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

Little is known about the polychlorinated biphenyl (PCB) pollution of tropi cal environments, although part of the contribution to global PCB contamina tion originates in the tropics. The objective of this study was to compare PCB concentrations and patterns in urban soils of Bangkok with data from th e 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 20 9 (=Sigma 12PCBs) ranged from 0.19 to 11.4 mu g/kg, which was lower than va lues reported for urban soils in the temperate zone. On average, the hexa-c hlorinated PCBs 138 (mean of Sigma 12 PCBs+/-s.d., 22.7+/-8.1%) and 153 (19 .9+/-9.0%) were most abundant. The Bangkok soils contained higher percentag es of lower chlorinated PCBs ( less than or equal to 4 Cl) and correspondin gly lower percentages of higher chlorinated PCBs (>4 Cl) than soils in 3 te mperate cities. The differences may be explained by different sources, a lo wer age of contamination and therefore lower volatilisation, or anaerobic d echlorination during water-stagnant periods. The comparison of the PCB profiles in Bangkok soils with those of widely us ed commercial PCB mixtures indicated that the major PCB sources of Bangkok soils were the highly chlorinated Clophen A60, Aroclor 1260, or similar mix tures dominated by hexa-chlorinated PCBs.