Rubber mulch is a type of

mulch A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area. A m ...

used in

garden A garden is a planned space, usually outdoors, set aside for the cultivation, display, and enjoyment of plants and other forms of nature. The single feature identifying even the wildest wild garden is ''control''. The garden can incorporate both ...

s and

landscaping Landscaping refers to any activity that modifies the visible features of an area of land, including the following: # Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal o ...

that is made from recycled rubber, most often

crumb rubber Crumb rubber is recycled rubber produced from automotive and truck scrap tires. During the recycling process, steel and tire cord (fluff) are removed, leaving tire rubber with a granular consistency. Continued processing with a granulator or c ...

sourced from waste tires.

Composition

Rubber mulch generally consists of either waste

tire A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineering), t ...

bits or nuggets of

synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubbe ...

from tires that are shredded or ground up whole, after having their steel bands removed. Almost any tire can be used to make rubber mulch, including passenger vehicle tires and large

truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...

and trailer tires. Bits or nuggets are produced from shredding and steel removal from waste tires. Rubber Mulch (Bits and Nuggets) range in size from 10 mm to 32 mm, or 3/8 inch to 1 inch.

Advantages

Rubber mulch provides some advantages over plant mulches. For

and gardening purposes, both nuggets and buffings insulate soil from heat, allowing a 2 or 3 degrees F higher soil temperature difference over wood mulches. Rubber mulch is beneficial for soil moisture, as rubber is non-porous and does not absorb water on its way through to the soil. It also reduces

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

growth and

plant growth Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant a ...

, and becomes a weed barrier, as weed seeds dehydrate in the mulch before reaching the soil. Another advantage over plant-material mulches is its

elasticity Elasticity often refers to: *Elasticity (physics), continuum mechanics of bodies that deform reversibly under stress Elasticity may also refer to: Information technology * Elasticity (data store), the flexibility of the data model and the cl ...

, which gives it a springy quality when used in a fairly thick layer. This makes it a choice for

playground A playground, playpark, or play area is a place designed to provide an environment for children that facilitates play, typically outdoors. While a playground is usually designed for children, some are designed for other age groups, or people ...

s, where the springiness provides additional safety for children when they fall off of playground equipment. Tests have shown that rubber mulch is superior in breaking falls to traditional

bark mulch A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area. A m ...

es. The International Play Equipment Manufacturers Association has certified some rubber mulches for

ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...

F1292-09.

Disadvantages

Unlike organic mulch, rubber mulch does not enrich soil or increase

soil biodiversity Soil biodiversity refers to the relationship of soil to biodiversity and to aspects of the soil that can be managed in relative to biodiversity. Soil biodiversity relates to some catchment management considerations. Biodiversity According to the ...

through

decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...

. Neither nuggets nor buffings provide any

humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...

compacted soil In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water (or othe ...

types. At worst, it leads to

soil contamination Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...

(see

Environmental Impact and Safety Testing A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...

) Some recycled varieties may

leach Leach may refer to: * Leach (surname) * Leach, Oklahoma, an unincorporated community, United States * Leach, Tennessee, an unincorporated community, United States * Leach Highway, Western Australia * Leach orchid * Leach phenotype, a mutation in ...

chemicals (some

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

) which are harmful to plants Rubber mulch is a particular hazard if ignited because of the resulting fumes that resemble those produced in

tire fire Tire fires are events that involve the combustion of large quantities of tires, usually waste tires, typically in locations where they are stored, dumped, or processed. They exist in two forms: as fast-burning events, leading to almost immediate ...

s. Rubber mulch is also more likely to ignite and harder to extinguish than other mulches. Compared to organic mulches, rubber mulch can become extremely hot when in direct sunlight. There is concern about the potential for negative effects of rubber mulch nuggets migrating into waterways.

Environmental impact and safety testing

In the US, the

Environmental Protection Agency A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...

(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 EPA previously studied air and surface samples at four fields and playgrounds that use recycled tires. 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. In addition, the overall study protocol and many of the methods were found to be appropriate and could be implemented in the field.EPA fields and playground study
/ref> 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. More recently, the EPA has released a comprehensive spreadsheet with toxicity reference information. The California Office of Environmental Health Hazard Assessment (OEHHA) used guinea pigs, in an animal study, to test skin

sensitization Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. Sensitization often is characterized by an enhancement of response to a whole class of stim ...

by playground surfaces made of recycled tires and observed no sensitization. This suggested that these surfaces would not cause skin sensitization in children, nor would they be expected to elicit skin reaction in children already sensitized to latex. 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. Although rubber mulch is generally regarded as safe, recycled tire rubber

leachates A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate is a widely used term in the environmental sciences whe ...

do contain certain minerals and compounds which may be

ecotoxic Ecotoxicity, the subject of study in the field of ecotoxicology (a portmanteau of ecology and toxicology), refers to the biological, chemical or physical stressors that affect ecosystems. Such stressors could occur in the natural environment at ...

in high concentrations. Recycled tire mulch can contain trace amounts of various minerals from the tire manufacturing process and other chemicals that may have been picked up during the tire's service life. The greater the surface area of

waste pellets, the greater the potential for breakdown into harmful constituents. For leached

tire debris Road debris, a form of road hazard, is debris on or off a road. Road debris includes substances, materials, and objects that are foreign to the normal roadway environment. Debris may be produced by vehicular or non-vehicular sources, but in all ...

, the (potential)

environmental impact Environmental issues are effects of human activity on the biophysical environment, most often of which are harmful effects that cause environmental degradation. Environmental protection is the practice of protecting the natural environment on t ...

of the ingredients

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

and organic

toxicant A toxicant is any toxic substance, whether man-made or naturally occurring. By contrast, a toxin is a poison produced naturally by an organism (e.g. plant, animal, insect). The different types of toxicants can be found in the air, soil, water, or ...

s has been demonstrated.

References

External links

New York artificial turf field studyThe Myth of Rubberized LandscapesArtificial Turf: Exposures to Ground Up Rubber Tires - Athletic Fields, Playgrounds, Garden Mulch
Recycled building materials Pavements Tires {{Rubber