September 21, 2019

The Comprehensive History of Rubber Tire Mulch

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Rubber tire mulch is a recycled product with a large market.  The mulch is used in landscaping and valued for not changing color or rotting, unlike wood chip mulch.  It is also marketed for use in playgrounds as a “green” alternative to wood chips or pea gravel. How did rubber tire mulch become so common in children’s playgrounds?  Is it sustainable to use recycled tires in a product meant for children?

History

People have been using rubber for hundreds of years.  When Christopher Columbus arrived in the new world, he found natives using balls made of natural rubber.  Rubber is produced naturally in the sap of a rubber tree. It is extracted with taps in the same process as maple syrup.   It was not long before rubber and rubber trees were exported to Europe, where people found many uses for the durable tree extract.  

The name “rubber” comes from Joseph Priestly, a theologian, author, and chemist.  In the late 1700’s Priestly discovered that this material was useful for rubbing away pencil marks, thus inventing erasers and giving the material its modern name.  Another early use for rubber was the Mackintosh.  Charles Macintosh invented this waterproof raincoat using layers of fabric and rubber.  The first Mackintosh raincoat was sold in 1824.

In 1832, American Charles Goodyear discovered that adding sulfur to rubber changed the material’s properties.  This process is called sulfur vulcanization. While natural rubber can be melted and remolded, vulcanized rubber holds a permanent shape.  Goodyear patented this process in 1844.

His patent application emphasized the product’s indestructible qualities, stating, “No degree of heat, without blaze, can melt it.”  Goodyear also patented two processes for recycling vulcanized rubber. These processes involved grinding the rubber and then mixing it with virgin rubber, or heating and pressing the ground rubber and scraps into a new form.

The first rubber tire was created by Scottish inventor John Boyd Dunlop in 1887.  It was used on a bicycle for Dunlop’s son.  The tire gained attention after bicycles using Dunlop’s tires began winning bicycle races.  Soon, a company was formed to manufacture the tires for wide-scale production.  The mass production of personal automobiles happened at almost the same time, with the Ford Model T arriving in 1908.

The Scrap Tire Problem

As more and more people began driving cars, more and more used tires were, quite literally, piling up.  Just as Goodyear had noted in his patent application, tire disposal is difficult because tires do not decompose.  They do not melt. They cannot be easily reshaped. Since tires need to be replaced after a certain number of miles, scrap tires became a growing problem.

In the 1960s, a German named Berleburger Schaumstoffewerke improved on the process for recycling rubber.  Like the earliest process described by Goodyear, this recycling process involved grinding the rubber into smaller pieces and then pressing it into new forms.  Schaumstoffewerke used the recycled rubber to manufacture materials used in athletic complexes, such as runnings tracks and floors in gymnasiums. He also manufactured floor tiles to be used in children’s playgrounds.

Schaumstoffewerke’s work was novel but not widespread.  The scrap tire problem continued and worsened. In the US, disposed tires were stockpiled in landfills and private dumps.  The tires collected water and created a breeding ground for disease-causing mosquitoes. They also presented a fire hazard.

In 1983, a fire started at a tire landfill in Winchester, Virginia.  The fire was extremely dangerous, creating toxic black smoke and hot oil waste.  Due to the chemical components of the tires, the fire could not be extinguished with water.  Authorities had no choice but to let the fire burn itself out, which took months. In 1984, another tire landfill caught fire, this time in Everette, Washington.  The results were the same.

In the aftermath of these fires, the United States Environmental Protection Agency (EPA) took steps to address the scrap tire problem.  In 1985, the EPA published a report titled The Scrap Tire Problem: A Preliminary Economic Analysis. The report found that approximately 240 million scrap tires were traded in that year.  Of those 240 million scrap tires, almost 70 percent – 170 million tires – went directly to stockpiles and landfills. The EPA recognized the urgent need for a better solution. One of their biggest recommendations for addressing this problem was to find more ways to recycle the scrap tires.

The EPA released another report about scrap tires in 1991.  This report, Markets for Scrap Tires, noted that by 1991 Americans were now producing 242 million scrap tires per year.  At the time, less than 7 percent were being recycled. Among the markets for scrap tires listed, the report highlighted a company in New Jersey called Tire Playground, Inc.  Tire Playground, Inc. repurposed old tires to create new items such as swings and obstacles for climbing. The report noted that demand for tire playgrounds was small and, even if popular, would not use up enough scrap tires to adequately address the problem.  

Another use for scrap tires mentioned in the 1991 report was “Playground Gravel Substitute.”  In 1991, this product was one of five recycled tire products which interested the EPA. However, around 70 percent of scrap tires were still landing in stockpiles and landfills.

Improvements to the rubber recycling process were discovered in 1999 at the The Chelsea Center for Recycling and Economic Development, a part of the University of Massachusetts Center for Environmentally Appropriate Materials.  In a report describing this work, the lab explained that its goal was “to develop a technique that enables one to make high value added recycled rubber products from scrap rubber powder.” More recycled tire products could now be produced more easily, making tire recycling a viable business.  The number of scrap tires being recycled in the US rose from 7 percent in 1991 to 60 percent in 2001.

Rubber Mulch on Playgrounds

This impressive increase in recycling can be linked to several efforts.  States developed grant programs funding the use of recycled tire rubber. A grant program in Kentucky, for example, gave grants to municipalities, school districts and others to fund the use of tire rubber mulch as a playground gravel substitute.   In ten years, Kentucky’s grant program had funded the use of recycled tire mulch in almost 300 playgrounds.

Recycled rubber manufacturers expanded to meet the demand and advertised to grow the market.  One of the largest providers, Liberty Tire Recycling, promotes recycled tire mulch as safer than alternative playground surfaces.  According to the website for their rubber playground mulch, the product “cushions a child’s fall and provides up to 2.5 times more fall height protection than grass, dirt, sand, pea gravel, wood mulch, engineered wood fiber (EWF), rubber tiles or poured in place surfaces.”

When Barack Obama began his first term in 2009, the Obamas installed a playground for their daughters at The White House.  The first official White House playground featured recycled scrap tire rubber mulch manufactured in New Jersey. The mulch was chosen for its safety properties.  It met all guidelines published by The International Play Equipment Manufacturers Association (IPEMA) and the Americans with Disabilities Act (ADA).

Questions About Safety

Early concerns about the safety of rubber tire mulch focused on the composition of the product.  Tires are not constructed entirely of vulcanized rubber. They also contain steel wires and bands to support the tire’s shape.  While modern recycled tire mulch now claims to be 99% free of metal, there is still a possibility for children to come in contact with steel scraps while playing in rubber tire mulch.

There were also questions about the volatile organic chemicals (VOCs) contained in tire rubber.  The health risks of VOCs include effects on the respiratory system, allergies, and immune systems of children.  A report on playground safety conducted in California and published in 2003 found that recycled tire rubber includes at least seven carcinogens, chemicals capable of causing cancer.  

Concerns rose after a small fire was discovered in the rubber tire mulch at Yulupa Elementary School in Sonoma County in August of 2003.  Suspected to be intentionally started by vandals, the fire was fueled by rubber mulch made from chips of recycled tires. The fire burned for approximately 15 minutes and affected about half of the mulch surface of the playground.

The EPA hired a contractor to inspect the site of the playground fire.  The contractor was to determine the following:

  1. Was the soil below the burned chip layer contaminated?
  2. Should soil removed from the playground be classified as hazardous waste?
  3. Did clean-up workers breathe air contaminated with chemicals found in rubber?

The studies found that scrap tire rubber mulch did leach chemicals into the surrounding soil and groundwater.  However, the levels of VOCs and other tire-derived chemicals were determined to be within EPA recommended levels.  The study’s conclusion stated, “it seems doubtful that recycled tire rubber in outdoor applications such as playground surfaces releases high enough levels of chemicals to cause toxicity to animals and plants living in the vicinity.”

Despite the EPA’s assurances, consumers are skeptical.  “It seems doubtful” does not convey the same confidence as a statement declaring “no risk whatsoever.”  Is it really alright for children to play in mulch derived from waste that many states classify as toxic waste?  

In October of 2014, NBC News published a story questioning the safety of artificial turf.  After several Washington State soccer players developed similar cancers, an investigation was launched into the safety of artificial soccer fields.  The turf investigated used crumbs of recycled scrap tires as fill to add shock-absorption to the fields.

NBC examined available studies from the EPA and others.  They interviewed scientists and industry professionals. The story concluded the researchers were “ unable to find any agreement over whether crumb turf had ill effects on young athletes, or even whether the product had been sufficiently tested.”

A follow up story in December of 2014 focused specifically on the use of rubber tire scraps on playgrounds.  The public was concerned that children were playing in the same material that had not been conclusively found safe for use in artificial turf.  Parents complained that the mulch left black marks on their children’s clothing and skin.

As a concerned mother explained, “We know that there are chemicals in tires, and we know that they are most likely not removed just by shredding and putting them on a playground.”  Another person interviewed for the story was Dr. Philip Landrigan of Mt. Sinai Hospital in New York, a doctor who focused on the effects of chemical exposure on children.  Dr. Landigan noted that “Little children should not be put in a situation where they’re forced to be in intimate contact with carcinogenic chemicals.”

The NBC stories were seen by many people and started conversations among concerned parents.  Schools began to reconsider the great deals they were getting on scrap tire mulch through state-funded grants.  The EPA, working to avoid landfills and toxic fires, had an incentive to create a market for the recycled tires.  Questions were raised about the reliability of the studies that had been conducted to date.

Replacing Rubber Mulch

In 2016, the Board of Education in North Shore Long Island, NY, voted unanimously to remove and replace the rubber mulch in their playgrounds.  The board agreed to budget $500,000 for the removal of recycled tire rubber playground mulch at three elementary school playgrounds. The mulch was replaced by mulch made of wood chips.  

Another school district funded $630,000 to replace the rubber tire mulch with wood chips at their playgrounds.  Duluth School board in Minnesota motioned to remove all rubber mulch chips on in January 2017. A mother explained the reasoning behind this decision, “It wasn’t a matter of, do we need a study to confirm it, it’s just, we don’t need our kids to keep playing on it until we have definitive proof, we just need to get them off of it now”.

In Connecticut in 2017, efforts to remove tire mulch from playgrounds were conducted by Environment and Human Health, Inc (EHHI).  EHHI reached out to schools with information regarding the questions around tire mulch safety and recommended replacing recycled tire mulch with wood chip mulch on playgrounds.  On their website, EHHI notes the difficulties they have encountered in changing legislation or receiving the help of any state agency in changing policies covering the use of tire mulch.

Decisions were made to replace the shredded tire mulch at East Durham Park in 2018 after parents voiced concerns of possible health risks.  Durham’s mayor objected to the decision, stating he preferred to wait for the results of a new EPA study regarding the safety of recycled tire mulch used in playgrounds.

Present Developments

In 2016, a inter-agency study had been announced by the EPA, Centers for Disease Control and Prevention (CDC), and the U.S. Consumer Product Safety Commission (CPSC).  The effort is called the Federal Research Action Plan on Recycled Tire Crumb Used on Playing Fields and Playgrounds.  The government research will examine possible exposure to the chemicals contained in rubber tire crumbs.  A summary of the Tire Crumb Rubber Characterization Study is expected to be released later in 2019.

As they wait for the latest studies, recycled tire mulch manufacturers continue to cite prior inconclusive studies as proof of their product’s safety.  Liberty Tire Recycling offers a resource on their website titled Playground Rubber Mulch Research. The webpage lists links to prior reports, many of them referencing studies that are more than 10 years old.  The most recent document linked by Liberty is a fact sheet from the Kansas Department of Health and Environment, published in 2013. The fact sheet notes that Kansas also operates a grant program to encourage recycled tire products.  Kansas depends on this program in order to combat scrap tire waste. It concludes, “…at the present time, there is inadequate evidence to modify the recycled tire product grant program or restrict the use of recycled waste tire products.”

It is unclear how many playgrounds are still using or considering the use of rubber mulch.  It is difficult to find even concrete numbers on the total number of playgrounds in the US. One data set estimates that there are almost 90,000 public and private elementary schools nationwide.  A prominent tire recycling company recently claimed to close sales with around 100 new accounts per year, including schools, daycares, and military facilities.  Would these facilities continue to purchase rubber mulch if they understood the possible health risks?  

Since the invention of rubber tires and the resulting tire landfills, recycling scrap tires has come a long way.  Improvements in recycling efficiency have significantly contributed to the EPA’s efforts to solve this waste problem in the US.  However, the use of rubber tire mulch in children’s playgrounds includes many health risks. Studies to determine those risks have been inconclusive regarding this product’s safety.  Until those risks are fully understood, the sustainability of this product is in question. While it is important to recycle and find new uses for tire waste, we must do so in a way that is also sustainable for the health of our children.

References

1 Environmental Impacts of Recycled Rubber in Light

Fill Applications

2 Wikipedia – Mackintosh

3 Environmental Impacts of Recycled Rubber in Light

Fill Applications

4 Powder Processing Techniques to Recycle

Rubber Tires into New Parts from 100%

Reclaimed Rubber Powder/Crumb

5 Wikipedia – John Boyd Dunlop

6 Wikipedia – Ford Model T

7 City Reporter – Know The History Of Rubber Mulch

8 The Scrap Tire Problem: A Preliminary Economic Analysis

9 The Scrap Tire Problem: A Preliminary Economic Analysis

10 EPA – Markets for Scrap Tires

11 Powder Processing Techniques to Recycle

Rubber Tires into New Parts from 100%

Reclaimed Rubber Powder/Crumb

12 Liberty Tire Recycling – Playground Rubber Mulch

13 First Ever White House Playground Uses Recycled Playsafer Rubber Mulch and Rubber Curbs from Rubberecycle, As seen on 60 Minutes

14 Wikipedia – Volatile Organic Compounds

15 Evaluation of Health Effects of Recycled Waste Tires in Playground and Track Products

16 Evaluation of Health Effects of Recycled Waste Tires in Playground and Track Products

17 Evaluation of Health Effects of Recycled Waste Tires in Playground and Track Products

18 NBC News – How Safe Is the Artificial Turf Your Child Plays On

19 NBC News – Is Rubber Mulch a Safe Surface for Your Child’s Playground?

20 North Shore BOE Votes to Replace Rubber Mulch at School District Playgrounds

21 Parents and School Board Officials Take Steps to Replace Rubber Mulch

22 A model for getting toxic tire mulch removed from children’s playgrounds

23 Durham park’s rubber mulch getting replaced, but at a cost

24 US Consumer Protection Agency – Crumb Rubber Information Center

25 Fact Sheet – Health and Safety Considerations Associated with the Use of Recycled Waste Tires for Playground Surfacing

26 Statista – Elementary schools in the US, Statistics & Facts27 Recycled Rubber Products – Personal Correspondence

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