Decontamination of Josefwiese due to elevated dioxin levels

For the safety of young children, certain areas of the Josefwiese in Zurich are For the safety of young children, certain areas of the Josefwiese in Zurich are covered with wood chips and will soon be decontaminated. Image: City of Zurich
Researchers have analyzed soil samples from the Josefwiese on behalf of the city of Zurich and detected elevated dioxin levels. Although the levels are still well below the decontamination limit, the city has decided to clean up the site to protect the population, especially children who play there.

In 2022, the Canton of Zurich tested the surroundings of waste incineration plants for dioxins and published the results in November. The sample from the Josefwiese was within the range of the legal test value of 20 nanograms of toxicity equivalent per kilogram (ng TEQ/kg). Based on this result, City Councilor Simone Brander, head of the Department of Civil Engineering and Waste Management, commissioned an in-depth investigation. In cooperation with the cantonal Office for Soil Protection, soil samples were taken from nine unpaved areas of the Josefwiese and analyzed at Empa.

The new samples from the meadow area were below the test value of 20 ng TEQ/kg. However, analyses on certain other areas showed values of up to 48 ng TEQ/kg in the top soil layer. These values are well below the decontamination value of 100 ng TEQ/kg. However, in case of repeated contact with the contaminated soil, a health risk cannot be ruled out. The use of the affected areas must therefore be restricted for children under six years of age as a precautionary measure in accordance with legal requirements. The city has thus decided to clean up the affected parts of the Josefwiese. In total, an area of 6000 m2 of the approximately 21,000 m2 site will be decontaminated.

Markus Zennegg, a chemist at Empa’s Advanced Analytical Technologies laboratory, led the sample analysis and considers the city’s approach appropriate. "In principle, all people are exposed to a certain level of dioxins through their food intake. This exposure should, however, not be increased further by the possible ingestion of contaminated soil, especially in young children." By covering the affected areas and then decontaminating them, this goal can be achieved, Zennegg said.