August 12, 2019
Should You Be Worried About Crumb Rubber?
By Michael D. Shaw
What, you might ask, is “crumb rubber”? Crumb rubber, aka recycled tire crumb, is the name given to any material derived by reducing scrap tires or other rubber into uniform granules with the inherent reinforcing materials such as steel and fiber removed, along with any other type of inert contaminants such as dust, glass, or rock. Typical applications include:
- Athletic surfaces and fields
- Agricultural mats and equestrian footing
- Automotive parts and tires
- Landscape, trails, and walkways
- Playground and other safety surfaces
While there are currently no federal standards applicable to crumb rubber, customer requirements have driven the industry to accept certain quality guidelines. Important are low fiber content (less than 0.5% of total weight); low metal content (less than 0.1%); and moisture content limited to 1%.
ASTM International does offer two standards on crumb rubber:
ASTM D5603—Classifies vulcanized particulate rubber according to maximum particle size, size distribution and parent materials including whole tires, tire peels, buffings generated from the tire tread and shoulder; and buffings generated from tire tread, shoulder, sidewall, and non-tire rubber.
ASTM D5644—Discusses methods of determining particle size and particle size distribution for crumb rubber. The standard refers to the use of a mechanical sieve shaker for determining particle size and particle size distribution for crumb rubber and gives experimental details of running the test.
Any concern over crumb rubber has to do with its use in synthetic athletic surfaces and playground/safety surfaces. The controversy seems to stem from various athletes who had played on the turf developing cancer (usually Hodgkin lymphoma) at a young age. Many of these individuals were soccer goalkeepers, who remember seeing rubber particles on their uniforms, and assume that they must have ingested some of the stuff, thus possibly causing their disease.
The linked article (previous paragraph) starts off with the case of Emily Prince, a college athlete, who also played soccer as a child. As any victim would, she wanted to know why cancer would strike someone so young and healthy. Oddly, she missed out on a glaring reason—or, if not a reason per se, at least a significant statistic. According to the American Cancer Society, people can be diagnosed with Hodgkin at any age, but it’s most common in early adulthood (especially in their 20s) and in late adulthood (after age 55).
Moreover, the relatively common college-age affliction of infectious mononucleosis is also a risk factor. Thus, seeing instances of Hodgkin in people in their 20s is not exactly earth-shattering. There are certainly many others in this age group who get the disease, and are not college athletes. Etiology cannot be assumed, but must be proved.
The Synthetic Turf Council has addressed the health and environmental issues head on…
“More than 50 independent and credible studies from groups such as the U.S. Consumer Product Safety Commission, and statewide governmental agencies such as the New York State Department of Environmental Conservation, New York State Department of Health, and the California Environmental Protection Agency, have validated the safety of synthetic turf.”
Cited papers include this 2010 study from the California Natural Resources Agency; a 2009 study from the New York agencies mentioned above; and a 2008 effort from CPSC. In fairness, the CPSC study was partially disavowed, but much subsequent work has been performed.
On July 25, the EPA released Part 1 of a report entitled “Synthetic Turf Field Recycled Tire Crumb Rubber Research Under the Federal Research Action Plan.” Part 1 of this report presents results of the tire crumb rubber characterization research (i.e. what is in tire crumb rubber). This massive work comprises two volumes for a total of 790 pages. Part 2—to be released later—will summarize the potential exposures that may be experienced by users of synthetic turf.
While the agency emphasizes that the entire effort (both parts 1 and 2) do not represent a risk assessment, a key finding supports the premise that while chemicals are present as expected in the tire crumb rubber, human exposure appears to be limited based on what is released into air or simulated biological fluids. An astonishingly comprehensive spreadsheet lists the 355 screened analytes and toxicity data. Rest assured that if elevated levels were encountered, EPA would have sounded the alarm.
So, to answer the question posed in the title of this piece: No, you shouldn’t be worried about crumb rubber.