Fish are often at the top of aquatic food chain and when pollutants build up in the food chain, they are more disposed to accumulate heavy metals in their bodies. Fish are widely used to evaluate the health of aquatic ecosystems. They may concentrate large amounts of metals from the water and therefore are responsible for adverse effects and death in the aquatic systems. Metal accumulation in fish tissues poses a direct threat for human being [1]. The distribution of metals varies between fish species, depending on age, development status and other physiological factors. The ingestion of food is an obvious means of exposure to metals, not only because many metals are natural components of food stuffs, but also environmental contamination and contamination during processing. The ingestion of heavy metals by fish via food and water may affect not only the productivity and reproductive capabilities of such fish, but ultimately affect the health of man that depends on these organisms as a major source of protein [2]. The distribution of fish species was effected by both biotic and abiotic factors [3]. Predation factor was the main factor affecting fish populations with direct and indirect movements. Besides, the literature associated with resource fractionalisation among fishes suggest that competition plays an important role in the local organization of communities. On the other hand, abiotic components of both systems can be divided into chemical and physical factors [4].

Fisheries are the most important element in the economy of many nations as they have been a stable item and a good protein source in the diet of many people. Fishes are bio-monitors of aquatic ecosystems especially in estimating pollution of heavy metals [5]. Heavy metals pollution in the aquatic environment is a globally increasing problem because they are highly persistent, indestructible and possess the ability to bio-accumulate [6]. Fishes are suitable indicators of heavy metal contamination and are extensively used to evaluate the health of aquatic ecosystem since they are of different sizes and occupy different trophic levels [7]. Since fishes are at the end of the aquatic food chain they reflect the water quality and are indicators of pollution. Metals in the aquatic environment accumulate in the food chain and lead to ecological damage as well as human health risks after eating such aquatic organism [8]. Hence, monitoring the contamination of fish tissue is important as early warning indicator of water quality contaminations and helps taking rights actions in the interest of public health and the environment [9].

 Among environmental pollutants, heavy metals are of particular concern; due to their potential toxic effect and ability to bio-accumulate in aquatic ecosystems [10], thus, the pollution of the aquatic environment with heavy metals has become a public health problem worldwide during recent years. Heavy metals that are deposited in the aquatic environment may accumulate in the food chain and cause ecological damage as well as threat to human health [11, 12]. Studies have shown that fish accumulate these heavy metals from the surrounding water bodies thereby leaving a health risk if taken as food [13]. Heavy metal intake has also been reported to be essentially due to drinking contaminated water and ingestion of contaminated food [14, 15, 16].

Heavy metals such as copper, iron and nickel are essential metals since they play important roles in biological systems, where as cadmium and lead are non- essential metals, as they are toxic, even in trace amounts [17]. However, these essential metals can also produce toxic effects when the metal intake is excessively elevated [18]. Heavy metals are taken into biological systems via inhalation, ingestion and skin absorption. If they enter and accumulate in body tissue faster than the body’s detoxification pathways can dispose of them, a gradual build-up of these toxins will occur and result in toxicity. High concentration exposure however, is not necessarily required to produce a state of toxicity in the body tissue as overtime low concentrations can also reach toxic levels [19]. Therefore, this study seeks to assess the heavy metal concentration in some organs of fish selected from Omambala River, Anambra State.

The Study Area (Omanbala River)

This study was carried out in Omambala River in Omambala, Otuocha, which is a town and Headquarters of Anambra East Local Government Area of Anambra State, Nigeria. Omambala River is found in Umuleri and is a major Umuobanam clan. The name “Omambala” emanated from the “Oche coasts “called “Otuoche” owned by the “Amuka-Adegbe Exogamous village of Ikenga Umueri” .Omambala is made up of many communities such as Nsugbe, Nkwelle, Ezuneke baton into the river Niger as a tributary. Omambala River is located on the map along the latitude 6’33’33’’N and longitude 6’85’12’’E. it is a tributary of River Niger, on the north east by Emu stream, south east by Ezu River and south west by Akor River. Also close to the river is the Nigerian Marine police, to manage and see to the activities carried out in Omambala River. It has a large population, comprising many people from different ethnic groups in Nigeria. These people that dwell here do not only include original natives of Umuleri and Aguleri but others from other parts of Nigeria. This study lasted for a duration of 8 weeks (2 months).

Description of Sampling Areas

Three sampling points (SP) were chosen and named S.P.1, and S.P.11 where S.P III. These points were chosen based on the characteristic features of the area (Fig 1).

Fish Sample Collection, Preparation and Analysis

Eight (8) samples of each species (C. gariepinus, O. nilotucus and , C. obsura) were collected for each species making a total of 32 fish samples The fish samples were placed in plastic container and immediately preserved on ice prior to heavy metal analysis to meet the analytical holding times.

Figure 1: Map of the Study Area.

Methods for the Heavy Metal Analysis

Heavy metal analysis was conducted using Varian AA240 Atomic Absorption Spectrophometer according to the method of APHA 1995 (American Public Health Association). Atomic absorption spectrometer's working principle is based on the sample being aspirated into the flame and atomized when the AAS's light beam is directed through the flame into the monochromator, and onto the detector that measures the amount of light absorbed by the atomized element in the flame. Since metals have their own characteristic absorption wavelength, a source lamp composed of that element is used, making the method relatively free from spectral or radiation interferences. The amount of energy of the characteristic wavelength absorbed in the flame is proportional to the concentration of the element in the sample.

Sample Digestion

2g of the sample was weighed out into a digestion flask and 20ml of the acetic acid mixture (650ml. Conc. HNO3; 80ml perchloric acid; 20ml conc. H2SO4) added the flask was heated until a clear digest is obtained. The digest was diluted with 100ml. with distilled water. Appropriate dilutions are then made for each element. The filtrate was analysed using FS240AA Agilent Technology.

Preparation of Reference Solution

A series of standard metal solutions in the optimum concentration range was prepared, the reference solutions were prepared daily by diluting the single stock element solutions with water containing 1.5ml concentrated nitric acid/litre. A calibration blank was prepared using all the reagents except for the metal stock solutions. Calibration curve for each metal was prepared by plotting the absorbance of standards versus their concentrations.

 Water Quality Parameters

The values of pH, electrical conductivity, and water hardness were determined by the method described by APHA [20].

Statistical Analysis

Statistical Package for Social Science (SPSS) version 20.0 Statistical Package for Social Sciences (SPSS) and data was subjected to one-way analysis of variance (ANOVA) to assess the differences in fish, tissues and stations. The results will be expressed as mean ± standard deviation.

The result of the heavy metal concentration in fin, gills and muscle of Clarias garipienus from Omambala River is presented in Table 1. The result revealed that there is a significant difference (p<0.05) in the level of arsenic and manganese while lead and cadmium were not significantly different (p>0.05). The result of the heavy metal concentration in fin, gills and muscle of Channa obscura from Omambala River is presented in Table 2. The result revealed that there is an observable difference (p<0.05) in the level of Arsenic and Manganese while Lead and Cadmium were not significantly different (p>0.05). The result of the heavy metal concentration in fin, gills and muscle of Orochromis niloticus from Otuocha River is presented in Table 3. The result revealed that there is an observable difference (p<0.05) in the level of Arsenic and Manganese while Lead and Cadmium were not significantly different (p>0.05). The values for physicochemical parameters of waters from Omambala River are presented in Table 4.4. There was no significant difference in all the parameters from the sampling stations.

Figure 1 illustrates the concentrations of selected heavy metals (lead, arsenic, cadmium, and manganese) in the fin, gills, and muscle of Clarias gariepinus collected from Omambala River.Cadmium recorded the highest concentration among all metals, with the greatest accumulation observed in the gills, followed by the fin, while the muscle showed negligible levels. Lead was predominantly detected in the fin, with lower concentrations in the gills and no detectable levels in the muscle. Arsenic was not detected in any of the examined organs. Manganese occurred at relatively low concentrations across tissues, with slightly higher levels in the muscle compared to the fin and gills. Figure 2 presents the concentrations of selected heavy metals (lead, arsenic, cadmium, and manganese) in the fin, gills, and muscle of Channa obscura. Cadmium exhibited the highest concentration among the analyzed metals across all tissues, with the fin showing the greatest accumulation, followed by the gills and muscle. Lead was detected at relatively low levels, with slightly higher concentrations in the gills compared to the fin and muscle. Arsenic occurred at minimal concentrations and was nearly uniform across the organs. Manganese was present at moderate levels, predominantly in the fin, with lower concentrations in the gills and muscle. Figure 3 shows the concentrations of selected heavy metals (lead, arsenic, cadmium, and manganese) in the fin, gills, and muscle of Oreochromis niloticus. Cadmium recorded the highest concentration among all metals in the examined tissues, with the fin exhibiting the greatest accumulation, followed by the gills and muscle. Lead was present at comparatively lower levels, with slightly higher concentrations in the gills than in the fin and muscle. Arsenic was detected at minimal concentrations and showed nearly uniform distribution across all organs. Manganese occurred at moderate levels, predominantly in the fin, while the gills and muscle contained lower and comparable concentrations.

Table 1: Heavy Metal Concentration in Fin, Gills and Muscle of Clarias Garipienus from Omambaa River (Mean± SD).

Values with the same superscript on the same column do not differ significantly at (p<0.05)

Table 2: Heavy Metal Concentration in Fin, Gills and Muscle of Channa Obscura from Omambala River (Mean± Sd).

Values with the same superscript on the same column do not differ significantly at (p<0.05)

Table 3: Heavy Metal Concentration in Fin, Gills and Muscle of Orochromis Niloticus from Omambala River (Mean± SD).

Values with the same superscript on the same column do not differ significantly at (p<0.05)

Table 4: Physicochemical Parameters of Waters from Omambala River (Mean± SD).

Values with the same superscript on the same column do not differ significantly at (p<0.05)

Figure 2: Concentrations Of Heavy Metals In The Organs Of Clarias Gariepinus Sampled From Omabala River.

Figure 3: Concentrations Of Heavy Metals In The Organs Of Channa Obscura Sampled From Omabala River.

Figure 4: Concentrations of Heavy Metals in the Organs of Oreochromis Niloticus Sampled From Omabala River.

Heavy metals are one of the most serious pollutants in our aquatic environment due to their toxicity, persistence and bioaccumulation problems (Adewunmi et al., 2017). Most heavy metals have no beneficial functions to the body and can be highly toxic if they enter into the body through inhalation, ingestion and skin. They accumulate in the body tissue faster than the body’s detoxification pathways can dispose them off [23]. The result of this study showed that the level of lead was highest (0.19±0.27) in the fin of Clarias gariepinus compared to the gills and muscle. The concentration in fish sample were under the permissible limit of 0.5 mg/Kg. Lead causes renal seizure and liver harm in people. Pb exposure is also known to cause musculoskeletal disorder, reproductive and developmental [24]. The results contradicts the finding of Ismaniza and Saleh [25] where the concentration of heavy metals in fish was high. It was also reported by Irwandi and Farida [26] that Ca, Mg, Fe, Cu, Zn and Pb exhibited bio-accumulation from water to fish. These authors reported higher concentrations of metal in fish than in water, which indicates the bio-accumulation. Cadmium was highest in the gills (0.37±0.45mg/l) followed by fin (0.26±0.38mg/l) while the muscle had the least concentration (0.15±0.23mg/l). The main reason for the presence of these heavy metals could be due to long-term disposal of sewage treated water into the river, which resulted in the accumulation of toxic heavy metals in river water. This may adversely affect the growth of various aquatic vertebrates and invertebrates including fishes. The concentration of manganese ranged from 0.03 mg/kg to 0.07 mg/kg with the highest level found in the muscle while the fin had the least concentration. The result showed that the level of cadmium was the highest in Clarias gariepinus followed by lead while Arsenic was not present.

From the result of the study, Cadmium was found to occur highest in all the species and the organ having the highest of cadmium concentration is in the gills of the three species of fish studied. This result supports the assertion that, of all the tissues and organs of fisheries, the gill is the major route through which dissolved metals enter the fish. This could be due to their sensitivity to variations in the water and the ability of gill filaments and lamellae to get in contact with the contaminants in water [27]. The gills of the fish are one of the major sites that play active role in heavy metal accumulation [28]. This could be due to the fact that this (gill) (i.e. gill lamellae) organ is used for respiration.The values obtained for Mn in the present investigation in the muscles, and gills are below 0.50mg/kg recommended by WHO [29]. It thus implies that all the fishes examined are within the range recommended for human consumption. Accumulation of manganese could pose manganese related health problems which manifest in the form of impulsive and aggressive behavior in some cases euphoria and sexual stimulation [30]. The result obtained for Mn in this study contradicts the reports of Obasohan [31], Idodo-Umeh [32], and Okoronkwo [33] who obtained 0.67-3.50, 2.81-4.61 and 0.193-0.435mg/kg in fishes at Ogba river, Olomoro water bodies and River Niger respectively in Nigeria.

The values obtained for Pb in all the muscles, fin and gills of the three fish species studied are below the prescribed standard safe limits of 2.0 mg/kg for lead in food fish by WHO, [29] and FEPA [34], thus indicating that the fishes studied are safe from lead related health hazards. Lead toxicity can cause palsy and encephalopathy characterized by muscular fatigue, ataxia, insomnia and gradual seizures in children [35]. The values obtained for Pb in this report is lower than the report of Obasohan [31] who obtained 2.67-7.33 mg/kg in fishes from Ogba River Nigeria but differed from Oguzie [36], who reported lead concentration of 0.007-0.03 mg/kg in fishes form Ikpoba River, Nigeria. Lead which form a high proportion of metals, paints, dyes batteries, petrol and diesel from the industries in Anambra area are also found in large proportion in pesticides, fungicides and fertilizers used for agriculture along the banks of the river. Metals from these substances along with domestic wastes and human activities (washing of clothes, sand mining and car wash) may have been washed into the River system during the rains accounting for their high proportion in the fishes examined during the rainy season.

The monitoring of heavy metal concentration is normally done by measuring the concentration of metal contain in sediment, water, biota in water-based system and organs. This study ascertains heavy metals amount in fish (Clarius garipinus, Channaobscura and Orochromis niloticus) samples collected from the three study locations. The result shows high heavy metals from fish samples. Cadmuim was observed to be the highest occurring heavy metal in all the three fish species investigated. All the concentration of the heavy metals were within the tolerable range.

In view of the importance of fish to diet of Man,

• It is necessary that regular biological monitoring of the river and fish meant for consumption should be done to ensure continuous safety of fish food.
• Safe disposal of domestic wastes or sewage and industrial effluents should be practiced and where possible recycled to avoid these metals and other contaminants from getting into the river.
• Sand dredging and car washing in the river should follow adequate regulatory environmental measures to prevent further contamination of the river and fish.
• Further studies on the concentration of heavy metals on other fish tissues (brain, liver, kidney, intestines and heart) are recommended.

1. Papagiannis I, Kagalou I, Leonardos J, Petridis D, Kalfakakou V. Copper and zinc in four freshwater fish species from Lake Pamvotis (Greece). Environ. Int. 2004; 30: 357-362.
2. Fonge BA, Tening AS, Egbe AE, Awo EM, Focho DA, Oben PM, et al. What controls who is where in fresh water fish communities-the roles of biotic, abiotic, and spatial factors. Can J Fish Aquat Sci. 2001; 58: 157-170.
3. Kadye WT, Moyo NAG, Magadza CHD, Kativu S. Stream fish assemblages in relation to environmental factors on a Montane Plateau (Nyika Plateau, Malawi). Env Biol Fishes. 2008; 83: 417-428.
4. Adeniyi AA, Yusuf KA. Determination of heavy metals in fish tissues, water and bottom sediments from Epe and Badagry Lagoons, Lagos, Nigeria. Environ Monit Assess. 2007; 37: 451-458.
5. Olusola JO, Festus AA. Levels of heavy metals in some selected fish species inhabiting Ondo state coastal waters, Nigeria. J. Environ Anal Toxicol. 2015; 5: 303-314.
6. Ade S. Dredging Impact Study: A Report Submitted to Shell Petroleum Development Company (SPDC) Warri AdeSobande and Associates. 1998.
7. Farkas A, Salanki J, Specziar A. Relation between growth and the heavy metal concentration in organs of bream Abramisbrama L. populating Lake Balaton. Arch Environ Contam Toxicol. 2002; 43: 236-243.
8. Al-Bader N. Heavy metals levels in most available fish species in Saudi market. J. Food Technol. 2008; 6: 173-177.
9. Mansour SA, Sidky MM. Ecotoxicological studies. 3. Heavy metals contaminating water and fish from fayoum Governorate, Egypt. Food Chem. 2002; 78: 15-22
10. Censi P, Spoto SE, Saiano F, Sprovieri M, Mazzola S, Nardone Get al. Heavy metals in coastal water systems. A case study from the northwestern Gulf of Thailand. Chemosphere. 2006; 64: 1167-1176.
11. Van den Broek JL, Gledhill, KS, Morgan DG. Heavy metal concentration in the mosquito Gambusia holbrooki, in the Manly Lagoon Catchment. In: UTS Freshwater Ecology Report. Department of Environmental Sciences. University of Technology, Sydney. 2002.
12. Gagnaire B, Thomas-Guyon H, Renault T. In vitro effects of cadmium and mercury on pacific oyster, Crassostrea gigas (Thunberg), haemocytes. Fish and Shellfish Immunology. 2004; 16: 502-512.
13. Prusty AW. The Use of Fish in Monitoring Water Pollution. Tour of Biotechnology. 2004; 21: 4-7.
14. Machado W, Rodrigues APC, Bidone ED, Sella SM, Santelli RE. Evaluation of Cu potential bioavailability changes upon coastal sediment resuspension: an example on how to improve the assessment of sediment dredging environmental risks. Environ Sci Pollut Res Int. 2011; 18: 1033-1036.
15. Federal Environmental Protection Agency. Guidelines and Standards for Environmental Pollution Control in Nigeria. 2002; 239.
16. Asonye CC, Okolie NP, Okenwa EE, Iwuanyanwu UG. Some physico-chemical characteristics and heavy metal profiles of Nigerian rivers, streams and waterways. African J Biotechnology. 2007; 5: 617-624.
17. Fernandes C, Fontaínhas-Fernandes A, Cabral D, Salgado MA. Heavy metals in water, sediment and tissues of Liza saliens from Esmoriz-Paramos lagoon, Portugal. Environ Monit Assess. 2008; 136: 267-275.
18. Begüm A, Amin MDN, Kaneco S, Ohta K. Selected elemental composition of the muscle tissue of three species of fish, Tilapia nilotica, Cirrhina mrigala and Clarius batrachus from the fresh water Dhanmondi Lake in Bangladesh. Food Chemistry. 2005; 93: 439-443.
19. Praveena SM, Radojevic M, Abdullah MH, Aris AZ. Application of Sediment Quality Guidelines in the Assessment of Mangrove Surface Sediment in Mengkabong Lagoon, Sabah, Malaysia. Iranian J Envron Health Sci Eng. 2008; 5: 35-42.
20. American Public Health Association. Standard Methods for the Examination of Water and Wastewater (20th Edition). American Water Works Association and Water. Environmental Federation, Washington DC. 1998.
21. World Health Organization.Guideline for Drinking Water quality (electronic Resource). Incorporating first Addendum 1, Recommendations. 2008.
22. Adefemi OS, Olaofe O, Asaolu SS. Concentration of Heavy metals in water sediment and fish parts (Illishaafricana) from Ureje dam, Ado-Ekiti, Ekiti State. Nigerian Journal of Biology and Physical Sciences. 2008; 3: 111-114.
23. Ekeanyanwu CR, Ogbuinyi, CA, Etienajirhevwe OF.Trace metals distribution in fish tissue, bottom sediments and water from Okumeshi River in Delta state, Nigeria. Environ. Res. J. 2011; 5: 6-10.
24. Todd GD, Chessin RL, Colman J. Toxicological profile for total petroleum hydrocarbons (TPH). 1999; 230.
25. Enger DE, Bradley FS. Environmental Science: A Study of Inter Relationships. Wm Brown Publishers, London, England. 1992; 231.
26. Olaifa FE, Olaifa AK, Adelaja AA, Owolabi AG. Heavy metal contamination of Clariasgariepinus from a lake and fish farm in Ibadan, Nigeria. African Journal of Biomedical Research. 2004; 7: 145-148.
27. Olguno?lu MP, Artar E, Olguno?lu IA. Comparison of Heavy Metal Levels in Muscle and Gills of Four Benthic Fish Species from the Northeastern Mediterranean Sea. Polish J. Environ Studies. 2015; 24: 1743-1748.
28. Eneji IS, Shaato R, Annune PA. Bioaccumulation of Heavy Metals in Fish (Tilapia zilli and Clarias gariepinus) Organs from River Benue, North Central Nigeria. Pak. J. Anal. Environ. Chem. 2011; 12: 25-31.
29. Guideline for Drinking Water Quality, 3rd edn. World Health Organization, UK. 2010.
30. Aderinola AH. Levels of heavy metals (Fe, Cu, Ni, Cr, Pb, and Zn) in muscle and gills of Oreochromis niloticus and Tilapia zilli from the Northeastern Mediterranean Sea. Polish J. Environ. Studies. 2009; 24: 1743-1748.
31. Obasohan EE. Heavy metals concentrations in the offal, gill, muscles and liver of a fresh water mudfish (Parachanna obscura) from Ogba River, Benin city Nigeria. Agrican Journal of Biotechnology. 2007; 6: 2620-2627.
32. Idodo-Umeh G. Pollution assessments of Olomoro Water bodies using Physical, Chemical and Biological Indices. PhD. Thesis. University of Benin, Nigeria. 2002; 387.
33. Okoronkwo IP. Heavy Metals Content in Water and Fish of River Niger at Yelwa-Yauri. Msc Thesis, University of Benin, Benin-City, Nigeria. 1992.
34. FEPA/ (FMEnv). Guidelines and standards for environmental pollution control in Nigeria. Washington, DC: Federal Environmental Protection Agency. 2003; 238.
35. Morenikeji OA, Adepeju AI. Helminth communities in cichlids in natural and man-made ponds in South-West Nigeria. Researcher. 2009; 1: 84-92.
36. Oguzie FA. Heavy mettas in fish, water and effluents of lower Ikpoba river benin City. Park. J. Sci. Ind. Res. 2003; 46: 156-160.