The study looked at 258 rivers across the globe, including the Thames in London and the Amazon in Brazil, to measure the presence of 61 pharmaceuticals, such as carbamazepine, metformin and caffeine. The study, from scientists at the University of York, found that pharmaceutical pollution is contaminating water on every continent.
Speaking to Express.co.uk, Dr John Wilkinson warned that high concentrations of drug pollution in rivers could lead to a decrease in the population of fish.
He said: “There’s a chemical that’s called ethinylestradiol, which is in oral contraceptive pills, and its intended to prevent pregnancies in humans.
“The way that chemical works is very well conserved in other organisms, meaning that the chemical receptors that make that medicine work in humans also exist in fish for example.
“They’re very sensitive and in very small concentrations of this chemical, you can see effects in fish in a river.
“These fish can actually have their gender modified, in essence, have eggs growing in male reproductive tissue, as being exposed to certain levels of endocrine-disrupting compounds like oral contraceptive pills.”
Dr Wilkinson warned that in past decade or so, scientists have found that chemicals like this can affect the physiology in male fish in particular.
In such situations, the testes of the fish would begin to develop eggs in a similar way as seen in female fish.
He said: “The abundance of that sperm in the testes is massively reduced, which then reduces the organism’s ability to reproduce.
READ MORE: Despair at UK river pollution levels
“Mostly because it needs to be at a certain concentration of this chemical before you can see effects.
“Where we see risk to fish in terms of population and physiological effects are in rivers that tend to be quite small and rivers that are dominated by sewage treatment affluent.”
Rich Quelch at pharmaceutical experts Origin warned against swimming in UK rivers that heavily polluted.
He said: “While levels found in the UK are unlikely to be toxic to humans, river water should never be treated as ‘clean’.
READ MORE: Our waterways are ‘nowhere near’ the condition they should be