Traces of drugs thought to have been taken by American and Chinese tourists are among nearly 30 found in river water in York, according to a new study.
Scientists have said they believe the levels of pharmaceuticals found in the Rivers Ouse and Foss are higher than in other parts of the world.
The York University team stressed that although the levels were extremely low – drinking two litres of river water would give you about a millionth of a patient’s daily dose of one drug – there were concerns over the long-term implications.
Professor Alistair Boxall from the Environment Department, looked at samples from 11 sites in the city over a 12-month period.
Professor Boxall said there was currently no evidence proving exposure to the chemicals was dangerous to humans, but he added: “It is important to realise that 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.”
He also said there were also questions over the impact of the drug traces on the ecosystem.
The study, published in Water Research and funded by the EU’s Seventh Framework Programme, showed seasonal spikes, with higher levels of antihistamines in the summer and higher levels of drugs associated with cold and flu symptoms in the winter.
The team said the study has laid the foundations for a new global project led by York University, looking at water samples taken from 60 rivers around the world.
They said the results of this should be known by the end of the year.
Previous studies have found traces of illegal cocaine in British rivers, as well as drugs used to treat cancers.
More than seven million tourists visit York every year, according to the tourism agency Visit York, with those from North America making up the biggest international contingent.
The historic Minster as well as the National Railway Museum are among the star attractions.
Some of the drugs found in the University of York’s samples were those not available in the UK.