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When June Leahy's daughter first started playing soccer on artificial turf, she thought it was a big improvement over the rocky, muddy dirt fields where the talented goalie had been honing her skills since kindergarten.

"We certainly didn't think that it was harmful because we never questioned what was in it, what the make of it was," Leahy says. "It was just a new surface that had a bit of cushioning."

But by 2008, Leahy and her daughter, Austen Everett, had questions about the synthetic materials. The University of Miami athlete had just been diagnosed with non-Hodgkin's lymphoma — and was learning about three other goalies who had also fallen ill.

Everett died from the cancer in 2012. Her grieving mother said it was soon after that, as she found out about even more sick players, that she came to believe that turf was the culprit.

"I realized, 'Oh my God, the thing that she loved most probably killed her,'" Leahy said. "And that was hard."

Portrait of Austen Everett and her mother. Everett died of non-Hodgkin’s Lymphoma three years ago at the age of 25. Courtesy June Leahy

Leahy says that since her daughter's death, she still hasn't gotten enough answers — or action from lawmakers and regulators.

Crumb rubber turf, which is used in thousands of U.S. schools, parks and professional stadiums, is made from pulverized tires — which can contain carcinogens — and green nylon blades of fake grass.

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No research has linked crumb or shredded rubber to cancer, and the turf industry says dozens of studies have shown the surface poses no health risk.

Dr. Laura Green, an MIT-educated toxicologist and independent consultant who recently worked for the turf industry, said that the process used to manufacture tires ensures that chemicals and carcinogens remain trapped inside.

“There’s zero reason to be concerned that playing on synthetic turf will put your child at risk for cancer,” she said. “It’s simply not true.”

Some parents and activists, however, say there should be more testing and that federal regulators should take a position on its safety.

Everett grew up in Washington state and started playing soccer when she was a little girl, initially on dirt fields. When she was in sixth or seventh grade, she began playing on crumb rubber regularly, her mother said.

As a 10-year-old, Everett attended a soccer camp run by Amy Griffin, now an assistant coach with the University of Washington.

"She was the youngest keeper...and she did most of the demos because she was so fearless," Griffin said.

Griffin kept in touch with Everett as she grew up and went first to the University of California Santa Barbara and then to Miami to play for the Hurricanes.

Amy Griffin, Associate Head Coach for the women's soccer team at the University of Washington. HANNAH RAPPLEYE / NBC News

Everett became one of the first names on a list Griffin started keeping of goalies with cancer who had played on crumb rubber. After NBC News reported on the list in 2014, more people began contacting Griffin, and the number of names has grown from 34 to 63.

But Griffin's list of goalies is anecdotal, not a scientific data set.

Leahy has chosen to honor her daughter's memory by carrying on the foundation she started before her death, which links kids battling cancer with professional and college sports teams.

The foundation website includes an essay that Everett wrote early on in her fight, which she compared to her on-field exploits.

"I have begun to think of my recovery like a soccer match," she wrote.

"I was getting daily feedback from my team of doctors and I wanted to destroy Cancer just as I had against countless opponents on the soccer field.

"I prepare myself for treatments just as I did against UNC," she continued, referring to the most dominant team in women’s college soccer. "I put my hospital gown on as if it said Miami on the front and I walk the halls of the Seattle Cancer Care Alliance just as I had imagined I would walk out for the NCAA championships."