Pharmaceuticals accumulate in sediments – new insights into impacts on life below the surface
Pharmaceuticals do not just end up in the water; they also partition to mud, silt, and sand at the bottom. This is one of several factors behind the effects of pharmaceutical residues in aquatic environments, according to a doctoral thesis at SLU.
Pharmaceutical residues that cannot be handled by wastewater treatment facilities reach the environment. They do not just disappear when they are led out in the water, and as medicines have a specific chemical structure designed to work at low concentrations, their presence in nature can alter animal behaviour and ecosystem functions.
– There is a continuous outlet of pharmaceuticals into the aquatic environment, and we need to know more about what that means. That is why I chose to study how pharmaceuticals in the environment behave and are dispersed between water, sediment and living organisms, says Sara Nicoline Grønlund Thorsted, a double-degree PhD student at SLU and Roskilde University (RUC).
Sara explains that whilst it is relatively easy to measure the amount of pharmaceuticals in the water itself, the ecosystem of a lake or the sea is more complex than that. Through laboratory experiments, she has examined the environmental fate and effects of six different pharmaceutical substances. These include anti-anxiety and antiepileptic drugs that are commonly found in the environment.
Fish are exposed twofold
It has long been known that sediments can act as a reservoir for pollutants, and this thesis shows that pharmaceutical residues are also bound there.
One effect observed by the researchers is that the benthic invertebrates living in the sediment are exposed to and has the potential to absorb contaminants. This, in turn, affects the fish that eat them, according to the thesis.
– The fish take up pharmaceuticals not only from the water they live in, but also through their food. They are therefore exposed twice over, says Sara Nicoline Grønlund Thorsted.
The medicines distributed differently among the tissues of the fish depending on their specific mode of action. The researchers also observed that chemical properties and mode of action influenced how the substances were distributed differently between sediment and water.
– This is an important insight for understanding their fate and effects, says Sara Nicoline Grønlund Thorsted.
Observed an impact on dragonfly larvae
Animal behaviour can be affected by pharmaceuticals in the environment. One of the studies on insect larvae found that medicines for depression and allergies affected dragonfly larvae movement, predation efficiency, and eating, which may affect the interaction between predators and prey.
The thesis illustrates the complexity of working with sediment in the laboratory and Sara hopes that her work and the development of new methods can contribute to future research.
– My findings suggest that we need a better understanding of how medicines affect all parts of the aquatic ecosystem and not only water and water-living organisms, says Sara Nicoline Grønlund Thorsted.
Public defense of the thesis
Sara Nicoline Grønlund Thorsted will defend her thesis, "Environmental fate and effects of pharmaceuticals in the aquatic environment Incorporating an ecotoxicological testing perspective" on Monday, September 14, 2026, at SLU in Umeå. The defense will also be broadcasted online. Sara defended her thesis at Roskilde University June 15, 2026.
Contact
Sara Nicoline Grønlund Thorsted, double-degree PhD student at the Department of Wildlife, Fish, and Environmental Studies, SLU and Roskilde University (RUC) sara.nicoline.gronlund@slu.se or sanigr@ruc.dk +4520889308
Frida Wengberg, Communications Officer
frida.wengberg@slu.se +46725669778