“Soil Pollution Hazardous to Environment”: A case study on the chemical composition and correlation to automobile traffic of the roadside soil of Jeddah city, Saudi Arabia

Abstract

Soil samples from different roads in Jeddah city were collected and analyzed for their elemental composition. The effects of traffic conditions were critically investigated to reflect the effect of the heavy and light traffic on the soil composition. Samples were analyzed for K, As, Co, Cr, Ni, Pb, Sb, V, and Zn. The results revealed great dependence of lead and zinc contents on traffic conditions. The lead content lies in the range 0.3–104.8 ± 0.003 mg/kg for the samples of high traffic conditions and 0.3 ± 0.0 mg/kg being for the sample with no traffic activity, whereas 104.8 ± 0.003 mg/kg was for the one of the most used highways area in Jeddah city. Zinc level lies in the range 56.59 ± 0.003–456.93 ± 0.06 mg/kg which is quite close to lead pattern. The high zinc concentration was found along the main turn roads. The high zinc content in tested soil samples may come from traffic sources, especially vehicle tires. Concentrations of other elements showed little dependence on traffic conditions.

Introduction

Traces of heavy metal ions are ubiquitous in modern industrialized environment [1]. Countries usually regulate and set up limits on levels of trace metals in the environment that should not be exceeded [2]. Thus, metal pollution in urban environment represents an important issue and has attracted large number of researchers during past decades [3], [4], [5], [6], [7]. The introduction of pollutants from human activity in many parts of the world has seriously degraded our environment [4]. Sources of soil pollution may be domestic, agricultural or industrial. An industrial waste is often conducted without regard to the deterious environmental impact upon the receiving soil body [2], [3], [4], [5], [6], [7], [8]. Heavy metals are introduced into soil through, dumping wastes, effluents leading to heavy metal runoff of terrestrial system (industrial and domestic effluents) and geological weathering [8], [9]. Due to processes of remobilization, these metals released and moved into the soil and concentrate in food chain, thereby reaching humans and causing chronic or acute diseases [9]. Heavy metals occur in minute concentrations in natural soil and bottom sediments exerting a beneficial or harmful effect on plant, animal and human life.

Recent years have seen an upsurge of interest on monitoring trace metal pollution in soil caused by traffic road dust, agricultural soil near motorways and source identification [2], [3], [4], [5], [6], [7]. Other investigations include migration and transformation of metals [10], [11] bio accessibility of metals as an important field of study. This class of investigation represents an important way of monitoring of trace or ultra trace toxic metal ions to assess their effects on the level of pollution to human health [12]. Paved road dust contributes significantly to airborne metal content of the atmosphere. Other major sources for particulates in air include vehicular exhaust, building activities, sea salt, and biomass burning [13]. Fine particles in air have shown a great dependence on wind speed and direction [14], [15], [16].

Along with industrial activities, automobiles are one of the major pollutants of soil, their consumption of gas, various oils, and ware and tare; all contribute to soil contamination. Traffic-related elements such as platinum group elements (PGEs), zinc and copper have shown sharp decrease in concentration with increasing distance from the traffic lane [17]. Before the abandonment of leaded gasoline in Saudi Arabia in 2001, gasoline was the major source of lead pollution in the county. Although leaded gasoline is no longer used in automobiles, soil acts as a reservoir for lead pollution in the soil through the years [18]. The presence of lead in dust is strongly correlated to soil lead concentration [19]. Furthermore, once pollution-derived lead is airborne, it could be transported to the environment causing further dispersion of the pollution into uncontaminated territories [20]. Hence, monitoring of trace metal ions in soils close to urban areas represents an important task in our environment. Therefore, the present manuscript reports levels of lead and other elements linked to vehicular sources e.g. As, Ni and Cr on the roadside soil of Jeddah city, Saudi Arabia. Zinc level is also determined since it represents a product of tire tare on roads [21]. Such investigation on the roadside soil was also aimed to achieve a deeper understanding of the mechanism of soil pollution and will also reveal other metal pollutants and sources of their occurrence.