Lead Extraction Methods in Roadside Soils and Its Relationship with Soil Properties

Lead (Pb) is an environmental pollutant, and its concentration in the soil environment has received greater attention. Studies on the interrelation of Pb and major soil properties using different extraction methods have been poorly documented. The lead extraction method is important to be identified, which may accurately reflect Pb extractability from soils. Therefore, a study was conducted to investigate the Pb pollution of roadside soils. Four extractants: ammonium acetate (NH₄OAc), hydrochloric acid (HCl), diethylenetriaminepentaacetic acid (DTPA), and sodium hydroxide (NaOH). Soil samples were sieved for three particle sizes: finer to coarser particles (0.5 to 2 mm). Results showed that there were substantial differences for Pb concentrations among sampling sites depending on the extracting reagents: HCl > DTPA > NH₄OAc > NaOH. The extractability of Pb from soil was apparently enhanced with the increasing strength of a reagent used for the soil solution. The NH₄OAc extractable Pb concentrations in the surface soil samples from the Abbottabad area ranged from 67.9 to 246.7 mg kg⁻¹, and in Haripur, the Pb concentrations ranged from 97.6 to 242.5 mg kg⁻¹. At 20% HCl solution, the average Pb concentrations were 2.6 times higher than the NH₄OAc solution in the topsoil of Abbottabad area. The roadside soils contained Pb concentrations higher than the permissible limits. The control soil samples (from a distance of 200 m) exhibited Pb concentrations in the relative range of 28.5 to 61.7 mg kg⁻¹. Pb concentrations in the topsoil and subsoil were found to be apparently inconsistent. The concentration of Pb was higher in the soil containing a higher amount of organic matter and clay content. The soil pH and particle size were inversely related to extractable Pb in the soil. Higher Pb pollution in the soil could be associated with the higher traffic density.