There's a good chance you know what crumb rubber is – it's those little rubbery black pellets you see in turf, that act as bedding for the fake grass and get kicked into the air over and over during games.
What most people don't know (and many are trying to figure out) is whether they're bad for your health.
After a couple of high-profile recent cases in Minnesota, where critics questioned the use of crumb rubber on surfaces kids were using, the state's Department of Health reiterated its stance on the little black pellets Monday.
There's not a ton of evidence they're a serious health risk, but they still might be, so we need more data, the department says. It's essentially the same stance many other agencies have right now.
So what is crumb rubber?
It's shredded tires (and other rubber), that's often used to cushion and supplement turf on athletic fields. But it also shows up in floor mats, as a packaging filler, in foundation for roads and railroads, and other places, the Minnesota Department of Health says.
For example in Edina, school administrators want to transition some natural grass fields to turf, the Star Tribune reports – which some parents aren't happy about.
It's also being used as full padding at playgrounds, including a school in Duluth (which the Duluth News Tribune says, again, some parents are not happy about).
And what's the problem?
Some people are concerned the crumb rubber can cause cancer or other serious health issues, especially after high-profile news stories (like this one from ESPN last year) suggested a link.
Tires themselves contain chemicals that we know are harmful if there's significant exposure, the Minnesota Department of Health says. But previous studies from California and New York have shown that exposure to those harmful ingredients from crumb rubber seems to be small, and probably wouldn't pose any health risk.
There have been renewed calls though in recent months, including three U.S. lawmakers earlier this year asking for a full federal review of the product, NBC News reported. An industry group, the Synthetic Turf Council, has said the crumb rubber is safe and welcomes all additional research, according to the news organization.
On the plus side, unlike a natural grass field that needs 500,000 (or more) gallons of water every year to maintain, plus pesticides and fertilizer, a synthetic field with crumb rubber is just ready to go. That can be a boost for low-income neighborhoods too, giving low-maintenance spaces for people to engage in physical activity.
So where does the Minnesota Department of Health stand?
They say the synthetic turf is "widely used" in Minnesota right now, and since there haven't been any real health issues reported and tied to their use, it's unlikely the turf and crumb rubber is "a significant, acute public health concern."
But they need more information to properly gauge the long-term effects, if there are any.
So what's the next step?
There are two studies the department is tracking.
One is being done at the federal level, by the Environmental Protection Agency. That was launched just a few months ago.
It says the studies and information out there right now don't give a full enough picture. They'll release a draft later this year, pointing to some conclusions but also outlining next steps.
Then there's a study being done by a California agency, looking at the potential health impacts of playing on fields with the crumb rubber. That includes figuring out the chemicals the crumbs release, and how it affects the air athletes are breathing in above them. It's supposed to be done in June 2018.
The Minnesota Department of Health called the California study "very comprehensive," and will consider the results of both when making any future recommendations.
In the meantime, to be safe, you should wash off with soap and water after being on the surface (especially any scrapes or cuts), shake off your clothes and shoes before going home so you don't bring little crumbs with you, and cover food and drinks you have on the field so they aren't exposed to the shredded tire bits.