Seasonal Variations in Heavy Metal Status of the Calabar River, Cross River State, Nigeria

The study examined heavy metal status of the Calabar River in Cross River, Nigeria. Surface water samples were collected during the wet and dry seasons for ten months across five stations and analyzed for heavy metal parameters using standard methods. Result showed that the concentrations of iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), lead (Pb) and total hydrocarbon (THC) in the dry and wet seasons were low and within WHO and FEPA tolerable limits The proportion of copper (Cr), cadmium (Cd), barium (B), nickel (Ni), vanadium (V) and mercury (M) were not detected indicating the absence of these metals in the sampled stations. The low levels of heavy metal contents across the sampled stations showed they were not polluted and as such suitable for aquatic live. Independent samples test result indicated seasonal difference in the proportion of Fe, Zn, Cu, Pb and THC (p<0.01). The study identified runoff from industrial, agricultural and residential areas as sources of heavy metal pollution in the wet season and effluent discharges from industrial and municipal wastes as major sources of pollution of the Calabar River in the dry season. To sustain the ecological status of the Calabar River, waste management practice of waste re-use through the use of retention ponds is encouraged. Introduction World-wide, heavy metal contamination in water, sediment or plant is an increasing environmental concern (Ahmed et al., 2005). In different parts of the world, rivers have been used as a major sink of industrial and municipal wastes as well as a recipient of toxic and solid waste from agricultural runs off. Water pollution by heavy metals due to human activities is causing serious ecological problems in many regions of the world. Metals which are discharged into natural waters at increased concentrations in sewage, industrial effluents or from mining operations can have severe toxicological effects on humans and aquatic ecosystems (Mondol et al., 2011). Heavy metals are environmental pollutants, and their occurrence in water, soil and plant indicates the presence of natural or anthropogenic sources (El Bouraie et al., 2010). The main natural sources of metals in waters are chemical weathering of minerals and soil leaching. The anthropogenic sources are usually associated with industrial and domestic effluents, urban storm, water runoff and landfill among others (Zarazua et al., 2006). Human and industrial activity has disturbed the natural environment, particularly the aquatic ecosystems. The production and use of heavy metals has led to widespread environmental contamination and cause of concern now in urban and rural areas. Some of these compounds are the object of study because of their toxicity and ubiquity and they are known to remain stable in the aquatic environment (Singh and Singh 2006). Heavy metals are non-degradable and harmful to plants, aquatic organisms and human health at certain levels of exposure (Mustafa and Nilgun, 2006; Singh and Upadhyay, 2012). The Calabar River is adjoined by the Calabar Port Authority, residential, agricultural and mangrove land-uses. The Calabar Port ecosystem contributes immensely to the economic development and environmental security of the state and country as a whole (Offiong et al., 2012), but, the presence of industries and increasing urbanization in the area are immensely affecting the water resources available. The poor effluent management from industries has negatively impacted on the water quality resulting in the change of its natural contents. The industrial activities in the area include food processing, fuel bunkering, corrugated iron sheets, logging and shipping. The most serious risks of industrial production activities in the area include air and water pollution which stems from the discharge of effluents (in gaseous, solid and liquid forms) without prior treatment into the Calabar Rivers. This perhaps is of great concern to the terrestrial and aquatic environment. Indeed, the Calabar River is a major sink of industrial, agricultural and municipal wastes in the area. The present study was carried out to assess the seasonal proportion of heavy metal in the Calabar River. Materials and methods Study Area The Calabar River was the study environment found in Calabar, Cross River State. The river encloses Esuk Nsidung Calabar south Adiabo brige in Odukpani Local Government Areas. The Calabar River is a major tributary of the Cross River, originates from Oban hills Nigeria and flows through black shale and siltstone, Journal of Natural Sciences Research www.iiste. org ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online)