CONTENTS-
Abstract
Introduction
Material and Methods
Results and Discussion
Conclusion
Acknowledgement
References

The present paper deals with the accumulation of heavy metals (Cu, Zn, Cd, Fe and Ni) in different organs (gills, muscles and intestine) of the fish species ( Sarotherodon mossambica , Cyprinus carpio and Catla catla ) of Singanallur lake determined by Atomic Absorption Spectrophotometry.   The study was carried out over a period of 12 months (Jan 2000 to Dec 2000).   The trend in accumulation of heavy metals indicated that irrespective of species, zinc showed higher concentration as compared to other metals.   Higher concentration of heavy metals was recorded in intestine as compared to other parts of the body i.e. gills and muscles.

Heavy metals are known toxicants, which inflict acute disorders in aquatic organisms.   Uptake of heavy metals through food chain in aquatic organisms may cause various physiological disorders like hypertension, sporadic fever, renal damage, cramps, etc.    Presence of heavy metals in the aquatic ecosystem and its impact on flora and fauna has   been reported by many investigators (Hemelraad   et al., 1987; Radhakrishnaiah, 1988; Kargin and Cogun, 1999; Ay et al., 1999; Shrinivas et al., 1999; Zyadah and Abdel-Baky, 2000; Misra et al., 2002).   The tendency of metals to get accumulated in organisms is one of the important properties of metals and bioavailability of trace metals is the key factor determining tissue concentrations.   The bioaccumulation of metals depends on availability and persistence of the contaminants in water, food and physico-chemical properties of the toxicants.   Bioaccumulation patterns of metals in fish tissue can be utilised as effective indicator of environmental metal contamination (Larsson et al., 1985, Sultana and Rao, 1998).   Heavy metals, being non-biodegradable primarily necessitate   the knowledge on their uptake, distribution and persistence in tissues of various organisms.

The fishes form an important target for biomagnification of metals as they are at the top of the food pyramid and act as a possible transfer media to human beings.   Hence, the fishes ( Sarotherodon mossambica, Cyprinus carpio and Catla catla ) of Singanallur lake were   assessed for the accumulation of heavy metals, which are being regularly used by the local people.   Although there has been no record of any adverse effect of this fishes on human health, even then to ensure that the fishes of this lake is safe for human consumption, the heavy metal concentrations in the different parts of the fishes were evaluated in the present investigation.

2.1   Collection, storage and digestion of fish samples

Fish samples were collected from Singanallur lake.   Three species of fishes namely Catla catla, Cyprinus carpio , and Sarotherodon mossambica were selected for the study.   The fish species were placed in ice and packed in plastic bags.   Immediately on bringing them to the laboratory, the fishes were dissected for their different organs like gills, intestine and muscle which were then digested in Kjeldahl flasks using 8 ml concentrated sulphuric acid and 2 ml concentrated perchloric acid.   The distillate was made to 50 ml with double distilled water and metal analysis was carried out using Atomic Absorption Spectrophotometry (Perkin - Elmer model 3300).

Monthly metal concentration in the fishes collected from Singanallur lake water was recorded and the minimum and maximum concentrations along with mean values for the entire study period are given in Table 1.   The metals except Pb and Zn were higher in S. mossambica .   The Pb and Zn load in C. catla was higher when compared to other metals.     The order of concentration of metals among the fish species was S. mossambica > C. catla > C. carpio for copper, iron and   nickel, C. catla > C. carpio > S. mossambica for zinc and lead and S. mossambica > C. carpio > C. catla for cadmium.

Seasonal variations of different metals in fish species were also recorded and presented in Table 2.   Seasonally, C. catla showed high levels of copper, zinc, nickel, cadmium, iron and lead during northeast monsoon period than the other periods.   In C. carpio southwest monsoon showed high concentration of copper and zinc.   In the same species the concentration of metals like cadmium, iron and lead recorded high values during winter period.   Among the different tissues analysed intestine showed high accumulation of metals in all the seasons than the   other tissues of C. catla .   Accumulations of metals like copper, nickel, cadmium and lead in the muscle tissue of C. catla were below detectable level during all the seasons of the study.   The higher level during monsoon could be due to the influx of metal rich runoff, which may contain domestic, agricultural and industrial wastes from adjacent areas (Senthilnathan and Balasubramanian, 1998).

Accumulation of various metals in selected tissues of fish species collected from Singanallur lake indicated wide variation (Table. 3).   Irrespective of the species zinc and iron contributed to higher concentration than the other metals.   Among the metals in the intestine tissues of the fish species, iron, nickel and cadmium accumulation was high in the intestine and S. mossambica , followed by copper, zinc and lead in C. catla .   Concentration of selected metals of the present study in the different organs of the fish species   is given in Table 4.   Results revealed that the average metal concentration was high in C. catla (10.0 1 µ g/gm) followed by the intestine and muscle tissues of C. carpio.   The accumulation ratio of the metals in the tissues of the fish species was Muscle (1): Gill (10.92): Intestine (33) for C. catla , Muscle (1): Intestine (2.73): Gill (2.43) for C. carpio , and Muscle (1): Gill (14.33): Intestine (70.65) for S. mossambica .

The bioaccumulation of metals in any organism varies according to the bioavailbility, the uptake rate, their threshold limit and physiological efficiency of the organisms to excrete excess metals.   Though the large variation between minimum and maximum values for the concentration of each metal indicates seasonal variation in the present study a consistent pattern was not observed in any species.   The bioaccumulation of different metals at higher levels in intestine of fish species suggested that the metal accumulation was effective through the food chain rather than by direct contamination.   The results indicated wide variations in the levels of metals between species.   However the worked-out ratios indicated a better picture on the distribution pattern of metals in different parts of the body.   Zinc, lead and iron collectively contribute more than 75% of the total metal accumulated in the tissue   at Singanallur lake.

High Zn load would be largely due to the discharges of agricultural wastes and runoff from the nearby upland area and also due to their biological importance, as a constituent of metallo-enzymes (Senthilnathan and Balasubramanian, 1998).   The standards for metal contaminants in fish muscle have been given as 100 mg/kg, 250 mg/kg, 1 mg/kg and 10 mg/kg dry weight for Cu, Zn, Cd and Pb respectively.   The recorded range in muscle of different species of fish indicated that the levels had not exceeded the permissible limit prescribed for consumption.   The comparatively low metal concentration in fish muscle was reported by Krishnamurti and Nair, 1999.

From the present investigation, it is concluded that the fishes can be effectively used as monitors of water quality with respect to heavy metals.   It is apparent that the metal levels in all the fish species were well below the recommended level for human consumption, indicating that the present study area is relatively less polluted.

The first author is thankful to UGC, New Delhi for award of a Teacher Fellowship during the tenure of which the present work was carried out.

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1.       Department of Environmental Sciences, PSG College of Arts & Science, Coimbatore – 46.India

2.       Department of Environmental Sciences, PSG College of Arts & Science, Coimbatore - 46

3.       Adiparasakthi Agricultural College, Kalavai, Vellore District.

4.       Department of Environmental Sciences, Bharathiar University, Coimbatore - 46.