Rubber mulch

At worst, it leads to soil contamination (see Environmental Impact and Safety Testing) Some recycled varieties may leach chemicals (some toxic) which are harmful to plants[3][4][5] Rubber mulch is a particular hazard if ignited because of the resulting fumes that resemble those produced in tire fires.

[citation needed] In the US, the Environmental Protection Agency (EPA) has launched a multi-agency Federal Research Action Plan on Recycled Tire Crumb Used on Playing Fields and Playgrounds to study key environmental human health questions concerning the safety of recycled tire crumb.

The limited study, conducted in August through October 2008, found that the concentrations of materials that made up tire crumb were below levels considered harmful.

[8] The study, however, did note that due to its limited nature and the large diversity of materials used to make tire crumb, no definitive conclusions could be reached.

[10] The OEHHA has conducted additional studies on potential negative human health effects associated with the use of recycled waste tires in playground and synthetic turf products.

For leached tire debris, the (potential) environmental impact of the ingredients zinc and organic toxicants has been demonstrated.