Is it Safe to Use Recycled Tire Mulch?

Recycled rubber tire used for a playground.

Whether or not it's safe to use recycled tire mulch depends on how and where you plan to use it. The environmental impact of tire mulch depends largely on local conditions. Consider each situation on its own merits. If the rubber mulch will be used for padding a playground floor or soccer field, for instance, the dangers usually associated with this type of mulch are much less than when used in a garden.

TIP: Our expert gardening advisor, Rachel Klein adds, "Heath concerns aside, rubber mulch is less effective at controlling weeds than organic mulches such as leaf mulch or wood chips. In your garden, these organic mulches actually decompose and enrich the soil with nutrients. You will never have to worry about contaminating your garden and ground water with potentially harmful chemicals and heavy metals."

Tire Mulch on Game Courts

In point of fact, it is safer to use recycled tire mulch on things like playgrounds or soccer fields than in gardens. In such cases, the safety factor actually flows both ways. It is safer for the environment because most playgrounds and sports fields are built on top of concrete or blacktop foundations.

The recycled tire mulch is laid out on top of these foundations and in many cases does not come into direct contact with the soil or water in the area. On top of this, tire mulch makes it safer for the athlete and for the child on the monkey bars thanks to its elasticity. When laid down in thick layers, it becomes springy and will cause a falling object to bounce instead of smash.

In fact, the highest safe distance a child can fall from onto wood mulch is around 4 feet while the highest safe distance for tire mulch is 10 or 12 feet. Because of this double-sided safety feature, there are some uses for tire mulch which override its environmental safety issues.

However, due to the environmental concerns discussed below, rubber tire mulch should only be used in sites that do not come into direct contact with soil or water sources.

Tire Mulch in the Garden

When tire mulch is utilized for purposes other than activity safeguards it can indeed become a danger. However, it is still necessary to judge the dangers on a case-by-case basis and you may want to request the services of a professional to make these determinations.

Rubber mulch is by no means permanent and as it is broken down by microbes in the soil chemicals can be released. It is true that tire mulch can leach zinc and other chemicals and heavy metals into the soil and plants around it.

Two common rubber additives that have the potential of leaching are 2-Mercaptobenzothiazole (MBT) and polyaromatic hydrocarbons (PAHs). These chemicals pose health hazards to both humans and the environment in the event of leaching.

Other heavy metals found in tire rubber include aluminum, cadmium, chromium, copper, iron, magnesium, manganese, molybdenum, selenium, sulfur, and high concentrations of zinc. Zinc alone is known to stunt plant growth substantially. However, the leaching process is heavily dependent on the local conditions, such as humidity, temperature, pH levels, and the intensity of local weather in general.

There is no getting around the fact that minerals from the tire manufacturing process and other chemicals picked up during the service life of the tires can leach into the soil. In large quantities, it can even kill the plants it was meant to protect.

TIP: Rachel cautions you, "It is most harmful to use tire mulches if your soil is acidic, since the acidity allows your garden plants to absorb much larger quantities of heavy metals."

It can also contaminate ground water, of most concern for those living above residential wells. Current research shows huge negative effects of rubber leachates contaminating lakes and ponds, killing plankton, algae, snails, and fish.

Some tire mulch has come into contact with petroleum which is highly flammable. Research studies have shown that when rubber mulch that contains petroleum products is ignited it is more difficult to extinguish than any other kind of mulch, including wood chips.

It is also important to note that the manufacturers of recycled tire mulch rarely divulge any information on where the mulch was made and what types of chemicals it may have come in contact with. Always seek the advice of a professional to determine whether your local conditions are suitable for using tire mulch.