Abstract
The concentrations of polychlorinated dibenzo-p-dioxin (PCDDs) and polychlorinated dibenzofuran (PCDFs) in soil samples were measured for assessment of their contribution to environmental pollution. Subsequently, the relationship between their concentrations and the depth of soil sample, a comparison of the ratio of these concentrations with those in the air and their correlation with the ignition loss of soil samples were investigated. PCDDs and PCDFs in air dried soil samples were determined as follows. The soil samples were dried naturally in a room. The dried samples were extracted with methanol/benzene (1: 4, v/v) by Sohxlet extraction. After the addition of13C-PCDD and13C-PCDF as markers, the extracts were washed with potassium hydroxide solution, treated with sulfuric acid and cleaned by elution through a silver nitrate silica column, followed through a charcoal silica column. An aliquot of 1μl cleaned sample was analyzed by gas chromatography/high resolution mass spectrometry (GC/HRMS) . The summary of the results is shown below. PCDDs and PCDFs were detected in all soil samples. The concentrations ranged from 0.88 to 22 for total-PCDDs and 0.01 to 2.5 (ng/g, dry base) for total-PCDFs, respectively. In the PCDDs congeners, the highest level was found for the octachlorinated dibenzo-p-dioxin (71%) . The concentrations of PCDFs were less than those of PCDDs. The ratio of the concentration of each congener to total-PCDFs was in the range of 13-35%. The concentration of each congener of PCDDs and PCDFs in air decreased gradually with increase of number of chlorine substitution in both compounds. The concentrations of PCDDs and PCDFs were highest in surficial soil samples and decreased with the depth of soil. There was a relationship between concentrations of PCDDs and PCDFs, and the ignition loss of soil samples.
