Swimming Changes the Chemistry, Microbiome of Creeks

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What are you doing for the upcoming Labor Day Weekend? Since the weekend signals the unofficial end of summer, many chose to spend it in the water—swimming, splashing, tubing, etc. While fun for humans, that may not be the case for fish and other species that inhibit the waters often used for recreational activities.

In fact, in a first-of-its-kind study, researchers in Colorado have shown that recreation can alter the chemical and microbial fingerprint of streams. However, the environmental and health ramifications—if any—are not unclear.

“There's a lot of talk about things like wastewater getting into surface waters, but one aspect that hasn't really been thought about is people swimming in surface water—especially in relation to climate change and hotter summers, as water levels drop,” said Carsten Prasse, assistant professor of environmental health and engineering at Johns Hopkins University. Prasse and graduate student Noor Hamdan presented their research Wednesday morning at the fall meeting of the American Chemical Society (ACS).

On Labor Day Weekend last year, collaborative researchers at the Colorado School of Mines collected water samples from nearby Clear Creek. On many weekends, as many as 500 people per hour use the creek for tubing and swimming. The team also sampled an undisturbed location upstream for comparison purposes.

The researchers then looked for changes in chemicals in the water using inductively coupled plasma-mass spectrometry (ICP-MS) and liquid chromatography-high resolution mass spectrometry (LC-HRMS).

According to Prasse and Hamdan, the research team detected a slew of human-related compounds not typically present in the water, including human metabolites, pharmaceuticals, illicit drugs, sunscreens and more. Specifically, preliminary results show the presence of cocaine, lidocaine (a topical anesthetic), fexofenadine (an antihistamine), lamotrigine (a treatment for seizures and bipolar disorder) and gabapentin (a medication for seizures and nerve pain), as well as polyethylene glycol (used in medications) and phthalates (plasticizers). Organic sunscreens and UV filters were also detected.

The study results also showed that human recreation stirred up sediments in the creek, thereby raising the water’s concentration of metals, including copper, lead, zinc, aluminum and iron. Much of the metal was in particulate form, which means it’s small enough to affect underwater species—for example, by clogging the gills of fish.

In addition to the metal particulates, the team also found dissolved metals in the water, which could affect reproduction, species diversity and the health of aquatic species.

“We used software and high-level instrumental analysis to piece together a story of what people were doing to the stream,” said Hamdan.

In general, the scientists noted that tubing and swimming altered the creek’s microbial profile, increasing the abundance of microorganisms commonly associated with human waste. And while that sounds bad and could absolutely impact the creek’s water-dwelling species, a risk assessment paints a not-so-bad picture—or at least an unclear one.

Using EPA risk assessment software, the researchers found that most of the identified compounds are not prone to bioaccumulation. Still, Hamdan says, there is no data available on long-term toxicity or persistence in the environment, and there is insufficient data on exposure risks for many of the compounds.

“That's an important finding from this project,” said Hamdan. “We now know that these compounds are in the river. But we don’t know their concentrations or how they impact the fish or other species in the environment.”

The researchers plan to take water samples again this upcoming Labor Day Weekend to confirm their preliminary results that humans are indeed affecting the creek waters.

“These are sensitive ecosystems not used to having people swimming in them. People just need to be aware that they have an impact,” said Carsten. “I’m not saying people shouldn’t swim, but think about the use of chemicals and whatever you are taking into the water or spilling in the water.”

 

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