Crumb rubber

Continued processing with a granulator or cracker mill, possibly with the aid of cryogenics or by mechanical means, reduces the size of the particles further.

[2] Crumb rubber is also used as ground cover under playground equipment, and as a surface material for running tracks and athletic fields.

To date, there are nearly 100 studies and reports, from government bodies and independent researchers, that have assessed the potential for health risks based on various pathways of exposure.

However, as recently as 2017 and again in 2018, further chemicals have begun to be scrutinized further which were previously unregistered in that incarnation of the ANNEX report on rubber crumb.

[10] Volumes of research and testing from academics, federal and state governments including New York, California, Massachusetts and Connecticut, and school systems have examined everything called into question about synthetic turf.

Contradicting studies have found that the raw source material (automotive tires) contains high levels of polycyclic aromatic hydrocarbons and metals such as zinc which have proven dermal, acute, and long-term health effects.

The EPA is (as of fall 2015) investigating the health effects of exposure to crumb rubber and the initial results of this study were expected at the beginning of 2016.

The current study did not evaluate new fields under hot weather conditions and so the potential for acute risks under this circumstance is another uncertainty.

For example a study undertaken by the Danish Ministry of the Environment concluded that the health risk on children’s playgrounds that contained both worn tires and granulate rubber was insignificant.

The available body of research does not substantiate the assumption that cancer resulting from exposure to styrene-butadiene (SBR) granulate infills in artificial turf could potentially occur.”[13] Scientific Instrument Services, Volatile Organic Emissions from Automobile Tires, 1999, Santford V. Overton & John J. Manura : Tire "Brand A were found to contain numerous straight and branched chain hydrocarbons, aldehydes, alcohols, ketones, furans and benzene derivatives."

Tire brand B was..."found to contain high concentrations of the compounds sulfur dioxide (DOT), 2-methyl-1-propene, 2-propanone, 2-methyl-2-pentene, 2,4-pentanedione, acetic acid and 2,4-(1H, 3H) pyrimidinedione."

Generally, it takes 20,000–40,000 scrap tires to produce enough filling to cover an average football field (City of Portland, 2008)[19] Due to its small size, crumb rubber is however considered a significant source of microplastics pollution.

[20] A 2022 study uncovered the "potential adverse consequences of extensive rubber crumb application and exposure to environmental conditions."

The crumb rubber examined was found to contain high levels of PAHs, as well as zinc at concentrations that may "pose a risk to aquatic organisms in particular".

[21] The Connecticut Department of Environmental Protection found in a 2010 study that stormwater passing through crumb rubber regularly exceeded aquatic acute toxicity for zinc.