A team of international researchers is calling for urgent action as the world becomes increasingly reliant on medications that end up in rivers and lakes, where they pose a serious threat to fish and other aquatic species.

While pharmaceuticals are critical to human health and well-being, they are not fully biodegradable, and when they are ultimately flushed away, they can have profound effects on wildlife. Even everyday caffeine can be harmful once it reaches the waterways.

In a commentary recently published in the journal Nature Sustainability, researchers call for the development of greener drugs that are both effective for their users and able to break down quickly in the environment.

The group includes McMaster’s Karen Kidd, a leading expert on water pollution and its impact on aquatic life, who holds the Stephen A. Jarislowsky Chair in Environment and Health in the department of Biology.

“The disposal of drugs, whether it is through human excretion or flushing unused drugs down the toilet, leads to water pollution,” says Kidd.

“We are seeing mixtures of pharmaceuticals in rivers and lakes on every continent, especially in countries with poor or no wastewater treatment. This is a global problem.”

Exposure to drugs can cause severe developmental, physiological, morphological and behavioural changes in wildlife, the researchers write.

For example, exposure to caffeine makes fish more anxious, as shown by a team led by McMaster’s Sigal Balshine in the department of Psychology, Neuroscience & Behaviour.

Antidepressants lessen their sense of danger, making fish more vulnerable to predators, says Kidd, and even small amounts of estrogen from birth control pills released into lakes and rivers can feminize male fish, reducing reproduction.

Downstream drugs also pose a threat to human health. Antibiotics released into the environment can promote the proliferation of antibiotic-resistant genes and impact beneficial bacteria.

“In some countries, a prescription isn’t needed to get antibiotics, so many people take them unnecessarily,” Kidd says.

Still, harmful drug pollution can be mitigated.

The researchers are also calling on medical professionals to implement more sustainable prescription practices, and governments to improve treatment of municipal wastewaters worldwide.

In Canada, many wastewater treatment plants are undergoing upgrades in response to recent federal legislation regarding effluent, an investment that has the co-benefit of reducing pharmaceuticals going into the environment.

The general public can play an important role, too, Kidd says.

“We need to educate people about the proper disposal of unused drugs, which should be taken back to the pharmacy,” says Kidd. “Most people don’t think about drug pollution or consider their environmental impact. The good news is that this problem  can be fixed with collective actions.”

Kidd appeared recently on CBS News and CBC’s The Current to discuss the issue.