Abstract: During 2008-2012, Ostrea oysters (Crassostrea rivularis) were collected in coastal waters  of South China as bio-indicator of chlordane pollution of waters off the coast. Chlordane is a kind of pesticide commonly used in recent years. Contents of chlordane in soft tissues of oyster were determined using the technology of quartz capillary column - gas chromatography - microelectron capture detector. Results show that chlordane was detected in 17 samples out of a total of 115, collected from all the 23 stations, . The contents of chlordane were ranging from 2.1 to 9.3 μg·kg^-1 (wet weight), obviously lower than the residual limit for food safety in Canada and China, and much lower than that in European Union, Australia and Japan. The average chlordane content of the samples was 0.69 μg·kg^-1 w. w. in this study, relatively lower than that of the other bivalves in the waters off the Asian-Pacific coasts. Chlordane content in the oyster samples varied sharply with the location they were collected from, displaying an order of West Guangdong (1.17) > East Guangdong (0.77) > Hainan (0.63) > the Pearl River Estuary (0.41) > Guangxi (not detected). The annual mean was obviously high in 2008 reaching 1.61 μg·kg^-1 w. w and gradually declined down to 0.26 μg·kg^-1 w. w. in 2012, . The spatio-temporal variation of chlordane contents in oysters indicates that the sources of the chlordane in the habitats of the oysters are not completely fixed and not stable in intensity either. In the oyster samples, the ratio of trans-chlordane to cis-chlordane in content in the oysters was in the range from 0 to 1.58 with a mean of 0.58, which differs from that in industrial chlordane(the ratio was 1.26), indicating that the chlordane in oysters had already undergone isomer conversion or bio-degradation.

Key words: coast of South China, oysters, chlordane, spatio-temporal variation