MONITORING OF BIO-ACCUMULATION & BIO-MAGNIFICATION

Bioaccumulation is the ability of a living organism to concentrate, accumulate, the magnify a chemical substance either directly from a surrounding medium or indirectly through food chain. Benthic macro-invertebrates which are living at sediment-water interface are directly exposed to sediment-bound metals and are capable of accumulating metals from interstitial water and from ingested sediments. Such organism is often refereed to as bio-accumulative indicator, which accumulates metals in a way so as to reflect environmental levels of those substances of the extent to which the organism has been exposed to them. Concentration levels of heavy metals accumulated in aquatic organisms can be of several orders of magnitude higher then those in ambient water. As a consequence of bioaccumulation, short-term external, exposure can result long-term internal exposure of aquatic organisms. Because of it, not only man is at risk, but plants and animals, occupying the higher tropic levels in aquatic ecosystem, are also in danger of being affected by bioaccumulations. This is demonstrated best by the benthic fauna of river Yamuna at two stations, namely Palla, a relatively clean stretch, and Palwal the eutrophic stretch of Yamuna. The heavy metal accumulation study was carried out for two-year samples, 1991-92. An average of concentrations was calculated for both the stations. This was compared with the average heavy metal concentration in water and sediments. The indicates that the levels of heavy metal concentration in water at both the stations. Palla and Palwal, in river water were exceeding the environmentally safe concentration as shown in Table 2.

On the other hand, the levels metals in the sediments of at both the stations are far below the safe concentration level except Nickel and Zinc. It is also clear from the results that although the sediments are not e\very toxic to the benthic animals, the bioavaibility for t\heavy metals to accumulate in the biota is more form the water phase than the sediments. The through 10 indicate a comparison of heavy metal bioaccumulation at the two stations which are located at Yamuna upstream and down stream of Delhi, i.e. Palla and Plawal respectively. The increased levels of bioaccumulation of Palwal is mainly due to the input of domestic and industrial wastewater joining the river Yamuna from Delhi and from Ghaziabad through the river Hindon.