Abstract: Samples of oysters (Crassostrea rivularis) were collected from 23 observation sites along the coast of the northern South China Sea every year during 2008 - 2010. Contents of organochlorine pesticides in their tissues were analyzed with gas chromatography, and effects of the residues on edible safety of the oysters explored. Contents (μg·kg^-1, mean of wet weight) of the residues in the oysters were found to be in a decreasing order of DDTs (4.68 with a range of 1.53 - 9.77) > endosulfan (2.58, nd - 17.6) > chlordan (1.12, nd - 11.2) > dicofol (0.514, nd -4.42) > methoxychlor (0.300, nd - 2.26) > endrin (0.229, nd - 4.82) > heptachlor epoxide (0.182, nd - 1.65) > endrin aldehyde (0.159, nd - 1.16) >aldrin (0.138, nd - 1.72) > BHCs (0.130, nd - 0.727) > dieldrin (0.095, nd - 0.237) > heptachlor (0.056, nd - 0.531). However, they all were significantly lower than the residual limits stipulated by Australia, Russia, the European Union (EU), Canada, Japan and China for their aquatic products, livestock and poultry meats, except for endosulfan and endrin aldehyde. Even though the concentration of endosulfan was still below the limits set by Australia and Canada, however, in a few oyster samples, the concentration of endosulfan was a bit higher than the EU limit, and close to or beyond Japan's limit. The intake of α - BHC, β - BHC, γ - BHC, pp' - DDE, aldrin, dieldrin, endrin, endosulfan, chlordan, heptachlor and heptachlor epoxide with oysters was obviously much lower than the dosages harmful to human health. So their carcinogenic risks are acceptable.

Key words: northern South China Sea, edible oyster, organochlorine pesticide, security analysis