Analysis of heavy metal accumulation in water and fish (Cyprinus carpio) meat from Umiam Lake in Meghalaya, India.

Abstract

Water quality around the world is notably declining mainly due to human activities. Low lying water catchment areas are under considerable threat of accumulating higher pollutants including heavy metals due to natural drainage and upstream anthropogenic activities. The major group that gets affected is the aquatic animals. Bioaccumulation of toxic metals in these organisms causes potential threat to human health upon consumption as these metals tend to get biomagnified in higher trophic levels within a food web. Umiam reservoir in Meghalaya is of significant importance to the state as it is the source of hydel power generation and is a popular destination for water sport and adventure facilities. Downstream irrigation, fisheries and drinking water from the lake cater to local anthropogenic needs. In recent times due to the rising population in the capital Shillong which is situated upstream of the lake, the lake is becoming significantly polluted. With this background the present study was aimed at determining the level of heavy metals in water samples of the Umiam lake as well as in the most dominantly occurring fish species, Cyprinus carpio found in the reservoir that is widely consumed. Presence of metal ions was determined using atomic absorption spectroscopy that uses different lamps specific to a metal ion in the sample. The sequence of metal concentrations (in ppm) in the water sample was found to be Se (1.39) > Mn (0.186) > Fe (0.12) > Pb (0.06) > Cd (0.045) > Zn (0.031) > Cu (0.023) > Cr (0.016) > Ni (not detected). Comparing these values with WHO guidelines it was found that the levels of Se and Pb in the waters of the lake are significantly higher than the recommended values [for Se (0.04) and Pb (0.01) respectively]. A similar assessment conducted on fish meat collected from the lake showed high accumulation of Se (1.58 ppm) in the fish muscle. The order of occurrence of other metal ions in the fish muscle was Se>Zn>Fe>Ni>Cu>Cd~Mn>Cr>Pb revealing that if concentration of metal ions such as Zn, Fe, Cu goes up in the water, these ions would get preferentially accumulated in the fish muscle. The higher concentration of Se in the water as well as in the fish meat confirms bioaccumulation of this element. Although selenium is an essential trace element required in the human diet for synthesis of selenocysteine, high concentration in the body may lead to chronic selenium toxicity that manifest as selenosis, a condition associated with changes to the hair and nails, skin lesions and clinical neurological effects. Therefore, consumption of fish meat from the lake over a prolonged period of time may lead to biomagnification of this metal in human increasing the risk of chronic selenium toxicity. This study is important in bringing about awareness to general population about potential dangers of being exposed to continuous heavy metal toxicity, specifically those using this water from the lake for drinking.