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.