BIOACCUMULATION OF SELECTED TOXIC HEAVY METALS ALONG RIVERS OF MALAKAND DIVISION AND RIVER KABUL, PAKISTAN

Abstract

Heavy metals are well-known environmental pollutants due to their serious toxicity, persistence in the environment and bioaccumulative nature. A variety of natural and anthropogenic sources are the main reason of their release into the environment. Contamination of freshwater ecosystems such as rivers with toxic heavy metals is an environmental problem of public health concern. Being persistent elements, heavy metals are accumulated in the environment and are the major cause to contaminate the food chains. Accumulation of potentially toxic heavy metals in freshwater fish causes a potential health threat to their consumers including humans. It is very important to assess and monitor the concentrations of potentially toxic heavy metals in riverine waters and sediments as well as in the resident biota. The present research work aimed to assess the bioaccumulation of four selected heavy metals i.e., Cr, Ni, Cd and Pb in freshwater fish, rice and tobacco along three rivers in Malakand Division and River Kabul, Khyber Pakhtunkhwa, Pakistan. The different aciddigested environmental samples were analyzed for specified heavy metals (Cr, Ni, Cd and Pb) by flame atomic absorption spectrophotometry. Potential risk to the health of the fish consumers was assessed in terms of estimated weekly intake (EWI) values of the heavy metals and compared with their respective provisional tolerable weekly intake (PTWI) values set by international organizations. Generally, metal concentrations in muscles of the fish from the studied rivers were comparable. Generally, clear trends could not be observed for metal concentrations at different sites of the rivers when going from upstream to downstream. Regarding metal accumulation in fish muscles, generally, inter-species differences were statistically not significant, most probably due to more variance within samples. Generally, metal concentrations were higher in metabolically active tissues such as gills and liver compared to skin and muscles. Based on the current study, consumption of the analyzed freshwater fish species from the rivers was generally safe in terms of potential risk from Cd and Pb but the observed Ni accumulation may pose a potential health risk to regular/excessive fish consumers. Thus, efforts should be made to minimize heavy metal contamination in these freshwater ecosystems in order to safeguard the aquatic fauna and the health of the fish consumers.