A Canberra professor has warned that pharmaceutical residue contaminating waterways could be impacting on human health as drugs are transferred through the food chain.
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Professor Ross Thompson is urging the public to dispose of unused medicines properly to stop the problem escalating, on the back of alarming results in two recent studies.
The chairman of water science at the University of Canberra's Institute for Applied Ecology was involved in research which found that a platypus living in a stream on Melbourne's fringe could receive more than half a human dose of antidepressants every day.
The contamination of waterways is also problematic in Canberra, with wastewater analysis data released by the National Criminal Intelligence Commission this week revealing residents of the capital are among Australia's biggest users of pharmaceutical opioids like oxycodone and fentanyl.
Professor Thompson said while some of the effects of pharmaceuticals on ecosystems were already known, there was a risk people could also be affected.
Medications flushed down toilets or tipped down sinks are generally not removed from wastewater and can end up in rivers and creeks, where they are ingested by aquatic life including fish, platypuses and bugs.
"We have shown in the work in Melbourne that these compounds [of pharmaceutical waste] are finding their way into food chains and getting up into fish," Professor Thompson said.
"People who are then eating those fish will be getting a dose of an active compound.
"Obviously it’s very hard to control how much fish people eat, so there’s quite high variability in doses.
"Dosing people with pharmaceuticals in variable doses is not ideal, and we don’t really understand what that does because there’s not research that’s been done on it."
Professor Thompson said if a lot of small doses of antibiotics found their way into wastewater, they could generate antibiotic-resistant bacteria that caused disease and infection in humans.
"There's a real public health risk," he said.
Professor Thompson said animals and insects living in waterways were also having their food sources destabilised by pharmaceutical waste.
The impacts on invertebrate species were varied, with some growing to twice their normal size and others being unable to reproduce properly.
"But with fish, we know quite a lot," Professor Thompson said.
"We know, for instance, that fish that are treated with antidepressants are brighter coloured, they breed more readily and they’re happy little fish.
"But they also aren’t anxious enough, so they get predated at a higher rate.
"They’re basically just not scared enough, and so there’s a real risk of destabilising food webs by affecting them with these contaminants."
Professor Thompson said if people continued to dispose of unused medicine incorrectly, the problem was only going to get worse.
"The number of commercial prescriptions given out in Australia has about doubled over the last 30 years," he said.
"Things like antidepressants are prescribed at much higher rates than they ever have been."
While similar research has not been conducted in Australia, studies in the US have found more than 80 per cent of streams in that country contain small amounts of human medicines.
Unwanted or expired medicines can be returned to any Pharmaceutical Benefits Scheme-approved community pharmacy as part of the Return Unwanted Medicines project, an initiative funded by the federal government.
"The takeaway positive thing people can do is be really careful about how they dispose of pharmaceuticals," Professor Thompson said.
"When you’ve finished with your medicine, don’t flush it down the toilet."
Professor Thompson said there was an urgent need for more research into the effects of pharmaceutical pollution on waterways.
He said his student, Haysem Alhassen, was currently working on a PhD on the issue.
