Chlorinated pesticides and PCBs in sediments and molluscs from freshwater canals in the Hanoi region

The concentrations of organochlorine pesticides and PCBs were determined in surface sediments and freshwater molluscs (Angulyagra a sp.) from water ca nals in the region of Hanoi city. Results obtained show that the concentrat ion of Sigma DDT compounds in sediments range from 7 to 80 ng/g (dry weight ) and from 6 to 864 ng/g (dry weight) in the soft tissues of molluscs. The concentrations of Sigma DDTs were higher in populated sites and much lower in rural sites, indicating that the DDT has been used for mosquito control and not as a crop protection chemical. Hexachlocyclohexanes (HCHs) have als o been widely used in the region but the current environmental concentratio ns are much lower than those of DDT's, which is due to the less persistence of those compounds. Polychlorinated biphenyls (PCBs) were measured, for ex ample as aroclor 1254, in concentrations up to 40 ng/g (dry weight) and up to 76 ng/g (dry weight) in sediments and molluscs, respectively. Molluscs f rom water canals are a very popular food in the region. Taking into conside ration the high DDT levels measured in these molluscs their consumption is worrisome and may expose the population to high levels of endocrine disrupt ing substances. Current PCB levels in sediments are lower than usually meas ured in industrialized countries. Therefore, PCB concentrations in aquatic molluscs are still also relatively low. These snails do not have enzyme abi lity to metabolize most of the CB congeners and, thus, are passive accumula tors and a significant transfer pathway of CBs to consumers. Therefore, mea sures to phase out the use of these persistent and bioaccumulable chemicals should be adopted in order to prevent further environmental contamination. (C) 2001 Elsevier Science Ltd. All rights reserved.