The Myth of Rubberized Landscapes

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Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor

Puyallup Research and Extension Center, Washington State University

Wednesday, June 27, 2007

“Recycled rubber mulch is an environmentally friendly, non-toxic choice for landscapes”

The Myth

Discarded rubber tires are the bane of waste management; according to the EPA, we generate 290 million scrap tires annually. Scrap tire stockpiles can pose significant fire hazards, such as the 1983 Virginia tire fire that burned for 9 months. Obviously finding a market for these slow-to-decompose materials is desirable, and many innovative uses have been developed, including rubberized asphalt, playground surfaces, and landscape mulches. From an engineering standpoint, crumb rubber as a soil amendment has performed favorably in reducing compaction to specialty landscape surfaces such as sports fields and putting greens.

Rubber mulches are touted by manufacturers and distributors as permanent (“doesn’t decay away”) and aesthetically pleasing (“no odor” - “looks like shredded wood mulch” – “earth tones and designer colors” – “special fade resistant coating”) landscape materials. Furthermore, we are told that rubber mulch is “safe for flowers, plants and pets” (though it “doesn’t feed or house insects”) and “dramatically improves landscaping.” It seems to be an environmentally-friendly solution to a major waste disposal problem.

The Reality

Rubber mulches have not proved to be particularly good choices for either horticultural production or landscape uses. In comparison studies of several mulch types, rubber tire mulch was less effective in controlling weeds in herbaceous perennial plots than wood chips. Similarly, sawdust made a better mulch for Christmas tree production in terms of weed control, microbial biomass, and soil chemistry. Another comparative study found rubber to be less effective than straw or fiber mulch in establishing turfgrasses.

Not only do rubber mulches perform less effectively in the landscape, they possess an additional, unwanted characteristic. Compared to a dozen other mulch types, ground rubber is more likely to ignite and more difficult to extinguish. In areas where the possibility of natural or man-made fires is significant, rubber mulches should not be used.

“Permanence” of rubber mulch

Far from being permanent, rubber is broken down by microbes like any other organic product. Many bacterial species have been isolated and identified that are capable of utilizing rubber as their sole energy source. Such bacteria have been found in a variety of environments, including the cavity water of discarded tires. Although some of the additives used in tire manufacture are toxic to rubber-degrading bacteria, there are white-rot and brown-rot fungal species that can detoxify these additives. While isolating these microbes has been beneficial in developing natural mechanisms to recycle rubber products, it also points out the fallacy of assuming that rubber mulch is “permanent.” Furthermore, it alerts us to the very real possibility that car tires leach toxic compounds into the landscape.

“Non-toxicity” of rubber mulch

Current research at Bucknell University indicates that rubber leachate from car tires can kill entire aquatic communities of algae, zooplankton, snails, and fish. At lower concentrations, the leachates cause reproductive problems and precancerous lesions. A similar study exploring the use of tires as artificial reef substrates also found rubber leachate to negatively affect the survival of various seaweeds and phytoplankton. Marine and other saline environments are less sensitive to tire leachates, however, and the greatest threat of contamination appears to be to freshwater habitats.

Part of the toxic nature of rubber leachate is due to its mineral content: aluminum, cadmium, chromium, copper, iron, magnesium, manganese, molybdenum, selenium, sulfur, and zinc have all been identified in laboratory and field leachates. If rubber products have been exposed to contaminants during their useful lifetime, such as lead or other heavy metals, they will adsorb these metals and release them as well. Of these minerals, rubber contains very high levels of zinc – as much as 2% of the tire mass. A number of plant species, including landscape materials, have been shown to accumulate abnormally high levels of zinc sometimes to the point of death. One USDA researcher who has studied zinc and other metals in soils and plant materials for decades strongly believes that ground rubber should not be used “in any composting, or in any potting medium, or casually dispersed on agricultural or garden soils” because of zinc toxicity. Acidic soils and aquatic systems are particularly sensitive, since heavy metals and other positively charged elements are less tightly bound to the soil and more available to plant and animal uptake.

Rubber leachates are complex solutions. They include not only the minerals and organic building blocks of rubber, but also various plasticizers and accelerators used during the vulcanizing process. In high enough concentrations, some of these rubber leachates are known to be harmful to human health; effects of exposure range from skin and eye irritation to major organ damage and even death. Long term exposure can lead to neurological damage, carcinogenesis, and mutagenesis.

Some of these materials break down quickly, while others are known to bioaccumulate. One of the more common rubber leachates is 2-mercaptobenzothiazole, a common accelerator for rubber vulcanization. In addition to its known human health concerns, it is highly persistent in the environment and very toxic to aquatic organisms: its environmental persistence may cause long-term damage to aquatic environments constantly exposed to rubber leachates. Another family of organic leachates under scrutiny are the polyaromatic hydrocarbons (PAHs). These compounds, used as rubber softeners and fillers, have been repeatedly demonstrated to be toxic to aquatic life. PAHs are released continually into solution, and after two years in a laboratory test leachates were shown to be even more toxic than at the study’s inception.

It is abundantly clear from the scientific literature that rubber should not be used as a landscape amendment or mulch. There is no question that toxic substances leach from rubber as it degrades, contaminating the soil, landscape plants, and associated aquatic systems. While recycling waste tires is an important issue to address, it is not a solution to simply move the problem to our landscapes and surface waters.

The Bottom Line

Rubber mulch is not as effective as other organic mulch choices in controlling weeds
Rubber mulch is highly flammable and difficult to extinguish once it is burning
Rubber mulch is not permanent; like other organic substances, it decomposes
Rubber mulch is not non-toxic; it contains a number of metal and organic contaminants with known environmental and/or human health effects

Posted by Jason Borch on 02/09/2011 at 08:23 PM

Wood mulch. It’s been used as surfacing on playgrounds for decades, probably as far back as any of us can remember. Perhaps old-time playground owners may be excused for assuming that it was a safe option—and a cheap one. After all, wood mulch comes from era when smoking was considered ‘safe’, too.

See more info -

http://knol.google.com/k/jason-borch/h1n1-concussions-and-wood-mulch-what/34vfsqycmfcml/1#

http://www.youtube.com/watch?v=BZhuF0hK2EE

Posted by Sandi on 11/17/2010 at 08:59 PM

Our HOA just installed rubberized mulch in our tot lot and I have been sick ever since. The smell is horrible and filters into our home, our porch and our patio. It is sickening and the thought that people actually feel good about having our children and grandchildren play on this stuff blows my mind and infuriates me. Tires are toxic! If they weren’t, they would not be illegal to dump or when they catch on fire the smoke wouldn’t be so black or toxic. There is alot of money spent to promote this stuff but they rate up there with the tobacco industry as far as I am concerned. This stuff is bad for our children and bad for the environment and in a few more years, we are going to find our children with health issues that could have been avoided.

Posted by Audrey White on 06/15/2010 at 07:50 AM

It blows my mind that anyone would think it’s a good idea to put this hazardous waste all over playgrounds. I went to one in my neighborhood recently and my eyes stung from the noxious odor after 5 minutes. And this playground had been installed for months.

According to the EPA scientists who raised the red flag about recycled tire mulch in January 2008, “Tire crumb is a heterogeneous product because TIRE INGREDIENTS VARY WITH TIRE TYPE, DATE OF MANUFACTURE, AND SOURCE. Tires may contain metals such as arsenic, cadmium, chromium, manganese, mercury, and lead; aliphatic and aromatic organic compounds such as acetone, methyl ethyl ketone, choroethane, polycyclic aromatic hyrdocarbons, benzene and haogenated fire retardants; nylon and polyestser fibers; dys and latex.”

So how can anyone claim that they know for a fact that ALL rubber mulch is safe when THEY DON’T EVEN KNOW WHAT’S IN IT?? Are they doing analyses of every batch of mulch that goes on every playground? Not likely. In fact, the only loose rubber mulch the EPA tested after that statement was made was on1 playground in Colorado that was 4 years old. You can read this in the EPA’s own report posted on their web site.

I hope the EPA scientists win out over the politicians who are pressuring them to ignore science (google this, it’s out there). I’m all for recycling, but there are many other ways to do this without putting our children’s health at risk.

Posted by Morgan on 05/12/2010 at 03:51 AM

My biggest objection to using rubber mulch around the base of my shrubs is cost. If I could afford it I would put down a layer of heavy duty landscape fabric, then on top of this I would put a layer of rubber mulch. One must remember that in time the leaves from the shrubs will fall off and rot on top of the mulch which will form a wonderful place for weeds to get started. If the rubber manufacturers would supply coarser pieces then one could blow off the leaves with a weed blower periodically. When my financial ship comes in I will definitely switch to rubber mulch. Morgan

Posted by Rebecca on 07/23/2009 at 06:08 PM

Having researched Decorative Rubber Mulch and plain Rubber Mulch for 9 years now, I have dug very deep into this….................

I suggest to all of you to continue your research, get to the specific test results.

These tests results come from our Federal Government as far back as 1990. It is there proving plain as day that this is the SAFEST product to use anywhere.

Tests prove that it is safer than our drinking water!

There are a lot of politics involved here trying to sway a persons line of thinking.

In the past 8 years most INSURANCE companies have encouraged the use of Decorative Rubber Mulch. They have done their own testing and know that this product is the safest, reducing Liability on anyone.

Iit is a one shot installation, lowering Mainteance, no annual replacement and reducing water usage 50%-70%. It is cooler and warmer by up to 20 degrees. It is very clean and does not harbor pests. All water goes directly into your soil and plants as it should be.

It is not a product that will nickel and dime you to death like other products!
I don’t know about you but I am tired of using products that do not work.
I have seen how much more healthy plants, shrubs and everything is after the use of Decorative Rubber Mulch. It is like giving them a blanket and reducing the harshness mother nature can throw at them.

They are currently re- testing all materials and find that nothing will pass the current tests but the Rubber Mulch…........Where children and playground safety issues are of a concern. But remember we also have children and pets in our yards and homes too. Safety is the biggest issue then all the other wonderful benefits fall into place as well. Very Environmentally sound and smart.

Look at ASTM= American Safety and Testing of Materials website. That is our government and their test results.Back in 2005 they retested all 8 items on the list and deleted 4 out of 8 for not passing the current Impact Attenuation test. (The Bounce Test). As well as other safety issues.

Look at CPSC=Consumers Product Safety Commission. They are suppose to take ASTM’s test results and post them on their website to US, the consumer what is safe and what isn’t.

As of 2008 they had not updated their website since 2003??????? What’s up with this? Do the politics lie here. It appears so. Then when searching to see who is amongst the Board, it appears to be the Wood mulch and wood fiber MFG’s. I also suggest you research their products too, compare the two products together and you will be in for a big, big, big surprise.You will see for yourself why Decorative Rubber Mulch is on the rise and why the others are very concerned who have held the market for years. there is no comparison , they stand to lose a lot in the near future.

I am sorry but I haven’t the time for the politics I just want what is safe for me, my family, and my home.

The thing that surprised me the most was that Decorative Rubber Mulch is the very best when tested with all other products but there is NO representation on CPSC Board? Again I say what is up with all this!

All the more reason I continued my research to get to the bottom of this issue.

I have the answers to every statements I have read here so far indicating otherwise based on my research.

Continue your research and you will see it for yourself…...........

As with ANY product, it is always wise to get to know the MFG. Do your own research!

Remember there are always Good companies and also BAD companies.
Don’t hesitate to call and ask questions, I did…...... I could easily pick out the good and the bad…....

Size is the Most important issue in Safety for our children, pets and homes.
The 3/8” is the very safest throughout the United State. Clean and wire free by 99.9%.

The Coatings have to be Non-Toxic with UV protectants.
This will keep it from absorbing the heat and also keeping the colors lasting for years. The good companies track record on their product speaks for itself.
This is where getting to know your MFG and their process comes in Handy.You know you are safe!

If you drove by and saw it in someones yard stop and talk with them.

Find out everything you can, then make your own decisions.

I did, and I am loving life…......................................

I wouldn’t think of using anything but Decorative Rubber Mulch anywhere!
It is a safe, reliable great source of conservation not to mention lower maintenance. I am out in my yard because I want to be not that I have to be anymore.

I know it is safe! for everything and everyone.

Posted by Trish on 06/07/2009 at 09:33 AM

I live So Cal. where we are running out of water. Trying to be “green” I went to W**mart for some mulch. ALL THEY HAVE is rubber mulch. Now that I spread the 3 bags I bought to start with, I wasn’t feeling so great about it, and found this article when researching rubber mulch.
Guess that’s just another reason not to shop at W^^mart. I’m going to scoop it up and go buy some organic mulch…..

Thank you for your article. It changed my mind.

now… how to dispose of this stuff? Sheesh!

Posted by E.P.CHRISTENSEN on 06/04/2009 at 11:35 AM

We’ve recently installed Pet Turf and have concerns about our small pets safety. Certainly our thoughts were to provide a cooler alternative to cement in their dog run. It is, in reality, much hotter than the cement.

Another concern is for my grandson and his football team playing on athletic turf. In all I’ve read, there seems to be arguments on both sides.

Do you have any definitive data?

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