St. Gallen: Pollutants entering streams unchecked
Small streams in the canton of St. Gallen are heavily contaminated with pesticides and residues from pharmaceuticals and industrial chemicals. In the most extreme case, limit values were exceeded by a factor of 160.
The Office for Water and Energy of the canton of St. Gallen investigated the water quality of five streams over several months and has reached a concerning conclusion: quality criteria for problematic substances were exceeded for almost the entire duration of the measurement campaign, which ran from April to October 2018. Quality criteria refer to threshold values above which substances cause acute harm to organisms, or chronic harm following prolonged exposure.
The streams examined were selected on the basis of a preliminary study in which they had already shown notable levels of contamination, as the cantonal state chancellery announced on Wednesday. These were specifically the Latenbach and Wagnerbach in Rapperswil-Jona, the Nebengraben and Tankgraben in Benken, and the Äächeli in Au. The catchment area of the Tankgraben lies largely in the canton of Schwyz.
Pesticides as the main problem
The majority of the substances examined were pesticides, which were also primarily responsible for the poor water quality. However, residues from pharmaceuticals and industrial chemicals also exceeded the respective limit values.
Among the chemicals, experts found elevated levels of perfluorooctane sulfonate (PFOS), for example — a persistent substance that is also toxic to mammals and can accumulate through the food chain, as Vera Leib from the water quality department of the Office for Water and Energy explained to the Keystone-SDA news agency.
The use of PFOS has been banned in Switzerland since 2011, with few exceptions. PFOS is still permitted for certain applications, for example in specific paints and coatings, in hydraulic fluid for aviation, and in fire-fighting foams that were placed on the market before 2011.
Mysterious source
Where the PFOS in the streams comes from is therefore questionable, according to Leib. In four of the five streams, the concentration of PFOS exceeded the levels at which the chemical can be considered safe. In the Wagnerbach, the levels were so high that the source would definitely need to be investigated. It could possibly originate from landfills or fire training sites where old firefighting foam was still being used.
The pesticides and other substances could have entered the streams in various ways. For example, rain could have washed off recently applied spray agents, or pesticide residues could have been disposed of improperly. Faulty connections or combined sewer overflows during heavy rainfall are also possible causes.
Insecticides in particular are toxic to stream organisms even in the smallest quantities. Long-lived pollutants, however, could also accumulate through the food chain and cause damage beyond the streams themselves.
Identifying and addressing the causes
The specialists from the Office for Water and Energy now want to identify and address the causes in cases of high contamination. The problem is likely to extend beyond the five streams examined: the Office for Water and Energy had already assessed the biological condition of 78 streams in the canton in 2011 and identified deficiencies.
Various reasons may account for this, such as excessive nutrient input, water temperatures that are too high, or indeed pollutants. The detailed analysis of the measurement campaign now presented was intended to shed light on the role of pollutants.
A significant proportion of the canton's small streams flow through agricultural land and residential areas, from which pesticides and other substances could enter the waterways. Raising awareness among farmers, but also among professional and private gardeners regarding the proper handling of spray agents, was highlighted as important in the press release.
