BIOCONCENTRATION OF ZINC, LEAD AND CHROMIUM IN SERIALLY-CONNECTED SEWAGE-FED FISH PONDS

The distribution of Zn, Pb and Cr in serially-connected sewage-fed fish ponds was studied. The domestic sewage was passed gravitationally through three stabilization ponds and six fish ponds connected in series. The concentrations of the metals in sewage phytoplankton, zooplankton, fish and sediment from the fish ponds were determined. In all ponds the concentration of Zn was higher in all the trophic levels than Pb and Cr. The concentration of Pb and Cr decreased with increasing trophic level. The concentration of Zn increased with increasing trophic level from phytoplankton to zooplankton, but not to fish. The concentration of heavy metals was many fold higher in surface sediment than that in overlying water. The concentration of Cr in all the fish species was below the detectable limit (< 0.001 mu g/g). The heavy metal accumulation in the fish species was in the order of omnivorous feeder > phytoplankton feeder > zooplankton feeder > carnivorous feeder > macrophyte feeder. The concentration of metals in all fish species in all ponds was within the permissible limits.