Medicines do an excellent job of increasing the quality of life for humans around the world, but the drugs don’t stay with us forever, and are eventually flushed out into our wastewater. Now, new research suggests that not only are a staggering range of pharmaceutical products getting into the environment and accumulating in animals, they’re ascending up the food chain.
The problem of pharmaceutical pollution is largely the result of wastewater treatment facilities being unable to scrub out a rapidly-increasing concentration and diversity of drugs flooding into sewage lines. The still-very-functional active ingredients then get out into nature via runoff or wastewater effluents. Scientists are only now beginning to understand the scale of ecological contamination, and a study published today in Nature Communications adds a sobering pixel to picture. Over 60 different pharmaceutical compounds have been detected in the bodies of Australian aquatic insects, which are then passed on to their spider predators.
The team of researchers—based in the U.S., Australia, and Sweden—sampled nearly 200 aquatic insects from six different streams near Melbourne, Australia, testing their tissues for the presence of 98 different compounds. Those compounds included many from commonly-used painkillers like aspirin and ibuprofen, antibiotics, and antidepressants.
Their findings? These bugs were on drugs—lots of drugs. In total, 69 different drugs were detected in the aquatic insects. When the researchers compared insects collected between stream sites, they found that those from heavily-populated areas or downstream of wastewater treatment facilities had taken up much higher concentrations of drugs—as much as 100-fold in some cases. But even relatively-pristine areas like streams burbling through national parks, drugs were detected in insects.
Alarmingly, the contamination didn’t stop on the streambed. The team also sampled spiders that were building webs along streambanks to see if drugs were getting passed up the food chain once aquatic insects mature, leave the water, and fly around briefly before colliding with a spider’s silken death trap.
Distressingly, that’s exactly what they found. The researchers detected 66 drug compounds in the spiders’ tissues, often at concentrations ten times higher than in the aquatic insects. Pharmaceutical pollution, in other words, is concentrating up the food chain in a process called “biomagnification.”
To get an idea of what kind of dosages other animals may be already experiencing, the team looked at platypuses and brown trout, two species that eat the drug-infused insects in the study’s streams. Using the concentrations of drugs found in the insects and the estimated food intake of the predators, the team estimated the dosage the predators were receiving. Antidepressants featured at far higher levels than the rest, with trout expected to receive nearly 30 percent of a human’s daily dose, and platypuses to exceed 50 percent.
So how bad is all this for drug-steeped creatures? Frankly, scientists don’t really know, which makes the ubiquity of drugs at such high concentrations so concerning. Some pharmaceuticals are already known to impact animal behavior and physiology. Antidepressant waste makes shore crabs less wary of predators, and perch become more restless after feeding on insects loaded up with antidepressants. Amphetamines in streams mess with the timing of aquatic insects’ transition to their winged adult form.
“What we are yet to understand is the implications of consuming a chronic mixture of pharmaceuticals,” lead study author Erinn Richmond, a freshwater ecologist at Monash University in Australia, told Earther. “We do not know what it means for a trout or a platypus to be potentially consuming over 60 different pharmaceutical compounds.”
The ecological impacts of drug effects aren’t well-understood yet, either. Some of the compounds may mix and interact with each other in complex ways, influencing behavior in a manner that alters reproduction, or how predators catch their prey, or how prey avoid getting the axe. And pharmaceutical pollution may be even more widespread than this study suggests. After all, while the team measured about 100 different compounds, there are thousands of different drugs moving through markets worldwide.
There are plenty of unsettling unknowns here, but one thing is certain: If humans don’t find a way to keep their drug waste from getting into the environment, the cumulative impact—whatever it may be—is bound to get more extreme.
This article has been updated to include comments from Erinn Richmond.