Small streams may be excessively contaminated by toxic chemicals. Quality criteria for pesticides, drug residues or industrial chemicals are sometimes far exceeded. The latest measurement campaign of the Office of Water and Energy testifies to this.
Since 2011, the Office of Water and Energy has analyzed the biological status of 78 small creeks in the township with different uses in the watershed. For two-thirds, the legal requirements were not met. As part of the ongoing measurement campaign, cantonal experts have extensively surveyed five currents in the Zurich-Obersee and Rhine Valley regions, on trace substances such as pesticides , drugs or industrial chemicals.
Criteria not filled
In all rivers, quality criteria for problematic substances were exceeded for most of the observation period. In the most extreme case by a factor of 160. In the ongoing measurement campaign, samples were taken continuously from April to the end of October 2018. Compared to the respective monthly long-term average, the months from April to October, except August, were dry to very dry. The streams studied include the Lattenbach and Wagnerbach in Rapperswil-Jona, the side ditch at Benken, the reservoir ditch at Benken (mostly watershed in the Canton of Schwyz) and the Äächeli at Au. The Office of Water and Energy had selected the five streams after a preliminary study of 13 streams. Selected streams already had a significant load during the preliminary investigation.
Pesticides in a nutshell
Of the 109 substances tested, 74 belong to the group of pesticides. Most pesticides and residues of drugs or industrial chemicals are responsible for the poor quality of the water. For example, PFOS perfluorinated surfactant. The substance has been largely banned since 2011, but is still allowed for some applications. The results reflect water pollution from agricultural uses and stands in watersheds. Substances enter the water through runoff, mishandling, improper connections or sewer system discharges during heavy rains, and treated sewage.
The smallest quantities are harmful
Handling pesticides or other harmful substances requires a lot of care. With insecticides, even the smallest amounts can be toxic or even deadly to creek creatures. Small water courses make up 75% of the cantonal water courses network. About half of this is in the areas used. Their protection is of great importance for waters and biodiversity.