Lead loading of urban roadways by motor vehicle wheel weights: some Australian observations using novel methodology

Wheel weights fall off motor vehicles, accumulate on urban roadways and contribute to lead loading of the environment. The objective of the present research was to determine mass distribution, deposition rate, residence time, mass loss, and lead loading per annum on roadways in Melbourne, the capital city of Victoria, Australia. We surveyed wheel weights on 3-3.5 km segments of local/secondary roads over five years, and an 8.2 km segment of a primary arterial road over five month periods. The approach to steady state was also monitored using Global Positioning System (GPS) tracking of the position of weights deposited by motor vehicles. The average deposition rate and residence time were estimated using Poisson modeling of the observations. The distribution of wheel weight masses generally reflected the quantities supplied to the new car and tire market, with the 10 to 30 g range making up almost 70% of the total observed. The number of wheel weights observed was correlated with the commercial content of the route, but residence times depended on the location. The weighted average mass loss of wheel weights deposited on a primary arterial road was 5.9% and the average residence time was 38.1 days. Lead loading on Melbourne roadways was estimated to be 10.9 tonnes/year with 10.3 tonnes/year as intact pieces and 0.6 tonne/year as particulates (or dissolved).