The presence of 29 different types of pharmaceutical drug has been recorded in York’s rivers in a new study.
Samples taken from 11 sites on the Foss and Ouse revealed a range of drug compounds, including antidepressants, antibiotics and epilepsy medicines.
Some drugs which cannot be prescribed in the UK were also found.
Previous lab-based studies have revealed environmental impacts of pharmaceuticals, including altering the behaviour and reproduction of fish.
The University of York team behind the research said drugs excreted in urine and faeces could pass through waste water treatment plants without being completely removed and then pumped into rivers.
Seasonal spikes were recorded in the 12-month study, collected in 2016, with higher levels of antihistamines in summer and higher levels of drugs associated with cold and flu in the winter.
Prof Alistair Boxall, who was part of the research team, said the amounts recorded in York were likely to be “quite typical” of most UK cities.
He said: “It is important to realise these drugs are being emitted continuously into the environment and that we will be exposed to them across our lifetime.
“There is, therefore, a concern that some may be causing harm.
“It is a really complex issue to tackle and we don’t really have the methods to understand whether long-term exposure to low levels of pharmaceuticals matters or not.”
The university is leading a global study looking at water samples taken from 60 rivers around the world, with the results expected to be known by the end of 2018.
The levels found in the study were very low compared to a standard dose of a drug.
Concentrations of metformin, a diabetes drug, were recorded at about 500 nanograms per litre, meaning drinking two litres of this water would provide about a millionth of a daily dose.
Researchers said the wider impact of drugs in rivers needed “more investigation”.