Rubber infill is one of the main sources of concerns when it comes to the debate about whether or not synthetic grass is a safe product or not. It is feared that when the crumbs become airborne they can be breathed in and tracked into homes on clothes and athletic gear. There are also questions about dermal and ingestional exposures, and about ecosystem effects.

For athletes, the little black rubber pellets may seem little more than a nuisance. Others express more concern, especially when it comes to children’s exposure to the infill. Patti Wood, executive director of the nonprofit Grassroots Environmental Education, argues, “This crumb rubber is a material that cannot be legally disposed of in landfills or ocean-dumped because of its toxicity. Why on earth should we let our children play on it?” Some studies suggest that the same chemicals that can be released profusely during a tire fire may also be released slowly during deterioration of crumb rubber.

The California Office of Environmental Health Hazard Assessment (OEHHA), in the January 2007 report Evaluation of Health Effects of Recycled Waste Tires in Playground and Track Products, concluded that 49 chemicals could be released from tire crumbs. In a hand-wipe experiment, the OEHHA calculated an increased cancer risk of 2.9 in 1 million for ingestion of chrysene (a suspected human carcinogen found in tire rubber) via hand-to-mouth contact with crumb rubber infill. This estimate assumed regular playground use for the first 12 years of life and was termed by the authors to be “slightly higher” than the 1 in 1 million di minimis risk threshold.

The industry has answered the concerns raised by manufacturing new products such as no infill synthetic grass and the recommendation is that you do not need infill if your grassed area is less than 500 square feet and backyard landscaping purposes. The alternative is to move away from using rubber infill and going for sand infill.