Pharmaceuticals are not just in medicine cabinets. They also move through wastewater treatment plants, which clean what we send down drains but were not designed to remove many modern drugs.
A new study tested how well large municipal plants in Poland filter common medicines and found that several slip past, reaching rivers at levels that can harm aquatic life.
The research was led by Paulina Chaber-Jarlachowicz of the Institute of Environmental Protection, National Research Institute (NRI), in Poland.
The team sampled six large urban plants that follow the same treatment method, one used in many parts of the world. They examined incoming wastewater, treated water, and sludge for over a dozen commonly used medicines.
They measured concentrations down to nanograms per liter (ng/L) – billionths of a gram per liter – and calculated a risk quotient that compares measured levels with safe thresholds for algae, invertebrates, and fish.
Medicines slip through water treatment
All of the plants allowed some medicines to pass through into rivers and streams. Only a few types were regularly filtered out by the treatment process.
In some cases, the water leaving the plant contained even more medicine than when it entered. This shows that treatment can sometimes increase the release of active chemicals into the environment.
The risk assessment found that certain medicines were especially harmful to aquatic life at the levels detected. The concern applied across different types of species included in the study.
“Municipal wastewater treatment facilities using conventional mechanical-biological processes are ineffective at removing pharmaceuticals from wastewater,” said Chaber-Jarlachowicz.
“The annual emissions of pharmaceuticals to rivers from wastewater treatment plants in the study area amounted to at least 40 Mg.”
Limits of current technology
Most cities still use conventional activated sludge (CAS), a biological process where microbes eat organic matter and the solids settle out. Because many pharmaceuticals are designed to be stable and bioactive at very low doses, this system does not easily break them down.
Negative removal can happen because people excrete many drugs as conjugates that later revert to the original, active form during biological treatment. This deconjugation effect has been documented in peer-reviewed research.
Some compounds also bind to particles and then release slowly as water moves through tanks. That time lag can make the measured effluent appear higher than influent at a given moment, even if total mass is similar across the full day.
Medicine in treated water
This is not only a problem in Poland. Two decades ago, a national U.S. Geological Survey study detected one or more organic wastewater contaminants in 80 percent of 139 streams sampled across 30 states.
Across Europe, effluents from 90 wastewater plants carried a wide mix of polar organic contaminants, including many pharmaceuticals, in an EU-wide monitoring program. Tests showed that certain medicines frequently appeared in the treated water.
Aquatic effects at low concentrations are real. In a multi-year study, researchers exposed guppies to fluoxetine at nanogram-per-liter levels and observed changes in behavior, body condition, and reproduction over generations.
Those results matched the study’s warning that some medicines in treated water pose higher risks to aquatic life. When drugs designed to alter serotonin signaling show up in rivers, they can alter feeding, mating, and predator responses in non-target species.
Stronger treatment can help
There are known fixes. Advanced treatment with ozone or granular activated carbon can remove many hard to treat pharmaceuticals that slip past biological processes.
Controlled experiments that tested both approaches on persistent drugs such as carbamazepine and diclofenac have shown that.
Utilities that have added these steps report large reductions in micropollutants, but retrofits cost money and require careful operation. Targeted upgrades at plants with the highest loads, plus seasonal or flow triggered operation, can stretch budgets while reducing emissions.
Medicine use keeps rising
Sales and use of medicines continue to rise worldwide, which means more residues in household wastewater.
When conventional plants become steady sources of active drugs, rivers and lakes carry a chronic, low-level exposure that biology does not easily ignore.
The paper adds high-resolution data from large collections and shows how much mass leaves plants each year. It also identifies which compounds drive the load, giving engineers and regulators a clear starting point.
Next moves for clean water
Better source control can help, including pharmacy take-back programs and hospital-specific measures for high-use drugs.
Monitoring programs that include conjugated forms and transformation products will give a more complete picture of what is really passing through plants.
On the treatment side, pairing oxidation and adsorption, tuning contact times, and optimizing sludge handling can reduce both effluent- and sludge-borne risks. Real-time sensors and composite sampling can also reduce the odds of missing short spikes that matter for wildlife.
The study is published in the journal PLOS One.
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