About two million people receive their drinking water from Lake Mälaren, but the lake is not only Sweden's largest drinking water source but also a recipient of water from some of Sweden's largest wastewater treatment plants. The treatment plants cannot remove all pollutants and researchers from SLU have found several organic micropollutants in water from Lake Mälaren, collected over a period of one year.
Organic micropollutants are a group of compounds that includes pharmaceuticals, industrial chemicals, personal care products and per- and polyfluoroalkyl substances (PFASs). Most wastewater treatment plants are not designed for the treatment for the majority of organic micropollutants, and they are therefore continuously released into nature, where they can potentially be harmful for fish, plants, mussels and other aquatic organisms. The pollutants can also affect human health as they can end up in drinking water.
“Organic micropollutants are to a large extent of anthropogenic origin. However, they can occur naturally as well. They have been detected in water, sediments, soil and biota”, says Oksana Golovko, researcher at SLU and one of the authors of a recent study of organic micropollutants in surface water from Lake Mälaren.
In the study, the occurrence of 73 different organic micropollutants in Lake Mälaren was investigated. In total, 46 of the analysed contaminants were detected at levels high enough for the concentrations to be determined. The 12 most common pollutants, for example metoprolol, a beta blocker used to treat high blood pressure and the industrial chemical tolyltriazole, used as a corrosion inhibitor for copper, were found in 75% of the 69 samples. The highest concentration was found of lamotrigine, which is a drug used to treat epilepsy, among other things.
Although large lakes are important as drinking water sources, studies of organic micropollutants in lakes such as Lake Mälaren are rare.
“To our best knowledge, this study was the first one to comprehensively investigate the occurrence and fate of organic micropollutants in a large lake in Scandinavia. It shows that the occurrence of these pollutants in surface water depends on several factors, such as the distance to wastewater treatment plants and the characteristics of the different basins in the lake. This study therefore contributes to a better understanding of the fate and transport of organic micropollutants in large water bodies”, says Oksana Golovko.
Higher concentrations in spring
For most of the detected micropollutants, higher concentrations were found in spring.
“Some seasonal fluctuations could be associated with seasonal consumption patterns, for example for antihistamine, which is used to treat allergic reactions and more commonly taken in spring during the pollen allergy season. Other organic micropollutants were present at comparably similar high concentrations throughout the year”, says Oksana Golovko.
Lack of guidelines and monitoring
For many of the pollutants found, there are no guidelines for concentrations allowed in drinking water, and only a few are included in regular monitoring of lakes and streams. Systematic measurements of organic micropollutants and better knowledge of the toxicity of these compounds is important, especially taking the increasing demands for drinking water expected from a growing population in and around Stockholm and Lake Mälaren.
“The relevance of this study is underlined by the fact that Lake Mälaren is Sweden’s most important drinking water reservoir, and knowledge about the occurrence of pollutants is required to facilitate sustainable management of the water quality”, says Oksana Golovko.