Mercury accumulation in freshwater fish with emphasis on the dietary influence

The first part of the study investigated mercury (Hg) concentrations in freshwater fish collected from the Pearl River Delta and Hong Kong. Mercury concentrations observed in freshwater fish and fish pond sediments collected from the Pearl River Delta were 17.5–267 ng/g (dry wt) and 96 ng/g (dry wt)–1.67 μg/g (dry wt), respectively. As to samples collected from Hong Kong, Hg concentrations were 15.8–84.4 ng/g (dry wt) in fish flesh and 57–435 ng/g (dry wt) in sediments. Accumulation of Hg in fish was related to the spatial difference of Hg in sediment. Significant linear relationships were obtained for the concentrations of Hg in grass carp (r2=0.51, n=12), big head (r2=0.97, n=12) and tilapia (r2=0.55, n=24). The second part of the study investigated the dietary influence on the uptake of Hg by different fish species cultured in the wastewater treatment system at Au Tau Fisheries Station in Hong Kong. The effect of feeding habits of the six fish species in Hg accumulation was apparent. The highest levels of Hg were observed in black bass with the value of 56.7 ng/g (dry wt), moderately in big head (33.8 ng/g dry wt), grass carp (26.3 ng/g dry wt) and silver carp (20.8 ng/g dry wt), and the least in common carp (18.9 ng/g dry wt) and tilapia (13.7 ng/g dry wt).