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Public Webinar: Part 1 - Tire Crumb Rubber Characterization

On August 6, 2019, EPA and CDC/ASTDR hosted a joint informational webinar on the Synthetic Turf Field Recycled Tire Crumb Rubber Research Under the Federal Research Action Plan (FRAP) Final Report: Part 1 - Tire Crumb Rubber Characterization. EPA ORD's Jose Zambrana and Kent Thomas presented findings from the tire crumb rubber characterization research activities. Discussions included FRAP introductory information, summary of research activities, key findings, and next steps.

View the webinar slides here.

Webinar Questions and Answers

We have summarized the questions presented during the public webinar and have provided answers below. Additional questions and/or feedback can be sent to

Q. Given that measurements and concentration results appear [different] between tire crumb in  manufacturing/recycling plant and in the actual fields, can we say the results are alarming?  Did your analysis account for multiplicity or synergy of the 21 metals, 49 SVOCs and 31 VOCs that you found, and if not, are the conclusions still supported?

In general, the findings from the report support 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.

The FRAP report is an exposure assessment. The Executive Summary of the Part 1 Report highlights:

The presence of a substance does not directly equate with human exposure.

Air emissions tests were performed at both 25 °C (77 °F) and 60 °C (140 °F), temperatures chosen to represent moderate and high-end field temperature conditions, respectively. For most VOC and SVOC target chemicals, air emissions were low at 25 °C and in many cases, not measurable above the detection limit or above background levels. At 60 °C, higher emissions were measured for some, but not all, VOCs and SVOCs.

Only small fractions of metals were released into simulated biological fluids. For all metals, the mean bioaccessibility values averaged about 3% in gastric fluid and less than 1% in saliva and sweat plus sebum. These results fill important knowledge gaps about potential bioavailability of chemicals associated with recycled tire crumb rubber. Based on these results, a default to 100% bioaccessibility should not be used when assessing potential exposures to most metals in tire crumb rubber.

While there are many chemicals associated with recycled tire crumb rubber, our laboratory experiments suggest that the amount of chemicals available for exposure through release into the air and simulated biological fluids is relatively low.

Risk is a function of both hazard (toxicity) and exposure; therefore, understanding what is present in the material (Part 1) and how individuals are potentially exposed (Part 2 to be released at a future date) is critical to understanding potential risk.

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Q. With the higher levels of many organic chemicals at indoor fields, are you considering alerting the public to this fact as a precaution, while you continue to investigate?

Additional research is needed to determine whether indoor field users experience higher exposures than those using outdoor fields as a result of these differences.

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Q. Given concerns of heterogeneity on fields for metals – e.g., lead hotspots found in other studies - can you provide the rationale for composite sampling? Did you do a pilot to determine the spatial variability of the concentrations? Did you examine within-field variability of lead and other metals?

The Part 1 Report discusses an assessment of within-field variability. Here are relevant findings from Section 4.9 pages 154 and 155:

An important gap exists for information about the variability of chemicals associated with tire crumb rubber, both within synthetic turf fields and between fields in different locations. This is important for several reasons. First, there are few U.S. studies with data available for assessing the range of tire crumb rubber chemical concentrations across the country, and thus, the potential range of exposures people may experience. Likewise, there are few data to assess differences in chemicals associated with tire crumb rubber within a field. Within-field differences are important for understanding whether there might be different exposure potentials across a given field and how best to collect samples to provide representative results for a field.

This federal research study was designed to help fill gaps in knowledge about within-field and between-field variability in chemicals associated with tire crumb rubber infill. Measurements were performed at several different scales to assess measurement precision, homogeneity, and variability.

Tire crumb rubber infill samples collected at a subset of five fields, at different locations on the field, were analyzed separately. This was done to assess within-field variability of chemicals associated with tire crumb rubber at the spatial scale of a single field.

Individual results for multiple locations in the same field are shown in the report for selected metals (see Table 4-57) and selected organic chemicals (see Table 4-60).

(From Section, page 32): For metals in synthetic turf field infill, higher between-field variability was measured for cobalt and zinc, while arsenic, cadmium, chromium, and lead had higher within-field variability.

For SVOCs in synthetic turf field infill, there was uniformly higher between-field variability than within-field variability, with the amount of total variance accounted for by between-field differences typically greater than 75%.

For lead, the average results from the seven individual locations were substantially different than the composite sample measurement for two [of the five fields.] There was substantial variability at individual locations for lead at [one of those fields,] and as noted earlier, and there was substantial within-sample bottle variability for lead.

No lead value higher than 160 mg/kg was measured in any sample, individual or composite.

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Q. Does the tire crumb material have PAHs (polycyclic aromatic hydrocarbons)?

Yes, the tire crumb rubber materials contain PAHs. The levels of PAHs are discussed in Section 4 of the report. Average concentrations of PAHs measured in tire crumb rubber collected from tire recycling plants ranged from 0.37 mg/kg for acenapthylene and fluorene to 18 mg/kg for pyrene. For tire crumb rubber collected from synthetic turf fields, average PAH levels ranged from 0.008 mg/kg for 1-methylnapthalene to 8.8 mg/kg for pyrene at outdoor fields and 0.07 mg/kg for naphthalene to 19 mg/kg for pyrene at indoor fields.

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Q. Does this tire crumb contain per- and polyfluoroalkyl substances (PFAS)?

The study did not specifically test for the presence of any PFAS target analytes.  No PFAS chemical was identified in the non-targeted analyses (see Section 4.12).

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Q. Because dibenzo[def,p]chrysene is high in tires and a very potent carcinogen, should it be added to the PAH assays?

Dibenzo[def,p]chrysene was not on the target analyte list for this study. It was not identified in the non-targeted analyses.

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Q. Is there a timeline for risk assessment, and when it will be released?

The goal of the Federal Research Action Plan on Recycled Tire Crumb Used on Playing Fields and Playgrounds (FRAP) is to characterize potential human exposures to the substances contained in tire crumb rubber.  Results of the research effort for synthetic turf fields are being reported in two parts. Part 1 (the document that is being released now), communicates the research objectives, methods, results, and findings for the tire crumb rubber characterization research (i.e., what is in the material). Part 2, to be released at a later date, will attempt to characterize potential human exposures to the chemicals found in the crumb rubber material during use on synthetic turf fields. The Part 2 exposure characterization will include results (not currently available) from a biomonitoring study being conducted by CDC/ATSDR.

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Q. Given that players often get cuts and scrapes that result in bleeding, creating open wounds that are directly exposed to crumb rubber, will exposure to open cuts, eyes, ears and tire crumbs being swallowed be intensely examined in part 2?

 No. We appreciate the concern about increased exposure potential through abraded skin. However, for the current activities, we cannot implement that type of analysis in the current timeframe. The Part 2 report will discuss our efforts in dermal sampling, and whether it may be possible to estimate the potentially increased dermal exposure through abraded skin areas for different sized abrasions.

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Q. What are plans to test and compare synthetic turf fields with natural grass sports fields and other types of materials like playgrounds with engineered wood fiber (EWF)?

The research study was exclusively aimed at synthetic turf fields with tire crumb rubber and was not designed to compare to natural grass fields. 

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Q. Would you consider using passive sampling wristbands for the biomonitoring study?

The planned CDC/ATSDR biomonitoring study will not utilize wristbands. Section 4.15 of the Part 1 report discusses an initial testing of silicone wristbands. Part 2 will include information on a pilot effort on wristband deployment.

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Q. Has this information with the results been shared with the employees of the recycling plants?

Results for specific participating recycling plants and fields were shared with the owners and/or their designated representative who requested this information.

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Q. Were bioaccessibility experiments run on SVOCs? Was the tire crumb tested at both temperatures for bioaccessibility?

Bioaccessibility testing was conducted only for metals at 37°C (normal body temperature). Bioaccessibility tests were not conducted for SVOCs. There were no validated methods for SVOCs at the time of the sample analysis.

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Q. Given concerns about inhalation as an exposure route, will the exposure study include not only air samples, but exposure to inhaled tire crumb, as well as considering whether the material will get into players’ eyes, nose, cuts, etc? Will you calculate harm levels based on daily play on fields, e.g., considering the bioaccessibility finding of lead in gastric fluid?

Part 2 on exposure characterization includes exposure pathway modeling that includes the inhalation, dermal, and ingestion routes. One of the goals of the exposure measurements and modeling is to better understand the relative importance and magnitude of exposures from the inhalation, dermal, and ingestion pathways. The study was not designed to assess the risks associated with playing on synthetic turf fields with recycled tire crumb rubber infill.

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Q. When will we know if there is an increased risk of a soccer goalie getting cancer?

This study will not make a determination regarding the acceptable/unacceptable levels of exposure. This report is not a risk assessment, nor can the information be used to identify a level above which health effects could occur. Part 2, to be released at a later date, will attempt to characterize potential human exposures to the chemicals found in the tire crumb rubber material during use on synthetic turf fields.

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Q. Given concerns for goalkeepers (e.g., that goalkeepers spend more time exposed to the tire crumb rubber, and may get tire crumb in their eyes), will the effects on soccer goalkeepers be examined?

The tire crumb rubber characterization study was a pilot study and did not produce information for examining different sports roles or positions.

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Q. How is this information being presented and/or explained to PE teachers, coaches, and facilities and maintenance employees at public schools and in municipalities?

The information is available online. Briefings can be provided upon request.

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Q. How characteristic is the presence of staphylococcus compared to a grass playing field? Can you quantify and compare household item bacterial levels with those found in fields?

Bacteria have been reported at similar concentrations in environments that humans encounter, such as indoor air (5.6 log10 bacteria-like particles [BLP]/m3), outdoor air (8.4 log10 BLP/m3; Prussin et al., 2015) and common household items, including mobile phones (4.2 log10 gene copies of 16S ribosomal ribonucleic acid (rRNA) genes per phone; Koljalg et al., 2017) and kitchen hand towels (7.2 log10 CFU per towel; Gerba et al., 2014).

In another study (Vidair, 2010), researchers cultured Staphylococcus and methicillin-resistant Staphylococcus aureus (MRSA) from samples collected at five synthetic turf field and two grass fields. In that study, 2 of the 30 samples collected from synthetic turf were positive for a species of Staphylococcus compared to 6 of 12 samples collected from natural turf. No MRSA was detected on synthetic turf, while a single sample of blades from natural turf was positive for MRSA. Vidair (2010) concluded that their data indicated that the new generation of synthetic turf containing tire crumb rubber infill harbors fewer bacteria than natural turf, including Staphylococcus and MRSA.

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Q. Given that artificial turf fields get much higher than 140 F in summer in warm climates, was the tire crumb rubber tested/analyzed at room temp or heated like fields? Why didn't you evaluate hotter fields?

No additional studies are planned at higher temperatures. While higher and lower temperatures may occur, the temperatures chosen for the study, 25°C and 60°C (77°F and 140°F) are expected to reasonably cover the exposure range.

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Q. What does it mean that the sampling does not represent fields in the US?

The selection of fields for sampling is not statistically representative of all synthetic turf fields in the United States with tire crumb rubber. Researchers aimed to recruit and seek consent from 40 synthetic turf fields with recycled tire crumb rubber infill – 10 fields in each of the four U.S. census regions. CDC/ATSDR used a convenience sampling approach to recruit community facilities with synthetic turf fields. CDC/ATSDR researchers obtained participation agreements from 21 community fields, including 9 outdoor fields and 12 indoor fields. Researchers also collaborated with the U.S. Army Public Health Center (APHC) to identify 19 synthetic turf fields at Army installations across the United States for participation in the study, including 16 outdoor fields and 3 indoor fields. For more information on field recruitment, see Section 3.2.2 “Synthetic Turf Field Recruitment and Selection” of the Part 1 report.

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Q. Were any playgrounds studied, or only fields?

Only synthetic turf fields were included for this portion of the study. The Consumer Production Safety Commission is conducting a separate research investigation for playgrounds.

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Q. What is the source of the tire crumb rubber - domestic tires? Mixture of sources? Unknown? Anything from China?

Researchers had no way to ascertain the specific tire sources for tire crumb rubber at any particular field. For more information, see the “Industry Overview” in Appendix A of the Part 1 report.

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Q. Where can I find the information on the study that was covered in the public webinar?

Information on the study is available at Feedback can be sent to

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Q. Are you aware that CAEPA/OEHHA has been conducting a study with similar study design and will you compare your results with the OEHHA study?

We are aware of the CA (OEHHA) study and the federal research team regularly consults with OEHHA scientists to discuss how the two studies can be mutually informative. The FRAP study shares similarities with the OEHHA, but also has important differences. The federal study is characterizing tire crumb rubber from recycling plants, indoor, and outdoor fields across the United States, while OEHHA focuses on outdoor fields in California.

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Q. How did you determine which target constituents to analyze?

Target analyte selection was based on a combination of information from previous tire crumb rubber research studies, information on potential tire manufacturing chemical ingredients, and analytical laboratory and method capabilities. The Literature Review/Gaps Analysis conducted by EPA, CDC-ATSDR and CPSC and published in the December 2016 Status Report (see Appendix C in the Part 1 report) identified several hundred chemicals that have been reported in the literature based on analysis of tire crumb rubber or playground surface rubber, rubber leachate, headspace analysis or environmental measurements. Some chemicals were included in the analysis because they were reported through the literature or other sources to be potential tire manufacturing components, process chemicals or degradates. Many of the VOC secondary analytes were included because the existing standards were available and included in mixtures typically analyzed in the laboratory.

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Q. Is it a reasonable assumption that other products made of crumb rubber share similar exposure risks - e.g., pickup truck bed mats?

This study  focuses on characterizing the tire crumb rubber used on synthetic playing fields. The study is not a risk assessment and should not be used to draw conclusions about other commercial products that utilize recycled tire crumb rubber.

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Q. Do you have any thoughts on why lead and bis-2-ethylhexylphthalate measured in crumb rubber were different than concentrations of these compounds measured in crumb coming from the recycling plants? Because lead is a heavy metal that has a very high settling velocity, could the increase be because the concentration increases over the years as other lighter compounds volatilize?

A few chemicals [e.g., lead and bis(2-ethylhexyl) phthalate] had higher average concentrations in samples from synthetic turf fields when compared to recycling plants. Additional research would be required before the Agency could answer these questions.

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Q. Can you describe the exposure pathway modeling anticipated to be issued from Part 2 of the study?

Exposure pathway modeling for inhalation, ingestion, and dermal exposures is being performed for several chemicals, covering a range of chemical and physical properties, using data from the literature and data from both the tire crumb rubber characterization and exposure characterization studies.

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Q. Because the effects of many of these compounds are simply not known - how can you state that exposure to a compound with unknown effects is in fact low? 

The study was designed to characterize the tire crumb rubber and present information on potential exposure. The document describes these results and conclusions. It is not and does not purport to speak to effects.

One or more toxicity reference values was identified for 167 (about 47%) of the 355 chemical compounds potentially associated with recycled tire crumb rubber as reported in the Literature Review and Gaps Analysis. See Section 5 of the Part 1 report for more information.

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Q. What about the tire crumb rubber impacts on creeks, rivers and groundwater? Has that been studied, or, for example, releases from landfills?

Examination of ecological endpoints was out of scope for this study.

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Q. Is EPA studying the broader impact of tire wear into the environment from auto tire wear, presumably much smaller particles that are distributed throughout the environment?

This tire crumb rubber characterization study does not study the broader impacts of tire wear, but EPA’s Office of Research and Development has conducted research over the last few years to characterize tire wear from on-road motor vehicles (e.g., see the SPECIATE database).

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Q. Previous literature studies have shown that particle size of tire crumb particles impacts the leaching of metals and organics. Have you considered this in your study?

Bioaccessibility testing was performed on tire crumb rubber samples collected directly from fields, including the entire range of particle sizes that was present.

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Q. Was there any characterization of the tire crumb and their emissions in the presence of UV light and heat, not just heat?

Emission experiments did not include application of UV radiation.

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Q. During the particle characterization, was the composition of the particulate matter assessed such as non-volatile organics?

We did not perform analyses of non-volatile organic chemicals; tests were conducted only for VOCs and SVOCs.

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Q. Can anything be grown in the soil beneath synthetic turf fields after they are removed? Or are they dead zones? What happens to the "recycled" tire crumb rubber when the field is disposed?

We do not have the answer to these questions as they were outside of the scope of the study.

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