Ife Journal of Science vol. 17, no. 3 (2015) 565 STUDY OF HEAVY METALS IN THE GASTROPOD, PACHYMELANIA AURITA (MULLER, 1774), SEDIMENT AND WATER FROM OLOGE LAGOON, SOUTH- WESTERN NIGERIA *Samuel, O. B., Osibona, A. O. and Chukwu, L. O. Department of Marine Sciences, Faculty of Science, University of Lagos, Akoka – Yaba, Lagos, Nigeria *Corresponding Author: [email protected]; [email protected] (Received: 5th June, 2015; Accepted: 22nd June, 2015) ABSTRACT The levels of Cu, Fe, Pb, Mn and Zn in the gastropod, Pachymelania aurita in relation to heavy metal contaminations in sediments and surface water of Ologe Lagoon, Nigeria were investigated over a twelve- months period. The mean concentration of metals in whole tissue of P. aurita and sediment collected from Ologe Lagoon was in the descending order; Fe > Mn > Zn > Cu > Pb while the mean concentration in the surface water of the site where P. aurita was collected was in the descending order; Fe > Zn > Cu > Mn > Pb. The computed metal pollution index (MPI) (46.76 - 99.03) indicated that there was high level of heavy metal load in the whole tissue of P. aurita, and Iron contributed the highest concentrations of metal load. Based on the bio- sediment accumulation factor (BSAF) and bio-water accumulation factor (BWAF), the amount of Cu, Fe, Pb, Mn and Zn accumulated by P. aurita was found to be about 1.49, 1.46, 1.87, 0.69 and 1.28 times higher than the level detected in the sediment respectively while it was about 4.34, 55.19, 1.67, 83.11 and 20.94 times higher than the level detected in the surface water respectively. Based on the concentrations of Cu and Fe exceeding World Health Organisation (WHO) permissible limits in fish food, P. aurita from Ologe Lagoon may be said to be unsafe for human consumption. Keywords: Heavy metals, Mollusc, Pachymelania aurita, Bioaccumulation, Sediment, Surface water INTRODUCTION 2007). Moreover, there is a growing concern The accumulation of heavy metals in our among citizens about chemicals and metals that environment has intensified in recent years due to are suspected of disrupting reproduction in population growth, industrialization and new aquatic organisms. These are tied to observations technological developments. This phenomenon is in humans and wildlife over the last 40 years of of great concern because heavy metals constitute worrying trends of adverse effects (Almeida et al., considerable hazards to human health due to their 2001; Licata et al., 2003; Berkun, 2005). toxicities, accumulative tendencies and persistence in the environment (Ayenimo et al., 2005). The Biological communities respond constantly to aquatic environment is the ultimate sink of toxic physical forces, chemical dynamics, and chemicals generated by man's industrial, ecosystem processes that change minute-to- agricultural and domestic activities. Pollutants minute and year-to-year but the difficulty is discharged into streams and rivers are transported establishing to what degree these changes affect over long distances affecting ecosystems miles an ecosystem, how much they are outside the away from the point of discharge. In view of the natural range of variability or disturbance above-mentioned, environmental managers are frequency (Nedeau et al., 2003). constantly faced with having to determine the extent of environmental contamination and Ologe Lagoon meets several socio-economic identifying localities and habitats at risk (Galloway needs (aquaculture, fishing, sand dredging and et al., 2002). drainage) of the various towns and villages bordering it. More importantly, it drains river The fact that heavy metals cannot be destroyed Owo, into which partially treated/untreated through biological degradation and have the effluents from the Agbara industrial estate is ability to persist in the environment make them discharged (Clarke et al., 2004). These discharges deleterious to aquatic environment and coupled with domestic inputs from the Agbara consequently to humans that depend on aquatic residential estates and satellite communities cause products for sources of food (Farombi et al., significant levels of pollution (Clarke et al., 2008). 566 Samuel et al.: Study of Heavy Metals in the Gastropod, Pachymelania aurita A previous study (Kusemiju, 2010) has revealed dominant gastropod molluscs in Ologe Lagoon the predominance of heavy metals in industrial and other south-western lagoon systems effluents discharged into this environment. With (Oyenekan, 1987; Ajao, 1990; Brown, 2002; respect to Ologe Lagoon, data exist on algal Uwadiae, 2009) of Nigeria. It is endemic to West composition (Clarke et al., 2008; Onuoha, 2009), Africa (Egonmwan, 2007) and is sought after by the fish and fisheries (Anetekhai et al., 2003) and natives of coastal towns and villages in Nigeria as heavy metal concentrations in fish (Kumolu- a staple source of protein. Johnson et al., 2010). However, there is a dearth of information on the heavy metal level of benthic MATERIALS AND METHODS macro-invertebrates in Ologe Lagoon. Description of Study Area The Ologe Lagoon (Figure 1) transverses Lagos Benthic macro-invertebrates are an integral and Ogun States, in Nigeria and is one of the nine component of the aquatic ecosystems. In addition lagoons in south-western Nigeria (Nwankwo, to some being a source of protein to humans, they 2004). It is a freshwater lagoon system that lies play important roles in energy flows, nutrient between latitudes 6° 27′ N and 6° 30′ N and cycling and maintaining community balances in longitudes 3° 02′ E and 3° 07′ E and has a surface these ecosystems. This study therefore area of 9.4 km2 (Anetekhai et al., 2007). Rivers investigates the level of heavy metals (Cu, Fe, Pb, Imede, Owo, Oponu and Ilo are major rivers Mn and Zn) in the gastropod, Pachymelania aurita of emptying into Ologe Lagoon. Its main outlet Ologe Lagoon in relation to heavy metal levels in empties into Elete creek through which it sediment and surface water. Pachymelania aurita connects with other creeks and lagoons such as (Mollusca; Gastropoda; Caenogastropoda; Iyagbe lagoon, Badagry lagoon and the Lagos Melaniidae) commonly known as periwinkle in Lagoon. Nigeria is one of the commonest and most Figure 1: Description of the Study Area Samuel et al.: Study of Heavy Metals in the Gastropod, Pachymelania aurita 567 Collection of Pachymelania aurita for Heavy Sediment Heavy Metal Analysis Metal Analysis Sediment samples (10 g) were oven-dried at 50 0C. Pachymelania aurita samples were collected for a After drying, visible remains of organisms and period of 12 months (January – December, 2008). debris were removed. The dried sample was The animals were collected by handpicking at the crushed in a mortar and sieved through a 200 mm edge (latitude 060 29.496'N, longitude 030 sieve to normalize particle size. From the dried 03.722'E) of the lagoon at depth less than 0.75 m. sieved sediment sample, 2 g was placed in a The collection was done in three replicates each kheljahl flask and 10 ml aqua regia (HCl: HNO3) month and three individual animals were added. The mixture was digested at 60 0C for combined to serve as a replicate. The collected about two hours. The digest was cooled and samples were taken to the laboratory and stored in transferred to a 50 ml standard flask and made up the freezer prior to digestion for analysis of the to mark with distilled water. The resulting digest heavy metal content. Collection of P. aurita from solution was subsequently filtered using this station was based on its availability throughout Whatman© filter paper into acid pre-washed the year. All samplings were carried out between polyethylene bottles. The metal content of the the hour of 10.00 and 15.00. digest was then determined by Flame Atomic Absorption Spectrophotometry on Perkin Elmer Collection of Water Samples AAnalyst 200. Water samples for physicochemical analysis were collected using acid washed and distilled water Heavy Metal Analysis of Pachymelania cleaned 2-Litre polyethylene containers by dipping aurita them 10 cm below the water surface. Water Whole animal tissue of collected P. aurita was samples for heavy metal analysis were collected extracted from the shell and dried in an oven at 50 into fresh 120 ml plastic bottles. To prevent 0C for several hours until constant weight was adsorption of metals into the walls of the 120 ml achieved. The dried tissue was crushed and containers, the samples were acidified with 2 homogenised using a domestic blender. Two drops of concentrated HNO3 (APHA, 1998) and 0 grams (2 g) of each sample was then digested with stored in a refrigerator (4 C). Water samples were concentrated nitric acid for 180 minutes in a collected for the duration of 12 consecutive Kheljahl flask at 60 oC on a hot plate. The digest months. was transferred into a 50 ml standard flask and made up to volume with distilled water. The Collection of Sediment resulting mixture was subsequently filtered Sediment samples were taken for a period of 12 2 through a Whatman© filter paper into an acid months, using a 0.1m Van Veen grab. The pre-washed polyethylene bottles. The metal samples were placed in a labelled polythene bags content of this digest was determined using for preservation in the laboratory deep freezer (0 Flame Atomic Absorption Spectrophotometer 0 C) prior to sediment analysis. (AAS) (Perkin Elmer AAnalyst 200). Heavy Metal Concentrations of Water (mg/l) Statistical Analysis The metals analysis was determined by the Atomic One way analysis of variance (ANOVA) and Absorption Spectrophotometric (AAS) method. comparison of means by Duncan Multiple Range 100 ml of the sample was placed in an Erlenmeyer Test (DMRT) was used to test for significant flask and 10ml concentrated nitric acid added. The differences in the level of heavy metals in the o resulting solution was heated at about 60 C for whole tissue of periwinkle samples collected two hours.