Nov. 10, 2003 MADISON - As mountains of scrap tires continue to rise above the landscape, researchers at the University of Wisconsin-Madison have found an environmentally friendly use for them: grind them up and place the rubber bits beneath golf course greens.
In a paper accepted for publication in the journal Waste Management, the researchers show that these ground tires can absorb excess chemicals from fertilizers and pesticides, preventing them from leaching into groundwater and contaminating the surrounding environment.
Golf courses are designed to improve playability, not environmental impact, says Jae (Jim) Park, a professor of civil and environmental engineering at UW-Madison and an avid golfer with a 6 handicap. But, as an environmentally conscientious person, Park is also aware of the unintentional side effects of the fertilizers and pesticides applied to the golf-course greens to keep them looking, well, green. These products contain chemicals that trickle into groundwater sources and contaminate the surrounding environment, he says.
"Because many greens are built near groundwater levels or wetlands," explains Park, "it is vital to consider the mitigation of environmental contamination caused by the pesticides and fertilizers applied to golf courses."
Used tires could provide a barrier, according to the new research led by Park.
The U.S. Environmental Protective Agency estimates that Americans discarded an estimated 273 million scrap tires in 2001, with only about 33 million being retread or recapped for additional use. Due to state regulations, most of these old tires were stockpiled, rather than dumped in landfills. Park says that storing this waste material in such a way creates several hazards: they collect rainwater, create breeding grounds for mosquitoes, and have a tendency to catch on fire.
"Tires are a waste material," says Park, "and we need to have safe ways to dispose of them."
Researchers throughout the world have been searching for ways to reuse tires that are accumulating in stockpiles. Civil engineers have utilized tires, either in scrap or ground-up form, to develop tire derived fuel, artificial ocean reefs, bumpers, playground equipment, asphalt additives that extend the life of roadways and shock-absorbent playing fields. Ground-up rubber products, including the soles from sneakers, can be found beneath the turfgrass at many athletic stadiums, including Camp Randall Stadium at UW-Madison.
Park has been studying the characteristics of tires for the last 12 years. In that time, he and his colleagues have shown that tire chips - ground-up pieces of this rubber material - can absorb harmful organic compounds from the environment. The findings, he says, suggest that they could be used as landfill barriers to prevent the leaching of pollutants into the ground.
Tire chips' ability to block these pollutants led Park, civil and environmental engineering graduate student Bob Lisi, and horticulture professor John Stier to consider another application: placing ground-up rubber beneath chemically treated golf-course greens.
Park says just under 1,000 pounds of pesticides are applied yearly to a single golf course. He adds that there are more than 23,000 golf courses in the United States.
In the latest study, he and his team found that tire chips can absorb nitrate - one of the main chemicals in fertilizers. Park says studies show that infants who drink water containing excess amounts of nitrate can become seriously ill and, left untreated, could die.
For the study, the researchers inserted tire chips just six to nine millimeters in diameter between layers of sand and peat root mix and gravel, both of which are commonly found beneath golf-green turf. The rubber layer was either five or 10 centimeters thick. The researchers studied the role of these layers in the lab, as well as on the field in three-by-three meter plots at the O.J. Noer Turfgrass Research and Education Facility in Madison, Wis. While the field sites were seeded with a grass, the lab samples were left bare.
To test the ability of the tire chips to absorb chemicals, the Wisconsin scientists applied water spiked with different concentrations of nitrate to each sample. Then, they measured the concentration that seeped out of the bottom gravel layer.
The main goal of the experiments, says Park, was to determine if the rubber layers would filter out chemical compounds carried in the water without affecting the health or quality of the grass.
In all experiments, the researchers found that the rubber layers did absorb the compounds. Compared to the control samples, the lab experiments with the five- and 10-centimeter layers of tire chips released 17.9 and 21.7 percent less nitrate, respectively, after one year of testing. During this time, the five- and 10-centimeter rubber layers in the field released 23 and 58.6 percent less nitrate, respectively.
Based on the experiments, Park says, "Excess amounts of fertilizer will be absorbed by ground tires. They'll be trapped right there instead of traveling." Over time, he adds, soil microbes will remove the nitrate from the rubber layer, which could remain intact for last years.
While some environmentalists may be concerned that chemicals released from the tires will percolate into the environment, Park says numerous scientific studies show that the amount released is minimal compared to the amount the tires can trap.
"We've proved that is not an issue," he says. "Some contaminants have been reported, but the levels are so low."
As part of the current study, Park and his colleagues visually assessed the quality of the field plots from seed germination to the end of the sampling period. Turfgrass quality, color, density or germination rate did not appear to be affected, he says. He adds that about one year later there was no significant difference in grass quality or density among the three putting green profiles, suggesting the rubber layer did not alter the turfgrass.
Besides absorbing chemicals harmful to the environment, Park says the characteristics of tire chips make them even more attractive: they're light weight, allowing for easier transportation and installation; they absorb shock, possibly alleviating foot pains of golfers; and they trap heat, promoting turf and root growth longer into autumn and earlier in spring.
But, above all, he says, "The technology reuses a waste material that's hard to dispose while it protects the environment." Park estimates that about 72,000 tires would be needed to include a 10-centimeter layer of tire chips for an 18-hole golf course - a number that could chip away at one of this country's major waste problems.
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