Assessment of Heavy Metals in Some Marine Fish Species Relevant to their Concentration in Water and Sediment from Coastal Waters of Ondo State, Nigeria

Copyright: © 2015 Olusola JO, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Assessment of Heavy Metals in Some Marine Fish Species Relevant to their Concentration in Water and Sediment from Coastal Waters of Ondo State, Nigeria


Introduction
The aquatic environment with its water quality is considered the main factor controlling the state of health and diseases in both cultured and wild fishes. Pollution of heavy metals in aquatic ecosystem is growing at an alarming rate and has become an important worldwide problem [1]. Increase in population, urbanization, industrialization and agricultural practices have further aggravated the situation [2]. As heavy metal cannot be degraded, they are deposited, assimilated or incorporated in water, sediments and aquatic animals and thus causing heavy metal pollution in water bodies [1]. Therefore, heavy metals can be bio accumulated and biomagnified via the food chain and finally assimilated by human consumers resulting in health risks [3]. As a consequence, fish are often used as indicators of heavy metals contamination in the aquatic ecosystem because they occupy high trophic levels and are important food sources [4]. Fishes are major part of the human diet and it is therefore not surprising that numerous studies have been carried out on metal pollution in different species of edible fish [5,6]. Predominantly, fish toxicological and environmental studies have prompted interest in the determination of toxic elements in seafood [7]. Analyzing pollutant in living organisms is more attractive and promising than analyzing pollutants of the abiotic environment, as living organisms provide precise information about the bioavailability of pollutants [8]. This may assist in predicting pollutants transfer exposure and its possible health consequence to humans. In addition, such information is crucial in making accurate risk assessment for seafood safety purposes. Report has shown that heavy metals have the tendency to accumulate in various organs of marine organisms, especially fish, which in turn may enter into the human metabolism through consumption causing serious health hazards [9]. In many cases, industry has main role in environmental crises especially in civil and energy projects. For example, more than 60 percent of annual greenhouse gas emissions are related to the industrial activities in the world (transportation fuels and distribution 25.3%, power stations 21.3%, industrial process 16.8%). Ondo State coastal water is a brackish water body located in southwestern Nigeria. The water is used by the local community for various purposes including fishery. Water and sediment quality within this coastal waters are increasingly polluted with contaminants especially heavy metals coming from oil spill from shell and chevron companies, sewage and run off-off from agricultural land [10]. Hence the main issue arises on whether the concentration of pollutants in the waters body represents a risk to human and aquatic biota. Generally, in environment field and related science, most previous studies have been carried out using classical methods and only the ways to deal with industrial pollution have been investigated. Researches about deal with challenges and using of new technologies have not been fully dealt with. However, valipour et al used environmental flow diagram to identify pollutants of industrial units, the source of production, transmission and conversion processes, and the recipient thus, making decision about environmental pollution simple. The present study is undertaken to investigate the bioaccumulation potential of six selected heavy metals viz. Cadmium, Copper, Chromium, Nickel, Lead and Zinc in different tissues of the selected fish species, Pentanemus quinquarius, Pseudoltolithus senegalensis, Trichirus lepturus, Plectorhynchus meditarraneus and Pseudotolithus typus from the coastal waters with associated water and sediment samples.

Study area
The coastal waters in Ilaje local government area is one of the largest water bodies in ondo state, Nigeria. The research was carried out in the Atlantic Ocean shoreline from the coastal waters in Ilaje local government area. The Local Government Area lies between longitudes 6°12°E and 6°30°E of the Greenwich Meridian and between latitudes 4°10°N and 4°6°N of the Equator. It is bounded in the West by Ogun State, in the East by Irele Local Government Area and Edo State, in the North by Okitipupa Local Government Area and in the South by Bight of Benin and Atlantic Ocean ( Figure 1). Due to oil exploration activities and urbanization as well as continuous industrial and agricultural growth in Ondo State, Nigeria. The coastal water has been heavily impacted by a number of pollutants originating from different sources including heavy metals. Such contamination must be an important issue regarding the health of the aquatic ecosystem and its animals and in turn, to human's health.

Sampling and sample analysis
Water and sediment samples were collected from randomly selected three sub location in each main location of the ocean shore line. Water samples were taken into pre-acid washed polyethene bottles. The water sample were acidified to a pH of less than 2 by adding 2 ml of analar grade conc. HNO 3 and kept in the refrigerator prior to analysis. Representative water sample (100 ml) from the three sub locations in each main location were digested by standard procedure. The concentrations of metals in each sample were determined against those of the blank and standard solutions using Buck scientific AAS. The sediment sample taken concurrently from the bottom surface using a sediment samples from the randomly selected three sub locations of each of the selected location were transported to the laboratory in a polythene bag that has been previously washed and leached with acid, and subsampled to obtain a representative sample for each location. The sediment was drained and kept in safe place for air drying prior to analysis. The air dried samples were ground and sieved through 2 mm aperture. Digestion of sediment samples was carried out by procedure described by Hulya [5]. Heavy metals in sediment sample was analyze using Atomic Absorption Spectrophotometer (AAS) Buck scientific model, 200A. Five to seven pieces each of (Pentanemus quinquarius, Pseudoltolithus senegalensis, Trichirus lepturus, Plectorhynchus meditarraneus and Pseudotolithus typus.) were caught from the water bodies with the assistance of local fisher men. The samples were transported to the laboratory, where the scales were removed where applicable, rinsed with distilled water to remove any adhering substance and each fish separated into eye, head, gills, bones and muscles with dissecting knife. The different fish organs were then separately oven-dried at 105 ± 2°C in a Gallenkamp moisture extraction oven until constant weight was obtained and then ground into powder. Extraction of metals from the fish samples was by mixed acid digestion. Heavy metal concentrations in water samples were determined having digested the samples in accordance with the standard procedure established by Parker [11]. The water samples (100 ml) were digested on a hot plate with the addition of 10 ml concentrated nitric acid. The solution was heated to almost dryness and the residue dissolved with 10% HNO 3 . The resulting solution was filtered through Whatman number 1 filter paper into 50 ml standard flask and solution made to the mark. The concentrations of metals in each sample were determined against those of the blank and standard solutions using Buck scientific AAS. The sediment samples were air dried ground and sieved through 2 mm aperture. About two grams of the sediment sample in each case were put into 250 ml beaker and digested with 20 ml of mixed hydrochloric acid and nitric acid in the ratio 3:1 and 2 ml 35% H 2 O 2 on hot plate in a fume cupboard for 2 hours [5]. On cooling, the digest was filtered into 50 ml standard flask and made to the mark with distilled water. The resultant solution was analyzed for heavy metals using Atomic Absorption Spectrophotometer (AAS) Buck scientific model, 200 A. Samples of various organs ranging from 0.5 g to 1.09 g were accurately weighed and digested using 10 ml of 65% HNO 3 , 5 ml of 37% HCl and 2 ml of 35% H 2 O 2 at 80 ± 50°C in a fume chamber until colorless liquid was obtained [12]. The solutions were allowed to cool at room temperature, filtered into a 50 ml standard flask. The filtrate obtained was made up to 50 ml mark with distilled water and used for heavy metals determination against those of the blank and calibration standards using Atomic absorption spectrophotometer, Buck Scientific model.

Heavy metal levels in water
Mean concentration and standard deviation of heavy metals level (mg/L) in the two sampled locations are presented in Table  1. The result were compare with federal ministry of Environment water standards for aquatic life fresh (FWA), USEPA and World Health Organization standard for permissible limit of heavy metals in water [13,14]. Heavy metal pollution in the marine environment is determined by measuring its concentration in water, sediment and living organisms. Levels of dissolved metals in water from the two main sampled locations at the Ocean shore line are presented in Table  1. No significant location-related differences were seen with respect to the levels of Cr, Cu and Ni in water. Metals concentrations in water were found in the following order: Pb > Cr > Cu > Zn >Cd >Ni in Location1, whereas they follow the order of Pb > Cu > Cr > Cd >Zn > Ni in Location 2. Of the six metals monitored, Pb and Cr were the most abundant. High concentration of Pb (0.57-0.79 mg/l) observed in the water may be associated to deposit of air born particulate matter as well as spill from fishing boat used as means of transportation. The mean concentrations of the metals in the coastal water were compared with guideline values recommended by USEPA and FME Table 1, Showed compliance with Cu, Zn and Ni, while Cr (0.31-0.34 mg/l) Cd (0.08-0.21 mg/l) and Pb (0.57-0.79 mg/l) were higher than the permissible recommended limits. Similar observation was made with the federal ministry of Environment water standards for aquatic life to which the metal Cr, Cd and Pb were also higher [15]. It is expected that the equilibrium of analyte between particular environmental components depend on the critical parameters responsible for kinetic processes that lead to this state. For the studied system the critic parameter should be as ordered as follows: the composition and physicochemical properties of neighboring rivers flowing into the coastal waters, type of the floated soil/sediment forming bottom sediment, current of flowing streams/rivers, seasonal parameters, and biological ability of particular environment al components for concentration of heavy metals.

Heavy metal levels in sediment
The mean results and standard deviation of heavy metals (mg/kg) in sediment samples from the two sampled locations are presented in Table 2. The results were compared with probable effect concentration of heavy metals in sediment as propose by McDonald et al., [16]. Sediments are essential component of aquatic ecosystem acting as carriers sink and potential sources of contaminants [17]. Heavy metals contamination in sediment can affect the water quality and bioaccumulation of metals in aquatic organisms, resulting in potential long term implication on human health and ecosystem [18]. The mean concentration of heavy metals in sediment has been found to reflect the degree of pollution in an area. The mean results of heavy metals recorded in sediment samples taken from the two sampled locations are presented in Table 2. Total metal concentrations of the bottom sediment varied slightly between the sampled locations especially in the values of Cr, Zn and Cu, but no significant differences (P<0.05) were observed in Pb, Cd and Ni concentration among the two locations studied. The value of Cr (0.02-4.19 mg/kg) and Zn (2.12-3.11 mg/ kg) was higher than those of other metals, while Ni remained within a relatively narrow range from BDL to 0.01 mg/kg. Cd and Pb were found to share a trend in their level at the two locations. The level of Cd and Pb in sediment of the coastal water could be attributed to industrial and agricultural discharges as well as from possible spill of petrol from fishing boat over the year. High level of metal at the Ocean shoreline could also be attributed to changes in velocity within the ocean which may lead to abundance of heavy metal at the ocean shoreline. Although the pH value of the sediment was not carried out, it has been show from literature that heavy metal are more accumulated in sediments with high pH value, which is one of the characteristics of the coastal water [10]. The order of abundance of these metals in sediments from the two locations were Cr> Zn > Cu > Pb > Cd > Ni ( Table  3). Concentration of some metals investigated in the sediment were similar to those reported for River Orogodo in Delta State [17], but were lower compared to previous study on Ondo State Coastal Water (Tables 4a-4e) [18] and those reported for some communities in Ilaje local government area of Ondo State (      [17,22]. Probable effect concentrations (PEC) of sediments metal levels Pb 128, Cd 5, Cr 111, Cu 149, Zn 159 (mg /kg) has been proposed by McDonald et al. [16]. The results of the present study show that the concentrations of Cd, Cu, Cr, Pb and Zn in the sediment samples were much below the probable effect concentration of sediment metals levels. Above this level, metals may have adverse effects on sediment dwelling organisms [16].  Tables 4a-e. Zinc was the most abundant in all the examined tissues. Tissues specific comparison of the accumulation of the investigated metals showed that the metals concentration were significantly high in the gill tissues compared to the muscle tissues. Jobling [23] attributed the high accumulation of heavy metals in gills tissues to the metallothionein proteins which are synthesized in liver and gills tissues when fishes are exposed to heavy metals and detoxify them. These proteins are thought to play an important role in protecting them from damage by heavy metal toxicants. Also, gills are the site directly exposed to the ambient conditions and also are known for their excretory function [24]. Chromium, copper and Zinc are essential element and are regulated by physiological mechanisms in most organism. However, occurrence of excessive levels of them is regarded as potential hazard which can endanger both animal and human health [25]. The level of these essential metals Cr, Cu and Zn in the muscle, gill, bone, eye and head are presented in Tables 4a-4e. Cr was not detected in the muscle of all examined fish species except Plectorhynchus meditarraneus (0.36 mg/ kg) this may be associated to their large size and long exposure period. Cr concentration recorded comparable value in most tissues of the examined fish species. The level of Cr in muscle and other organs were lower than USEPA limit 8 mg/kg [14].The levels of Cu and Zn in edible muscle of the fish species ranged from BDL-0.58 mg/kg and 0.25-0.36 mg/kg respectively. The USEPA limit for Cu and Zn in fish food for human consumption is 120 and 50 mg/kg respectively [14]. The level of Cu and Zn in edible muscle in all fish species were low and below the international limits. Hence, Cu and Zn levels have posed no threat for consumption of the fish muscle from the coastal water. However, because a metal concentration in the aquatic environment is low and considered to be naturally occurring or background does not mean that the concentration could not cause adverse ecological effects [26]. The presence of one metal can significantly affect the impact that another may have on an organism. The effect may be synergistic, additive or antagonistic. The low level of Cu and Zn in muscle could be associated to lower level of binding protein metallothioneins. Metallothioneins are a family of low molecular weight cysteine rich proteins that have been reported in vertebrate and several invertebrate. Their synthesis can be induced by a wide variety of metal ions including Cu, Zn and Cd. Hence metallothioneins has been proposed as biomarkers to indicate the presence of high metals in the environment [8]. Although Cu and Zn play a crucial role in several enzymatic processes, they are tentatively classified as highly toxic metals by Hellawell [27] and are sediments containing more sand and lower values of organic matter exhibit low metals enrichment. Also, the concentration of heavy metals in sediment increases as the amount of organic material increases [19]. It has also been reported that metals such as Cd, Cu, Pb and Zn have high tendency to binding tenaciously to organic matter contained in the soil, sediment and suspended particles within the water column, while sediment with high clay content has ability to concentrate most heavy metals compared to others such as carbonate which are selective [20,21]. Therefore the variation in heavy metals in the sediment samples analyzed may be due in part to contribution from these factors. By comparing the concentrations of heavy metals analyzed in the water and sediments samples, it can be concluded that heavy metals are highly     bioaccumulated in aquatic organism. The concentration of nickel in the tissues of all examined species is relatively low ranges from BDL-0.12 mg/kg. The result confirms that most fish species do not bio accumulate the metal contrary to what was previously reported by Hulya and Mendil [5,28]. The mean concentration of nickel in different fish species observed in this present study was below the permissible limit of 1.0 mg/kg prescribed by United State Environmental Protection Agency [14]. Lead and cadmium are non-essential elements which are accumulated in human tissue and harmful to human health. Comparison of Cd and Pb accumulation in the various organs shows that the highest concentration of Pb was found in head of Pseudotolithus typus (0.71 mg/kg) (

Concentration Factor
Concentration factors of the metals in fish relative to superficial water and sediment are presented in the tables below (Tables 5 and 6). Estimated concentration factor of heavy metals from water were greater than from sediment, suggesting bioaccumulation of the metals by the fish from water column. Fish has been reported to accumulate metals from water by diffusion via skin and gills as well as oral consumption/ drinking of water [29]. Similar observation has been reported by many workers in Nigeria [18,[30][31][32]. Figures 2 and 3 Show the comparisons of the ratio of investigated heavy metals levels in fish/water and fish sediment respectively.

Conclusion
The health safety of Ondo state coastal water for some fish species has been assessed, though there have not been reported cases of metal toxicity arising from direct use of water or consumption of fish from the area. The present results showed that metal concentration were lowest in muscle and highest in gill due to physiological roles in fish metabolism where the target tissues of heavy metals are the metabolically active ones. Therefore heavy metals in these active tissues are higher compared to muscle where metabolic activity is relatively lower. The result of these research has provided baseline information of heavy metals in water, sediment and tissues of some fish species from