Don't flush your drugs down the toilet, please

It's fairly common knowledge that prescription medication is becoming a concern in wastewater treatment (both municipal, and on-site). The systems that are in place to treat bacteria that is common in sewage aren't set up to deal with the other metabolites that tend to make their way into wastewater. This is increasingly leading to concerns with effluent making its way into drinking water supplies (both ground water, and surface water).

What is studied less often is the impact that illicit drugs have on the quality of wastewater effluent, and how they might affect drinking water quality. These compounds in sewage effluent and influent have the ability to not only impact on public health, but also to impact on the environment. As a biologist, I can only imagine the impact that cocaine and methamphetamine would have on fish and frogs who come into contact with the contaminated water supplies!

A group of French scientists decided to look at illicit drugs in a number of sewage treatment plants to determine how efficient the systems were at reducing the levels of the drugs and their metabolites, and also to identify patterns of illicit drug use in the country. Though the patterns of drug use are certainly of public health interest, they're not really of environmental health interest (although the data could help to identify areas where better sewage treatment would be best placed). The efficacy of "normal" sewage treatment plants at removing illicit drugs from wastewater, however, is of great interest.

The scientists looked at 17 different illicit drugs and their metabolites, including cocaine, methamphetamine, opiates, and cannabis. The indicator for cannabis (THC-COOH) was found in every single influent the researchers looked at. They found morphine, major metabolites of cocaine, and methadone and its metabolites in 75% of influents, but found methamphetamine and amphetamine, heroin and its metabolites, and minor metabolites of cocaine in less than 10% of influents. The study goes on to further discuss what compounds were found in influent/effluent, and in what amounts, and how this can be related to patterns of drug usage throughout France, but as mentioned above, the environmental health concern is more about how efficient the sewage treatment plants are in removing the drug compounds.

While THC-COOH was found in all of the influent samples, it was also noted to be the easiest of the illicit drugs to remove, regardless of sewage treatment plant technology. Methadone and its metabolite EDDP, on the other hand, appeared to be very difficult to remove from the wastewater. Falling somewhere in between were cocaine and its metabolites, and morphine. Based on the data, it appeared as though low-load activated sludge was more effective at removing the drug compounds than medium-load activated sludge or biofilters (likely due to the longer retention time associated with low-load activated sludge).

The results of the study should be of interest to public health practitioners, and to those involved with making decisions surrounding wastewater treatment. Treatment methods that are common in municipal sewage treatment plants just aren't effective for a large number of illicit drugs and their metabolites. Performing similar "sewage epidemiology" studies in specific geographic regions would allow local governments to identify the compounds of concern in their specific area, and work on identifying treatment methods that may be somewhat more successful than activated sludge. From a terrestrial biology perspective, working together with public health practitioners could lead to a mutually beneficial outcome: reduction of illicit drug metabolites in sewage effluent will lead to safer drinking water, and safer habitats for aquatic and terrestrial animals alike.

Source: Nefau, T., Karolak, S., Castillo, L., Boireau, V., & Levi, Y. (2013). Presence of illicit drugs and metabolites in influents and effluents of 25 sewage water treatment plants and map of drug consumption in France. Science of the Total Environment, 461-462, p.712-722. 

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