Heavy Metals Concentrations in Shellfish and Sediments of Andoni River , Rivers State , Nigeria

The pathway and partitioning of toxic substances such as heavy metals and polyaromatic hydrocarbons (PAHs) into various environmental compartments has become a worldwide problem in recent years. This is due to increased industrialization, production of household and industrial wastes and construction of roads. The aquatic system is mostly affected due to transportation of these toxicants to aquatic environment, via erosion, deposition of particulate materials from atmosphere mining, and dumps leachates [1, 2]. The effluents from industries and household waste are carried in drains from the discharge point to the aquatic system. Among the environmental pollutants; heavy metals are of particular interest due to their potential toxic effect and ability to bio-accumulate in aquatic system. Some examples of metals are iron, magnesium, lithium, zinc, copper, chromium, nickel, cobalt, vanadium, arsenic, molybdenum, manganese, lead, mercury, and cadmium. All living organisms requires trace amount of some trace elements such as cobalt, copper iron, manganese, molybdenum, vanadium and zinc. However, excessive concentration of these metals can become detrimental to organisms [1, 3]. Metals in their natural or pure state do not cause any harm to life, the carcinogenic form of metals include; the hydroxide, oxides, silicates or sulfide which can be adsorbed to clay, silica or organic matter. Soluble form of metals is generally ions or unionized organometallic chelates or complexes [4, 5]. The solubility of trace metals in surface water is predominantly controlled by the water pH, the type and concentration of ligands on which the metal is adsorbed, oxidation state of the mineral component, and the redox environment of the system. According to [4] more than 90% of the trace metal load in the aquatic system is bound to suspended particulate matter and sediment. Sediment play a very important role in physico-chemical and ecological dynamics. Any change in toxic concentration of trace metal residues in sediments will affect the natural aquatic life support system. Fish and other marine organisms contain protein and mineral salts that are essential for human life at low concentration. However, they become toxic at elevated concentrations, some other metals such as mercury, lead and cadmium are not required by humans at any known concentration. Heavy metals are non-biodegrable and can bioaccumulate along food chain producing their toxic effect at point far away from the source of pollution [6, 7]. The Abstract The concentrations of seven heavy metals Fe, Zn, Mn, Cu, Pb, Cd and As were investigated in two aquatic organisms oyster (Saccostrea cululata) and cockle (Andra granosa) of Andoni Rivers system. Similar sizes of each species of the organisms were collected from five stations. The aquatic organisms were prepared and digested with a mixture of mineral acids, HNO3 and HCl, while sediments by mixture of HClO4 and H2SO4. They were analyzed with Atomic Absorption Spectrophotometer model 205. The results obtained showed that of the essential elements, Fe had the highest concentration of 2896.48± 2083.11mg/Kg in sediment and the least concentration of 0.61 ± 0.302mg/Kg occurred in cockle. Of the non-essential elements Pb, Cd and As, As had the highest mean concentration of 0.7950 ±0.19mg/Kg, while Pb had the lowest concentration of 0.0680 ± 0.082mg/Kg in cockle. The results of ANOVA and Post Hoc Test (PHT) revealed significance difference at p<0.05 in the mean concentrations of some of the heavy metals. On the other hand, high pollution load index (PLI), were obtained at the stations. The consumer of shellfish in the area is at risk of being poisoned by heavy metals, as the values obtained were above standard set by WHO.