Re: tires (fwd)

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 source.  
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 
the 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, but...
> the study was done with tires that were to be "landfilled"
> in ponds.  Dumped.
> Anyway, the upshot of the research was that tires without metal
> belts were "stable," without any apparently harmful contaminants
> 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 ideas??

"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.