Study of metal concentrations in the environment near diesel transport routes

Abstract

In recent years, a river-dredging project has been executed in Nantou, Taiwan. A large number of diesel vehicles carrying gravel and sand shuttle back and forth on the main traffic roads (Tai-16 and Tai-21). The purpose of this study is to figure out the levels of metals contributed by those vehicles to the surrounding environment. Eight stations along the roadside of diesel transport routes were selected as exposure sites, while a small village located about 9 km away from the diesel transport routes was selected as the control site. The mass concentrations of coarse and fine particulate matter indicated that contributions from traffic fleets resulted in a higher percentage of coarse particulate matter in the ambient air at exposure sites in comparison with that at control site. Significantly higher values of EC (elemental carbon) concentrations and ratios of EC/OC (organic carbon) at exposure sites indicate that diesel vehicles at exposure sites contributed a greater amount of pollutants than gasoline vehicles. Exposure site concentrations for all metals measured (Fe, Al, Mn, Pb, Zn, Cu, Ni, Mo and As) for fine and coarse particulate matter were all higher than those at the control site. Recorded levels of metal contents in road dust and riverside soil near Tai-16 and Tai-21 showed that while the traffic fleet did not increase the metal contents of crustal elements in the road dust, it did significantly increase the metal contents of traffic-related elements. Enrichment factors (EFs) were calculated with respect to road dust (EF road) and with respect to the samples of riverside soil (EF river). Among these metals, Mo was the most highly-enriched metal. The extremely high EF river value (4300) of Mo indicates that these stations were highly polluted by diesel emission. Whereas the significantly high EF road value (810) of Mo implies that a considerable of Mo was emitted from tailpipe of diesel vehicles.