Myth busted: dumped pills aren’t main source of drugs in sewage | New Scientist
The next time you pick up a prescription, you might notice a message on the label exhorting you not to flush leftover pills down the toilet. This advice reflects the official belief in some countries, including that dumping medicines down the toilet is the number one source of pharmaceutical contamination in waste water. The trouble is, it’s not true.
“We’re not sure where this urban myth came from,” says Patrick Phillips at the US Geological Survey (USGS) in Troy, New York.
Phillips’s latest work, together with Christine Vatovec at the University of Vermont and colleagues, seems to well and truly bust the myth. It also reveals some surprising sewer epidemiology.
Why is it important to know the provenance of pharmaceuticals in waste water? They, and the compounds that result from mixing them, are becoming “chemicals of concern” – and only 50 per cent gets filtered out by treatment plants. The other 50 per cent could potentially end up in your drinking water.
Cocaine concentrations in US wastewater treatment plants have risen during and immediately after the National Football League Super Bowl. In Taiwan, levels of cocaine (and many other illicit drugs) spiked in waste water after 600,000 people arrived there for a music festival.
“But we haven’t been able to tie smaller-scale behaviours to consequences for wastewater,” says Phillips.
Testing the theory
Vatovec had an idea: test the “flush disposal” theory by analysing waste water right before and right after University of Vermont students left the school’s Burlington campus for the summer. At least a quarter of the town’s population is students, so the researchers were confident of seeing significant effects.
First they asked students to complete a questionnaire to assess what kinds of legal drugs they could expect to see in the waste stream (students reported having leftover antibiotics, birth control and pain medicines for example). Then they collected samples at the treatment plant every 15 minutes during the final days of classes and the first days of the summer break to measure levels of 109 compounds.
“The sampling would have revealed big influxes of pharmaceuticals like you’d see with dumping behaviours,” says Phillips. But the researchers found no evidence of drug concentrations in waste water rising dramatically in the week that the student body disappeared for the summer vacation. This suggests drugs enter waste water largely through human urine and faeces rather than through deliberate disposal of unwanted pills down the toilet.
That wasn’t the whole story, though: there was a spike in the days and weeks after the students vacated the town. Phillips was baffled, until he saw exactly which drugs had spiked: antidepressants, and drugs used for diabetes and ulcer treatment. The relatively pure effluent of the college kids, it turned out, had been diluting the far druggier waste water of Burlington’s older population.
“The age profile almost instantly jumped by about 20 years,” says Phillips.
Looking closer, he also found that concentrations of caffeine and cotinine (a metabolite of nicotine) fell off a cliff as the students left town. “Some things never change,” he says. “College is still coffee and cigarettes.”
The study is important, says Dana Kolpin, another USGS researcher who was not involved in the work. “We need a better understanding of the relationship between our behaviour and what’s in our water,” he says, one that can inform policy.
If it turns out that the major source of drugs in waste water isn’t people flushing them away, then we might need to “design greener pharmaceuticals that degrade more quickly after being metabolised”, he says.
We probably need to start redesigning treatment plants too – not just because they only manage to take out half the pharmaceuticals in waste water, but also because the US Environmental Protection Agency is starting to worry about new chemicals. It is becoming clear that it’s not just individual chemicals that are worrying, but also the mixtures they can form, says Ernest Blatchley at Purdue University in West Lafayette, Indiana.
Updating a facility is not trivial. “It’s millions and millions of dollars,” says Kolpin.
These kinds of studies also suggest that the optimal treatment plant may vary according to the demographics of a place. In the short term, identifying which treatment plants are failing to cope with the most recalcitrant chemicals would help decisions to add expensive clean-up methods such as UV sterilisation, advanced oxidation, and carbon filters.
This kind of “sewer epidemiology” is increasingly being used to take the health pulse of cities – and even monitor the health effects of major economic events. After the recession in Greece, for example, levels of antibiotics in the water went down, but illicit drugs went through the roof. We could also monitor waste water as a check on self-reported behaviours.
Phillips and his co-authors are now working on a follow-up study that will monitor illicit drugs, which they hope to publish next year. “I think that one’s going to get a lot of attention,” he says.