杏吧原创

The next time you pick up a prescription, you might notice a message on the label exhorting you . 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鈥檚 not true.

鈥淲e鈥檙e not sure where this urban myth came from,鈥� says Patrick Phillips at the US Geological Survey (USGS) in Troy, New York.
Phillips鈥檚 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 鈥渃hemicals of concern鈥� 鈥� 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 . In Taiwan, levels of cocaine (and many other illicit drugs) spiked in waste water after 600,000 people arrived there for a music festival.

鈥淏ut we haven鈥檛 been able to tie smaller-scale behaviours to consequences for wastewater,鈥� says Phillips.

Testing the theory

Vatovec had an idea: test the 鈥渇lush disposal鈥� theory by analysing waste water right before and right after University of Vermont students left the school鈥檚 Burlington campus for the summer. At least a quarter of the town鈥檚 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.

鈥淭he sampling would have revealed big influxes of pharmaceuticals like you鈥檇 see with dumping behaviours,鈥� 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鈥檛 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鈥檚 older population.

鈥淭he age profile almost instantly jumped by about 20 years,鈥� 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. 鈥淪ome things never change,鈥� he says. 鈥淐ollege is still coffee and cigarettes.鈥�

The study is important, says Dana Kolpin, another USGS researcher who was not involved in the work. 鈥淲e need a better understanding of the relationship between our behaviour and what鈥檚 in our water,鈥� he says, one that can inform policy.

If it turns out that the major source of drugs in waste water isn鈥檛 people flushing them away, then we might need to 鈥渄esign greener pharmaceuticals that degrade more quickly after being metabolised鈥�, he says.

Dangerous mixtures

We probably need to start redesigning treatment plants too 鈥� 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鈥檚 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. 鈥淚t鈥檚 millions and millions of dollars,鈥� 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 鈥�sewer epidemiology鈥� is increasingly being used to take the health pulse of cities 鈥� 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 . 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. 鈥淚 think that one鈥檚 going to get a lot of attention,鈥� he says.