GOTEBORG, Sweden-Aromatic oils in tread rubber can damage the environment when released through tire wear, according to a report from Sweden's Kemikalie-inspektionen unit. The Swedish Tire and Rim Organization (STRO), however, said the report greatly exaggerates the environmental risk from tire particulates and aromatic oils. That risk, according to the STRO, is ``almost negligible'' compared with other sources of pollution.
The report tracks the flow of tires and their potentially damaging ingredients as they pass into the Swedish environment, attempting to calculate how much material is released.
It quantifies the size of the Swedish car and truck/bus markets for new and retreaded tires and the market shares of each manufacturer. It also analyzes the flow of tires from manufacturers and importers through road use to retreading and disposal.
Some 66,000 tons of new tires (roughly equivalent to 6.6 million passenger tires) are consumed annually in Sweden, the report states. From that total, it estimates 11,000 tons of tread rubber are worn away and deposited in the environment by normal driving.
Authors Jan Ahlbom and Ulf Duus claim tires add approximately 15.4 tons of polyaromatic hydrocarbons (PAH) to the Swedish environment each year. The PAH comes from the polyaromatic oils used as softeners in tread compounds. This compares with 5 tons of PAH worn away from the road surface itself, the researchers said.
Based on these calculations, Messrs. Ahlbom and Duus claim PAH from tire wear is the largest environmental risk from tires, with PAH from uncontrolled tire burning a close second.
``It is very urgent to find alternatives to HA-oils from an environmental standpoint,'' the report states.
Tire wear also releases zinc, a vulcanization activator that can be toxic to wildlife, into the environment, constituting ``10 percent of the total anthropogenic zinc emissions in Sweden,'' according to the report.
Switching from pure zinc to zinc stearate, Messrs. Ahlbom and Duus claim, would lower those emissions.
The STRO said the report fails to consider the low-viscosity oils used in tire making, which have low volatility even at high temperatures.
``The PAH in...worn-out tires is fixed, and consequently the decomposition is slow,'' the STRO said. Furthermore, microbes found in nature degrade oils quickly, neutralizing their environmental threat.
More research needs to be done on the environmental effects of tire PAH before regulation is considered, the organization said.
The report, Nya hjulspar-en produktstudie av gummidack, (ISSN 0284-1185) is available from:KEMI, Box 1384, 171 27 Solna, Sweden.