One of the mantras for waste reduction and energy efficiency is the “Reduce, Reuse, Recycle” slogan, which indicates the order of preference for resource conservation: It’s best to use fewer things in the first place, but once you got ‘em you may as well reuse them. In the end, though, it’s better they get recycled than chucked in a landfill.
Not all products fall neatly into this hierarchy, though. Being round, an automobile tire should be a poster-child for the idea that what comes around should go around as many times as possible. One problem is that the customers most eager to reuse the estimated nearly 300 million car and truck tires that Americans discard each year are mosquitoes. And that fact that tough, durable construction is what defines a good tire makes recycling them a special challenge.
Early on, it was recognized that a discarded tire was a mosquito farm. So in the old days it was common to provide a dead tire with a shallow grave and call it good enough. But on average, a buried tire is 75% air space, so if it is not very deep it becomes perfect for the young rat couple or yellow-jacket queen looking for a nice starter home.
When tires were sent to landfills, one issue was that they could not be compacted, and therefore wasted a lot of space. And it turned out that they rose from the dead, becoming methane-filled and wriggling their way to the surface.
In 2004, the New York State Department of Environmental Conservation (NYSDEC) rounded up a statewide list of tire dumps, revealing 95 sites for a grand total of 29 million tires. Since then, more sites have been located, but the overall numbers of tires are slowly dropping due in part to a 2003 amendment to the Environmental Conservation Law called the Waste Tire Management and Recycling Act. This is the Act which requires garages to charge you a fee for proper tire disposal.
Prior to 1990, only about 25% of discarded tires were recycled, but these days the number is up around 80%, which is below the 95% rate found in Europe, but still a vast improvement. More than half of our recycled tires are used as fuel, mostly by industries such as cement kilns and steel mills. Tires are also shredded or ground, and the resulting crumb-rubber is added to asphalt or concrete for road construction, which imparts resiliency and shock-absorption qualities. For similar reasons, shredded rubber is mixed with soil under athletic fields, and is employed in playgrounds under swings and play structures to help cushion falls.
In recent years, ground rubber has been marketed as a mulch option for landscapers and homeowners. This seemed like a perfect end-use for recycled tires, but some researchers are questioning the wisdom of rubber mulch. According to Dr. Linda Chalker-Scott, an Associate Professor at the Puyallup Research and Extension Center at Washington State University, the toxicity of the rubber is a real concern, especially if it is used near vegetable crops.
In one of her published papers, Dr. Chalker-Scott has stated that “Part of the toxic nature of rubber leachate is due to its mineral content: aluminum, cadmium, chromium, copper, iron, magnesium, manganese, molybdenum, selenium, sulfur, and zinc…rubber contains very high levels of zinc – as much as 2% of the tire mass. A number of plant species…have been shown to accumulate abnormally high levels of zinc sometimes to the point of death.”
The paper notes that in addition to metals, organic chemicals which are “highly persistent in the environment and very toxic to aquatic organisms” leach out of shredded rubber. Chalker-Scott concludes that:
“It is abundantly clear from the scientific literature that rubber should not be used as a landscape amendment or mulch. There is no question that toxic substances leach from rubber as it degrades, contaminating the soil, landscape plants, and associated aquatic systems. While recycling waste tires is an important issue to address, it is not a solution to simply move the problem to our landscapes and surface waters.”
When asked what the best type of mulch is, I generally recommend “free.” Plastic mulch can be handy to smother tough weeds, and old bunker-silo cover is often free for the taking if you know a dairy farmer in your area. But where the rubber meets the road, so to speak, natural, plant-based materials are mulch better. They help conserve water and suppress weeds, as well as improve soil structure and enhance the mycorrhizal (beneficial fungi) community. They also act as a slow-release fertilizer. Rotted wood chips, mature compost, or spoiled hay can often be had for little or no cost. As long as you do not use weed-control on your lawn, grass clippings can be used in moderation (they are very high in nitrogen).
Recycling is great, but keep the tires out of the garden. You can help reduce the number of dead tires in the world by regularly rotating your vehicle tires and keeping them inflated properly, and by having your vehicle aligned as recommended in the owner’s manual. The NYSDEC has more information on waste tires, here.