Heavy metal deposition and soil pollution along two major rural highways.

Road traffic and maintenance induce a chronic heavy metal pollution in runoff water and roadside soil. A portion of these pollutants could be dispersed into the atmosphere or deposited onto soils as a result of wind dispersion. The atmospheric deposition and quality of roadside soil have been investigated alongside two major rural highways. Metal deposition decreases rapidly and seems to reach the background level at a distance of less than 25 m. The deposition of zinc was found to be the most significant, followed by Pb and Cu. The fluxes of metals dispersed by atmospheric deposition have been evaluated and compared to pollutant loadings in runoff water. Pollutant concentrations in soils decrease rapidly with distance from the roadway. The pollution is concentrated within a 5-m band and the lead content exceeds the limit value for contaminated soil at a distance of 0.50 m from the road at the older site; moreover, galvanised crash barriers constitute an additional source of zinc pollution. The EDTA extractions of metals show the high bioavailability of lead in polluted soils.