Are tire crumbs on fields a cancer threat?

• by Dr. Dev Mishra , Mar 18, 2015

* Artificial turf fields continue to grow in popularity, many of these fields use ground-up car tires (crumb rubber) as infill material.

* Many scientific studies have shown the safety of crumb rubber for use in athletic fields, but some of the research is old.

* Some health advocates claim there is a link between artificial turf fields and cancer formation.

* Proving a causal link between crumb rubber infill and cancer formation will be a long-term and difficult task, but at the least some additional study of turf fields could be very helpful.

Here in the San Francisco Bay Area where I live, our elected representatives have a strong history of taking up populist causes. One area currently being debated is the subject of whether the ground-up rubber particles found in the infill portion of artificial turf sports fields poses a health risk to the players, specifically, could the material lead to cancer in some players.

On the surface, it's always seemed to me to be a very good idea: millions of car tires were sent to landfills where they take up space and possibly contribute to production of hazardous gases, or possibly leak toxic products into the water table. Recycling these car tires and contributing to a consistently good playing surface for young athletes made sense to me.

But recently, some environmental and health advocacy groups have claimed that the crumb rubber infill, used in artificial fields since the 1990s, has contributed to cancer cases in soccer, football and field hockey players.

On the whole, re-use and recycling of used car tires has been enormously successful. Prior to 1990, there was a very limited market for used car tire products but since 1990 it is estimated that about 90 percent of used car tires are re-purposed. According to the EPA, only about 10 percent of used car tires end up in landfills today. Fifty-five percent are estimated to be burned as fuel; 10% are retreaded and resold; about 20 percent are used in civil engineering projects, and the rest are used for various other purposes. Some of the tires are ground up into particles called "crumb rubber" and can be used as infill in artificial turf sports fields.

My feeling as a team physician is that the absolute best playing surface for most outdoor field sports is perfectly manicured natural grass. Unfortunately, most communities cannot maintain perfect natural grass fields, and the newer versions of artificial turf fields have achieved a price point where it makes sense for many communities to install these fields. We debate whether injury risk to knees and ankles is higher on artificial turf than perfect grass, but I know one thing for sure: it's better to be on artificial turf than a beat-up and rutted grass/dirt field.

Health risk to knees and ankles is one thing, but cancer risk is entirely different. The potential problem with the crumb rubber infill is that they contain toxic substances such as heavy metals and chemicals. Is it possible that simply coming into contact with the crumb rubber on your skin can cause health problems?

There have been many tests of the toxicity of the crumb rubber, almost all of which have supported the safety of crumb rubber for use in sports fields. One often-cited study is by Liu and colleagues, which you can access here. The Liu article is a bit dated (from 1998), but concludes "In total, these laboratory tests indicate scrap tires are not a hazardous waste."

Then there is the question of forming a link between the crumb rubber and "cancer." Cancer is not a disease that is easily characterized; it requires a very specific and nuanced approach to description. Lung cancer is not skin cancer, skin cancer is not leukemia. You get the point, we need a more scientific approach here. Also, it's incredibly difficult to ascribe a cause to a specific type of cancer, since there can be many factors leading to cancer formation. Witness the fact that it took several decades to prove that cigarette smoking can cause lung cancer.

The tire reuse and recycling industry, and several health advocacy groups are bunkered down in their positions. From what I can read from the available literature, it seems that there isn't strong evidence to say we should tear out artificial turf fields now due to proven cancer risk. But some of the evidence in favor of safety is old and our thinking could evolve with additional scientific study.

Given the growing popularity of artificial turf fields it is possible that the study of the crumb rubber could now qualify as a public health issue, meaning that it might be time for the EPA to start a new round of widespread testing.

(Dr. Dev K. Mishra is the creator of the SidelineSportsDoc.com injury management program for coaches. He is a Clinical Assistant Professor of orthopedic surgery at Stanford University. Mishra writes about injury management at SidelineSportsDoc.com Blog, where this article first appeared.)