The benefits of recycling old tires are obvious. It saves energy. It avoids new or additional toxic manufacturing inputs. Recycling also forestalls landfilling tire waste. Tire dumps pollute groundwater and can catch fire and smolder for months or even years.
But there is a flip side to this equation that has, to date, been poorly considered: tires contain a host of toxic ingredients to which people may be exposed when this material is brought into homes, schools, gyms and offices.
Today, the Healthy Building Network released my new report, Avoiding Contaminants in Tire-Derived Flooring. I describe the challenges of safely using crumb rubber, and suggest steps for industry to implement a reliable, and certifiable, screening process that could ensure that chemicals of concern used in tire production – or gathered by tires during their service lives -- do not resurface in the built environment.
My research led HBN to conclude: we do not recommend the use of tire-derived flooring in interior applications until these safeguards are in place. Here's why:
Like fly ash, another voluminous waste product for which we would prefer a beneficial use, tire scraps are on the edge of being classified as hazardous wastes. Tire dumps, like coal waste impoundments, leak, ooze, and offgas contaminants. Heavy metals and polycyclic aromatic hydrocarbons migrate into streams and aquifers, poisoning drinking supplies.
The solution is not to shift this contamination indoors. Building products can release these same chemicals, in a number of ways including volatilization and abrasion through ordinary use or cleaning of the floor.
Tires harbor chemicals of concern from two sources: production processes, and contaminants that are picked up in everyday use.
Up to thirty percent of crumb rubber may contain toxic chemicals called distillate aromatic extract, used as processing oils. This is a complex combination of polycyclic aromatic hydrocarbons, including many that are highly persistent and bioaccumulative. Other process chemicals of concern include synthetic rubbers, carbon black nanoparticles, and zinc oxide.
In the course of their service lives, tires also pick up contaminants along the way, including the toxic heavy metal, lead. Balancing weights, typically made of lead, routinely fall off wheels and onto the road. Passing tires then pulverize and drive over the malleable lead. Lead is also present in some old highway striping paint: until recently, yellow lane markers contained lead sulfochromate pigment. When tire tread is reused, any lead present in the tread is incorporated into a finished recycled product, absent manufacturer screening processes.
Sampling programs to date have found widely varying levels of lead in scrap tires and in crumb rubber used in playgrounds and artificial athletic fields. Some samples exceed the US Consumer Product Safety Commission (CPSC)'s limit for children's products (100 parts per million). This is of great concern, for some common end uses of crumb rubber include playground fill and classroom floors.
In March, Public Employees for Environmental Responsibility (PEER) filed legal challenges to agency proclamations of the safety of artificial turf, in part due to concerns about crumb rubber. PEER says there is a "growing body of evidence documenting chemical exposure and other risks from synthetic turf."
Believe me, I wish my research into crumb rubber – which took place over the past two years, combing through industry cookbooks, patents, and government studies, and interviewing manufacturers – came to a better conclusion.
Where the rubber meets the road, here's the score. It is both technically and economically feasible for crumb rubber processors to effectively screen their materials to keep these hazards out of building products. From a human health standpoint, until manufacturing processes change, it makes no sense to live, work, or play in rooms floored by this waste.