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Swimming in a River of Drugs

A platypus living in a creek downstream of a wastewater treatment facility could be exposed to almost 60% of a human daily dose (per kg body weight) of antidepressants.   169169/Adobe

A platypus living in a creek downstream of a wastewater treatment facility could be exposed to almost 60% of a human daily dose (per kg body weight) of antidepressants. 169169/Adobe

By Erinn Richmond & Emma Rosi

A study finds that more than 65 pharmaceuticals accumulate in aquatic invertebrates and riparian spiders, and can then spread through the food chain to birds and other terrestrial animals.

Humans take and rely on medications to improve our quality of life. However, these drugs have a dark side that is easily overlooked.

When we take a medication, our bodies do not always use the entire dose. Consequently, we excrete small portions of that drug or a biologically active metabolite in our waste. These drugs are then flushed away, where they end up in wastewater treatment facilities. Unfortunately many of these facilities are not typically designed to remove these active compounds, which are eventually released into our streams and rivers. Ageing sewage infrastructure, septic tanks and even recycled municipal wastewater also contribute to this problem.

Almost two decades ago, the first landmark study on pharmaceuticals in our freshwater environment revealed that streams and rivers across the United States were awash with a cocktail of many drugs ( Since then, many studies have detected the presence of human pharmaceuticals in our waterways, including recently in Antarctica (

Pharmaceuticals are ubiquitous in the freshwater environments, so it’s not surprising that they pose a serious threat to “non-target” organisms. They have caused the feminisation of male fish and caused rapid mortality to vultures feeding on livestock carcases contaminated with veterinary drugs. Drugs including antidepressants can even change the way wild fish behave, making them more susceptible to predation.

We know that other contaminants can move through animal food chains, accumulating and increasing in concentration. Is this also true for pharmaceuticals? And if they do, what are the implications for predators and other animals living in streams and rivers?

We set out to answer these questions in a study that’s been published in Nature Communications ( We knew that wastewater is a prime source of pharmaceutical contamination in streams and rivers, so we decided to sample streams with different sources and concentrations of waste-water, including streams downstream of wastewater treatment facilities, known septic tank areas and urban infrastructure. We collected aquatic invertebrates and riparian spiders for analysis of 98 different pharmaceuticals.

Aquatic invertebrates are an important food source for many aquatic and terrestrial predators. Studies have found that exposure to drugs, including antidepressants and methamphetamines, can speed up the life stages of aquatic insects and can also influence the way snails graze on stream algae.

We are beginning to understand that drugs can alter the way invertebrates behave and live in streams, but what we were yet to understand was the ability of aquatic invertebrates to accumulate concentrations of pharmaceuticals in their tissues. Our study was the first to show that a diverse suite of pharmaceutical contaminants accumulated in aquatic invertebrates. We detected almost 70 different pharmaceuticals in stream dwelling invertebrates. The drugs detected included common antidepressants, antibiotics, antihistamines and non-steroidal anti-inflammatory drugs. Not surprisingly, our results showed that drug contamination in invertebrates was greatest downstream of wastewater treatment facilities, where the concentrations in invertebrate tissues were 10–100 times greater than at the other sites we sampled.

Many of these invertebrates have stream-dwelling larvae that emerge as terrestrial adults that fly away from the streams and rivers. Now occupying terrestrial habitats, these insects provide a significant food source for birds, bats and spiders. They can also transport chemicals, such as heavy metals and polychlorinated biphenyls (PCB), to terrestrial streamside food webs.

Alarmingly, we detected 66 different medications in riparian spiders. This means that drugs are being transported out of streams and rivers, where they are consumed by spiders and potentially birds, bats and other animals.

Aquatic invertebrates also make up the majority of the diets of platypus and trout. Although we did not directly sample trout or platypus, we were able to use previous studies on the feeding rates of these animals to estimate the daily dose of drugs they may be exposed to by eating aquatic invertebrates. We calculated that a platypus living in a creek downstream of a wastewater treatment facility could be exposed to almost 60% (per kg bodyweight) of a human daily dose of antidepressants, just by eating its daily meal of aquatic invertebrates.

We also found that trout are exposed to these drugs but at lower doses. This exposure is likely to have biological effects, but more research is needed. We know that single drugs can alter the behaviour of fish, but just what the effects are for a platypus living in a drug-contaminated stream consuming half a dose of antidepressants and other drugs remains unknown.

Pharmaceutical contamination of aquatic environments is likely to intensify as the proportion of the world with access to healthcare and medications increases. Although greater access to drugs has many benefits to humankind, the potential collateral damage to stream-dwelling and terrestrial animals needs careful consideration.

Our study illustrates that pharmaceuticals can accumulate in aquatic food webs and can cross into the terrestrial food webs as well. We still do not know the long-term consequences of pharmaceutical exposure to these animals, so more research on pharmaceutical contamination in food webs and the effects of this contamination is needed.

Erinn Richmond is a postdoctoral research fellow at Monash University’s Water Studies Centre. Emma Rosi is an aquatic ecologist at the Cary Institute of Ecosystem Studies in New York.