A hot topic in Duluth and nationally helped two Ordean East Middle School students win a prestigious award at the state science fair last month.

Erin Coleman and Teagan Flynn were given the Seagate Rising Star Award - which recognizes students whose research shows a high level of understanding of the scientific process - for their project that studies the potential toxicity of rubber mulch used on playgrounds, fields and in gardens.

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The students were studying the issue long before it became a conversation with the Duluth School Board, which ultimately decided this winter to rid the district's playgrounds of the material after parental advocacy. Studies to determine the toxicity of the material, also known as crumb rubber and used as infill for turf fields, are being conducted by federal agencies and the state of California.

The eighth-grade students last year studied the effects of mulch residue on plant life. This year they used daphnia, an aquatic invertebrate. In both projects they found the residue to be destructive.

"Tire chips are definitely harmful to daphnia," said Coleman, describing the mortality rates of daphnia exposed to the residue rinsed from the mulch that was purchased from a store and gathered from the Lester Park Elementary playground. The students' data suggests that the residue, or leachate, from the new, store-bought mulch had the most damaging effect on the daphnia, but the residue from the older, weathered Lester Park mulch also killed to a lesser degree. There was a control group exposed to nothing that had the smallest mortality rate.

"I think tire chips should stop being used on playgrounds, and especially around little kids, who like to eat them," Coleman said. "And if companies are going to keep selling them, we suggest they wash them or soak them to get the dust off."

Flynn said the experiments were engineered in a way to simulate runoff into area waterways.

Teacher Annette Strom runs the science club at Ordean East. The students worked on their project after school through the club, during lunch and in a school advisory period. Their work is advanced, Strom said.

The students likely won because they did what scientists do: They came up with new questions following one experiment, which led them to a new one, she said. And when they questioned their results, they repeated it.

"They went above and beyond," Strom said. "That's what real scientists do."

The students did 24-hour tests in December and in January. When the January result was different than that of December's, they wanted to know why. Liz Minor, with UMD's Large Lakes Observatory, helped them conclude that the amount of sunlight absorbed played a part in lessening the harmful effects.

"I was very impressed," Minor said, of the work Coleman did in her lab.

Coleman said that even if the residue becomes less harmful over time, the immediate damage it does means it's still bad for the environment.

"Daphnia are at the bottom of the food chain," she said. "So if the daphnia are dying off, there is less food for other fish and things that eat them, which affects the entire food chain."

Kevin Flynn, Teagan Flynn's father and a biologist for the Environmental Protection Agency in Duluth, provided the daphnia. Speaking as Teagan's father, he said, he was impressed with a project that is not only interesting scientifically, but also relevant.

"This has become a community-pushed issue and that brings interesting dynamics," he said. "The level of concern means your level of science is scrutinized a bit more. It's interesting that Teagan and Erin have kind of found themselves in the middle of this."

Coleman and Flynn were given $1,500 and will present their project to Seagate, the international company that judged them and gave the award. They also scored in the top 15 percent of all projects at the fair, including those of high school students.