At first it may seem inoffensive to repurpose tires. Recycled tires are crumbled and used in artificial turf filling for athletic fields and playgrounds across America.  But parents and environmental advocates have raised questions about the toxic elements of tire crumblings. Pulverized car tires can contain potentially dangerous chemicals and carcinogens.

In October of 2014 NBC News aired an investigative report on the hazards of tire crumblings. The story featured some young girls—all goalkeepers—who were receiving chemotherapy for non-Hodgkin lymphoma. Goalkeepers are constantly diving into the turf filled with tire crumblings. Small  fragments of rubber have the potential to end up in players’ mouths. With cuts and scrapes sustained on the field, the rubber can also get into the blood stream. The ingredients in tires are known to contain carcinogens. Doctors, advocates and parents told NBC they suspected the tire crumblings made the players sick.

No research has definitive link between cancer and crumb rubber turf.

However, the federal government has tapped scientists to investigate the link further. The Environmental Protection Agency (EPA), the Centers for Disease Control and Prevention (CDC), and the Consumer Product Safety Commission (CPSC) announced an “action plan” to answer questions and raise concern about synthetic turf made from recycled tires. The plan involves in depth research including: identifying the many ways in which people may be exposed to tire crumb; characterization of the chemicals found in tire crumb; and characterization of the exposure scenarios. The study also aims to better understand how children use playgrounds containing tire crumb.

The Washington Post explains that synthetic turf has an “infill” system:

involving a layer of tiny granules of rubber, sand, or other material between the turf fibers and a backing layer—introduced in the late 1990s and has since become a popular alternative to natural turf fields, according to the Synthetic Turf Council.

The EPA had initially promoted the use of tire crumbs as a way to repurpose car and truck tires. Until recently, the EPA acknowledged more testing needs to be done.

The U.S. has more than 11,000 artificial turf fields. Tire crumbling also have the potential to expose children to lead poisoning. Even at very low levels, lead can cause neurological damage, developmental delays, and organ damage in children.

The federal government says existing studies “do not comprehensively evaluate the concerns about health risks from exposure to tire crumb.” So for this round of research, tire crumb material has been collected from tire recycling plants and synthetic turf fields from nine tire crumb recycling plants, 19 fields located on US Army installations and 21 community fields including both indoor and outdoor fields. Analysis of the tire crumb samples collected from fields and recycling facilities, and the exposure characterization component of the study will continue in 2017.

While the feds determine a clearer position on the study, activists, athletes, and parents must assess the toxic exposure risks from artificial turf layered with tire crumb.