Chemical Speciation and Potential Mobility of Heavy Metals in Forest Soil Near Road Traffic in Hafir, Algeria

Background. Different fractions of metals, of varying origin and reactivity, are present in sediments of forest soil. Forest ecosystems are privileged sites for the deposition of persistent organic pollutants carried by the atmosphere. Objectives. The present study describes the current state of metallic contamination around the Hafir forest, located southwest of Tlemcen, Algeria, based on analysis of total sediment mineralization and the speciation of each metal to examine the effects of emissions due to road traffic. Methods. The distribution and migration of ten heavy metals were studied, including cadmium (Cd), nickel (Ni), cobalt (Co), chromium (Cr), manganese (Mn), lead (Pb), copper (Cu), zinc (Zn), iron (Fe), and silver (Ag), and four major elements: potassium (K), sodium (Na), magnesium (Mg), and calcium (Ca) in the superficial horizon of forest soil (0-20 cm) at different road distances (0-1700 m), in two sampling campaigns in the dry and wet seasons around the Hafir forest, Algeria. Results. Bioavailability appears to be relatively low due to the small amount of metals present in the carbonate fraction and the alkaline pH. The impact of road traffic was observed in the variability of the concentrations of several trace elements in forest soil, such as Co, Mn, Ni, Zn, Pb, Ag, Cd. They were generally observed at very high levels along the roadside due to dry atmospheric deposition. Conclusions. The high levels of metals in the carbonate, reducible and residual phases indicate a direct influence on the environment stemming from road traffic near the forest as well as contamination from rainfall in the area.