As temperatures rise on ballfields across America, so do concerns over the piles of tire waste upon which children play. Synthetic turf playing fields lie atop heaps of finely ground recycled rubber from old tires. In playgrounds, chopped up tire mulch is becoming as common as dirt. In the United States between 2007 and 2013, enough ground tire waste was used as playground mulch to leave the equivalent of two 4”-deep wheel-wide tracks along Earth’s equator.
In the 1990s, over one billion waste tires were piled high across the country, in tire dumps that frequently caught fire, sometimes for weeks. The tire industry launched an innovative solution: it began promoting the use of tire waste as a safe alternative to dirt in playgrounds. Now, at a rate of 25 million tires per year, the industry diverts ground rubber from tires into athletic and other playing surfaces. At any given moment, four million children in the United States may be playing atop tire waste.
Industry and government agencies have produced little hard data about the contents of crumb rubber. They have failed to examine the impacts of shifting the burden of tire waste pollution into playing grounds. A growing chorus is raising concerns about what crumb rubber might be doing to children’s health. From Virginia to Minnesota to California, people are trying to obtain state moratoria on using tire wastes to fill ballfields and playgrounds while regulators and scientists try to answer these questions. In recent weeks, agencies in Europe and the United States launched investigations into this industry’s potential impacts on children, adults, and workers.
Toxic Substances Along for the Ride
The industry’s response to this increased scrutiny has been to try and rebrand its material as “rubber” rather than tire-derived wastes. A video produced by the Recycled Rubber Council asserts, “The reality is this is about rubber, not tires, and rubber has been an everyday part of American life for nearly 200 years.”
The video adds this astonishing claim: “Chemically the rubber in recycled tires is the same rubber as used in sneakers, sidewalks, asphalt highways and roads, garden hoses, strollers, gym floors, mouthpieces and many other products widely recognized as completely safe.” (emphasis added) This oversimplification betrays the industry’s reluctance to engage in any discussion about what’s in tire crumb rubber. Rubber is a broad term that can mean anything from natural rubber tapped from trees to industrial products like neoprene. Many types of rubber go into tire formulations. Recipes vary greatly between manufacturers, who closely guard them as trade secrets.
- Polycyclic Aromatic Hydrocarbons
There is one constant in tire manufacturing, however: almost all tires contain high proportions of aromatic process oil, called distillate aromatic extract (DAE). Of the possible ingredients in tire crumb rubber, DAE is perhaps the greatest concern for children, athletes, and recycling workers.
Tire manufacturers use DAE to facilitate the processing of rubber compounds. These oils constitute about 20 percent of a tire’s mass. DAE process oils are mixtures containing polycyclic aromatic hydrocarbons (PAHs), which are particularly harmful substances. The European Chemical Bureau says these impurities in DAE are very persistent toxicants that bioaccumulate in the environment.
As peer reviewed articles in Environmental Science and Technology and Chemosphere have noted, the presence of these “hazardous organic chemicals” in tires and products made from tire waste represent a “potential previously unknown source of carcinogenic dibenzopyrenes to the environment.” In 2013, a research team from Universidad de Santiago de Compostela, Spain, found “extremely high” concentrations of PAHs in recycled rubber, reaching values up to 1% in pavers composed of crumb rubber.” A California state study noted that “exposure to carcinogenic polycyclic aromatic hydrocarbons (PAH) has been identified for the crumb rubber workers."
Earlier this month, concerns about PAHs in tire waste led the European Chemical Agency to launch an investigation into potential exposures from touching, ingesting, or inhaling these substances in both open air and indoor installations “by the general population (including children) and professionals.”
Also this year, the Agency for Toxic Substances and Disease Registry, part of the US Centers for Disease Control, announced that it will “evaluate and characterize the chemical composition and use of synthetic turf with crumb rubber infill and exposure potential to constituents in crumb rubber infill.”
In addition to the Recycled Rubber Council’s dubious claim that all rubber is the same, its video asserts that crumb rubber “has lower levels of lead and heavy metals than the safe standards set by the Consumer Product Safety Commission (CPSC) for children’s toys and the safe standards set by the EPA for urban and rural soil.” The tire industry has not published test results that support this claim. In fact, there is no standard industry screening procedure for lead content, or limits on any other contaminants, in tire waste used in playgrounds.
Lead compounds have been part of tire formulations since 1839, when Charles Goodyear heated a mix of natural rubber, sulfur and white lead, and created the world’s first melt-proof rubber blend. Lead oxide continued to be used in tire vulcanization until recently. Tires also can pick up lead content during their use, from fallen wheel balancing weights, and from lead oxide pigments used in highway striping.
Precious few tests have been conducted to determine the extent of lead contamination in tire playground mulch and athletic field infill. A little-noticed citywide survey of New York City parks is perhaps the most comprehensive on record. In 2008, laboratory testing found very high levels of lead in crumb rubber used to fill a synthetic soccer field at Thomas Jefferson Park in East Harlem. The field is adjacent to the New York City Housing Authority affordable housing community called Jefferson Houses. More than half (16) of these samples exceeded 400 ppm, which is EPA’s threshold for lead in bare soil in children’s play areas. This 400 ppm threshold is also New York’s soil cleanup objective for lead in residential construction. In three Thomas Jefferson Park samples, lead was present above 1,000 ppm, or 0.1% by weight: 1,158, 1,855, and 1,956 ppm. This is more than 100 times greater than the typical amount of lead in U.S. soil, which is around 10 ppm.
After finding the contamination in the Jefferson field, the NYC Parks Department contracted a laboratory to test all of the city fields - 99 athletic fields and 15 play areas - that contained crumb rubber. According to the department, the testing “has not found a lead hazard at any other fields.” However, the department used the EPA’s 400 ppm level to determine whether the results suggested a lead hazard. This 400 ppm threshold is less restrictive than many others, including New York’s objective for lead in “unrestricted use” soils, which is 63 ppm.
California’s Department of Toxic Substance Control (DTSC) uses a standard of 80 ppm to determine whether lead levels in soil are problematic. It recently lowered this threshold based on computer modeling determined to be more protective of children’s health. In the California scenario, a toddler “plays on bare soil, exhibits hand-to-mouth behavior, and therefore ingests higher-than-average amounts of soil.” The amount of soil ingested is small - just 100 milligrams, or 0.004 ounces each day. If the ingested soil contains 77 parts per million lead, according to their model, the child’s blood lead levels will rise by one microgram per deciliter. According to DTSC, “one μg/dL is the estimated incremental increase in the blood lead level in children that would reduce intelligence quotient (IQ) by up to one point.”
Every microgram per deciliter matters. Scientists determined in 2005 that “environmental lead exposure in children who have maximal blood lead levels < 7.5 μg/dL is associated with intellectual deficits.” The US Centers for Disease Control declared there is no safe blood lead level in children.
Reexamining the New York Parks Department test results with the California standard in mind yields a far different picture of the potential neurotoxic impact of crumb rubber infill: In eleven fields, crumb rubber contained between 80 and 353 ppm lead. In other words: One of every ten NYC fields that use crumb rubber contained lead exceeding California’s 80 ppm standard. This indicates a possible public health threat where the industry website and city website suggest none.
Other studies have identified levels of lead in tires and tire scrap at or above 100 ppm. A U.S Environmental Protection Agency study sampled playground mulch and found 440 ppm lead -- more than four times the lead than the federal government allows in children’s products. A California Integrated Waste Management Board analysis of waste tires found “analysis of combustible waste tires “shows lead at concentrations of 100 ppm.”
The Road Forward
The rubber tire industry has nearly erased scrap tire heaps from the national landscape, which is good news on one level. But governments and industry have barely considered the potential health toll from shifting this burden to playgrounds and ballfields. As with the dirt trade that I discussed in a Signal article earlier this week, government agencies do not regulate the use of tire crumb rubber in these so-called “beneficial use” applications. The tire industry has thrived in the regulatory void.
Here are some ways the tire industry might assure parents about tire crumb rubber’s safety far more effectively than its latest YouTube video. The industry could begin by disclosing the potentially toxic substances in crumb rubber, and by establishing testing and screening procedures to keep these toxics out of harm’s way. More sustainable solutions are found in fundamental efforts like waste prevention and developing green chemistry-based tire recipes. In the long run, extending the durability of tires, reducing per capita usage of vehicles, and eliminating toxic substances like PAHs from tire recipes will optimize the circular economy of the wheel.
 The Rubber Manufacturers Association (RMA) produces biennial reports on scrap tire markets. From 2007 to 2013 (the latest year for which it has published data), on average, RMA estimated that 274.15 million pounds of ground rubber per year were used as playground mulch. According to an online rubber mulch calculator, covering a 100 square foot playground 4” deep requires 1,092 pounds of material, or 10.92 pounds per square feet. The average tread of a tire is 215 millimeters or 8.5 inches. A square foot of mulch results in a 16.94”-long tread. Laying all of the ground rubber used for playground mulch along the tire-wide tread, four inches deep, leads to a track that is 49,976 miles long. Earth’s circumference at the equator is 24,901 miles. RMA biennial reports: Rubber Manufacturers Association. “2011 U.S. Scrap Tire Market Summary,” February 11, 2013. https://rma.org/sites/default/files/US_STMarket2011.pdf.
———. “2013 U.S. Scrap Tire Management Summary,” November 2014. https://rma.org/sites/default/files/US_STMarket2013.pdf.
———. “Scrap Tire Markets in the United States: 9th Biennial Report,” May 2009. https://rma.org/sites/default/files/US_STMarkets2007.pdf.
———. “U.S. Scrap Tire Management Summary 2005-2009,” September 2013. https://rma.org/sites/default/files/US_STMarkets2009.pdf.
 Schneider, Keith. “Worst Tire Inferno Has Put Focus on Disposal Problem.” New York Times, March 2, 1990. http://www.nytimes.com/1990/03/02/us/worst-tire-inferno-has-put-focus-on-disposal-problem.html.
 In its 2005 report, the RMA said “The use of scrap tires as a playground cover material was first introduced some six or seven years ago (around 1998). It took about two years for this concept to become accepted in the marketplace. Once the safety features were recognized, the demand for scrap tire-derived playground cover increased dramatically.” Rubber Manufacturers Association. “Scrap Tire Markets in the United States: 2005 Edition,” November 2006. https://rma.org/sites/default/files/US_STMarkets2005.pdf.
 According to the above referenced RMA data, a tire contains an average of 23.6 pounds of ground rubber. Between 2007 and 2013, also per RMA’s biennial reports, an average of 582.5 million pounds of ground rubber were used in athletic and recreational surfaces, including playgrounds. This works out to the equivalent of 24.7 million tires per year.
 A national standard recommends that each child using a playground have a minimum of 75 square feet of play space. Based on the RMA data, I estimate that, applied to 4” thickness, the amount of playground mulch sold between 2007 and 2013, would cover 175,705,128 square feet. This is the equivalent of 4,285,490 individual “play spaces.”
 Sterman, Jose. “Va. Lawmaker Proposes 3-Year Moratorium on Installation of Crumb Rubber Fields.” Arlington, Va.: WJLA, January 15, 2016. http://wjla.com/features/7-on-your-side/7-on-your-side-investigates-crumb-rubber-fields.
 Healthy Legacy. “Moratorium on Waste Tires in Playgrounds/Athletic Fields,” undated. http://healthy-legacy.squarespace.com/waste-tire-mulch/.
 Gutierrez, Melody. “Critics Say EPA Played Dual Role in Recycled Tire Controversy.” San Francisco Chronicle. February 21, 2015. http://www.sfchronicle.com/bayarea/article/Critics-say-EPA-played-dual-role-in-recycled-tire-6094382.php.
 Vallette, James. “Avoiding Contaminants in Tire-Derived Flooring.” Healthy Building Network, April 2013. https://www.healthybuilding.net/uploads/files/avoiding-contaminants-in-tire-derived-flooring.pdf
 Recycled Rubber Council. The Truth About Crumb Rubber and Artificial Turf, 2016. https://www.youtube.com/watch?v=pVZSVhyMv-A.
 There are at least a dozen types of rubber, with very different chemical components. Columbia Engineered Rubber, Inc. “Rubber Materials & Elastomer Compound Information,” undated. http://www.columbiaerd.com/materials.html.
 Crumb rubber Material Safety Data Sheets (MSDSes) confirm that DAE is typically present in recycled tires. A SpectraTurf MSDS lists this chemical at “approximately 20%.” (SpectraTurf. (February 15, 2006). Crumb Rubber [Material Safety Data Sheet]. https://www.pharosproject.net/uploads/files/sources/1828/1330041007.pdf) CRM, a recycler based in Rancho Dominguez, Calif., lists napthenic/aromatic oil at approximately 22% by total weight of its crumb rubber. (CRM Co., LLC. “Crumb Rubber Material Safety Data Sheet,” undated. http://oag.ca.gov/system/files/prop65/notices/2010-00070.pdf.)
 European Chemicals Bureau, and PBT Working Group. “Results of the Evaluation of the PBT/VPVB Properties of Extracts (petroleum), Heavy Paraffin Distillate Solvent. CAS Number 64742-04-7.” Accessed June 16, 2016. http://pharosproject.net/uploads/files/sources/1/1355942773.pdf.
 Sadiktsis, I., Bergvall, C., Johansson, C., & Westerholm, R. (2012). “Automobile Tires: A Potential Source of Highly Carcinogenic Dibenzopyrenes to the Environment.” Environmental science & technology, 46(6), 3326-3334.
 Llompart, M., Sanchez-Prado, L., Lamas, J. P., Garcia-Jares, C., Roca, E., & Dagnac, T. (2013). “Hazardous organic chemicals in rubber recycled tire playgrounds and pavers.” Chemosphere, 90(2), 423-431.
 Public Health Institute. Tire-Derived Rubber Flooring Chemical Emissions Study: Laboratory Study Report. California Department of Resources Recycling and Recovery (CalRecycle). October 2010. http://www.calrecycle.ca.gov/Publications/Documents/Tires%5C2011002.pdf
 Directorate-General for Internal Market, Industry, and Entrepreneurship and SMEs, and Directorate-General for Environment, Green Economy. “Subject: Request to the European Chemicals Agency - to Assess Whether the Presence of Certain Substances in Recycled Rubber Granules Used as Infill in Synthetic Turf Could Pose a Risk to Human Health; - to Assess Whether the Presence of Bisphenol S in Thermal Paper Could Pose a Risk to Human Health; - to Review the Derogation for Cadmium and Its Compounds in Mixtures and Articles Containing Recovered PVC.” European Commission, June 1, 2016. http://echa.europa.eu/documents/10162/13641/echa_rest_proposals_rubber_granules_en.pdf.
 Agency for Toxic Substances and Disease Registry, and U.S. Centers for Disease Control. “Proposed Data Collection Submitted for Public Comment and Recommendations - Collections Related to Synthetic Turf Fields with Crumb Rubber Infill.” Federal Register 81 FR (February 18, 2016): 8201–2.
 Rappleye, Hannah, Stephanie Gosk, Kevin Monahan, and Monica Alba. “Is Rubber Mulch a Safe Surface for Your Child’s Playground? - NBC News,” December 3, 2014. http://www.nbcnews.com/news/investigations/rubber-mulch-safe-surface-your-childs-playground-n258586.
 American Chemical Society. “U.S. Synthetic Rubber Program - National Historic Chemical Landmark,” undated. https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/syntheticrubber.html.
 According to a state of California study, :Tires have been historically manufactured with appreciable amounts of lead oxide. Lead oxide was used during vulcanization processes and has been used frequently in European countries.”
 Long Island Analytical Laboratories. “Re: Al Oerter Recreation Center (North),” memorandum, January 12, 2009. http://www.nycgovparks.org/sub_things_to_do/facilities/Turf_Binder_CrumbRubb er.pdf
 Holmgren, G.G.S., M.W. Meyer, R.L. Chaney, and R.B. Daniels. “Cadmium, Lead, Zinc, Copper, and Nickel in Agricultural Soils of the United States of America.” Journal of Environmental Quality 22 (June 1993): 335–48.
 “Synthetic Turf Lead Results: NYC Parks.” Accessed December 18, 2015.
 “View Document - New York Codes, Rules and Regulations.” Accessed December 18, 2015 https://govt.westlaw.com/nycrr/Document/I4eadfca8cd1711dda432a117e6e0f345 ?viewType=FullText&originationContext=documenttoc&transitionType=Category PageItem&contextData=(sc.Default)
 Alison Young and Peter Eisler. “Some neighborhoods dangerously contaminated by lead fallout,” April 20, 2012. http://usatoday30.usatoday.com/news/nation/story/2012-04-20/smelting-lead- contamination- soil-testing/54420418/1. See also Alison Young, “EPA fails to revise key lead-poisoning hazard standards,” March 10, 2013. http://www.usatoday.com/story/news/nation/2013/03/10/epa-has-not- revised- lead-hazard-standards-for-dust-and-soil/1971209 and Jim Carlisle, Powerpoint slides, https://www.dtsc.ca.gov/HazardousWaste/Projects/upload/2015-08- 20_OEHHA-Pb-CHHSL.pdf
 California Department of Toxic Substances Control. “Preliminary Endangerment Assessment Guidance Manual,” October 2015. https://www.dtsc.ca.gov/PublicationsForms/upload/PEA_Guidance_Manual.pdf
 Lanphear, Bruce P., Richard Hornung, Jane khoury, et al. “Low-Level Environmental Lead Exposure and Children’s Intellectual Function: An International Pooled Analysis.” Environmental Health Perspectives 113, no. 7 (March 18, 2005): 894–99. doi:10.1289/ehp.7688.
 Advisory Committee on Children Lead Poisoning Prevention, and Centers for Disseas Control and Prevention. “Low Level Lead Exposure Harms Children: A Renewed Call for Primary Prevention,” January 4, 2012. http://www.cdc.gov/nceh/lead/acclpp/final_document_030712.pdf
 A Scoping-Level Field Monitoring Study of Synthetic Turf Fields and Playgrounds. United States Environmental Protection Agency. November 2009. http://www.epa.gov/nerl/features/tire_crumbs.html
 California Integrated Waste Management Board. “Effects of Waste Tires, Waste Tire Facilities, and Waste Tire Projects on the Environment,” May 1996. http://www.calrecycle.ca.gov/publications/Documents/Tires%5C43296029.pdf .