LEVELS, CHEMICAL FRACTIONATION, AND SOLUBILITY OF LEAD IN ROADSIDE SOILS OF CARACAS, VENEZUELA

Abstract

The author investigated the level, chemical fractions, and solubility of Pb in several roadside soils of heavily traveled areas of Caracas, Venezuela. Using 1 N HNO/sub 3/ extraction, he studied the levels of lead in 25 roadside soil samples and found a very high level of Pb (average enrichment factor 21.0), indicating a strong lead pollution of Caracas roadside soils by heavy traffic of motor vehicles. Lead accumulation was most localized in the top soil layer (0 to 5 cm) and in soils located within 1 m from the roadside. Chemical fractionation and solubility experiments on three surface soil samples containing high Pb levels showed that less than 0.7% Pb was in exchangeable form in these soils. The nonexchangeable Pb was found to be associated mainly with the organic and residual fractions in two of the three soils, and predominantly bound specifically to inorganic sites in the third soil. The amount occluded in iron oxides was low in the three studied soils. Solubility studies showed Pb to be less soluble at higher pH values and pointed to a direct relationship between total and exchangeable Pb content and solubility. In the soils studied Pb seems to be associated with several soilmore » components by different sorption mechanisms acting concurrently, the predominant mechanism or mechanisms being stronger than normal ion exchange. This behavior was considered to have practical implications, such as low Pb mobility in the soil profile, as well as low availability to plant roots and soil biota.« less