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Regarding concerns of using
shredded tires as mulch, I did some searches on www.google.com and came up with some useful
information.
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Two of the most pertinent
studies I found are in .pdf (adobe acrobat) format on the Rubber Manufacturer's
Association web site at:
Two 5-year studies done in
Maine suggest that there is negligible discharge to soil and groundwater from
shredded tires:
However, the evaluation of
impact depends on the existing background levels of metals such as zinc,
manganese, and iron. Anyone familiar with basic soil chemistry will recognize
these as basic soil micronutrients. So, the question becomes how much is OK, as
usual with just about everything except things like plutonium. Another question
is whether these micronutrients are provided in a form that is ultimately
compatible with the soil and vegetation, especially certain natural plant
communities. Then, of course, one should question whether the site-specific
conditions of these studies would hold true in most cases, who paid for the
studies, what wasn't said, and what did the researchers honestly not know. Also,
can we expect that tire composition is homogenous enough, across worldwide
sources, that potential discharges would always be limited to those observed in
these studies, and can we expect that shredded tire mulch will always be just
that, and not contain other materials in the mix that someone wants to get rid
of? My opinion is that it's wise not to put ourselves in a position where we
have to worry about it. Better to stick to natural, vegetative material for
mulch. Even then there could be problems, but less chance than with a material
like tires. From purely an aesthetic perspective, do we really want to create
non-native soil deposits any more than we must?
Besides, it seems the main
reason tires are being used as mulch and in other capacities is not so much
because of some superior quality for that particular use, but that people are at
a loss as to what else to do with the huge volumes of scrap tires we generate.
But, in my internet search, I also found that Goodyear recently developed a
process to "de-vulcanize" tire rubber to produce a truly recyclable
rubber substance that can be used to make new tires. There is some question as
to whether the process will ultimately prove feasible on a large scale and
actually turn a profit, but definitely a step in the right direction in my
opinion.
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This 1997 information is from a
California Integrated Waste Management Board web site at:
I understand that in
considering mulch, we are not necessarily considering the by-products and
residuals from combustion, except that shredded tires on the ground surface will
undergo oxidation (a slow combustion) and other break-down processes, such that
the final result in terms of material release would probably be nearly the same
for metals. So, in the short-term, a decade or so, there may be little concern.
But in the long-term, decades, there may at least be increased concern. And, the
long-term is really what we should be looking at for
everything.
"Laboratory analysis of
soil samples taken from a tire fire in Bakersfield indicated the total
concentration of zinc exceeded the total threshold limit concentration (TTLC)
[7800 mg/kg and 15800 mg/kg]. The TTLC for zinc is 5,000 mg/kg. Zinc
concentrations at the Panoche Waste Tire Site were also found to be extremely
high (32,800-156,000 mg/kg). Background zinc soil concentrations for the site
averaged 64 mg/kg while underlying soil beneath the ash concentrations ranged
from 74 to 179 mg/kg. At the Rhinehart Tire Site elevated levels of zinc were
identified in surface water samples and on site soils. A comparison of zinc
levels in background sediments (93 ppm) with the highest zinc level found on the
site (2880 ppm) showed a significant increase. (See reports for more specific
emission data information.)" >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
A 1993 letter from Rev. Benet
Luchion, Committee For Universal Security, Zero Tolerance Toxic Campaign to New
Yorker Magazine: http://www.webcom.com/zerotox/mcphee.html
"... tires are laden with
transdermic compounds, such as MBT, CFC's, 1,3,butadiene, urethane,
chlorobenzenes, polyvinyl choride to name but a few." >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
DEQ finding of inertness for
tires, 1997:
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Typical ingredients of a tire
from the Scrap Tire Management Council:
typical composition of a tire:
synthetic rubber, natural rubber, sulphur and sulphur compounds, silca, phenolic
resin, oil: aromatic, napthenic, paraffinic, fabric: polyester, nylon, etc.,
petroleum waxes, pigments: zinc oxide, titanium dioxide, etc., carbon black,
fatty acids, inert materials, steel wire.
And while some of these
substances may appear of no concern, a question is always the origin of these
substances; a natural source or by-product of other processes in which they
might contain things of concern beyond just natural impurities (silica from
foundry sand?). Another concern should be, hopefully in rare cases, whether
someone has chosen to illicitly dispose of hazardous substances by mixing in
small amounts with the usual materials. Such things are not unheard of, like
when a school in Port Huron received fill soil for a new track and field area
that was full of debris such as ground metal and glass.
Bill Collins Huron Ecologic, LLC
3335 Crooks Road Rochester Hills, Michigan 48309 USA phone & fax: 248-852-4682 e-mail: huronecologic@netzero.net Huron Ecologic provides wetland delineations,
wetland permitting, wetland mitigation design & monitoring, tree
inventories, botanical & ecological surveys, natural area protection, nature
education, and technical training.
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