Female worker collecting water sample
Even though some known hazardous PFAS substances are forbidden, the PFAS levels in Lake Mälaren are historical high.

PFAS in Lake Mälaren

NIRAS’ sampling in Lake Mälaren reveals cutting-edge results

In cooperation with Stockholm University and Örebro University, NIRAS is tasked by the City of Stockholm to sample water and sediment samples in Lake Mälaren in order to investigate the contents of environmental hazardous PFAS substances. The unique samplings, which contain previous un-explored variants of PFAS, indicates that Lake Mälaren are placed on a historical high level.

PFAS, per- and polyfluoroalkyl substances is the common name for over 4730 various chemicals, which purpose are to reject water, dirt and fat. Among other it is used for water resistant textiles, firefighting agents and teflon pans. Currently, many research studies are investigating how PFAS influences humans, animals and nature. Among others research indicates that animals may be influenced with hormonal disturbances. It is not yet established what the substance does to humans, however indications are suggesting that it may lead to infertility and cancer.

According to the National Food Agency in Sweden, PFAS is a significant threat to the drinking water. Since 2016, NIRAS cooperated with Stockholm University and Örebro University investigating the content of the substance in Lake Mälaren. The goal was to provide the City of Stockholm and the society with enhanced knowledge about the occurrence of PFAS in Lake Mälaren. As the lake currently supplies approximately two million people with drinking water and the treatment of PFAS is rather problematic by current drinking water plants. 

Comprehensive sampling

NIRAS was tasked by the City of Stockholm to sample water and sediment samples in seven basins in Lake Mälaren, within Stockholm's city limits. The project had a unique scope. Previous sampling has focused on analyzing single water and sediment samples. NIRAS applies a new methodology, which identifies the occurrence of PFAS substances that are biodegradable but usually are not analyzed. NIRAS conducted sampling of water in water columns in order to investigate if PFAS are uneven divided on the surface and the bottom. When sampling the sediment, NIRAS conducted sampling of the sediment cores. By investigating the sediment’s layers, it was possible to see that the PFAS content has developed and increased during the years. Sampling both water and sediment samples has led to the understanding that while the water samples indicate good levels according to the National Food Agency in Sweden’s action levels, the sediment samples indicate that the PFAS content increases.

With this project, we hope to learn more about the prevalence of PFAS in Lake Mälaren, and how these substances end up there. We need this knowledge in order to implement the proper measures to reduce the concentration in our bodies of water.

Maria Pettersson, environmental analyst and project manager at the Chemical Centre under the Stockholm Environment & Health Protection Administration

Historical high PFAS levels

Based on NIRAS’ comprehensive sampling, completely new results emerged. Despite the fact that some known hazardous PFAS substances are forbidden, Lake Mälaren contains historical high PFAS levels.
A large part of the problem with PFAS is the great lack of knowledge within the area, when and how it is spread. Furthermore, the levels continue to increase in the sediments. In order to deal with this and stop the spreading it is necessary with further research. NIRAS’ sampling result is a sign of the methodology being applicable for larger prospective research projects within the area. NIRAS will be conducting additional sampling in order to investigate the rainwater being led to Lake Mälaren.