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Re:tires (this list is never 'tiresome')

  • Subject: [cg] Re:tires (this list is never 'tiresome')
  • From: Don Boekelheide dboekelheide@yahoo.com
  • Date: Wed, 5 Jan 2005 21:44:08 -0800 (PST)

Hi, all,

Much prefer Adam's post on garden joys and good
eating, but this kind of tire exchange is one of the
invaluable contributions of this list.

I'd like to pass along information on old tires in the
garden from a USDA agronomist who has focused on
composting and soils, Dr. Rufus Chaney. Seems like a
good reliable place to start. Before his remarks, a
couple of comments - 

The product I'm most concerned about is shredded tire
'mulch', as opposed to using whole tires as planters.
Part of the problem is aesthetic - the 'mulch' stinks
and gets sticky in hot weather. Sometimes, you see it
advocated for playground use. Our car-intoxicated
culture generates a huge number of old tires. Figuring
out an environmentally sound method of dealing with
them is a high priority. This foul smelling 'mulch'
ain't on my list. 

My thought is that old tires are best re-integrated
into pavement and, maybe, as 'frames' for inexpensive
structures  (Michael Reynold's 'Earthships'). 'Whole
tire' planters probably are not much of a short-term
risk, especially if painted with a tough non-toxic
paint and/or lined with plastic (don't forget drain
holes!), because of their relatively low surface area
in contact with soil and microbes. But I still don't
use 'em. I don't like the way they look, and,
long-term, anything in the rubber will end up in your
soil, as Dr. Chaney says. I completely agree that
tires are especially inappropriate (and impractical)
as compost containers. In two words - no, thanks.

Here are Dr. Cheney's comments (from the SARE website,
Sustainable Agriculture Research and Education,
www.sare.org. Damn fine outfit.). It is in response to
a post about recycled tires and their ag uses:

>As you can see below, Pat Millner sent me a copy of
the questions and responses about tires. I have been
part of the USDA composting team since 1973, and
studied metals in soils and food-chain from any

Tires normally have 0.5-2% Zn. Most rubber items have
this much Zn. In many situations, when rubber was used
in plant growth media, or burned tires residues were
on soils, Zn killed plants. There is an interaction
between soil or medium pH and Zn toxicity. At a
reasonable rate of application, rubber would be a high
grade Zn fertilizer over time because the Zn in rubber
is purified, with very low Cd concentrations.

I have cited a number of papers over the years about
Zn phytotoxicity 
from rubber, but not conducted research on this
myself. This Spring, I 
attended a meeting in NC where one speaker noted that
farmers had heard from one another that if you put a
tire around a tree stump and started it afire, it
aided in buring the stump to the ground. But when they
tried to grow Zn sensitive crops, even at neutral pH,
Zn killed peanuts and some other species.

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. If you need 
references, please write back. This topic was first
reported in the 
early 1970s, and then re-done in the 1990s by people
who didn't search literature. A nice demonstration of
negative effects of rubber in 
potting media was recently reported from Australia by
Handreck, I think in Commun. Soil Sci. Plant Analysis.


Rufus L. Chaney
Environmental Chemistry Lab
USDA-Agricultural Research Service
Bldg. 007, BARC-West
Beltsville, MD 20705
Phone: 301-504-8324
Fax: 301-504-5048

On Wed, 5 Mar 1997 pmillner@asrr.arsusda.gov wrote:
> ---------- Forwarded message ----------
> Date: Wed, 5 Mar 1997 10:07:02 -0600 (CST)
> Subject: Re: tires
> I'm sorry that I cannot cite the original
reference--I cannot 
> remember it, and I don't have time to look it up,
> the study was done with tires that were to be
> in ponds. Dumped.
> Anyway, the upshot of the research was that tires
without metal
> belts were "stable," without any apparently harmful
> or breakdown products leaching into water. However,
tires with 
> exposed metal belts (ruptured, blown, whatever)
leached trace 
> amounts of heavy metals into water. 
> It was research conducted in the US.

I agree that tires are being recycled in many ways.
But use in the root 
zone has caused severe Zn phytotoxicity in numerous
locations. Ash from tires is a toxic material, and
barren soils (some declared hazardous sites) resulted
where huge piles of tires burned (one in Washington
State several years ago).

I am not familiar with any aspect of the breaking of
the surface of the 
rubber which was involved. Over time, rubber is
biodegraded, and the 
constituents of the rubber become part of the soil.
Rubber also contains considerable sulfide, which will
acidify the soil making the Zn more phytotoxic. The
higher the surface area of the rubber in the soil, the
greater the transfer of Zn from the tire to the soil
root zone. But 
whether you start with large chunks or small chunks of
rubber, eventually between microbial and
photodegradation, the matrix is lost and the Zn become
under the control of the soil chemical processes. If
acidic, plants are killed. I have a paper on Zn
phytotoxicity in the book "Zinc in Soils and Plants",
edited by Robson, 1993.

> > Used tires are being recycled in many ways-road
beds, building materials for
> > houses, fuels for kilns, erosion stablization,
shredding to improve turf field
> > drainage.
> > 
> > But---What about food production? Creating raised
beds out of used tires and
> > growing vegetable crops.

Tires around soil as a raised bed garden has been used
by many people. I have not heard of problems from
that, but the surface area in contact with soil is
small. In the short term, it may be little problem.
But eventually the rubber degrades, Zn gets in the
soil, and if the soil pH is 6 or below, uptake may be
too much. Again, the higher the surface area, the more
rapid the release of Zn and toxicity observation.

> > What are any possible problems with this (e.g.,
heavy metals, xenobiotics)?
> > Current thought is that tires are stable, with the
only problems being in
> > rodent and insect populations increasing. any

"Stable" is relative. Over time, microbes biodegrade
rubber as a good 
source of energy. Toxicity to plants from ground
rubber used as a mulch or a component or potting
media, or burned tire residues in soils, have killed a
wide range of plant species.<

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