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Trends in Applied Sciences Research

Year: 2007  |  Volume: 2  |  Issue: 6  |  Page No.: 492 - 499

Bioaccumulation of Zinc, Copper and Lead in Upper Stretch of Gangetic West Bengal

A.K. Bhattacharya, S.N. Mandal and S.K. Das

Abstract

Concentration of zinc, copper and lead were investigated in the gill, gonads, skin and muscle tissues of six commercially edible fishes from upper stretch of the Ganga River at West Bengal, India. The study area receives a wide variety of wastes generated by municipalities and the industries like paints and pigments, metal processing industries, thermal power plants, electro-processing industries etc. situated on the both side of the river Ganga. Simultaneous analysis of the metals was also carried out in the sediment and aquatic phases to monitor the degree of contamination. Although in the study area, the availability of heavy metals is still below alarming level (the acceptable limit for human consumption of the heavy metals are copper 10 μg g-1, zinc 150 μg g-1 and lead 1.5 μg g-1) but if the present trend continues, the level might get elevated and the consumption of the contaminated fishes might pose severe health hazards to human beings in times to come. The results of this study indicated that the six commercially edible fishes through food, water and sediment leading thereby to bioaccumulation took the metals present in the river ecosystem. The degree of bioaccumulation was directly proportional to the concentration of heavy metals in water phase and found to follow the order pre-monsooncopper>lead.

Table 2), pH and temperature were recorded at site with a pre calibrated portable pH meter (sensitivity ±0.01) of Cyberscan pH 110 and a standard RTD thermometer, Eutech, Singapore make. Turbidity and total dissolved solids were determined at site with a pre-calibrated portable Nephelometric turbidity meter of waterproof TN 110 and Ecoscan Palmtop TDS meter, Eutech, Singapore make. The total alkalinity was determined by standard method as laid down in APHA, AWWA (1998). All analysis was carried in duplicate to avoid any conspiracy in experimental results.

RESULTS AND DISCUSSION

The level of heavy metal concentrations in ambient media (water, sediment) as well as in different muscle tissues of commercially edible fish samples during the period of study exhibited a unique seasonal oscillation. The concentration of heavy metals follow the trend: zinc>copper>lead. The seasonal variation of different metals considered for the study in water and sediment phase at sampling station Bally, Uttarpara, West Bengal in the upper stretch of Ganga River is shown in the Table 1. The concentrations of zinc, copper and lead in water phase were found to be maximum during monsoon period which may be characterized by extremely low alkalinity and pH of the aquatic medium (Table 2). During the pre-monsoon period the concentration of metals attained it’s minimum value with high surface water temperature. The parameters like pH, alkalinity, TDS and turbidity value also reached to their highest values during the pre-monsoon period. The resulting effect was observed in sediment phase with highest heavy metal concentration in pre-monsoon period followed by post monsoon and monsoon period.

The above fact was supported by Mitra et al. (1994), Laksmann and Nambisan (1983). A change from sediment phase to the water phase due to influence of physicochemical parameters (Table 2) could be the only reason. Heavy metals observed to undergone compartmentation process resulting in the increase of dissolved heavy metals in water phase and decrease of biologically available heavy metals in sediment compartment during monsoon. High concentrations of heavy metals during monsoon period have been recorded very recently in the coastal zone of West Bengal and in the present situation, their is a keen relationship of the urban and suburb run off that responsible for maximum load of heavy metal during monsoon from several paint and pigment unit, electroplating units, thermal power plants and fertilizer industries situated in the nearby areas of estuarine environment.

The concentrations of heavy metals in different tissues of fish samples from upper course of River Ganga were shown in Table 3-6, the monsoon period got the highest concentration of heavy metals followed by post-monsoon period and pre-monsoon period. Muscle tissues and gill showed higher concentration of zinc, copper and lead than gonads and skin. Zinc and copper accumulation are much higher than lead of different fish species. Gonads showed the lowest concentration of heavy metals compare to the any other tissues of the fish samples studied at the sampling station during the period. Metal accumulation was found to be the function of their respective membrane permeability and enzyme system. This is why different degree of zinc, copper and lead accumulation has been observed in different tissues. Metal accumulation follows the same trends as observed in water phase. Therefore, heavy metal concentration showed a sharp seasonal oscillation.

Table 1: Heavy metal distribution in water and sediment phase

Table 2: Environmental characteristics of the investigated course of the Ganga river

Table 3: Concentrations of analyzed heavy metals (in µg g-1 dry weight) in the muscle of fish of the Ganga river
BDL = Below Detection Limit

Table 4: Concentrations of analyzed heavy metals (in µg g-1 dry weight) in the gonads of fish of the Ganga river
BDL = Below Detection Limit

Table 5: Concentrations of analyzed heavy metals (in µg g-1 dry weight) in the skin of fish of the Ganga river
BDL = Below Detection Limit

Table 6: Concentrations of analyzed heavy metals (in µg g-1 dry weight) in the gill of fish of the Ganga river
BDL = Below Detection Limit

Therefore, it may be said that aquatic life is more prone to heavy metal contamination in monsoon period while comparing with the other two period of the season. In fact, the level of heavy metals in the body of the fish depending upon their chemical environment in which they exist (Yazdandoost and Katdare, 1999).

Further, the metal accumulation was not same in all edible fishes, which may be due to difference in the degree of membrane permeability (Bhattacharya et al., 2001, 2006) for each metal. Membrane permeability depends on a particular fish species and therefore, metal accumulation in of fish species were varied from zinc, copper and lead.

Results of analysis showed the order of accumulation of zinc is:

Apocryptes bato > Glossogobius guris > Gudusia chapra > Mastacembelus armatus >Eutropiichthys vacha > Cynoglossus punticeps

The level of copper accumulation is:

Apocryptes bato> Gudusia chapra >Mastacembelus armatus > Glossogobius guris Eutropiichthys vacha > Cynoglossus punticeps

In case of lead the trend is:

Glossogobius guris> Cynoglossus punticeps > Mastacembelus armatus > Eutropiichthys vacha > Apocryptes bato> Gudusia chapra

It has been suggested that fish may accumulate large amounts of heavy metals though ingestion or direct uptake from polluted water (Gras et al., 1992). However, significantly high positive correlation between the tissue metal concentrations and dissolved metal of the ambient water is a pathway to detect kind and degree of pollution at different fishing sites (Ramakrishna et al., 1997).

CONCLUSIONS

The phenomenon of bioaccumulation and bio-magnification intensified with concentration of heavy metals at different tropic levels. In aquatic ecosystem the primary producers absorb the metallic ions, which in turn pass to the consumer level through predictions. The degree of bio-magnification of heavy metals at different levels depends upon the bioaccumulation capacity of the flora and fauna. In water they occur as complex and diverse mixtures of soluble and insoluble forms such as ionic species, inorganic and organic complexes and/or associated with colloids and suspended particulate matter (Pani et al., 2002).

Today, fishes have become the major diet and there have been attempts to devise ways to enhance fish production. The bioaccumulation of zinc, copper and lead in edible part of the fishes indicates the extent of stress posed on this highly productive ecosystem. Muscle tissues and gill showed higher concentration of zinc, copper and lead than gonads and skin. In fact, lowest concentration of heavy metals was observed in tissue of gonads for all the different fish species from the upper course (Bally, Uttar Para region) of Ganga River. The metal accumulation trend was observed to zinc > copper > lead.

Also the major findings of the study reveals that heavy metal concentrations in muscle, gonads, skin and gill of Apocryptes bato, Glossogobius guris, Gudusia chapra, Mastacembelus armatus, Eutropiichthys vacha and Cynoglossus punticeps from the river Ganga were significantly alarming and in general exhibited a unique seasonal variation. The highest metal accumulation was observed during the monsoon.

Carnivores at the top of the food chain such as birds and mammals including humans, obtain most of their pollutant burden from aquatic ecosystems by way of their food especially fish (Mason, 1990). People who eat contaminated fish regularly, therefore, are most exposed to the risk of chronic poisoning (Milagros, 1996). Although in the study area, the availability of heavy metals is still below alarming level (the acceptable limit for human consumption of the heavy metals are copper 10 µg g-1, zinc 150 µg g-1 and lead 1.5 µg g-1 dry weight (Nair et al., 1997) but if the present trend continues, the level might get elevated and the consumption of the contaminated fishes might being severe health hazards to human beings in longer duration. Therefore, proper monitoring and control is utmost important to keep the health of this highly productive ecosystem intact.

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