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ANALYSIS OF HEAVY METALS CONCENTRATION IN PERIWINKLE (TYMPANOTONOS FUSCATUS) IN CROSS RIVER ESTUARY (ITU RIVER), QUA IBOE RIVER ESTUARY (IBENO), AND IMO RIVER ESTUARY (IKORIVERESTUARY,EASTERNOBOLO,AKWAIBOMSTATE,NIGERIA.
1.1 Background of Study
Environmental pollution is the universal problem and most important pollutants are the heavy metals in aquatic environment because of their toxicity and accumulation by aquatic organisms. Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. They are substances with high electrical conductivity, malleability, and luster, which voluntarily lose their electrons to form cations (MacFarlane and Burchett, 2000). Heavy metals are generally referred to as those metals which possess’ specific density of more than 5g/cm3. They are an important group of chemical pollutants whereby food and water is the main route for entry into our body (World Health Organization 2000).
The pollution of the aquatic environment with heavy metals has become a worldwide problem and of scientific concern because the metals are not degradable and most of them have toxic effects on organisms (MacFarlane and Burchett, 2000; Oronsayeetal., 2010). Heavy metals enter rivers and lakes from a variety of sources that include the rocks and soils directly exposed to surface water, in addition to the discharge of various treated and untreated liquid wastes to the water bodies (APHA, 2005; Alaa and Osman, 2010).examples of heavy metals are Arsenic(As), Cadmium (Cd), Iron (Fe), Vanadium (V), Lead (Pb) Manganese (Mn), Mercury (Hg), Nickel (Ni), and zinc (Zn), that have a particular significance in ecotoxicology, since they are highly persistent (Storelliet al., 2005).
Toxicity is realized when these heavy metal levels are higher than the recommended limit which is different for individual elements in drinking water, organisms in the marine environment as it will be consumed by human. Sources include, Weathering of rocks, a variety of anthropogenic activities that are affected by seasons, increase the concentrations of these heavy metals (Oguzie and Izevbigie, 2009).It is difficult to remove them completely from the environment once they enter into it [APHA 1998, ATSDR 2005]. These metals in the form of inorganic compounds from natural and anthropogenic sources continuously enter the aquatic ecosystem where they could pose serious threat to the food chain.
Periwinkle (Tympanotonos fuscatus), the West African mud creeper is a proso-branch gastropod mollusk with soft bodied and externally covered by hard calcareous shell that is segmented. Tympanotonusfuscatus, commonly known as periwinkle, can also be described as a brackish Gastropod belonging to the family Potamididae. It is small and is characterized by turreted granular and spiny shell with a tapering end. This organism is endemic in Nigeria and West Africa. As part of the fauna of the mangrove community, it occurs mainly in the tidal mudflats of estuarine ecosystems. The genus Tympanotonos comprises of a single species which has two varieties Tympanotonos fuscatus and Tympanotonos fuscatus var. radula (Egonmwan, 1983).
Periwinkle (Tympanotonos fuscatus ) is a very popular well relished and forms a delicacy in the diets of most riverine communities in Niger delta, as it provides relatively cheap source of animal protein together with its medicinal and nutrient capabilities; its shells can be used for construction purposes, for decoration in art and as a source of calcium in animal feeds, the potential of the organism as a food source is well documented. Despite the numerous benefits derived from Tympanotonos fuscatus, its sustainability is threatened by human activities as a result of urbanization. Humans in quest for development have overtime, reduced the habitat of this organism through land reclamation for housing, crop farming and industries.
The common periwinkle is mainly found on rocky shores in the higher and middle intertidal zone. It sometimes lives in small tide pools. It may also be found in muddyhabitats such as estuaries, and can reach depths of 180 feet. When exposed to either extreme cold or heat while climbing, a periwinkle will withdraw into its shell and start rolling, hoping to hit the water. They are common in intertidal zone of mangrove swamps, estuaries, lagoons, creeks where the substratum is muddy and rich in detritus (Jamaboet al., 2009).
Since they are found in the intertidal area, they could be hand-picked especially during low tide. They are deposit feeders, taking in mud and digesting the detritus and other organic matter in the mud, nature of the bottom deposit; water depth and current are factor that affects their distribution in the coastal area of West Africa (Deekae, 1987). The organism is also very medicinal for cases like endemic goiter due to its iodine content. The calcium, phosphate and iron content also recommend it for pregnant women (Bob-Manuel, 2012).
These important food sources constitute a major part of the diet in the Niger Delta region of Nigeria; however, these organisms may bioaccumulate heavy metals in substantial amount in the tissues over a long time which may be unfavorable to the health of inhabitants of this area that consume them. These metals in the form of inorganic compounds from natural and anthropogenic sources continuously enter the aquatic ecosystem where they could pose serious threat to the food chain. Heavy metals are hazardous to humans because they tend to bioaccumulate in vital organs (Opaluwa, 2012). Heavy metals such as lead, cadmium, chromium and mercury pose a number of health hazards to humans. Humans are exposed to these metals by ingestion (drinking or eating) or inhalation (Abiaobo et al., 2017).