If you've ever popped into a restaurant and been surreptitiously asked by your phone if you'd like to review the place, you know just how good our devices are at tracking our locations. Now, researchers have combined the location services on phones with data from sewage analysis to reveal a more accurate picture of the drugs we take, even while traveling or commuting.

The idea of examining wastewater to find out which pharmaceuticals and illicit drugs a community is taking is called sewer epidemiology and was born around 2008. Just as an archeologist might sift through the garbage of a certain culture to learn about its patterns, chemists can analyze sewage to learn about the drugs we pop, then excrete in trace amounts.

The Norwegian Institute for Water Research has been a pioneer in this field, publishing a year-long study in 2011 that showed how effective wastewater analysis can be in determining a community's drug use.

In that study they found that cocaine use went up on weekends, the use of the antihistamine Cetirizine increased in summer months, and ecstasy ingestion spiked during the month of May, a time that corresponds to "russefeiring," a celebration of high school students in their final term. They also determined that the daily consumption of cocaine was, on average between 0.31 and 2.8 grams per 1,000 inhabitants.

While those numbers seem pretty precise, the researchers weren't satisfied with the accuracy of their own methods. That's because the best they could do was analyze the wastewater from a particular community and use census numbers to divide their findings and develop rough per-person figures.

Such a method doesn't take into account people who leave or travel to a certain area on vacations, or those who might live in an area served by one sewer system, but work somewhere served by a different one. The researchers concluded that their measurement system could have up to a 55 percent inaccuracy rate.

So, they turned to cell phone data and found that laying it atop the results from sewer analysis gave them a clearer and more accurate picture of drug use.

In the study, the researchers focused on a sewage catchment area in Oslo. By tracking the ebb and flow of the population using that sewage system with anonymous cell-phone data, they found that populations in a given area can change by over 40 percent in a 24-hour period. They also reconfirmed their observations regarding seasonal drug use, finding that illicit substances increased in the months of June and July, when people vacation in the area, and that the use of ecstasy shot up on the weekends.

The researchers hope that the new method of analysis can help public health officials and law enforcement agencies get a better grip on the drug use trends in their communities.

The results of the study have been published in the journal Environmental Science and Technology.

Source: American Chemical Society via EurekAlert!