Environmental Background Values of Heavy Metals and Spatial Ecological Risk Assessment in Roadside Soils Influenced by Urban Traffic

Using background values from different geological areas can lead to misinterpretation of ecological risk levels; therefore, selecting appropriate environmental background values is critical. We compared results from various sources and utilized empirical soil background values from parent materials. This study focused on soil properties and the presence of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) along the two highest traffic density highways in Thailand. The findings showed that out of 40 collected roadside soil surface samples, organic matter was significantly related to all heavy metals, except As. Fine-textured soils were the controlling factor for Fe, As, Cu, and Zn concentrations. Positive correlations among the concentrations of Cd, Cr, Cu, Pb, and Zn suggested these metals likely share common origins, primarily from traffic-related sources. Evaluation of the geoaccumulation index (I_geo), the enrichment factor (EF), and the contamination factor (CF) highlights Zn as particularly influenced by human activities. The potential ecological risk index (PERI) revealed low to moderate risks along both highways, while the pollution load index (PLI) indicated varying pollution levels between the two highways. Variations in heavy metal concentrations and ecological risks between the two highways stemed from traffic-related factors and differing environmental conditions. Implementing effective traffic management plans and zoning regulations is crucial for preserving soil resources and safeguarding environmental health. This study suggested that for areas with similar soil formation backgrounds, our background values can serve as proxies for ecological risk evaluation in other studies.