The very first level of the very useful hierarchy of resources scale we use in permaculture design tells us very clearly to opt for 'waste materials' (or resources that would create pollution if not used) as a first resort, whenever we design or build something.
But what do we do when those materials are (or are suspected of being) toxic?
.... to be continued ......
Here is a very good article on 'Weed-free raised vermicompost Gardens' which (apart from showing how to build an interesting type of garden) also addresses the safety concerns of growing food in tires.
Quoted from the article:
According to the EPA, at the end of 2003, the USA generated approximately 290 million scrap tires, and although more and more uses for them are being implemented to avoid waste, about 27 million scrap tires (9.3%) are still estimated to be disposed of in landfills or monofills. How can you do your part to reduce the local carbon footprint of tire waste in your own community? Why not use them for your flower beds or gardens?
First, we settle the safety concerns about using tires to grow food in. According to Linda Chalker-Scott, Associate Professor and Extension Urban Horticulturist, WSU Puyallup Research and Extension Center, "rubber tires will be a constant source of leached metals, PAHs, and other pollutants as the tire degrades." But is it enough to effect human health? First off, PAH is only released during the burning of tires, and we won't be burning any tires in our gardens.
The EPA doesn't treat scrap tire piles as hazardous waste, but if they ever caught fire, then tires break down into hazardous compounds including gases, heavy metals, and oil-- at that point, it is treated as a hazard. (A side note: pill bugs, aka rollie-pollies break down heavy metals in soil, so whatever little compounds that may come from tires are going to be taken care of by our little bug friends)
Used tires are often shredded and used as playground turf where children play, or made into pellets for sports turf. There is an issue with the pellets as they are heated to make the pellets which does raise the levels of PAH. But unheated tires are not likely to release them at any level that would cause concern.
Fears about the health implications of the use of recycled tire crumb in playgrounds spurred a study by the EPA. However, their limited Scoping-Level Field Monitoring Study of Synthetic Turf Fields and Playgrounds was not done over a long term.
Their intent was to test a method for measuring possible emissions. Only four sites were studied and the concentrations of components monitored were below levels of concern. However, since the study was so limited in its scope, it may not be possible to reach comprehensive conclusions without the consideration of additional data or longer term studies. Granted, the turf would be far more of a concern than an intact whole tire (less water run-off exposure from a tire, and no extreme heat exposure).