In March 2026, the California Office of Environmental Health Hazard Assessment (OEHHA) published a long-awaited final report on its effort to estimate health risks from exposure to tire crumb in artificial turf infill.
Tire crumb, also referred to as “crumb rubber,” is composed of small pieces of waste tires. It is used as infill in many artificial turf fields; OEHHA notes that a single artificial turf field can contain over 200,000 pounds of tire crumb. Tire crumb is known to contain a large number of chemicals, many of which are toxic to human health. Tire materials also pose environmental concerns, including toxicity to aquatic species.
OEHHA completed the study in collaboration with CalRecycle, the California state agency whose duties include managing tire waste in the state. The acknowledgments note input from multiple US federal agencies, the European Chemicals Agency, and two industry associations. Initiated in 2015, the study was designed specifically to examine tire crumb, and did not examine other components of artificial turf systems, such as the artificial grass carpet. Separately, the California Department of Toxic Substances Control is examining artificial turf carpet under California’s Safer Consumer Products regulation.
OEHHA’s press release
OEHHA issued a press release titled “Landmark study finds no significant risk from key component of synthetic turf fields.” The press release quotes the OEHHA Director: “Athletes of all ages can use these fields without parents worrying about this commonly used material.”
Based on the press release, families and decision-makers might interpret the report findings as providing evidence of safety of tire crumb, or even artificial turf more broadly, in areas where children play. However, the press release does not make clear the study scope and limitations that are described in the body of the report. In this blog post, we share a few key points about what the study can and can’t tell us about health risks related to recycled tire crumb.
Study scope
For the study, OEHHA gathered information about 35 artificial turf fields with tire crumb infill. Among other study elements, they sampled air above the fields, performed laboratory tests using artificial sweat and artificial gastric fluids, conducted surveys of athletes, and collected and analyzed video footage of players, focusing on soccer. They compiled and analyzed toxicity information on individual chemicals and used information related to hazard and exposure to develop quantitative estimates of excess disease risk. The final report provides detail on these and other aspects of the study, including the scope and limitations of each study element.
The study was designed only to assess health effects of chemicals in tire crumb. It does not examine other hazards, such as risk of heat illness or injuries on artificial turf fields, and it does not address environmental impacts.
What is a risk assessment?
OEHHA’s study is a human health risk assessment. More than a dozen risk assessments have been published on the use of tire crumb in recreational settings, drawing a range of conclusions, and OEHHA’s study adds to that existing literature.
Risk assessments use models that are designed to estimate expected levels of excess disease associated with an exposure. For example, a risk assessment can be designed to estimate how many people will develop cancer or a neurological disorder from exposure to one or more chemicals of concern. Risk assessments build in information on hazard (inherent properties of a chemical, such as carcinogenicity) as well as exposure (how much of a chemical gets into the body).
As explained in a previous blog post, risk assessments can yield widely variable results depending on the assumptions that risk assessors make in designing their models.
Risk assessments for a single chemical can be highly complex, and risk assessments for chemical mixtures are even more complicated. Among other issues, the health effects of a mixture can be different from, and greater than, the effects of the individual chemicals on their own. For this reason, many scientists have made the case for building in a mixture assessment factor.
To learn more, see Dr. Richard Clapp’s comments on risk assessments in this short video, and Dr. Christina Rudén’s comments on mixture assessment in this short video.
Chemicals included in the study
OEHHA’s press release states, “OEHHA’s groundbreaking study focused on more than 100 chemicals that could pose a risk — unlike past studies that only looked at a small number of chemicals.” “More than 100” sounds like a lot, but it represents just a subset of the chemicals that OEHHA tentatively identified in tire crumb. The final report explains, “OEHHA’s study tentatively identified more than 400 organic chemicals initially,” and then focused on a smaller number of organic chemicals as well as metals and metalloids for targeted analysis and the risk assessment. (Chapter 7)
It may be useful to look at how OEHHA calculated cancer risk. A number of previous studies have discussed the presence of a variety of carcinogens in tire crumb. For example, Perkins et al. (2019) classified chemicals in tire crumb with regard to carcinogenicity, and Donald et al. (2019) identified PAHs that had not previously been discussed in the literature on tire crumb.
For its cancer risk calculation, OEHHA constructed a list of chemicals using its air monitoring and laboratory data. For inhalation exposures, OEHHA distinguished between “field-related” and “non-field-related” carcinogens (chemicals that were likely to have come from other air pollution sources). Putting together the “field-related” chemicals in air and a handful of additional chemicals considered to be relevant via the dermal or ingestion routes, OEHHA’s list consists of sixteen carcinogens: aniline, arsenic, 1,3-benzothiazole-2-thiol, chromium, lead, methyl isobutyl ketone, styrene, and nine polyaromatic hydrocarbons (PAHs).
Meanwhile, additional scientific information continues to emerge about chemicals in tire crumb. McMinn et al. (2025) describe numerous transformation products measured in aged tire materials.
Exposure estimates
Exposure information can be gathered in a variety of ways. Some studies use skin wipes to identify chemicals that are being deposited on people’s skin. For example, one study used skin wipes to determine the amount of flame retardants on the skin of gymnasts. Other studies have used personal air monitors to approximate what chemicals people may be inhaling.
Additional information can be obtained through biomonitoring. Biomonitoring studies are designed to determine what chemicals are in people’s bodies, whether by testing for the chemicals themselves, for their metabolites, or for other biochemical signals of exposure. Biomonitoring studies can be conducted on urine, blood, hair, nails, or other tissues or secretions, depending on how the chemical is processed in the body and the needs of the particular study.
Of the many studies that have been published on potential health effects of artificial turf, most have not included any biomonitoring data, although a federal study published in 2024 included a small pilot biomonitoring study. The OEHHA study did not conduct biomonitoring but rather estimated exposures using information including video footage, athletes’ reported time for practice and play, and laboratory tests of chemical releases from tire crumb.
It is also important to understand that OEHHA used average expected exposures rather than the exposures of athletes who reported the largest amount of time on tire crumb, as explained in Chapter 7.
Environmental concerns outside the study scope
A casual reader of the press release could miss the distinction between health effects and environmental effects. OEHHA’s mandate focused on human health and did not include any consideration of environmental effects from zinc, 6PPD/6PPD-quinone, or other chemicals that have been shown to be elevated in leachate or runoff from tire crumb. (Learn more at this link.) OEHHA notes that a separate study by the California Department of Toxic Substances Control found that “release of zinc from tires into water bodies could harm aquatic organisms (DTSC, 2021).”
OEHHA emphasizes this point in Chapter 5:
“The scope of this study also does not cover ecological receptors, thus did not analyze, for example, runoff to streams potentially resulting in exposure of fish to toxic metals and organic chemicals.” (p. 5-3)
What does the study tell us?
This study confirmed that tire crumb contains many chemicals known to be toxic to human health. OEHHA’s study estimated average exposure to these chemicals, and used that information to calculate expected levels of excess disease or disability from playing on tire crumb. Chapter 7 of OEHHA’s report provides an additional level of qualification regarding the design, purpose, and implications of the study:
“OEHHA’s study of 35 synthetic turf fields with crumb rubber infill adds to the growing literature about exposure to chemicals that may be released from crumb rubber. The OEHHA study is a risk assessment based on detected chemicals with TC [toxicity criteria] values for which exposure assessment was conducted, and it is not a health impact study or an epidemiological evaluation.” (page 7-11)
Contributions from this study include identification of potential exposure patterns, development of toxicity criteria (TCs) for certain chemicals for which TCs were not previously available, and calculation of excess disease risk associated with specific estimated exposures.
On the other hand, the study does not provide biomonitoring data, does not assess risk for the most highly exposed athletes, and does not assess the effect of exposure to the entire mixture of chemicals present in tire crumb. The study makes a substantial contribution to the literature, but does not necessarily support a summary statement that “athletes of all ages can use these fields without parents worrying about this commonly used material.”
Where do we go from here?
Risk assessments ask the question, “How much excess disease will result from use of this chemical or material?” Findings from a risk assessment are then used in policy decisions, which ask the question, “What level of excess disease is acceptable?”
To achieve more precise results in a risk assessment, it would be useful to obtain biomonitoring data. To make the risk assessment results more biologically relevant, it would be useful to include a mixture assessment factor. And of course, it would be informative to expand the analysis to include the full set of chemicals that can be released from tire crumb, including transformation products that can form as the material ages. However, it is also possible to pose a different set of questions.
The toxics use reduction methodology asks the question, “Is this exposure necessary? Is there a safer alternative?” Rather than calculating excess disease risk, this approach focuses on finding options for reducing or eliminating toxic exposures.
This is the first in a series of blog posts discussing the OEHHA study. Also see Waste Tires in Artificial Turf Infill (Part 2): Not a long-term solution. To learn more about artificial turf hazards and safer alternatives, see:
- Icahn School of Medicine at Mount Sinai
- Lowell Center for Sustainable Production
- CHE resources on artificial turf
- Waste Tires in Artificial Turf Infill (Part 2): Not a long-term solution
Dr. Rachel Massey is Senior Science and Policy Advisor at the Collaborative for Health and Environment and Senior Research Associate at the Lowell Center for Sustainable Production at the University of Massachusetts Lowell.
Dr. Sarah Evans is Associate Professor of Environmental Medicine and a member of the Institute for Exposomic Research at the Icahn School of Medicine at Mount Sinai. Her research focuses on the impacts of early life exposures to environmental chemicals on child development. She also leads a multi-disciplinary team in the development of effective strategies to communicate research findings to study participants and the lay public with the aim of empowering individuals to make more informed, health-centered choices and activate community-level change.