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The occurrence, temporal trend, sources and toxicity of PCBs and organochlorine pesticides were investigated in sediment samples from the sewer system of Hanoi City, including the rivers Nhue, To Lich, Lu, Set, Kim Nguu and the Yen So Lake. In general, the concentrations of the pollutants followed the order DDTs>PCBs>HCHs (beta-HCH)>HCB. However, the pollution pattern was different for the DDTs and PCBs when the sampling locations were individually evaluated. The concentrations of the DDTs, PCBs, HCHs, and HCB ranged from 4.4 to 1100, 1.3 to 384, <0.2 to 36 and <0.2 to 22 ng/g d.w., respectively. These levels are higher than at any other location in Vietnam. Compared to measurements from 1997, the DDTs, PCBs, beta-HCH and HCB levels show an increasing trend with DDT/DDE ratios, indicating very recent inputs into the environment although these persistent compounds are banned in Vietnam since 1995.

Organochlorine pesticide and polychlorinated biphenyl residues were determined in soils and surface sediments collected from Hanoi City, Viettri City and Halong Bay, which are representative of industrial and agricultural areas in northern Vietnam. Polychlorinated biphenyls (PCBs) and organochlorine insecticides such as DDT and its metabolites (DDTs) and lindane were detected in all samples analyzed, indicating the widespread contamination by these compounds in the environment of the north of Vietnam. Concentrations of DDTs and lindane were found to be highest in sediments from Halong Bay, followed by those in Viettri and Hanoi. PCB residues ranged from 0.64 ng g–1 120 ng g–1 (dry weight basis) in sediments and these levels were generally higher than those in soil samples. In general, higher concentrations of pesticides and PCBs were recorded in Halong Bay, suggesting the local sources in this area, probably from mining activities. High accumulation of DDTs in soils, sediments and biotafrom north to south Vietnam indicates that the recent input of DDT is still occurring throughout the country.

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