Summer 2022 eNewsletter

Communicating the Impact of Road Salt Pollution in the Great Lakes

University of Wisconsin Milwaukee graduate student Lexi Passante sampling Wisconsin’s Kinnickinnic River. Photo Credit: Lexi Passante.

In snowy climates road salts are applied to keep roads safe, but they end up in waterways where chloride (a chemical compound found in road salts) permanently pollutes freshwater and can be harmful to aquatic organisms. Current research on chloride pollution focuses on transient measures of chloride levels in surface and some groundwaters, and its toxicity to aquatic life. However, not much is fully understood of the long-term impacts of chloride.

Lexi Passante, a graduate student in Dr. Sandra McLellan’s laboratory at the University of Wisconsin Milwaukee (UWM) School of Freshwater Sciences, took a microbiological approach to investigate these impacts. For her Master’s research, Passante sampled sediment at riverine sites located in a Lake Michigan drainage basin and helped raise awareness of road salt impacts.

“We selected a total of seven riverine study sites, assessing them as either urban or rural based on land use,” said Passante. “Sediment and surface water grab samples were collected through 2021 and into winter of 2022. In addition to chloride measurements, the microbial community in the sediment was analyzed using culture-dependent and independent methods to specifically look for halophilic bacteria.” Halophiles, or salt-loving bacteria, generally require the presence of salt to survive (like found in our oceans), which makes them an attractive candidate in determining chloride impaired areas.

“Our findings were very surprising!” said Passante. “Our chloride measurements showed the urban sites continued to exceed the acute toxicity standard in the winter months, and were well above the chronic toxicity standard throughout the year, long after road salt runoff occurred. Through culture-dependent methods, we found highest colony forming units (CFUs) that contained salt tolerant and potential halophilic bacteria at our urban compared to the rural sites in winter and spring, when chloride concentrations were also highest.”

“We thought it would be difficult to find widespread halophile populations sustained in freshwater—so, we definitely wanted to share our results with the hope of educating others about chloride pollution,” said Passante. With support from a CIGLR ECO Award, Passante teamed up with Wisconsin Salt Wise, Oconomowoc High School, Waukesha County, and the UWM Film Department to create educational materials through Data Nuggets and a video series that documented Passante’s research. “The data we collected was incorporated into the Data Nuggets educational page for students and the public to learn how to work with environmental datasets,” explained Passante. The videos are currently promoted by the Wisconsin Salt Wise social media team to advance chloride awareness.

“Ultimately, we hope that our work has raised awareness of the impacts of chloride pollution and set the foundation for developing a biological indicator to assess chloride-impacted freshwaters as halophilic bacteria thrive under high salt conditions,” said Passante.

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