CHAPTER ONE
Introduction
Trace elements are natural components of the earth’s crust; they are stable and persistent contaminants of coastal waters and sediments. They are serious pollutants due to their facility persistence and bioaccumulation problem Pekey, (2006). They exhibit toxicity by forming complexes with organic compounds and active sites of enzymes. The impact of anthropogenic activities is most strongly felt by the estuarine and coastal environment adjacent to urban areas Nouri, Kabassi, and Mirka, (2008).
Tympanotonus fuscatus is among the popular sea foods consumed by people living in the coastal area of Nigeria, apart from being a major delicacy; they equally serve as a source of economic empowerment for the people in the area. Although periwinkles are marine dwellers they immigrate into the brackish water systems during their post larval stages, grow fast attain maturity in waters and lagoons. Their exposure to both marine and estuarine environment has all effects on the body burden of metal bioavailability from the natural as well as anthropogenic set up of the environment (Mohapatra et al, 2009). The interest on trace elements from the marine mollucs arose from three area of concern; nutritional, environmental and toxicological. Trace elements such as Mg, Na, Ca, Fe, Zn, Co, K are necessary for the maintenance of human body and health. Trace elements like Cd, Pb, As, Hg, V could pose toxicological effect on human. Their tissue sample can be used as bio-indicator to assess bioavailability of contaminant concentration in coastal water studies.
The sources of toxic metals in the environment are fossil fuels, mining industries, waste disposal and municipal sewage. Farming and forestry also contribute to the metal content of the environment due to the use of fertilizers, pesticides, herbicides and as a consequence of environmental pollution the contaminants may enter the food chain, since humans ingest food for survival, the major  route of entry for most metals into the body is through diet. Thus it is essential to know the toxic metal content in food stuff human consume every day (Chowdhury et al, 2011).
However information on the studies of accumulation of trace metals by periwinkle Tympanotonus fuscatus in the Niger delta is scarce though being the region the highest number of industries, oil installations refineries, and the resultant pollution of the aquatic environment. Few studies conducted in Niger delta region revealed that the surface waters and aquatic organisms have heavy burden of trace metals, sometimes reaching levels that constitutes health hazard to consumers Edema and Egborge, (1992); Agada, (1994); Ovuru and Alfred-ockiya, (2001).This implies that seafood is a significant path way to trace element exposure for people consuming them, and this study is aimed at assessing the trace element concentration in periwinkle flesh obtained from ifiayong creek.
Background of Study
Tympanotonus fuscatus var-radula is found in the intertidal zone at low water mark in several parts of the world. Tympanotonus fuscatus var-radula crawls about under water but usually remain passive when left uncovered by the tides, considerable amount of Tympanotonus fuscatus are obtained daily for food and they have been found to be rich in protein and carbohydrate (Egonwan, 1980) estimated the crude protein of Tympanotonus sp to be 21.04, the muscle tissue contains high concentration of free arginine, aspartic acid and glutamic acid (Watt and Meril, 1950; Jay, 1978). They are invertebrates belonging to the phylum Mollusca and class gastropoda; Tympanotonus sp are valuable commercially, their collection and marketing forms and important industry in Niger delta.