Pharmaceutical compounds that are slowly fed into the water supply can impact the behaviour of wildlife, scientists have found.
Male starlings have been found to sing less during mating rituals to females that have been given small doses of antidepressants, according to research by the University of York.
Sophia Whitlock, a researcher on the project, said: "Singing is a key part of courtship for birds, used by males to court favoured females and used by females to choose the highest quality male to father their chicks.
"Males sang more than twice as often and as long to untreated females compared to females that had been receiving low doses of Prozac.
"Here is the first evidence that low concentrations of an antidepressant can disrupt courtship of songbirds. This is important because animals that are slow to find a mate often won't get to breed."
There are a number of ways prescription medication can make its way into the water supply, for example, unwanted tablets are often flushed down the toilet.
More commonly, our bodies do not always absorb all of the drugs that we take and so some compounds are passed into the sewage system.
The water from sewage is filtered and chlorinated but often the particulates of the drugs are too fine to be caught by normal filtration systems.
A number of these compounds are entirely stable in the environment and will break down quite slowly.
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During 2016, there were 64.7 million antidepressant items prescribed in the UK – resulting in small concentrations of a variety of fluoxetine (commonly known as Prozac) and other pharmaceuticals being found in plants and insects around sewage treatment works.
"With many wildlife populations in decline, we have to ask whether more could be done to remove chemical contaminants like pharmaceuticals from our sewage," said Dr Kathryn Arnold, the lead researcher on the study.