Several studies exist on the issue of safety of crumb rubber (aka rubber mulch):
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"A Review of the Potential Health
and Safety Risks from Synthetic
Turf Fields Containing Crumb
Rubber Infill"
Please download the file on the right:
Prepared for the New York City Department of Health and Mental Hygiene
Prepared by: TRC, Windsor, CT
May 2008
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"Review of the Human Health & Ecological Safety
of Exposure to Recycled Tire Rubber found at
Playgrounds and Synthetic Turf Fields"
please download the file on the right:
Prepared for the Rubber Manufacturers Association, Washington, DC
Prepared by: ChemRisk, Inc., Pittsburgh, PA
July 17, 2008
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Reprinted with permission from
Dr. Thomas Obreza, Professor of Soil and Water Science, University of Florida
Chemical Leaching from Tire Mulch?
We now have several options for landscape mulches (see the next article for more specific information). The newest mulch options have come from recycling old tires. Tire mulches are produced in a variety of colors, last indefinitely, and like other mulches it retains water and suppresses weeds.
The use of tire mulch has come under some criticism resulting from concerns of metal leaching into soil. Tire mulch is made from ground steel-belted tires and zinc is used to coat the steel metal. Most of the metal (approximately 98%) is removed prior to the grinding process. Any metal left is covered by the synthetic tire substance.
According to Dr. Thomas Obreza, Professor of Soil and Water Science, corrosion of metal due to exposure to the elements and acid soils (pH of < 5.5) might allow miniscule amounts of zinc to dissolve, but the metal ends must be exposed to the environment. He stated, in general, the amount of contact with the corroded metal ends and soil would be minimal. Even if zinc were added to land directly, in the form of a biosolid, it is permissible according to the EPA and the Florida DEP to apply 125 pounds per acre per year. There is no way the zinc from tire mulch would or could reach that level.
Zinc is the 23rd most abundant element found on the earth’s crust. Zinc is also a necessary element for proper development and growth of humans, animals, and plants; it is the second most common trace metal, after iron, naturally found in the human body.
It is important to note that zinc is commonly found in soil samples and it is an important plant micro-nutrient necessary for plant growth. A micro-nutrient is a nutrient found in small amounts in the soil. Most of the zinc in soil stays bound to soil particles, but it can be absorbed through plant roots. In plants, zinc functions in the formation of chlorophyll and it is used in plant enzyme activity.
So, what mulch should we use? The University of Florida has done research on a number of mulches, but not tire mulch. When discussing the variety of mulch choices, Dr. Mary Duryea, Professor and Assistant Dean of Restoration and Urban Forestry, suggested pine bark was her number one pick. Her reasons were based on the fact that pine bark is biodegradable, a trash by-product of milling timber, and it possesses an apparent chemical ability to suppress weeds. However, Dr. Duryea is a proponent for recycling and stated she preferred grinding tires and putting it in the landscape rather than leaving them in dumps and landfills.
Of course all mulches have advantages and disadvantages. Each consumer must weigh the options and decide what will best suite their budget and landscape needs. Hopefully this information will help make your decision easier. Now, go out there and grow something!
Mulches for the Landscape
A mulch is any material applied to the soil surface for protection or improvement of the area covered. Mulches are frequently applied around plants to modify the soil environment and enhance plant growth. The mulch material may be organic such as bark, wood chips, leaves, pine needles, or inorganic such as gravel, pebbles, polyethylene film or woven ground cloth.
Mulching has many beneficial effects upon the soil and plants such as: water loss prevention caused by evaporation, suppression of weeds, uniform soil temperature, and reduction of soil erosion. Organic materials used as a mulch can improve soil structure by adding nutrients to the soil. Mulches also add to the beauty of the landscape by providing a cover of uniform color and interesting texture to the surface. In addition, mulched plants have more roots than unmulched plants.
Florida law prohibits disposal of pine needles, leaves, grass clippings and plant trimmings in lined landfills. Instead, yard trash is usually placed at curbside and collected separately from the rest of our garbage for municipal disposal by burning, composting, or burial in an unlined landfill. Much of this yard trash can be recycled on-site as mulch. On-site use of yard trash offers the advantage of retaining in your landscape the nutrients found in yard trash. On-site is also more efficient and may help save tax dollars otherwise spent in transporting and disposing of the yard trash.
Pine needles and leaves can each be used alone as a mulch or in combination. Of the two, pine needles are the best mulching material. They are attractive, not easily removed from beds by wind or rain, and don't "mat down" excessively. However, they don't last more than 6 months due to rapid decomposition. Leaves do best as a mulching material when they are shredded.
Plant trimmings such as twigs and small branches should be shredded before they are used as a mulch. A mechanical chipper/shredder is needed for this process.
There is some reluctance to use yard trash because it is not as attractive as some commercial mulch materials. This problem can be overcome by adding a thin layer of a more uniform mulch over the yard trash. In spite of being expensive, cypress mulch is a very popular mulching material. Much of its popularity is due to its rich brown color and longevity. It is best to keep an area around the root ball of shrubs and trees to allow moisture to reach the root area. Pine bark makes a very attractive, usually dark-colored landscape mulch. It can be purchased in various particle sizes, but the large-size particles 1.5 to 3 inches in diameter (called "nuggets" or "chunks)" are more attractive, last longer and are more effective for weed control than finely ground pine bark. Wood chips are obtained when the bark is removed from large logs. This material contains bark and pieces of wood of various sizes. Straw can be used as a mulch but it is not attractive, decomposes rapidly, and may contain seed that will germinate and become weeds in the landscape. Place a layer of mulch between 2-3 inches deep around trees and shrubs. Pull mulch 1 to 2 inches away from the stems and trunks of plants. The high moisture environment created by mulch increases the chances of stem or trunk rot which can result in plant death.
Adapted from “Mulches for Landscapes” by Robert J. Black, Edward F. Gilman, Gary W. Knox and Kathleen C. Ruppert
More Studies can be found online at:
http://www.rma.org/scrap_tires/scrap_tire_markets/playgrounduse.cfm
http://www.shercomindustries.com/industries/birkholz-crumb%20safety%20paper.pdf
http://www.ehponline.org/members/2005/7629/7629.html
http://www.scraptirenews.com/99oct2.html
reprinted from the above document:
Allergy
We consulted a pediatric allergist who informed us that the latex in tires is not the same as the allergy-causing latex in gloves and that any tiny allergy risk was more than offset by the increased safety of this surfacing. He also pointed out that kids have been sitting on tire swings for almost a century with no problem. We also consulted with a landscape architect, who had sent a sample to Children's Mercy Hospital for analysis. It was given a clean bill of health, particularly since it is not prone to grow mold or other slimy stuff. They also said the average playground usage does not provide enough friction for tiny lung injuring particles to be released.
Some more information we found researching this issue:
http://www.latexallergyresources.org/topics/AskExpertDetail.cfm?ExpertID=13
“Ask the Expert”
Automobile tires are being recycled and used to produce outside playground mat surfaces. Do these products represent a problem for children who come in contact with the mat and are sensitized to natural rubber latex allergens?
By Robert G. Hamilton, Ph.D
The short answer is a qualified no.
In one community in Maryland, we directly examined this issue as it involved a playground that was planned with recycled automobile tires as its surface. In this community, there was also a severely latex allergic child. His parents were concerned for their son's safety if he were to come into contact with the mat's surface. We received a sample of the mat material from the company and we analyzed it by extracting it in a physiological buffer (1 gram per ml) and testing it in a human IgE anti-latex based competitive inhibition assay for latex allergen. The result was that we were not able to detect any extractable latex allergen in the recycled auto-tire matting material. Studying this further, most auto and truck tire companies do not use natural rubber latex in their manufacturing. If natural rubber is present, it is in a small percentage, with the majority of the material being synthetic butyl rubber that contains no natural rubber latex allergens. The tire is alsoa molded product that by its nature is known to poorly release allergenic proteins, if they are present.
So, based on our limited experience, the one recycled tire surface material that we evaluated was not a problem for latex allergic children in the Maryland community. This is not to say that all rubber surfaces are totally free of natural rubber allergens, but it appears that (in general), these surfaces should be a safe alternative to other playground surfaces. If there are specific questions about a particular tire related mat material, the material can be tested for latex allergen content.”
This is from the American Latex Allergy Association…They can be contacted at:
American Latex Allergy Association
P.O. Box 198
Slinger, WI 53086
Toll Free:
1-888-972-5378
E-mail:
alert@latexallergyresources.org
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