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
On Wed, 5 Mar 1997 firstname.lastname@example.org 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.