The Known Unknowns: Is rubber tire mulch safe for playgrounds?

February 27, 2017


Jennifer Martin-Romme
Zenith News

When Avesa Rockwell encountered new evidence that contradicted her hypothesis, she did what she teaches her students to do: She revised her hypothesis.

Rockwell is the mother of two girls, president of the Parents Association at Myers-Wilkins Elementary, and teaches writing at the University of Minnesota Duluth. “You weigh the evidence and then look at whether someone else could use the same evidence to come to the opposite conclusion. I teach my students to think this way, and yet I wasn’t applying it myself.”

Rockwell is part of Duluth Parents for Healthy Playgrounds, a group that organized to remove rubber mulch from playgrounds in the Duluth School District, due to their belief that the mulch—which is made from recycled tires—poses a health hazard.

The Duluth Parents tackled the mulch question with remarkable industry and empirical rigor. They raised enough money from donations to commission their own sampling and laboratory tests. They produced a 45-page review of the existing literature. When questions arose about current surfacing practices, they conducted a survey of every school district in Minnesota. Then they submitted their project results for review by a toxicologist, a biologist, and a physician.

That’s where things took a turn that Rockwell wasn’t expecting. “The mulch wasn’t as toxic as [the reviewers] thought it would be.”

Although the group’s work was a success politically—the School Board voted unanimously last June to replace the rubber mulch—a scientist-friend of Rockwell’s showed her where the group’s work had been riddled with confirmation bias.

So, on January 20, Rockwell addressed the School Board again, this time urging them to slow down the replacement. “I’d still like to see [the rubber mulch] gone...But I know parents have been really affected by my campaign, and they’re really alarmed. I felt a moral obligation to say something.”

Some of the other parents, however, painted Rockwell as a turncoat. “The Lowell parents who were at that meeting were very angry with me. One of them said, ‘Well, I don’t take your toxicologist friends the least bit seriously!’ They were reading my own report back to me. It was surreal...I just don’t think the evidence is there that this is going to harm our kids, and certainly not overnight.”

Read more: At-Large School Board Member Harry Welty's thoughts on rubber tire mulch, click here.

Synthetic surface materials have been in use since AstroTurf rolled out in the 1960s. By the ’80s, the bright green plastic “grass” was standard issue on athletic fields. It was easy to install and maintain, but the scratchy surface tended to cause “rug burn” and its lack of cushioning was a concussion risk.

Recycled tires were introduced in the ’90s, first as rubber crumb infill (a mixture of pulverized rubber and sand to add cushion to synthetic turf), and later as tire mulch—the shredded old tires Duluth’s schoolchildren are playing on today.

Rubber has a number of advantages as surface material. It’s inexpensive, easy to install, and relatively low-maintenance. Unlike wood-based surfacing products, rubber doesn’t compost. It doesn’t mold or grow fungus or encourage weeds. It doesn’t absorb water and then freeze in the winter. Unlike sand, gravel, or natural grass, animals don’t urinate and defecate in it.

Most importantly, rubber beats wood, sand, gravel, and natural grass in “impact attenuation”—the rate at which a material absorbs and disperses the energy from a fall. Its high attenuation rating led the Consumer Product Safety Commission to heartily endorse the use of rubber mulch on playgrounds during the early ’00s, because it reduces the severity of head injuries. Though falls on the head are not common, they are a particularly lethal type of playground injury.

But there are downsides to tire mulch, too. Athletes found out a decade ago what Duluth parents are finding out now: Rubber crumb and mulch sheds a ubiquitous black dust—“turf bugs,” athletes call it—that gets in the eyes, ears, nose, mouth, and hair. It leaves black streaks on clothes and skin that defy soap and water. Not to mention ground-up tires baking in the sun smell about as good as you’d expect.

“The smell is nauseating,” says Cory Kirsling, who removed his son from the Duluth Schools, largely because the tire mulch was causing his son daily headaches and stomachaches. “He would blow his nose and [the black dust] was in his snot.”

Kirsling brought his concerns to then-District Facilities Manager Kerry Leider (who since retired last September). “His response was pretty insulting. He said the reason why it was there was for attenuation and head injury. But then at the end of the email, he said, ‘Tires have been on the road for a long time, so you shouldn’t have any fears.’ It was patronizing.”

Kirsling is a maintenance engineer, with a frank demeanor and an encyclopedic recall of playground facts and their sources. “I’m a blue-collar guy. I’m not an environmentalist. I was not trying to search for the answer I wanted, especially in my line of work, where I deal with chemicals all the time.”

When he removed his son from Lester Park Elementary—and its tire mulch playground—the headaches and stomachaches vanished.

Kirsling acknowledges that his son may have an allergy. “But I can tell you that it’s not just him that had a problem. Even the playground monitors have sinus problems and headaches...The kids come off the playground looking like coal miners.”

In response to parents and athletes all over the country who have voiced doubts about rubber surfacing materials, the Environmental Protection Agency (EPA) is currently revisiting the subject with a Federal Research Action Plan, in conjunction with the Consumer Product Safety Commission and the Agency for Toxic Substances and Disease Registry of the Centers for Disease Control.

Last December, the EPA released its review of the existing literature, including an analysis of gaps in the knowledge and a plan for further testing to be completed this year. Out of 93 past studies, five were thrown out for irrelevance or insufficient peer review, bringing the number of studies to 88—none of which found any serious risks to human health or the environment from rubber tire surfacing materials.

Gaps in the knowledge range from methodology issues (e.g., small sample sizes), to exactly the kinds of questions the Duluth Parents have raised: Are school-age children at more risk—either developmentally or because of how they interact with the mulch (e.g., putting in their mouths)? What about long-term effects? Or cumulative effects of multiple substances?


“That’s the lynchpin of my own concerns as a parent,” says Aaron Crowell, a Lester Park father with the Duluth Parents. “You might get multiple chemicals at once. How do they affect each other in a synergistic way? And does it affect kids differently since they’re still growing?”

The Crowell family moved to Duluth right as the rubber mulch controversy was unfolding. A stay-at-home dad, Crowell brought his kids to the playground, where his initial reaction to the mulch was, “It smelled bad, but it was bouncy.”

He was horrified to learn that it was made out of used tires. “I’m more of the mindset that it never should have been on playgrounds in the first place with all the chemicals in it...I want to learn about [the science], but I want to take a whole step back first. Wood comes from trees; it’s natural. Tires are a petroleum product with things added to them.

“I don’t think [the EPA] is going to tell us anything we don’t already know. They’re not diving into the science. They’re just starting to think about it...It’s not just that there are toxic chemicals in it. There are a lot of questions out there.”

Kirsling isn’t optimistic about the upcoming research either. “This is a product that the EPA and the Consumer Product Safety Commission have advocated for for years. I don’t think they’re going to come back and say anything definitive. I think it’ll just lead to more questions.”

A common complaint among the Duluth Parents is that every study of rubber surfacing is qualified by limitations, areas for additional study, alarming conclusions that “can’t be ruled out,” and more questions raised for every question the study answered.

“You’d be hard-pressed to find a study worth its salt that doesn’t identify its limitations and other areas for study,” says Jim Kelly, the Environmental Surveillance and Assessment Director at the Minnesota Department of Health.

“If you collect samples of chopped-up tires—crumb rubber—they do have chemicals that have been shown to be toxic. But the first question is: Can those chemicals actually get into people’s bodies?...Just playing on it isn’t exposure.”

A whole series of things have to happen for “exposure” to occur. First, the chemical has to be separated from any binding materials. Kelly uses the example of asphalt, which has “a lot of nasty stuff in it,” but the cement in asphalt acts as a binder.

Next, there has to be a route of introduction—a path by which the chemical can enter the body, such as through the mouth, nose, or skin.

Then, if a chemical makes it that far, it also has to be bioavailable, or able to be absorbed by cellular tissues. Many potential toxins are not bioavailable and are simply excreted from the body harmlessly.

And then even if exposure does occur, there’s dosage and duration to consider: How much is the body exposed to, how often and for how long?

“The mere presence of these chemicals, even near small children, is not, in my opinion, a health concern...Even if there is exposure, it’s not much and it’s only for a short time. Every [playground] surface you can think of has one problem or another.”


The Duluth Parents want to replace the rubber with an engineered wood product called Fibar, which uses entirely virgin wood. But wood degrades and molds. “If they’re telling them it doesn’t degrade and mold, it’s because there’s been a chemical added to it.”

Sand, gravel—even natural soil and grass—harbor disease-causing microbes, which is why the Consumer Product Safety Commission’s recommendations for playing in tire mulch are virtually identical to public health recommendations for playing outdoors in the dirt: Don’t put it in your mouth; don’t eat or drink while playing in it; and wash thoroughly afterwards, especially your hands.

“There’s just no evidence that being around this material is unsafe,” Kelly says.

Now that the School Board has already resolved to replace the tire mulch anyway, there’s the question of how to pay for overhauling the elementary school playgrounds—some of which are still brand-new from the long-range facilities plan.

The initial estimate of $150,000 ballooned to $300,000 and then to more than $600,000, when Kerry Leider informed the Board that it wasn’t going to be a simple matter of just scooping out the rubber mulch and laying down wood fiber in its place.

Because rubber has a higher attenuation rating than wood, the playground equipment will all have to be lowered closer to the ground, requiring removal and replacement of all the foundations and water drainage systems underneath the equipment.

Then the funding mechanism fell apart—twice. The first plan was to use long-range facilities funds, but that money is only available for some of the finishing touches to the Red Plan that haven’t been completed yet, such as the playground at Stowe Elementary.

The second plan was to pay for it out of capital funds, but state law only allows tapping capital funds for “necessary” expenses. Unless the EPA finds something alarming that the first 88 studies didn’t find, it will probably be tough to argue necessity.

That leaves the General Fund—still sorely depleted and a source of School Board hand-wringing every year, as teachers and programming have to be cut to cover the shortfalls.

Undeterred, the Duluth Parents applied themselves to the funding problem with the same elbow grease and do-it-yourself pluckiness that characterized the first part of their campaign.

They partnered with Conservation Minnesota to start crowdfunding to pay for as much of the new mulch as they can—an easier proposition when the price tag was $150,000, but they’ve already raised nearly $3,000 in three weeks, and additional fundraisers are already in the works.

The group briefly offered to literally resurface the playgrounds themselves as volunteer labor, until the District squelched that idea due to liability.

Most recently, they’ve lobbied Duluth Representative Jennifer Schultz to change the law to allow capital funds to pay for the resurfacing. Kirsling says Schultz assured him it can already be paid for with capital funds. However, in response to a Zenith inquiry, officials at the Department of Education were unable to confirm that the capital fund can be used, citing only the “necessity” requirement in current law.

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