Most prescriptions carry a message on the product inserts of the drug products — “do not flush the contents down the toilet” – or something similar. Most people, it seems, ignore this warning and instead of returning unused medication back to the pharmacist they flush away the contents.
The presence of disused medications in the sewage system creates problems for water cleaning and also carries the risk of promoting antimicrobial resistance. It is a big concern that many discarded products are antimicrobial and this means that they could promote drug resistance among human pathogens. For example, an antibiotic resistance gene, against a major human pathogen called Klebsiella pneumoniae, was recently detected in wastewater treatment plants in northern China.
To add to this, in 2013 it was reported that antibiotic-resistant bacteria had been isolated in specific spots along the Hudson river, from the Tappan Zee Bridge to lower Manhattan. The cause was linked to raw sewage being pumped into the water. Similar research has uncovered the same trend in the U.K. in the river Thames.
Another concern is with the quality of drinking water, New Scientist reports. With pharmaceutical compounds in wastewater, typically only 50 per cent gets filtered out by treatment plants. The other 50 per cent could potentially end up in your drinking water. This comes from a recent University of Vermont study, looking into the city’s water supply.
The high levels of pharmaceuticals in wastewater are outlined in the journal Science of the Total Environment paper “Investigating dynamic sources of pharmaceuticals: Demographic and seasonal use are more important than down-the-drain disposal in wastewater effluent in a University City setting.”