Histopathological Effects of Metal Exposure on Freshwater Mussels (Anodonta marginata) from Challawa River, Nigeria

Abstract

The widespread contamination of aquatic bodies by heavy metals has engrossed worldwide attention due to their persistence and accumulative nature. The present study determined the bioaccumulation of some heavy metals and their histological impacts on freshwater mussels. Metals assessed were Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), and Nickel (Ni) in a bivalve mussel (Anodonta marginata) with their levels in sediment and water of Challawa River, Kano, Nigeria. Metals were assessed using atomic absorption spectrophotometer. Gill and digestive gland tissues were dissected and fixed, sections were analysed for histopathology. Water samples analysed had mean concentrations of Cd (0.088mg/L), Cr (0.457mg/L), Pb (0.127mg/L) and Ni (0.101 mg/L) above the World Health Organization's permissible limits of 0.003, 0.05, 0.01 and 0.07 mg/L respectively. The trend of heavy metals in water levels was Site B > Site C > Site A > Site D; similar to the trend recorded in mussels. Pearson correlation revealed positive interactions in levels of metals in water, sediment and mussels. Moderate to severe histopathological changes were recorded in the form of disruption of epithelium, necrosis, and degeneration of tissues. This was attributed to metal pollution, through several mechanisms such as oxidative stress, inflammation, changes in cellular functions and homeostasis etc. Findings highlight the need for effective waste management practices and enforcement of environmental regulations, particularly at the industrial areas where effluents are being discharged into the water.