David Hjortenkrans and colleagues at the University of Kalmar compared metal emissions from brake linings and tires to other metal emission sources in Stockholm during 1995 and between 1998 and 2005. They found copper and zinc emissions from brake linings remained relatively unchanged at high levels, making them a major pollution source.
Brake linings were also found to be a source of another toxic metal, antimony. By contrast, lead and cadmium emissions from brake linings decreased by one-tenth during the period.
The scientists found metal emissions from tire tread rubber declined between 1995 and 2005, as manufacturers reduced metal concentrations in tire treads. Tires, however, remained one of the largest sources of zinc and an important source of cadmium.
"As Stockholm represents a rather average city in most respects, the results from this study may be relevant for many other urban areas," the scientists said.
The research is to appear in the Aug. 1 issue of the journal Environmental Science & Technology.