Sediment pollution and its effect on fish through food chain in the Yangtze River

Suspended sediment adsorbs pollutants from flowing water in rivers and deposits onto the bed.However,the pollutants accumulated in the river bed sediment may affect the bio-community through food chain for a long period of time.To study the problem the concentration of heavy metals(Cr,Cd,Hg,Cu,Fe,Zn,Pb and As) in water,sediment,and fish/invertebrate were investigated in the middle and lower reaches of the Yangtze River during 2006-2007.The concentrations of heavy metals were 100-10,000 times higher in the sediment than in the water.Benthic invertebrates had relatively high concentrations of heavy metals in their tissues due to their proximity to contaminated sediments.Benthic invertivore fish had moderately high concentrations of heavy metals whereas phytoplanktivore fish,such as the silver carp,accumulated the lowest concentration of heavy metals.The concentrations of Cu,Zn,and Fe were higher than Hg,Pb,Cd,Cr,and As in the tissue samples.The concentration of heavy metals was lower in the river sediments than in the lake sediments.Conversely,the concentration of heavy metals was higher in river water than in lake water.While a pollution event into a water body is often transitory,the effects of the pollutants may be long-lived due to their tendency to be absorbed in the sediments and then released into the food chain.The heavy metals were concentrated in the following order:bottom material > demersal fish and benthic fauna > middle-lower layer fish > upper-middle layer fish > water.