THE INFLUENCE OF SOIL TEXTURE AND ORGANIC CONTENT ON THE MOBILITY OF LEAD (II) IN EXPERIMENTALLY AGED SOILS

Lead contamination of soils is a persistent health issue due to its connection with high amounts of child lead poisoning, particularly in urban areas. The study of the fate and transport of Pb(II) in soils is necessary in order to ascertain the remediation methods necessary for an area and more importantly how safe a contaminated area is. Accelerated aging of soil is a technique used in order to obtain data that is comparable to that of data obtained from field experiments. There is, however, a lack of standardization of this technique. In this study we present a method that can be used in laboratory settings to simulate field conditions in order to assess long-term environmental impacts of contaminations in soil systems. In order to test the validity of this method we tested two soil samples, a clayey and sandy soil, with varying amounts of organic matter experimentally added (0%-80% of the total weight) and artificially contaminated with Pb(II) (1000 ppm). The samples were exposed to alternating high (100 ˚C) and low (-13 ˚C) temperatures every 2.5 days in order to see the effect of accelerated aging on the metal fractionation and mobility of Pb(II) in the soil samples. The metal fractionation after the accelerated aging process showed a decrease in the concentration of exchangeable Pb in the sandy and clayey soil samples as the percent of total weight of organic matter was increased. In the clayey soil with 0% organic matter, an average 12 μg/L exchangeable Pb was present in aqueous extractions, which dropped down to 3 μg/L exchangeable Pb in the clayey soil with 80% organic matter. The sandy soil with 0% organic matter had an average of 32 μg/L exchangeable Pb, which dropped down to 3.5 μg/L with 80% organic matter. The effect of adding organic matter was similar in both clayey and sandy soils, lowering extracted Pb to 3-4 μg/L in both soils. Without organic matter, however, the clayey soil more effectively retained Pb (II). These results correspond to what was expected out of these experiments based on previous studies. This method of artificial aging is therefore useful in the expedited simulation of field conditions for the understanding of long-term persistence of Pb(II) in the soil environment. An understanding of the fate and transport of Pb(II) in the soil environment is essential in order to assess contaminated areas to avoid outbreaks of lead poisoning in the future.