Pollutants in Hong Kong Soils: Organochlorine Pesticides and Polychlorinated Biphenyls

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were investigated in 138 soil samples collected in Hong Kong. Results showed that within the selected OCPs, only DDT and its metabolites (DDD and DDE) were frequently detected. Of 138 soil samples, 18% were non-detected for any DDT residues, while 25% were contaminated sporadically with DDT only (non-detected to 1090 μg kg-1) and 57% contained various combinations of DDT, DDD and DDE (2.03 to 1118 μg kg-1). In contrast, total PCBs (∑66 congeners) contamination was distributed more evenly (0.22 to 154 μg kg-1) than DDTs, but serious contamination was found in industrial areas and soils collected near highways. Concentrations of 7 indicator PCBs ranged between non-detected to 34.5 μg kg-1. The ratios of DDT/metabolites were typically greater than 1, thus suggesting recent application of DDT. Medium-range deposition from industrial areas within as well as away from the city is also suspected to be the origins of DDTs and PCBs found in Hong Kong soils. The concentrations of DDTs and PCBs in all soil samples did not exceed the recommended values in soil quality guidelines except 3 samples for DDT from locations far away from densely populated districts such as Tuen Mun and Tin Shui Wai. Therefore, DDTs and PCBs were not of significant concern in terms of their impacts on public health and environment.