Studies On Fish Species Specific Metals Bioaccumulation Patterns In Relation To Water, Sediments And Plankton In The River Ravi

The toxicity of heavy metals, aluminium, arsenic, barium, chromium, nickel and zinc in the water, sediments, plankton and fish at the three main public fishing sites of the river Ravi, Shahdara bridge, Baloki headworks and Sidhnai barrage has been studied for one year. The water, sediments, plankton and fish samples were collected on monthly basis. Five fish of each species belonging to both major carps, Catla catla, Labeo rohita and Cirrhina mrigala and carnivore fish i.e. Rita rita, Mystus sperata and Wallago attu were sampled randomly for analyses. The concentrations of aluminium, arsenic, barium, chromium, nickel and zinc in the fish body organs, gills, liver, kidney, intestine, reproductive organs, skin, muscle, fins, scales, bones and fats were determined. The water physico-chemical variables, water temperature, dissolved oxygen, carbon dioxide, pH, total alkalinity, turbidity, electrical conductivity, total nitrates, total hardness, calcium, magnesium, sodium, potassium, chlorides and total ammonia were analyzed on monthly basis and their relationships with the uptake and accumulation of metals in water, bed sediments and planktonic biomass (dry weight) were established. In the river Ravi aquatic ecosystem the relative variability of metals followed the order: aluminium>zinc>nickel>chromium>arsenic>barium. Among the three public fishing sites, Sahahdara bridge had significantly higher metallic toxicity of water, sediments and planktonic biota attributed to the bulk discharges of untreated effluents, originated from adjacent industrial areas, discharged through various small tributaries , Mahmood Booti nulla, Hudiara nulla, Shad Bagh nulla, Farrukhabad nulla, Munshi Hospital nulla and Taj Company nulla. The metallic toxicity of both sediments and plankton, in the river Ravi, followed the order: aluminium>zinc>nickel>chromium>arsenic>barium. However, the toxicity of these metals fluctuated significantly at all the three sampling stations with season. Metallic toxicity of water at all the three sites was generally low but the contamination levels in both sediments and biota were significantly higher. Among the metals, aluminium and zinc concentrations in water, sediments and plankton were significantly higher. The toxicity of aluminium, zinc, nickel, chromium and arsenic in water showed variability that was dependent upon total alkalinity and pH of water while chromium toxicity showed inverse relationship with water temperature. The elevated levels of all metals in the river bed sediments beyond the permissible limits indicated the failure of detoxification ability of sediments in the river Ravi due to continuous influx of heavy metals discharged through various tributaries. The uptake and accumulation of all metals by the sediments and plankton were dependent positively and significantly upon metallic toxicity of water. However, metallic ion uptake by the plankton showed significantly direct dependence on the metallic toxicity of sediments. The fish at Shahdara bridge had significantly higher metals in their body organs than those collected from the both Baloki headworks and Sidhnai barrage. Significantly higher accumulation of metals were observed in fish liver, followed by that of kidney, gills, intestine, reproductive organs, skin, scales, fins, bones, muscles and fats. The significant enrichment of metals in fish body organs showed direct dependence on the metallic toxicity of water, sediments and plankton. All the organs of both herbi– and carnivorous fish species showed significantly variable accumulation of metals that followed the sequence: liver > kidney > gills > intestine > reproductive organs > scale > skin > fins > bones > muscles > fats. Fish liver and kidney showed significantly higher abilities for the accumulation of all metals while the same remained significantly lowest in fish muscle and fats. The health status of river Ravi at three main public fishing sites, Shahdara bridge, Baloki headworks and Sidhnai barrage, with respect to eco-toxicity of aluminium, arsenic, barium, chromium, nickel and zinc, was above the recommended standards of EPA (USA) and Pakistan. Based on the calculated individual contamination factors, the metallic toxicity was in the order of aluminium>zinc>nickel>chromium>arsenic>barium posing highest risk to the sustainability of river ecosystem. The risks associated with the consumption of fish, irrespective of the source of fish, are higher since the levels of aluminium, arsenic, barium, chromium, nickel and zinc in fish have been found above their respective EPA (USA) permissible limits. Therefore, potential of danger may become more severe in future depending upon the extent of industrial and domestic wastewater influx into the river Ravi due to man-made activities in the adjacent areas