Millions of people flock to Michigan lakes every summer to helm their boats and enjoy the pristine water on which the state prides itself. But new research presented at the 2024 Water Science Conference found that motorized boats may be adding highly toxic pollutants to these lakes.
Molly Gilpatrick, an undergraduate researcher in conservation biology at Lake Superior State University, and a team of researchers detected naphthalene, an EPA priority pollutant, in two small, inland Michigan lakes—one with and one without access for motorized boats. They found concentration levels of the pollutant were about 1.8 times higher in the lake with boat access during the study period.
Though anthropogenic activities such as boating are known to release pollution into water bodies, this is among the first studies to focus on polycyclic aromatic hydrocarbons (PAHs) such as naphthalene in the waters of inland Michigan, which is home to an estimated 11,000 lakes.
A Tale of Two Lakes
“It got me thinking, ‘How would the water quality and the chemistry differ from all of the other lakes that allow for [motorized boats]?’”
While Gilpatrick and her parents were strolling past Lake Geneva, a 36.4-hectare (90-acre) lake in the northeastern Lower Peninsula of Michigan, her parents mentioned that because of the lake’s position within a private club, motorized boats weren’t allowed in the water.
“It got me thinking, ‘How would the water quality and the chemistry differ from all of the other lakes that allow for [motorized boats]?’” Gilpatrick said.
She discussed her idea with one of her professors, Lake Superior State hydrologist Hari Kandel. The two developed a project that focused on Lake Geneva and Little Wolf Lake, a 37.2-hectare (92-acre) lake about 51 kilometers (32 miles) south. The lakes are similar in size and depth, but unlike Lake Geneva, Little Wolf Lake is accessible to motorized boats.
Finding Naphthalene
From June to August 2023, Gilpatrick collected water and sediment samples from both lakes and brought them back to a lab for chemical analysis. She and the team found that naphthalene concentrations in all of the samples exceeded the EPA’s Health Reference Level of 140 micrograms per liter. The Health Reference Level is a preliminary health effect level the agency outlined in a document about the regulation of naphthalene.
“The detection of naphthalene is definitely surprising because the lakes are not that big.”
PAHs are a suite of chemicals that concern scientists because of their toxicity, persistence, and tendency to accumulate in water and on land. The EPA has even classified naphthalene as a possible human carcinogen. “The detection of naphthalene is definitely surprising,” Kandel said, “because the lakes are not that big.”
Small lakes in Michigan tend to be found in rural settings, Kandel explained. This means they often have fewer recreational boats and are farther from potential pollution sources, such as pesticide-treated lawns and charcoal combustion from campfires.
However, Chris Marvin, an environmental chemist at Environment and Climate Change Canada who was not involved in the study, wrote in an email to Eos, “Given the fact [naphthalene] can be derived by so many sources and travel long distances, no, it’s not surprising to me that it was detected in these lakes.”
Lakes at Stake
Gilpatrick and her colleagues attributed the naphthalene in both lakes to a combination of insecticides and pesticides from nearby farms, car exhaust, and wood and charcoal combustion. Kandel and Gilpatrick strongly believe that the elevated levels in Little Wolf Lake are because of the presence of motorized boats in Little Wolf Lake, but they are currently rerunning the lab analyses to verify their results.
“That naphthalene concentrations are higher in the lake with motorized boats wouldn’t come as a surprise,” Marvin said. “Internal combustion engines are certainly a source of PAHs.”
Kandel hopes this study inspires more research into how to mitigate the effects of burning fossil fuels, and Gilpatrick hopes it spurs more people to study smaller, inland lakes that don’t get a lot of attention.
—Andrea Tamayo (@andreaxtamayo), Science Writer
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Citation: Tamayo, A. (2024), Motorized boats likely adding toxins to Michigan lakes, Eos, 105, https://doi.org/10.1029/2024EO240299. Published on 18 July 2024.
Text © 2024. The authors. CC BY-NC-ND 3.0Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
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