Urban soil contamination in Bangkok: concentrations and patterns of polychlorinated biphenyls (PCBs) in topsoils

Abstract

Little is known about the polychlorinated biphenyl (PCB) pollution of tropical environments, although part of the contribution to global PCB contamination originates in the tropics. The objective of this study was to compare PCB concentrations and patterns in urban soils of Bangkok with data from the temperate zone to detect indications for possible differences in sources and fate of PCBs.

The sum of congeners 1, 8, 20, 28, 52, 101, 118, 138, 153, 180, 206, and 209 (=Σ12PCBs) ranged from 0·19 to 11·4 µg/kg, which was lower than values reported for urban soils in the temperate zone. On average, the hexa-chlorinated PCBs 138 (mean of Σ12 PCBs± s.d., 22·7 ± 8·1%) and 153 (19·9 ± 9·0%) were most abundant. The Bangkok soils contained higher percentages of lower chlorinated PCBs (≤ 4 Cl) and correspondingly lower percentages of higher chlorinated PCBs (>4 Cl) than soils in 3 temperate cities. The differences may be explained by different sources, a lower age of contamination and therefore lower volatilisation, or anaerobic dechlorination during water-stagnant periods.

The comparison of the PCB profiles in Bangkok soils with those of widely used commercial PCB mixtures indicated that the major PCB sources of Bangkok soils were the highly chlorinated Clophen A60, Aroclor 1260, or similar mixtures dominated by hexa-chlorinated PCBs.