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Tubing and swimming alter the chemistry of rivers and streams

A recent study reveals that recreational activities can shift the chemical and microbial balance of our local rivers and streams. But what does this mean for the environment and our health? The consequences are not yet understood.

The research, which was presented at the American Chemical Society (ACS) Fall 2023 hybrid meeting, sheds light on an overlooked dimension of human-water interaction.

The study originated from a discussion between Dr. Carsten Prasse and Dr. James Ranville.

“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 Dr. Prasse.

How the research was conducted 

Dr. Ranville, affiliated with the Colorado School of Mines, proposed the nearby Clear Creek as the study’s focal point. The team analyzed inorganic contaminants like metals and nanoparticles. 

Meanwhile, Dr. Prasse’s team from Johns Hopkins University zeroed in on organic pollutants, including traces of pharmaceuticals. Dr. John Spear was recruited to investigate the creek’s microbiological nuances.

During the Labor Day weekend, and also on a quieter weekday, the researchers collected water samples. The chosen segment of Clear Creek, during peak weekends, receives up to 500 visitors per hour. 

For comparison, the team also collected samples from an untouched upstream location. Cutting-edge analytical methods, such as inductively coupled plasma-mass spectrometry and liquid chromatography-high resolution mass spectrometry, were used to distinguish any chemical alterations.

What the researchers discovered 

“Our sophisticated software and instrumental analyses painted a vivid picture of human-induced changes to the stream,” said Noor Hamdan, a graduate scholar from Dr. Prasse’s team. 

According to Hamdan, a broad spectrum of human-linked compounds, potentially from skin wash-off, sweat, or even urine, were identified. Among the detected substances were cocaine, lidocaine, fexofenadine, lamotrigine, gabapentin, polyethylene glycol, phthalates, and several organic sunscreens and UV filters.

Increased metallic content

Carmen Villarruel, a doctoral student under Dr. Ranville, discovered that human activities disturbed creek sediments, increasing the water’s metallic content with copper, lead, zinc, aluminum, and iron. 

Villarruel cautioned about the risks these particulate metals pose. “For aquatic life, such as fish, these sediments could obstruct their gills, hampering oxygen absorption.” 

Dr. Ranville noted that dissolved metals might jeopardize aquatic species’ reproductive capacities, diversity, and overall health.

Altered microbial composition 

The researchers also discovered a shift in the creek’s microbial composition, with a spike in microbes typically linked with human waste. Such a change, Spear indicates, could influence naturally existing microorganisms and river-dwelling species like fish, both fundamental to ecosystem balance.

Using tools from the Environmental Protection Agency, the researchers gauged the risk associated with these compounds. They found that most of the compounds aren’t particularly prone to bioaccumulate, noted Hamdan. 

Further research is needed 

But the researchers also emphasize that there are no data available on long-term toxicity or persistence in the environment, and there are insufficient data to evaluate exposure risks for a lot of the compounds.

“So 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.”

Further research is needed to monitor these trends over extended periods. 

As a word of caution for eager swimmers and tubers, Dr. Prasse advises against urinating in rivers. 

“When you urinate into a toilet, the water goes to a wastewater treatment plant before it is discharged into a river. But if you urinate into a river, all those chemicals go directly into the water. We know that things like pharmaceuticals can impact aquatic species, such as fish, even at very low concentrations.” 

Dr. Prasse also recommends using mineral sunscreens, such as zinc oxide, instead of sunscreens that contain UV filters, which can be toxic to aquatic organisms.

Microbial balance of streams 

Streams are often perceived as simple and serene components of the natural landscape. But beneath the surface, they are bustling with life. 

This life is not just the fish and plants we can easily observe; it also includes microscopic organisms, or microbes, that play a critical role in maintaining the health and function of the entire aquatic system. 

Stream microbiome 

The stream microbiome is a diverse collection of bacteria, archaea, fungi, algae, and viruses. Each has a specific role. 

Bacteria and archaea are perhaps the most abundant. They decompose organic matter, transform nutrients, and even help detoxify pollutants.

Fungi primarily decompose complex organic substances, especially plant materials, aiding in nutrient recycling.

Algae are photosynthetic organisms that produce oxygen and serve as a primary food source for various aquatic creatures.

Viruses play a role in controlling bacterial populations and transferring genetic material between microbes.

Balance is Key

The microbial balance of a stream is a complex, dynamic system, foundational to the health and functioning of freshwater habitats. Here’s why this balance is crucial:

Nutrient cycling

Microbes facilitate the breakdown and recycling of organic materials, ensuring that nutrients are available for plants and other aquatic life.

Water quality

Some microbes help neutralize or degrade pollutants, thus maintaining or even improving water quality.

Food web

Microbes are the foundation of the aquatic food web. They provide sustenance for organisms like zooplankton, which in turn are consumed by larger animals.

Threats to the balance

Several factors can disrupt the microbial balance, including pollution, climate change, human activities, and physical alterations.

Monitoring and restoration

Understanding and maintaining the microbial balance of streams is crucial for both ecological and human health reasons. Regular monitoring can provide early warnings of imbalances or contamination. 

Furthermore, efforts like reforestation of stream banks or reducing pollutant runoff can aid in restoring or preserving this fragile balance.


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