What have you been smoking? Researchers are analyzing sewage for clues about illicit drug use in Europe.

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Flushing Out Drug Users

Tabloid journalists have long known that you can discover dirty secrets by going through people's garbage. Now, researchers have done something similar in the name of science, albeit on a grander—and smellier—scale. They have analyzed the sewage of 19 European cities to find out how much of certain illicit drugs people in those cities consume.

"The technique needs further work and validation, but this paper shows that it is a feasible approach for estimating drug use on a large scale," says Fritz Sörgel, head of the Institute for Biomedical and Pharmaceutical Research in Nuremberg, Germany, who was not involved in the work.

To put figures on illicit drug use, researchers routinely use surveys, supplemented by data from police and customs. But they have been pushing for more accurate and objective methods to estimate the amounts consumed. One possibility is to sample the sewage of a city and look for chemical traces of the drugs themselves or metabolites created when a drug passes through the human body. "The surveys tell you what people take, but not how much, not how big the market is," says Kevin Thomas, a toxicologist at the Norwegian Institute for Water Research in Oslo and one of the authors of the new paper. "Sewage tells you that."

During one week in March 2011, Thomas and colleagues collected daily samples representing 24 hours of sewage flow from 21 sewage treatment plants in 19 cities across Europe—from Antwerp to Zagreb. The samples were analyzed for traces of five different drugs by local labs according to a fixed protocol.

Cannabis consumption appeared to be similar throughout Europe—although the researchers didn't test for it in all cities—but there were striking regional differences in the use of other drugs. Cocaine use per capita was highest in Belgium and other parts of west and central Europe, but lower in the north and the east. Ecstasy use was also highest in the Belgian city of Antwerp, London, and cities in the Netherlands. More residues of both drugs could be found during the weekend. Meanwhile, methamphetamine levels per capita were highest in Scandinavian cities and Budweis in the Czech Republic. "This is really a snapshot of the drug flow through these European cities in March 2011," says Thomas.

Some of the peaks may be due to drug production rather than consumption, however, Thomas cautions. For instance, sewage from cities in the Netherlands and Antwerp in Belgium showed high levels of amphetamines, but previous surveys suggest the use of those drugs is actually two to three times lower there than in the rest of Europe. Some of the substances may get into the sewer system from illicit drug production labs which cluster in the region. And a spike in the ecstasy load in Utrecht, the Netherlands, might be due to a drug bust that coincided with the testing. "We are going with the theory that they tried to get rid of the evidence by shoving it down the toilet," says Thomas.

In the study, published in Science of the Total Environment, the researchers estimate that overall, around 355 kilograms of cocaine was used in Europe every day during the week of the study. "But that number is just a rough estimate, since we extrapolated from cities to whole countries," says Thomas.

Sörgel, a pharmacologist, cautions there is more uncertainty in the numbers because much is still unclear about drug metabolism in the body. The authors assumed that on average, 38% of a cocaine dose is excreted. "How good that value really is still needs to be shown," Sörgel says.

Meanwhile, Thomas and colleagues have started a follow-up study that will include at least one U.S. city. Samples have already been collected and Thomas hopes to present the data at a conference in Austria in May 2013. The study will provide the first direct comparison of what is going down the drain in the United States and Europe.