Freshwater Mussel (Anodonta Cygnea) as a Bioindicator for Monitoring of Pollution Status in River Kabul, Pakistan

Abstract

The main objectives of this work were to investigate physico-chemical and heavy metal contaminations in water and sediments as well as their accumulation, histopathology and genotoxicity in Freshwater mussels of River Kabul. For this purpose water sample A (reference site 1), water sample B (polluted site 2), water sample C (polluted site 3) and water sample D (polluted site 4) upstream and downstream of River Kabul were collected during winter and summer periods and analyzed for eight physico-chemical parameters (pH, TSS, TDS, TA, Cl, K, EC, Na) and nine heavy metals (Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn) and compared with water sample A and NEQS recommended limits. All the studied physico-chemical and heavy metal parameters in water samples A, B, C and D except TSS and Hg were below the NEQS proposed limits, where the values of TSS and Hg were above the NEQS recommended limits in all the water samples A, B, C and D. Thus the overall sequence of different water samples was D > C > B > A. This highlights that water sample D had higher and sample A had lower physico-chemical and heavy metal contaminations. Water samples A and B had highest TDS and lowest K for low flow and had highest TSS and lowest K for high flow seasons. Similarly water samples C and D showed highest TDS and lowest pH for low flow and showed higher TSS and lower K for high flow periods. Among heavy metals water sample A had highest Zn and lowest Cr for both summer and winter seasons. Water sample B showed higher Zn and lower Cu for summer and greater Zn and smaller Hg for winter seasons. Similarly water samples C had greater Zn and smaller Cu for both summer and winter seasons. Similarly water samples D had higher level of Zn for summer and greater Zn and lower Hg for winter seasons. Similarly among the studied heavy metals in sediments sample A had highest Fe and lowest Hg for both summer and winter seasons. Sediments sample B, had highest concentration of Fe and lowest concentration of Hg for both summer and winter seasons. Similarly sediments sample C had highest Fe and lowest Hg for both summer and winter seasons. Similarly sediments sample D had highest concentration of Fe and lowest concentration of Hg for both summer and winter seasons. This investigation was further aimed to determine bioaccumulation of heavy metals including Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn in soft tissues of freshwater mussels. Overall order of metals concentration in different tissues showed that Fe was the highly and Hg was the lowest accumulated metals. This study was further meant to investigate histopathological impacts of heavy metals in soft tissues were degeneration of epithelium, lipofusin pigments, atrophy, inflammation, necrosis and granulocytoma in digestive gland. In gonads necrosis, inflammation, atresia, lipofusin pigments and granulocytoma were found. While in gills the degeneration of cilia, fusion of gills lamellae, haemocytic infiltration and gills swelling was recorded. Similarly in intestine degeneration of epithelium and its cillia were found. The highest intensity of histopathological lesions was recorded in site 4 and lowest in site1. Furthermore the present investigation was conducted to assess genotoxical impacts of heavy metals in hemolymph of selected freshwater mussels. Therefore degree of DNA damage like TCS and comet class 0, class 1, class 2, class 3 and class 4 were determined. The order of sites according to DNA damage was 4 > 3 > 2 > 1, i.e. the highest DNA damage was noticed in site 4 while lowest in site 1.