Pharmaceuticals in urban sediments reveal wastewater treatment effectiveness

by Sarah Derouin
Friday, October 13, 2017

Scientists collected sediment samples from a dammed pond on the Loiret River in Orléans, France, to investigate the accumulation of pharmaceutical products downstream of wastewater treatment plants. Credit: ASRL.

People take pills to relieve headaches or syrups to ease a hacking cough, and eventually these medications can make their way into streams and rivers around the world as humans excrete the chemicals. Scientists are now using concentrations of common pharmaceutical products (PPs) in river sediments in Orléans, France, to determine how effective four water treatment plants have been at removing chemicals from the environment.

Researchers dug into a 50-year record of sediments in the dammed Saint-Samson millstream pond, which traps PPs within its sediment layers. The millstream is on the Loiret River in Orléans — a city setting fed by both natural sources of water and urban runoff. It is a perfect location for studying PP accumulation considering its low water flows, its position within a growing urban area and the presence of water treatment plants, says Thomas Thiebault, lead author of a new study published in the journal Anthropocene. The location has another key factor that helps when looking at excreted pharmaceuticals: a lot of sewage. “The rate was about 20 percent of the total flow of the river,” Thiebault says.

Between 1989 and 2009, four water treatment plants were installed to deal with wastewater, with some secondary treatments applied to remove PPs from effluent before it enters the river.

The scientists cored samples from sediments ponded behind a dam downstream of the water treatment plants. They tested for eight of the most common PPs (including beta blockers, psychotropics, painkillers and antibiotics) within the cores, and used one core to determine the age of each sediment layer. The researchers used the first appearance of PPs as unique stratigraphic markers to mark anthropogenic impacts on the environment, similar to using the appearance of plastic microbeads or pesticides to date sediment deposits.

Thiebault and his colleagues say that their sediment cores show distinct time frames when PPs were first used, as well as the chemicals' decreasing presence after water treatment processes began. “The message of this study is very positive — we can see that the chemical contamination of sediments is diminished in the last 10 years,” Thiebault says.

Much of the previous work studying the fate of PPs in the environment has focused on dissolved portions of the chemicals in water, not the portions that are stored within sediment, trapped in the environment. “Looking at urban sediments for contaminants has [also] been done before — especially for PCBs and ‘legacy contaminants,'” says Michael Focazio, program coordinator for the Toxic Substances Hydrology Program at the U.S. Geological Survey in Reston, Va., who was not involved in the study. But looking at PP concentrations in sediments puts a new twist on an established methodology for determining chemical persistence, Focazio says.

Zeroing in on the effects pharmaceuticals have on the environment and public health would be a helpful next step, Focazio says. “It costs a lot of money to remove contaminants from water,” he says. “To determine if that investment is worth it, you need to know how well it will reduce the risk of specific health issues.”

Thiebault agrees that the approach his team has taken “is a first step” toward monitoring changing concentrations of chemicals in the environment over time. Sampling sediments downstream of treatment plants, he says, “can be used in more directed studies to better understand the amount of PPs and the reactivity of the sediments” to help drive management decisions for water treatment.

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