Nearly 4.9 tonnes of medicine enter Danish waters each year

Nearly 4.9 tonnes of active pharmaceutical substances may enter the sea each year, according to calculations by the Danish think tank Tænketanken Hav, reported by DR. The estimate is based on 13 medicines, including painkillers, antidepressants, antibiotics and contraceptive pills.

When people take medicine, the body absorbs what it needs, while some of the active substances leave through urine and faeces. They are then carried to wastewater treatment plants.

Large amounts are not removed during treatment and either end up in sewage sludge used as fertiliser on farmland or are discharged directly into the aquatic environment.

“We take large amounts of active pharmaceutical substances every day for the sake of our health. But those substances ultimately end up in the marine environment, where they will have the same effect on animals as they do on us,” said Henriette Selck, a senior consultant at Tænketanken Hav and professor of ecotoxicology at Roskilde University.

There are around 1,450 active pharmaceutical substances on the Danish market. For its analysis, Tænketanken Hav examined 13 substances, including paracetamol, metformin, antibiotics, antidepressants, heart medication and contraceptive hormones.

Effects on worms and fish

Researchers at Roskilde University have studied how aquatic animals are affected when they absorb antidepressants. In experiments on worms that normally burrow into the seabed when threatened by fish, exposure to antidepressant substances caused them to move rapidly back and forth before eventually collapsing.

“They become more indifferent to escaping when a predatory fish approaches. They do not flee as quickly as they normally do, or they do not flee at all,” Selck said.

She said this could reduce the worms’ numbers and leave less food for fish, potentially affecting fish populations over time.

According to the report, residues from contraceptive pills can cause male fish to develop eggs in their testes, a process known as feminisation that affects reproduction. Painkillers can cause changes in the reproductive glands of mussels and affect the immune systems of oysters, while heart medication can affect the heart rate of fish larvae.

Estimate rather than direct measurements

The analysis is based on medicine purchases, estimates of how much of each substance is excreted by the body, and calculations of how much passes through wastewater treatment plants. It is not based on direct measurements in the sea or in animals, as few such measurements are available.

This makes it difficult to determine exactly how serious the impact of pharmaceutical residues is. John Jensen, a senior researcher and deputy head of the Ecoscience department at Aarhus University, said medicines generally break down and settle more quickly than substances such as PFAS. They are also diluted more in the sea than in a narrow stream, where concentrations are measured.

Tænketanken Hav estimates that 645,148 kilograms of active substances are purchased each year from the 13 substances examined. Based on assumptions about excretion, treatment and discharge, it estimates that 4,861 kilograms are released annually.

Medicine residues are one of several pressures on the marine environment, which is also affected by chemical pollution from industry, fish farms and agriculture, as well as oxygen depletion and fishing.