Risk assessment of residual DDTs in freshwater and marine fish cultivated around the Pearl river delta, China

Six species of freshwater fish collected from 10 fishponds in Shunde and Zhongshan, China, four species of marine fishes collected from different mariculture farms [four in Hong Kong (Tung Lung Chau, Ma Wan, Cheung Chau and Kat O) and two in mainland China (Daya Bay and Shenzhen)] together with feed (both trash fish and commercial pellets) and sediment were analyzed for DDTs. Total DDTs in freshwater fish flesh decreased in the order of: carnivores [1742 μg/kg lipid weight (l.w.)][herbivores (165 μg/kg, l.w.)[omnivores (42.5 μg/kg, l.w.), with the highest concentration detected in mandarin fish (Siniperca chuatsi) (2641 μg/kg, l.w.). For marine fish, snubnose pompano (Trachinotus blochii) and orangespotted grouper (Epinephelus coioides) collected in Ma Wan contained elevated levels of total DDTs (2590 and 2034 μg/kg l.w., respectively). Trash fish used in both freshwater and marine fish farms contained significantly higher levels (86.5-641 μg/kg l.w.) (p<0.05) of DDTs than in commercial pellets, but correlations between DDT levels in fish feed and muscle were not significant. The elevated biota-sediment accumulating factor for tilapia (Tilapia mossambicus) (24.1) indicated that accumulation of DDTs from sediment to the fish was evident. It can be concluded that trash fish should not be used for fish culture in order to lower the level of residual DDTs in fish muscle.