In the debate about the climate effects of carbon dioxide emissions from transportation it is assumed that fuel is the key source of pollution from vehicle traffic.
“What you seldom think about is the huge amounts of brake linings and tires that are worn out in traffic and the fact that these products contain considerable amounts of metals,” says David Hjortenkrans, one of the scientists at The University of Kalmar in Sweden who performed a new study of the issue.
Despite the fact that authorities have regulated the metal content of auto parts and the fact that the auto industry has made improvements, brake linings and tires are still among the major sources of metals in urban environments.
The study compares estimated metal emissions from brake linings and tires for the years 1995/1998 and 2005. The release of copper and zinc from brake linings has remained unchanged over this period.
“It is gratifying to see that efforts to remove cadmium and lead from auto products have yielded results, with decreased emissions as a result,” says Professor Bo Bergbäck.
It was also shown that there are now large quantities of the metal antimony in brake linings, which is among the newer metals whose use has increased in society in the last few years (cf. the element platinum in catalytic converters). It was also revealed that, despite their lower metal content, tires are one of the major sources of zinc and cadmium in cities.
The study, published in Environmental Science & Technology, has created quite a stir, especially in the United States.
“The study presents findings that are not entirely favorable for a nation that has the highest number of vehicles registered per inhabitant in the world,” says David Hjortenkrans. More stringent control of emissions might substantially hamper the mobility of many people.
Source: Environmental Science & Technology, 41 (15), 5224 -5230, 2007