Mercury concentration in the muscle of seven fish species from Chagan Lake, Northeast China
Chagan Lake is located downstream of the Second Songhua River basin in Northeast China. It is one of the top ten inland freshwater lakes, and an important aquatic farm in China. The lake has been receiving large amounts (currently at 1.5 × 108 m3/a) of water from the river since 1984. This would pose a threat to the aquatic system of the lake because the river was seriously polluted with mercury in 1970s–1980s. The current study is the first to report the total mercury concentrations in fish found in the lake. Mercury concentrations in seven fish species collected from the lake in January 2009 were determined. The related human health risk from fish consumption was also assessed. The average concentration of mercury in the fish was 18.8 μg/kg of wet weight, ranging from 4.5 to 37.6 μg/kg of wet weight. A large difference in the mercury concentrations among the fish species was found. The mercury concentration was found to be higher in carnivorous species and lower in omnivorous and herbivorous species. This demonstrates greater mercury bioaccumulation in fish species at higher trophic levels. Mercury concentrations in fish showed significant positive correlations with age, length, and weight. No significant relationship was found between mercury concentrations in fish and the habitat preferences. Mercury concentrations in fish from the lake were within the limits of the international and national standards of China established for mercury. According to the reference doses established by the United States Environmental Protection Agency, the maximum safe consuming quantity considering all the fish was 297.3 g/day/person, which was more than five times as much as the current quantity (50 g/day/person) consumed by the local residents. This investigation indicates that the historical pollution of the Second Songhua River has not caused mercury bioaccumulation in fish muscle tissue of Chagan Lake. The present consumption of fish from the lake in the local area does not pose a threat to human health.
Synopsis of freshwater fishes of China
Water albedo of fish pond has close relation with its physico-chemical features. As compared with most other free actual surfaces. w,ter surface in thisregion is characterized by lower reflection ratio and higher absorption. Except the features of reflection ratio on general water surfaces, the reflection ra ratio on fish ponds has good negative ralation with productivity of phytoplankton in the fish ponds this reason, utilization ratio of light energy has positive relaiton with primary productivity in fish ponds.
Potential of Lemna polyrrhiza for removal of heavy metals
Lemna polyrrhiza (Spirodela polyrhiza) (duckweed) exposed to 10 mg l−1 of Zn, Pb and Ni for four days accumulated 27.0, 10.0 and 5.5 μg mg−1 of Zn, Pb and Ni, respectively. Zinc accumulation in Lemna was greater than in any other organism thus far studied. Metal uptake occurred rapidly for 12 h, and then plateaued. Rootless test plants exhibited lower uptake of Zn and Ni. Darkness inhibited metal uptake. Metals reduced chlorophyll in the following order: Zn>Pb>Ni. Substantial losses of Ca, Mg and K occurred from test plants exposed to metals; Zn was the most effective. Greater toxicity of Zn to Lemna appears to be related to the high amount of accumulated Zn.