Pollutants in the streams »Wild in the game

The Water and Energy Department of the Canton of St. Gallen has been studying for several months the water quality of five water courses and is worried about what Quality criteria for problematic substances were exceeded during most of the measurement campaign from April to October 2018. Quality criteria are the thresholds above which substances cause acute or prolonged contact with damage. chronic for the organisms.

The studied creeks were selected on the basis of a preliminary study in which they already presented a remarkable load, announced Wednesday the State Chancellery of the canton. These included Latenbach and Wagnerbach in Rapperswil-Jona, the side ditch and the tank ditch in Benken and the Äächeli in Au. The Tankgraben catchment area is mainly located in the canton of Schwyz.

Pesticides as the main problem

The majority of the substances studied were pesticides, which are also responsible for most of the poor quality of water. But also the residues of drugs and industrial chemicals have exceeded the respective limits.

Among the chemicals, experts have found, for example, high levels of perfluorooctane sulfonate (PFOS), a long-lasting mammalian substance that can accumulate throughout the food chain, said in a statement. Keystone Agency Vera Vera Leib, Department of Water Quality. SDA explained.

The use of PFOS has been banned in Switzerland since 2011, with a few exceptions. For individual applications, PFOS is still allowed, for example in certain paints and coatings, in aviation hydraulic fluids, as well as in fire fighting foams, marketed before 2011.

Enigmatic source

The source of PFOS in streams is debatable, says Leib. In four of the five streams, the concentration of PFOS exceeded values ​​until the chemical could be classified as harmless. In Wagnerbach, the values ​​were so high that it was absolutely necessary to look for the source. It could come from landfills or fireplaces where old moss was still used.

Pesticides and other substances could have entered streams in different ways. For example, the rain could have been washed away by recently released sprays or improperly disposed pesticide residues. Connection errors or discharges from the sewer system due to heavy rain are also possible.

Insecticides, in particular, are toxic even for the smallest quantities present in the stream. However, long-lived pollutants could also accumulate in the food chain and cause damage beyond watercourses.

Find and repair causes

Experts from the Office of Water and Energy now want to find the causes and solve the cases with a high load. However, the problem is likely to go beyond the five currents studied: the Department of Water and Energy had already verified the biological status of 78 creeks in the canton in 2011 and found deficits.

This is due to a variety of reasons, such as excessive nutrient inputs, high water temperatures, or simply pollutants. The detailed analysis of the measurement campaign now presented should provide a better understanding of the role of pollutants.

A significant portion of the township's small waterways cross agricultural areas and settlements from which pesticides and other substances could enter the waters. The sensitization of farmers, but also of professional and private gardeners to proper handling of spraying agents, has been important.