This weekend, people all across the United States will be enjoying the last hurrah of summer, perhaps with a trip to the nearest swimming hole. But an influx of bathers, tubers, and paddle boarders could significantly change the composition of freshwater streams, according to new research published in ACS ES&T Water.
“People are exposed to other chemicals based on the choices of their fellow swimmers. And you’re all swimming around in it like a soup,” said Carsten Prasse, an environmental chemist at Johns Hopkins University and an author on the study, in a statement.
Not-So-Clear Creek
Most research studying how recreation affects water bodies has focused on oceans and tested for specific compounds rather than attempting to identify the array of organic, inorganic, and microbial elements present. Prasse and his colleagues took the latter approach, using multiple mass spectrometry methods and gene sequencing to determine as many components of the stream as possible.
The team collected water samples upstream and downstream of a section of Clear Creek in Golden, Colo., a popular river tubing destination, during Labor Day weekend in 2022 as well as on the morning of the following Tuesday, when there was no tubing activity.
The microbial community in the river shifted, too, containing more species associated with the human gut.
Downstream of weekend tubing, the stream’s composition changed significantly. The water contained a very different array of organic compounds, mostly from personal care products such as lotions, shampoos, and makeup. The research team also identified compounds that originate in plastic products, such as phthalates, and compounds known to be toxic to fish, including oxybenzone (an ultraviolet filter used in sunscreens). Traces of pharmaceuticals and illicit drugs, including acetaminophen and cocaine, were also present.
The microbial community in the river shifted, too, containing more species associated with the human gut.
By the following Tuesday, most of the compounds and microorganisms were no longer detectable, showing that the changes to the stream were short-lived.
The team expected to see a change in the occurrence of metals such as titanium and zinc because of mineral sunscreens washing off into the water, Prasse told Eos. But sediment in Clear Creek already has naturally high concentrations of metals, and recreational activity suspends this sediment in the water. “The background signal was basically too high to distinguish any additional metal particles from sunscreens.”
Recreation Risks
“They discovered a new chemical cocktail.”
“The new angle here is that…everyday activities leave a water quality fingerprint that we can now detect with all these cutting-edge tools,” said Sujay Kaushal, a biogeochemist at the University of Maryland who was not involved in the study. Capturing a holistic picture of the composition of a stream, as this study did, can help to make future water management strategies more effective because managers can consider how all components in the stream are transported together and interact, he said. “They discovered a new chemical cocktail.”
The next step is to determine the impacts this cocktail of chemicals and microbes has on surrounding ecosystems or people, Prasse said. But scientists know very little about the environmental health impacts of many of the compounds detected in Clear Creek. The team also didn’t measure the concentrations of the compounds in the water, so it’s hard to tell what the magnitude of the environmental impacts may be, he said.
Prasse emphasized that his team’s findings don’t mean people should stay out of water bodies this weekend, but they should be more aware of the substances they’re introducing into the environment. Using mineral sunscreens instead of those containing oxybenzone is one place to start, he said.
—Grace van Deelen (@GVD__), Staff Writer
Citation: van Deelen, G. (2024), Labor Day dips alter stream composition, Eos, 105, https://doi.org/10.1029/2024EO240397. Published on 30 August 2024.
Text © 2024. AGU. CC BY-NC-ND 3.0
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