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E-M:/ tire mulch

Regarding concerns of using shredded tires as mulch, I did some searches on www.google.com and came up with some useful information.
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.   
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:
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.