of the observation period from spring to fall. In addition, the requirements of the Water Protection Ordinance were often exceeded in many cases in all streams.
Immediate measures implemented
Together with the St. Gallen Agricultural Center (LZSG), the Office for Water and Energy sensitizes professional and private users of pesticides and biocides for responsible handling and use. The LZSG has organized round tables with farmers who cultivate the soil in the catchment area of the respective streams. Data had been reviewed and the causes of substance discharges into water bodies had been analyzed in order to prevent them in the future. Farmers have implemented immediate measures. For example, they repaired defective manholes in the fields or set up washing stations for sprayers on the farms.
The use of PFOS has been banned in principle since 2011. However, the chemical is still permitted for individual industrial applications. It enters waters via municipal wastewater treatment plants or diffusely via contaminated surfaces. Measures to reduce the input of the substance are very difficult to implement, writes the AWE.
Sensitization benefits
The AWE and the Agricultural Office also studied a specific stream over several years. It had been shown that substance inputs into the water body could be significantly reduced with targeted sensitization of users. Very toxic substances such as insecticides from the class of Phyrethroids and Organophosphates would remain problematic despite restrained use, as they have a harmful effect on aquatic life even at extremely low concentrations, according to the AWE.
Large ecological deficits
The measurement campaigns follow biological investigations of nearly 100 small streams since 2011, which revealed major ecological deficits, according to the office. Three quarters of the watercourses in the canton are small streams. These are valuable habitats for many plants and animals. These streams fulfill important ecological functions and their protection is of great importance for the preservation of biodiversity. Many of these small streams are located in heavily used areas. They are therefore exposed to an increased risk from material inputs. (Source: AWE)
Further information on the topic and the fact sheets on the Measurement campaigns are available here.
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