The Danish think tank Tænketanken Hav estimates that nearly 4.9 tons of active pharmaceutical substances end up in the marine environment every year through wastewater. The analysis was published on August 26, 2026.
DR reports that the calculations cover 13 pharmaceutical substances, including painkillers, antidepressants, antibiotics, diabetes medicine and contraceptive pills. Around 1,450 pharmaceutical substances are on the Danish market, and the think tank selected 13 central ones.
According to DR, part of the active substance in medicine leaves the body through urine and feces and travels to wastewater treatment plants. Large amounts are not removed there, and either end up in sewage sludge used as fertilizer on fields or are discharged directly into the water environment.
Henriette Selck, senior consultant at Tænketanken Hav and professor of ecotoxicology at Roskilde University, told DR that the substances have the same effects on animals in the sea as they have on people. She also said the size of the quantities surprised her.
Amounts per substance
The think tank’s press release, distributed via Ritzau, breaks the total down by substance. It lists about 2,158 kilograms of paracetamol, 1,599 kilograms of the diabetes drug metformin and 555 kilograms of diclofenac each year. The figures also include 227 kilograms of the antibiotic azithromycin and 88 kilograms of venlafaxine.
At Roskilde University, researchers have studied worms exposed to antidepressants, DR reports. The worms normally burrow into the seabed when a fish approaches, but exposed animals flicker quickly back and forth and eventually collapse. Selck said they become less inclined to flee, which over time can mean less food for fish.
Save up to 2,800 DKK on Your Electricity Bill
FindElpriser helps you switch electricity providers quickly and easily.
The report also describes feminization of male fish from contraceptive pill residues, with eggs developing in the testicles. Painkillers can alter gonads in mussels and affect the immune system of oysters, while heart medicine can affect the heart rhythm of fish larvae.
The analysis is based on calculations using purchased medicine, excretion from the body and removal rates at treatment plants, not on direct measurements in the sea or in animals. John Jensen, senior researcher and deputy head of the Ecoscience department at Aarhus University, told DR that this makes it hard to assess exactly how serious the problem is. He added that other substances in wastewater are more toxic and accumulate more in food chains, but that the combined volume of pharmaceuticals has driven attention toward the new urban wastewater directive.
Under that directive, larger treatment plants must remove 10 of the pharmaceutical substances included in the analysis, with full implementation in 2045, according to DR. A 2025 answer from the Ministry of the Environment to the Danish Parliament states that Denmark must select at least six of 13 indicator substances and cut their concentrations by at least 80 percent at large plants.
Tænketanken Hav states that full implementation could reduce discharges of the 13 studied substances by 58 tons by 2045.
