I admit I don't like the stuff for two reasons - odor and persistence. When you're done with it being a play area, what will you do in that location? Would you then want the rubber mulch there?

You might also consider the other issues address in the article below from Linda Chalker-Scott.

Here is a link that might be useful: Rubber Mulch

Do a little bit of research on the toxicity of rubber mulch and you'll come to the conclusion that it's not healthy for plants, for the soil, for soil microorganisms, for the macroorganisms that come into contact with the leachates......and most importantly......it's not good for the kids.

That aspect aside, have you smelled this stuff on a hot, summer day? Or felt how beastly hot it gets after absorbing a few hours of sunlight?

I don't believe it would significantly harm plants planted in the soil later, after it was removed.

Some people do use it in planting beds, and if it killed plants, I don't think they would sell much of it. :-D

I am aware of several municipal and school playgrounds that put down shredded rubber and then removed it and replaced that with pea gravel. I cannot, however, find much information on the whys although I do recall parental objection to the odor on hot summer days.
Given that tire dumps found around this state were treated as hazardous materials dumps and very high levels of lead, cadmium, and other heavy metals were found in the soils under these tire dumps that required the soil be removed as well as the tires, that is not something I would consider using on my children's playground.

kimm's comment about a material on a playground being replaced reminded me that the after-school care our kids go to replaced the rubber mulch in their play area with bark nuggets after many parents complained about the filth (kids and their clothes picked up a lot of black dirt from the stuff) and the transport of little black rubber particles home in kids pockets, clothes, etc.

The public playgrounds in our area have about a six or eight inch layer of small bark chips. They have edges built around it so they can maintain the depth. It actually feels very springy to walk on. If you are looking for a "soft landing", this might be an alternative to the rubber.

According to EPA's scrap tire web page:

"There have been concerns about the health implications of the use of recycled tire crumb in playgrounds and in synthetic turf athletic fields. In response to these concerns, EPA conducted a Scoping-Level Field Monitoring Study of Synthetic Turf Fields and Playgrounds. The final report was issued in 2009 and concluded that on average, concentrations of components monitored in this study were below levels of concern. To supplement this studyâÂÂs limited data, EPA met with state and local representatives in 2010 to review other available field monitoring studies including a 2010 study conducted by the state of Connecticut which concluded that exposures and risks were not elevated (relative to what is commonly found in outdoor air) for either children or adults using the fields.

"A 2010 report (PDF) (125 pp, 2.2MB) by the California Department of Resources Recycling and Recovery examined the possible human health risks of outdoor athletic fields made from artificial turf containing recycled crumb rubber with respect to skin abrasions, bacteria harbored by the turf, inhalable particulate matter, and volatile organic compounds. The report concluded these fields do not pose a serious public health concern, with the possible exception of an increased skin abrasion rate on artificial turf relative to natural turf.

"At this point, EPA does not believe that the field monitoring data collected provides evidence of an elevated health risk resulting from the use of recycled tire crumb in playgrounds or in synthetic turf athletic fields. Ultimately, the use of recycled tire crumb or any other playground materials is a state and local decision."

I have not seen any data from an actual dump site indicating soil was significantly contaminated by metals. Not that it doesn't exist, and if it's out there I'd like to see it. I don't know of any beneficial uses of Cd or Pb in rubber either, but I'm not a polymer chemist, only and environmental one.

Here is a link that might be useful: Scrap Tire Health and Environmental Concerns

tox - great summary. I'd completely forgotten about the crumb from recycled tires used on artitifical turf, in spite f the fact that about 10 years ago I was appreciably involved with materials used, including the backfill (crumb from recycled tires).

Here's another reference that addresses many of the same issues - it's a 2006 consultant study done for the natural turfgrass folks who are constantly battling the competitive threat of the plastic stuff.

Heavy metals, specifically Cd and Zn, associated with tire disposal come from steel belts. As far as I know the belts are excluded from rubber the crumb used for mulch and artificial turf backfill. Zn is often used as a binding agent in the "rubber", I believe in amounts of 1-2%, so the zinc potential remains.

Here is a link that might be useful: Shredded Crumb Rubber - Environmental Toxicity and Potential Contamination

Given that millions of tires ply the roadways every day throughout North America, and given that these tires do wear down, I'd be willing to bet a cup of coffee and a donut that there is already far more 'tire dust' in the environment than what any play area will contribute.

Lloyd

This post was edited by pt03 on Wed, Sep 11, 13 at 23:40

True Lloyd, but the exposure of a kid will be much greater in a playground situation compared to all the stuff along the roads, which they aren't rolling in. "The dose makes the poison", as they say.

It's rather complicated to generate a 'safe' level of a particular chemical in a particular matrix and exposure scenario, and it hasn't been done for tire rubber mulch. But we can extrapolate from levels acceptable for residential soil and probably get in the ball park.
Zinc is not particularly toxic, and is actually a nutrient we need. My state uses a level of about 2% in surface soil as a safe limit for residential yards. By my reckoning, metals aren't a big risk in rubber mulch. I still don't like the stuff but that's not why. :-]

Thanks for the link TX, I'll add that to my stack.

In spite of the claims by some, I am still not aware of shredded tire mulch killing any plants. The stuff actually seems to be gaining in popularity, if the push by the big-box home improvement centers is any indication.

For me it's a matter dirty, smelly, and later an issue to deal with.

Cars drive on the streets in front of houses too. How many millions of pounds of material worn off tires are on peoples lawns?

Lloyd

Lloyd,

To your question the following from the U.S. Geological Survey in 2004 (link below):
"For 1999, the quantity of Zn released by tire wear in the U.S. is estimated to be 10,000-11,000 metric tons."

Okay if I have the math right that's 22 million pounds of zinc, and at 1% of the rubber compositions that puts 2.2 billion pounds of tire "dust" in the environment per year.

Here is a link that might be useful: Tire-Wear Particles as a Source of Zinc to the Environment

This post was edited by TXEB on Thu, Sep 12, 13 at 22:55

Using some data from studies noted above, and some commercial product info plus a wee bit of math here's what I come up with ...

Assume a 2" layer of shredded tire rubber mulch. That stuff has a bulk density of ~ 20 lbs/cubic foot. For making the calc's easy let's just use 100 sq. ft. A 2" layer over 100 sq. ft leads to ~ 17 cubic ft, which translates to ~340 lbs of the shredded rubber. At 1% zinc that rubber holds 3.4 lbs of zinc. Leaching 1% of that (0.034 lbs) over 100 sq ft of soil leads to an addition of Zn to the soil of ~7.5 ppm using a 6" soil depth.

In my world 7.5 ppm Zinc in soil is a huge level. But, is 1% extractable reasonable? And over what time frame - a year, two, ten? I really don't think anyone knows, and it is probably highly variable depending upon the rubber, the weather where it is, the soil and terrain. What this does bring to mind though is the impact will probably be time dependent with longer time in place being a greater concern.

So to the OP question - does it poison the soil? I believe the answer is it depends - on how much rubber mulch, the soil, the weather, the nature/quality of the mulch, how long it is in place, and finally the sensitivity of the plants of interest to soil Zn levels.

This post was edited by TXEB on Fri, Sep 13, 13 at 4:06

I am well aware that the EPA's position on tires has changed from when I was on the county HazMat team and now find they do not produce the hazards they did back then. When we were called to a tire dump to clean it up and soil tests were done back then very high levels of heavy metals, Cadmium, Lead, Zinc, etc., would be found in the soil under the tires. Later when companies wanted to sell shredded tires as mulch these problems seemed to disappear.
Since shredded tires, rubber mulch, adds nothing worthwhile to the soil there is no good reason to put them down as mulch.

For rubber mulch from tires about the only metal you need to be concerned about is zinc (Zn). The other metals found under tire dumps, (e.g., cadmium) have been traced to the steel belts. The rubber used in mulch is separated from the belts, so there is no steel tire belting in the mulch.

The USDA looked into this over a period of years, and one of their researchers (Rufus Chaney) weighed in on this via SARE - link below. His conclusions is, "Because of the numerous adverse effects of rubber-Zn, I have advised against using rubber in any composting, or in any potting medium, and casual dispersal of rubber on agricultural or garden soils."

Here is a link that might be useful: Chaney - Rubber Mulch from Tires

I don't know what alloys they're using for steel belts, but I find it odd that Cd and Pb are involved. Those don't usually come up when talking about steel alloys. Ductility, strength, hardness and other properties are usually controlled by carbon content, and metals like Ni, Cr, Mo, Mn and V. Not to argue with your data kimmsr, I'm just having a hard time explaining it.

Unless the same junkyards also had piles of batteries.

Here is a link that might be useful: Steel Alloys - Wikipedia

I seriously doubt they are alloy additives, but more likely trace contaminants. One of the problems with those kinds of reports, and there is a similar result published from the U.K. , is that there is typically not a good background for comparison. So how much of what was found (very, very low) can be traced to the disposal of tires is largely unknown. But, for the mulch application it appears to be irrelevant anyway.