ABSTRACT
A study was determined the heavy metals concentration in water and sediments of the Meghna river during the period from April to December 2018. The water and sediments samples were collected in monthly basis covering both in wet (April to June) as well as dry seasons (October to December) from three sampling stations as St-1 (Kauriapara), St-2 (Nagoriakandi) and St-3 (Kamargaon). In water, available Pb, Cu, Zn and Mn contents were varied seasonally and spatially from 0.002 to 0.0.019, 0.00 to 0.026, 0.001 to 0.082 and 0.003 to 0.062 mg/l, respectively. The Zn was the most abundant in the water during dry season as Zn is normally associated with a variety of other metal activities and mining. In sediments, Pb, Cu, Zn, and Fe contents were also varied seasonally and spatially from 6.34 to 20.46, 1.39 to 28.06, 81.30 to 98.90 and 2274.28 to 34.62.10 mg/kg, respectively. The Fe content in all sediment samples were above the EPA guideline whereas the content of Cu and Zn fall in the criteria of moderately polluted range. So, the water is not completely safe for aquatic organisms in respect of heavy metal pollution in the Meghna river.

Key words: Heavy metal, Meghna river, water and sediment

Introduction

Water is known as blue gold, one of the most priceless gifts of nature is also regarded as the life line on earth, because evolution of life and development of human civilization could not have been possible without water (Islam et al., 2015). Again the river water quality is a key concern as it is used for drinking and domestic purposes, irrigation and aquatic life including fish and fisheries (Uddin et al., 2014). Large number of rivers flowing through Bangladesh originated outside of the country and these carry heavy loads of sediments and other debris including domestic wastes, agrochemicals and industrial wastes from local and far places. Thus making the water body saturated and times over saturated with organic and inorganic pollutants which creates serious environmental impacts. So, pollution become serious problem all over the world and is getting aggravated in developing countries particularly like Bangladesh (Sarker, 2005). Bangladesh is one of the most polluted countries, which currently holds 1176 industries that discharge about 0.4 million m3 of untreated waste to the rivers in a day (Rabbani and Sharif, 2005). The industrial discharge is one of the major sources of heavy metal. Heavy metals are stable, xenobiotic and are nonbiodegradable, once taken they persist in the body, tissues and cells. Exposure to the toxic environment is done by inhalation of air contaminated with metal dusts, fumes and small particle generated by combustions, intake of contaminated food, eating at contaminated site, eating without washing hands (Bhargava et al., 2017). Studies on heavy metals in rivers, lakes, fish and sediments have been a major environmental focus especially during the last decade (Fernandes et al., 2008; Pote et al., 2008; Praveena et al., 2008). Heavy metals accumulation and distribution in sediments, water and environment are increasing at an alarming rate causing deposition and sedimentation in water reservoirs and affecting aquatic organisms as well (Mohiuddin et al., 2011).Though some metals like Fe, Cu and Zn are essential micronutrients, they can be detrimental to the physiology of the living organisms at higher concentrations (Kar et al., 2008; Nair et al., 2010). Others like chromium, lead, cadmium, arsenic, etc. exhibit extreme toxicity even at trace levels (Miller et al., 2003).Once the heavy metals are consumed they keep on accumulating and at higher concentration they form complex compounds within the cells and tissues, leading to diseases. On intake, the heavy metals become integral part of some body parts like bones, kidney, liver and brain (Bhargava et al., 2017). Acute Pb poisoning may results in a dysfunction in the kidney, reproduction system, liver and brain resulting in sickness and death. Zinc compounds affect the