Distribution of PCDD/Fs and PCBs in soils and pine needles in Ulsan, South Korea

Abstract

Polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCBs), known as persistent organic pollutants, are unintentionally released from anthropogenic sources (incomplete combustion and formulation of commercial products). There have been no domestic studies such as widespread distribution of target compounds in bioindicator (pine needle) and indicator (soil) to be carried out. In this study, the spatial distribution and the contamination characteristics of PCDD/Fs and PCBs in terms of their regional features were investigated. The soil and pine needle samples were collected at 30 sampling sites including suburban (S1−13), urban (U1−7), and industrial (I1−10) sites in Ulsan in December 2018. Soil and pine needle samples were extracted by Soxhlet extractor for 24 hours, and only pine needle samples were conducted with sulfuric acid treatment and filtered with bulk silica gel for removal of interfering substances. Then, soil and pine needle samples were cleaned up in multilayer silica gel columns. The target compounds were 17 PCDD/Fs and 18 PCBs (dioxin-like PCBs and indicator PCBs) analyzed by gas chromatography/high solution mass spectrometry (GC/HRMS). For interpreting the data, spatial distributions, compositions, and correlations of PCDD/Fs and PCBs in soils and pine needles were carried out. The mean concentrations of PCDD/Fs, dioxin-like PCBs (dl-PCBs), and indicator PCBs in soils were 77.73, 90.11, 452.98 pg/g dw, respectively, and the mean concentrations of these compounds in pine needles were 6.26, 31.36, 166.37 pg/g ww, respectively. In general, industrial sites showed higher concentrations of PCDD/Fs and PCBs in soil samples than those in urban and suburban sites, indicating that industrial processes were mainly influenced the compounds in the industrial areas. However, there was no significant difference in PCDD/F and PCB levels between three sites in pine needles due to the long-range transport and unstable deposition state based on the physicochemical properties of organic pollutants. The average composition of ∑7PCDDs in soils accounted for about 77% of the normalized concentrations, whereas ∑10PCDFs in pine needles were predominant about 82% of the normalized concentrations. Fractions of dl-PCBs and indicator PCBs in soils accounted for about 85%, 60% of penta- and hexa-CBs, respectively. In the case of pine needles, about 87% of tetra- and penta-CBs for dl-PCBs, about 80% of tri- to penta-CBs for indicator PCBs were accounted for the normalized concentrations, respectively. Based on the correlation results, PCDD/Fs and PCBs were positively correlated with each other. Total organic carbon content was significantly correlated with furans and heavy chlorinated PCBs, but lipid content had a negative or no correlation between any compounds.