IMPACT OF INTRODUCING NON-LEADED PETROL IN RELATION TO LEAD DISPERSION ALONG MAJOR MOTORWAYS

Neil I. Ward*, Robert J. Hares (ICP-MS Facility, Department of Chemistry, School of Physics and Chemistry, University of Surrey, Guildford, Surrey, GU2 5XH, UK.)

Over the past three decades there has been an avalanche of published papers reporting the discharge of lead from motor vehicles into the environmental corridor of busy motorways. Most of these studies have involved an assessment of the total lead content of soils and vegetation. In the late1980’s non-leaded petrol was introduced into the United Kingdom. By 1998 approximately 60% of motor vehicles were using non-leaded fuel. In 2000 only lead additive packages are available for addition to non-leaded fuel. Since 1986 four sampling sites around the London Orbital M25 motorway have been annually investigated for the lead content of motorway-side (distances of <5 and 50 m) air, dust, surface soil and washed/unwashed vegetation. The sites are located around the orbital motorway at positions of widely differing traffic densities, vehicle movement opportunities and motorway lanes (either 3 or 4). Throughout the period of study traffic density levels have steadily increased from 65,000 to >140,000 vehicles per day. The maximum lead levels measured were in late 1990 and corresponded to the <5m site: 6.7 mg/m³ air, 12750 mg/kg dust, 814 mg/kg surface soil and 1072 mg/kg dry weight unwashed flatweeds. The corresponding lead values at a distance of 50m were: 1.8, (no dust), 152 and 181, respectively. The highest levels occurred at the sampling site with the highest daily traffic density and poor traffic flow patterns. A steady decrease in lead levels has occurred at all four sites since 1991, especially for air and vegetation samples. This decrease has been slower for motorway-side surface soils and dust samples. Surprisingly, the latter media has retained a high lead burden probably as a result of the poor environmental dilution of the lead reservoir. These trends will be discussed in more detail along with a comprehensive review of all the data for the four sites covering the period 1986-99.