The Relationship Between Traffic Parameters and Lead and Cadmium Concentrations in Urban Roadside Soil

Lead and cadmium are heavy metal pollutants released by vehicles which are propagated into the urban environment by traffic flow. To study roadside soil pollution and to determine the traffic parameters affecting levels of lead and cadmium in soil, Isfahan was selected for a case study. In this city, soil samples were collected from 13 roadside sites and traffic parameters were determined. The traffic parameters studied include total traffic volume, daily traffic volume, total traffic volume to road oriented width, total traffic volume to total traffic capacity, speed, and aspect ratio. Average lead and cadmium concentrations in soil at distances from 0 to 50 meters from the road edge were found to be higher than background values, thus failing to meet maximum acceptable agricultural soil standards. The regression analysis of concentrations in stream soils versus selected traffic parameters showed that the total traffic volume was the parameter with the highest impact on soil metal content. Also, it was observed that lead and cadmium concentrations (as dependent variables) decreased logarithmically with increasing distance (as one of the independent variables) while each of the lead and cadmium concentrations increased linearly and exponentially, respectively, with increasing total traffic volume (as another independent variable). The regression models developed in this study can be used for predicting lead and cadmium levels in roadside soil in terms of distance from road edge and total traffic volume. The results obtained from this study may be used in urban traffic control, transportation management, urban design and architecture, and urban land use planning.