Tires and lead: A weighty issue
Lead has long been the material of choice in weights used to balance vehicle wheels, but a new analysis shows how often these weights fall off, posing potential risks to human and environmental health.
Tires crunch against street curbs or come to a screeching halt when drivers stop or swerve suddenly. In the process, one or more of the weights clipped to the wheels to balance the tires—2.5 oz/car wheel on average—may get thrown off onto the roadway. In 2003 alone, ~2000 t of lead may have been lost from vehicles in this fashion, according to estimates released in May by the U.S. Geological Survey (USGS).
The USGS study tracks the flow of lead-based wheel weights from their manufacture, through their use, recycling, and disposal. In 2003, ~28,000 t of lead were used in the production of wheel weights in the U.S., and ~65,000 t were attached to the 232 million registered cars, light trucks, and commercial vehicles traversing U.S. roadways, the analysis shows.
Given those figures, the 3% lost along roadways may not seem like much, especially when spread out across the entire continental U.S. But much of it is probably concentrated in urban environments, where most of the stop-and-go traffic occurs, notes Donald Bleiwas, a USGS minerals and materials specialist and author of the report. Additionally, lead wheel weights have been used on vehicles for nearly 70 years, so the cumulative amount of lead dispersed in the environment in this way could be significant.
How big an environmental problem that poses depends on what happens to the weights after they fall off. Do they get ground up by traffic? Do the abraded particles become airborne? Does storm water wash them off roads? Do they make their way into nearby soils, or get transported into urban ponds and groundwater? Do they get picked up by street sweepers? Do hobbyists pick them up and mold them into other items, such as lead weights used by anglers?
“I can’t answer that side of the equation,” Bleiwas admits, but wheel weights “could contribute to the presence of residual lead content in some soils in urban environments.” Historically, the main source of lead in U.S. soils was emissions from leaded gas, and they have decreased substantially since it was phased out beginning in 1973.
The USGS study is important because “it’s the first [official] attempt to try and get a grasp on what the inventory is and what the scope of the potential problem is,” says Jeff Gearhart, campaign director for the Ecology Center, an environmental organization. His group sponsors a project looking at toxic materials in vehicles. “Wheel weights are the second largest use of lead in vehicles after lead–acid batteries, and they’re the one use that continues to be dispersed into the environment more than any of the other uses,” Gearhart points out.
The EU began banning the use of lead wheel weights last year on new vehicles and replacement tires because of environmental concerns about losses along roadways and inappropriate disposal by tire retailers and scrap processors. No federal regulatory controls currently govern the use of lead wheel weights in the U.S., but car manufacturers, including most U.S. companies, are slowly moving toward other materials, Gearhart notes. Zinc and steel are the most common alternatives.
However, the vast majority of wheel weights—~80%—go into replacement tires, Gearhart says. Ironically, even though you might buy a new car with lead-free weights, lead will go back in once you put new tires on.
The U.S. EPA encourages tire dealers to begin using lead-free weights under a voluntary initiative, but the agency rejected a petition [414KB PDF] by the Ecology Center last year to ban the use of lead weights, saying more research is required. Nevertheless, a growing number of states, cities, and private fleets are moving in that direction because of environmental concerns. In 2004, Minnesota became the first state to begin replacing lead weights on its state fleet with lead-free alternatives.
“Our approach to this whole thing is pollution prevention,” says John Gilkeson, a principal planner for the Minnesota Pollution Control Agency. “We know lead’s a problem; we know it comes off wheels. If we’ve got an alternative, let’s do it.”
