Leaky sewers are likely responsible for large amounts of medications in streams

Thousands of medications are approved for human use in the U.S., and many of them are harmful to microorganisms, algae and insects when they make their way into lakes and streams through wastewater. The concentrations of pharmaceutical compounds are usually used to determine their impact on organisms living in streams and rivers. However, contaminant concentrations may change quickly from one day to the next, and so singular snapshots do not correctly illustrate their cumulative effects on aquatic life. Instead, load -- the mass of a pollutant that passes through a stream or river over time -- better represents the risks to downstream environments, where the contaminants end up. While loads are used in regulations for traditional pollutants, such as nutrients, they have not been considered for pharmaceuticals. So, Megan Fork and colleagues wanted to get an idea of the yearly load of medicines transported by an urban stream in Baltimore.

The researchers tested water from an urban stream draining into Baltimore's Inner Harbor in Maryland on a weekly basis for a year. At the outflow point, they found 16 pharmaceutical compounds whose presence and amount varied considerably from week to week, ranging from concentrations of parts per trillion to parts per billion. Trimethoprim -- an antibiotic -- was found most regularly, but acetaminophen -- a common pain reliever -- was at the highest concentrations. The team used their weekly measurements to estimate annual loads of pharmaceuticals, calculating that the equivalent of 30,000 doses of antidepressants, 1,700 doses of antibiotics and 30,000 tablets of acetaminophen entered the Inner Harbor through the stream. Interestingly, this watershed did not receive wastewater treatment plant effluent, so it's likely these compounds are coming from leaky sewer pipes. Improvements to aging infrastructure could reduce this source of harmful compounds to urban streams and other waterways, the researchers say.