Fish on antidepressants: Researchers develop new weapon against toxic substances in wastewater

Toxic chemicals from pharmaceuticals such as antidepressants pass through wastewater treatment systems every day and enter the aquatic environment. A new research project from the University of Copenhagen aims to offer wastewater treatment plants an overview of environmentally harmful substances.
The researchers analysed wastewater samples from a municipal treatment plant in Copenhagen, which receives wastewater from toilets, bathing water and kitchen sinks from roughly 350,000 residents in the Copenhagen area. Photo: Getty

Everytime we flush the toilet, wastewater containing more than tens of thousands of unknown substances, some of which may be toxic to animals and plants, runs into streams and the marine environment.

In a study published in Science of The Total Environment, a team of researchers from the University of Copenhagen investigated what happens to antidepressant medication on its journey from our bodies into the wastewater system, and finally into the natural environment.

The researchers analysed wastewater samples from a municipal treatment plant in Copenhagen, which receives wastewater from toilets, bathing water and kitchen sinks from roughly 350,000 residents in the Copenhagen area.

‘We can see that the concentration of antidepressants in wastewater rises during the winter, when people are most depressed. But it’s not that fish become happier on antidepressants. The substances are actually quite toxic in the marine environment,’ said Jan H. Christensen, Professor of Analytical Chemistry at the Department of Plant and Environmental Sciences, and one of the study’s authors.

Fish change behaviour and growth

About the study

The study "Fate of antidepressants in municipal wastewater: Activated carbon as the most effective removal strategy for amitriptyline, melitracen, and their transformation products." is published in Science of The Total Environment.

The authors are Isidora Dukic, Jan H. Christensen and Selina Tisler from the University of Copenhagen.

According to Jan H. Christensen, it is important to gain a better understanding of what happens to environmentally harmful substances in our wastewater — such as pharmaceutical residues — so that we can track and eliminate them. This has also been the aim of the study.

Previous research shows that substances such as amitriptyline and melitracen, which are found in antidepressants, can be toxic to freshwater ecosystems. Amitriptyline is also used to prevent migraines and as a painkiller.

‘Other studies show that, in high concentrations, these substances can cause growth problems and behavioural changes in fish, and they can harm beneficial algae and invertebrates. That’s why we need to monitor substances that are used so widely in society,’ says Jan H. Christensen.

In the Copenhagen wastewater, the researchers found an average of 0.39 micrograms of amitriptyline per litre of wastewater and 0.15 micrograms of melitracen per litre. They also measured four other toxic substances, all originating from the breakdown of antidepressants. With continuous exposure, these levels are high enough to pose an environmental risk.

‘The levels were higher than expected. These substances easily pass through conventional treatment processes at wastewater plants. Unless we introduce a method that can remove them, they will likely contaminate the surrounding aquatic environments,’ said Selina Tisler, Assistant Professor at the Department of Plant and Environmental Sciences and co-author of the study.

Removing toxic substances as cheaply as possible

Jan H. Christensen is now launching the research project GALADRIEL together with several partners, including Danish utility companies. The project begins on 1 May and will, over the next four years, monitor wastewater pollution using artificial intelligence and classify harmful substances according to which treatment methods are most effective at removing them.

The aim of the GALADRIEL project is to give Denmark’s wastewater treatment plants a new tool to help them use their resources in the most efficient way, focusing on the most problematic substances in the wastewater for the benefit of the environment.

‘If we focus only on active substances from antidepressants or four PFAS compounds, we risk overlooking substances that are far more problematic. Before we invest billions in new treatment facilities, we need to know exactly which technologies remove which substances and understand the dynamics within the plants. With this project, treatment plants can target their efforts and remove the most toxic substances at the lowest cost,’ said Jan H. Christensen.

At the same time, the project will help Denmark meet the requirements of a revised EU directive on urban wastewater treatment, which is to be implemented in Danish law in 2027 and will impose stricter demands on treatment plants.

‘Wastewater will never be completely clean. A good starting point is to select substances that represent different types of pollution. If you can remove those, you can remove the rest. Either we actively target these pollutants, and if that isn’t possible, we will need legislation that pushes industry to stop using them.’

About GALADRIEL

GALADRIEL – Redefining Wastewater Treatment aims to develop chemical fingerprints of wastewater, create a digital AI twin of treatment plants, and optimise treatment processes.

GALADRIEL is led by the University of Copenhagen and supported by the Innovation Fund Denmark with DKK 23.6 million. Eurofins, DHI, the Danish Environmental Protection Agency, ITG, the City of Copenhagen, and several Danish utility companies also participate in the project.

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