Synthetic Turf & Human Health

By Thomas Serensits, Manager, Center for Sports Surface Research, Penn State Department of Plant ScienceThe

The topic of synthetic turf is likely to spark spirited debate among sports field managers, athletes and even just your average sports fans. Strong opinions certainly exist and can make for entertaining conversation. While a number of issues are likely to be covered in such a discussion, none are more important than potential impacts of synthetic turf on human health. Fortunately, a growing collection of research is providing valuable information.

Research on human health and synthetic turf can be broadly divided into two categories — 1) potential health effects from exposure to synthetic turf components and 2) injuries. Both have been the subject of numerous research studies. Studies that are subjected to the peer review process and those conducted by governmental agencies are designed to provide scientifically-sound, unbiased results and will be the focus of this article. Of course, the entire volume of related studies cannot be presented in a magazine article. This article focuses on some of the most recent and pertinent research.

Potential Health Effects from Exposure to Synthetic Turf Components

The vast majority of synthetic turf fields currently in use today consist of plastic fibers measuring 2 to 2 ½" tall stitched into a backing and then infilled with a combination of crumb rubber and sand. The crumb rubber is typically manufactured by grinding used tires. Crumb rubber is the subject of most research studies that focus on potential health effects from exposure to synthetic turf components.

There is no debate that potentially harmful chemicals are present in crumb rubber. The question is how much of a risk do those chemicals pose to field users? Potentially harmful chemicals are all around us — from naturally occurring compounds in soil to cleaning products to cosmetic products — the mere presence of chemicals does not necessarily equate to a risk to human health. It is the potential exposure risk, or what many researchers refer to as “bioavailability,” that is the subject of numerous research studies.

In July 2019, a federal agency group led by the United States Environmental Protection Agency (EPA) released one of the most extensive evaluations to date of the crumb rubber used on sports fields and playgrounds (1) . In agreement with other studies, the researchers reported the presence of various compounds found in tires such as semi-volatile organic compounds (SVOCs) and volatile organic compounds (VOCs), along with bacteria on samples of crumb rubber collected across the country. As noted by the researchers, while chemicals were present, the amount of chemicals available for exposure through release into the air and simulated biological fluids is relatively low. The conclusion of the report was “These findings support the premise that while many chemicals are present in the recycled tire crumb rubber, exposure may be limited based on what is released into air or biological fluids.”

A potential link between synthetic turf and cancer has received considerable attention in the national media and has spurred a number of research studies. While no study has included a comprehensive, definitive cancer risk assessment, two recent studies have focused on cancer rates and synthetic turf.

A 2018 study published in the journal Cancer Epidemiology evaluated malignant lymphoma rates in California as a function of synthetic turf density (2) . The authors of the study reported that “In California, there was no evidence at the county-level that synthetic turf fields are associated with an increased incidence of lymphoma in adolescents and young adults.” Their conclusion was “avoidance of synthetic turf fields for fear of increased cancer risk is not warranted.” Similarly, a study released by the Washington State Department of Health in 2017 did not find increased cancer risk among a select group of soccer players based on expected cancer rates of Washington residents of the same ages (3) .

While the majority of studies have not reported a link between synthetic turf and health risks, several environmental and health advocacy groups have been critical of the methods and conclusions drawn by researchers. Several research reports such as an article published by several Yale University researchers emphasize that numerous carcinogens are present in crumb rubber and that human exposure pathways in relation to crumb rubber are poorly known (4) .

Injuries

The impact of synthetic turf on athlete injuries is another human health-related issue that receives considerable attention. Although today’s synthetic turf systems are designed to mimic natural turf, there is scientific evidence based on rotational traction testing that under certain conditions, an athlete’s shoe may not “release” as easily as it would on natural turf (5) . A player’s ankle or knee may be spared significant injury as a divot is created on natural turf, but that same release mechanism of divoting does not occur on synthetic turf. Instead, the forces are transferred to the ligaments of the lower extremities, potentially increasing injury risk.

A 2019 study comparing injury rates of NFL players on synthetic and natural turf provides real world evidence that aligns with rotational traction research (6) . The authors of the study tracked lower extremity injuries in the NFL from 2012–2016. Game play on synthetic turf resulted in a 16% increase in lower extremity injuries per play compared to natural turf. The effect of playing surface was greater for non-contact injuries as lower extremity injuries were 35% higher on synthetic versus natural turf.

A 2019 study examining knee injuries suffered by collegiate football players reported similar results (7) . Posterior cruciate ligament (PCL) were approximately three times greater on synthetic versus natural turf in the study that tracked injuries from 2004–2014. Anterior cruciate ligament (ACL) were 1.6 times more likely on synthetic turf for NCAA divisions II and III, although playing surface did not affect ACL injury rate in Division 1.

While recent NFL and NCAA football studies reported higher knee injury rates on synthetic turf, a 2019 study that tracked injuries in Major League Soccer (MLS), reported that playing surface type did not affect the occurrence of knee injuries (8) . However, injuries to ankles and Achilles injuries occurred at a higher rate on synthetic turf. The authors of the study concluded “the overall rate of injury on artificial turf was noninferior to that on natural grass” and that “artificial turf is a viable alternative to natural grass in elite-level soccer.” A number of additional studies focusing on injuries in soccer reported no difference in injury rate between synthetic and natural turf.

Research related to human health is much different from the typical turf-related research we normally see. Whether or not a particular herbicide kills a dandelion or how long a fungicide prevents dollar spot are fairly straightforward and relatively simple research questions to answer. Conversely, epidemiological studies, such as those examining effects of synthetic turf on human health, require much more data and cause and effect relationships are often difficult to confirm. It is impossible to conduct a study that takes into account all variables associated with human health, but with the release of each research report, more knowledge is gained.

I invite you to visit the Penn State Center for Sports Surface Research website (ssrc.psu.edu) and read some of the research studies related to synthetic turf and human health. Links to each of the studies referenced in this article are provided along with links to numerous other studies. There are currently links to more than 50 scientific, peer-reviewed and government studies related to exposure to synthetic turf components and more than 40 scientific studies comparing injury rates on synthetic and natural turf.

(1) United State Environmental Protection Agency. 2019. Synthetic Turf Field Recycled Tire Crumb Rubber Research Under the Federal Research Action Plant – Final Report Part 1 – Tire Crumb Rubber Characterization Volume 1. EPA/600/R-19/051.1

(2) Bleyer A. and T. Keegan. 2018. Incidence of malignant lymphoma in adolescents and young adults in the 58 counties of California with varying synthetic turf field density. Cancer Epidemiol. Apr 53:129-136.

(3) Washington State Department of Health. 2017. Investigation of Reported Cancer among Soccer Players in Washington State. https://www.doh. wa.gov/Portals/1/Documents/Pubs/ 210-091.pdf.

(4) Benoit, G. and S. Demars. 2018. Evaluation of Organic and Inorganic Compounds Extractable by Multiple Methods from Commercially Available Crumb Rubber Mulch. Water Air Soil Pollut 229:64.

(5) Kent, R., Forman J.L., Lessley, D., and J. Crandall. 2015. The mechanics of American football cleats on natural grass and infill-type artificial playing surfaces with loads relevant to elite athletes. Sports Biomech 14(2):246-257.

(6) Mack, C.D, Hershman, E.B., Anderson, R.B., Coughlin, M.J., McNitt, A.S., and R.W. Kent. 2019. Am J Sports Med 47(1)189-196.

(7) Loughran, G.J., Vulpis, C.T., Murphy, J.P., Weiner, D.A., Svoboda, S.J., Hinton, R.Y., and D.P. Milzman. 2019. Incidence of knee injuries on artificial turf versus natural grass in National Collegiate Athletic Association American football: 2004-2005 through 2013–2014 Seasons. Am J Sports Med 47(6)1294-1301.

(8) Calloway S.P., Hardin D.M., Crawford M.D., Hardin J.M., Lemak L.J., Giza E., Forsythe B., Lu Y., Patel B.H., Osbahr D.C., Gerhardt M.B., Mandelbaum B.R., and W.W. Baldwin. 2019. Injury surveillance in Major League Soccer: A 4-Year comparison of injury on natural grass versus artificial turf field.