Heavy metal levels in muscles of some fish species from Aladja River; Warri, Nigeria: a public health concern.Introduction
Accumulation of heavy metals has been studied in fish samples collected from Lake Beysehir and according to international criteria and Turkish regulations, heavy metal concentrations especially for cadmium Cd and lead Pb in Lake Beysehir were markedly above the permissible levels for drinking water . Demirak and coworkers  investigated the concentrations of heavy metals in water, bottom sediment and tissues (muscle and gills) of Leuciscus cephalus from the Dipsiz stream in the Yatagan basin (southwestern Turkey), the site of a thermal power plant. They found that there was metal accumulation in the gills compared to the muscle. Concentrations of Cd, Pb, Zn and Cr in the gills were higher than that in the muscle; however, Cu levels were higher in muscle than that in gills. Whereas many studies [10,8,12,30] have implicated industrial or human activities as possible source of pollution of the water body and biota the work of Karadede and Unlu  on the concentrations of some heavy metals in the water, sediment and fish species (Acanthobrama marmid, Chalcalburnus mossulensis, Chondrostoma regium, Carasobarbus luteus, Capoetta trutta and Cyprinus carpio) from the Ataturk Dam Lake, Turkey indicated general absence of serious pollution. Nigeria's crude is known to contain heavy metals in reasonable quantity . Previous studies have shown that fish species from water bodies in non oil producing regions of Nigeria such as Sokoto  and Lagos [25,26] show minimal heavy metal accumulation.
In Nigeria, many people consume fish because of their numerous nutritional and health benefits. Amongst the Niger Delta people of Nigeria fish based meal is a common diet irrespective of the level of poverty of the people. Smoked fish is served as snacks and also eaten between meals. It is often said that "if you are looking for a malnourished child in a poverty stricken community, do not come to the coastal states of Nigeria". This habit of fish eating is thought to convey some measure of good health to the locals who are predominantly peasant farmers and fishermen. The increased bio-accumulation of metals (resulting from burning of fossil fuels, incineration of waste, industrial effluents, agricultural practices and dissolution of metals from basement rocks by acidic solutions) in fish via lugworms, barnacles, algae, and other planktonic and benthic organism on which fish feed has necessitated public health concern worldwide.
In this work, we have investigated heavy metal levels in the different parts of some fish species from Aladja River which receives effluents from several industries that dot the area. Other relevant occupational fields within the area include steelmaking, foundry work, thermal cutting, welding, glass and ceramic production etc, seepages from numerous crude oil loading and off-loading jetties, refinery effluents and oil spillages that are characteristic of the area. This is part of our effort to compile an ecotoxicological data of the Niger Delta with the aim of advising the relevant governmental agencies for policy formulation.
Aladja town, from where the river derives it's name is one of the towns which has been subsumed by the cosmopolitan city of Warri and lies 50km from Ekpan (The site of Nigeria's largest refinery and petrochemical plant).The Warri River connects the Ekpan River with that of the Aladja. The Aladja River starts from Udu (a centre of high population density) which generates rural/urban wastes that are discharged into the river untreated, it meanders through its course before emptying into numerous creeks that are characteristic of the area. The river is unidirectional in the upper reach and tidal in lower reach. The upper bank consists of dense forest vegetation while the downstream reach is with mangrove. The area experiences tropical humidity of the semi-hot equatorial type-with a mean annual rainfall of about 3000mm . The wet season period stretches from April to October each year, though with occasional rainfall within dry season of November to March.
Materials and methods
Different fish species namely Oreochromis niloticus (body weight 293 g and length 30 cm), Tilapia zilli (body weight 136 g and length 22 cm), Serathrodon niloticus (body weight 305.4 g and length 40 cm), Clarias gariepinus (body weight 42.8 g and length 18 cm) and Ethmaliosa timbriata (body weight 12.4 g and length 9 cm) were used in this study. All the fish species were collected in the morning with the assistance of local fishermen and identified by a zoologist. The fresh fish species were dissected and different parts (brain, liver, muscles, gills and intestines) were separated. These fresh part (muscles 5 g,) were used for analysis .In another experiment 5 g of fresh water hyacinth, 2 g of soil sediment and water samples were used. Heavy metals--vanadium V, manganese Mn, cadmium Cd, chromium Cr, zinc Zn, nickel Ni, iron Fe and lead Pb were determined using standard method . Temperature, turbidity and pH were determined insitu using appropriate instrument. Dissolved oxygen DO and Biochemical oxygen BOD were determined by Redeal-Stewart modification of Winkler's method (Theroux 1943). Data were analyzed in duplicates. In all the levels of the heavy metals in the fresh fish species, fresh water hyacinth and wet soil sediments were expressed in mg/kg with respect to the fresh weight.
Results and discussion
Table 1 shows the levels of vanadium, manganese, cadmium, chromium, zinc, nickel, iron and lead in the muscles of Oreochromis niloticus, Serathrodon niloticus, Clarias gariepinus, Tilapia zilli and Ethmaliosa timbriata. The muscle of Tilapia zilli had the highest levels of Ni (6.82mg/kg) and Pb (0.60mg/kg). Ethmaliosa timbriata had highest Pb level of 2.40mg/kg. Clarias gariepinus which had the highest accumulation of the tested heavy metals in this order of ranking Fe>Zn>Ni> V> Mn> Cr>Pb>Cd.
With the exception of nickel and lead Tilapia zilli appear to be the least contaminated. However it can be concluded from this study that Oreochromis niloticus and Tilapia zilli appear the least contaminated
The ranking of heavy metal content is Clarias gariepinus>Ethmaliosa timbriata>Searthrodon niloticus> Tilapia zilli> Oreochromis niloticus. Oreochromis niloticus tended to be the least contaminated with the studied heavy metals.
The total amount of these heavy metals in each fresh fish were higher than the FAO/WHO recommended standard for fresh Fish weight in mg/kg-[Pb (0.20), Cd (0.05-0.20), Ni (0.10-0.90), Fe (1.00-4.50), Zn (5.00-10.00) and Mn (0.50-1.20)]. The concentration of metals in soil sediment, fresh water hyacinth (WH) and water is shown in Table 2. The soil sediment, WH and the water from the Aladja River showed high levels of all the tested heavy metals. The pH, temperature, turbidity, BOD and DO of river Aladja were found to be 6.85, 27.80oC, 12.70 Ntu, 15mg/l, and 4.25 mg/l respectively (table not shown).
We have investigated the levels of lead, chromium, cadmium, iron, manganese, zinc, vanadium and nickel in five different fish species which form part of daily diet of the Niger Delta people in Nigeria. These metals remain for a very long time in sea foods. As a result of series of reaction mechanisms, the metals can accumulate in the tissue of the sea food, concentrate to high amount and then pass on to the food chain. The process produces amount of metals in some food species which may be hazardous to human health, therefore an understanding of the concentration of metals existing in aquatic ecosystem is necessary . Metals contribute to a variety of adverse effects, that can impact human health and each will produce different behavioral, physiological and cognitive changes in an exposed individual. The degree to which a system, organ, tissue or cell is affected by a heavy metal depends on the toxin itself and the individuals degree of exposure to the toxin , those that are not directly toxic can produce their effects indirectly as a result of their decomposition or oxidation .
The different types of fish muscles were contaminated with the metals--Cr, Fe, Mn, Cd, Ni, V, Pb and Zn. The highest level of Pb, Cr, Cd, and Ni were seen in the Clarias gariepinus. Ethmaliosa timbriata contained high levels of all the heavy metals. In Lake Beysehir, the accumulation orders of heavy metals were Cd>Pb>Cr>Hg in the muscles of chub, carp, except for the muscle of pikeperch, in which it was Pb>Cd>Cr>Hg. The ranking of heavy metal content is Clarias gariepinus>Ethmaliosa timbriata>Searthrodon niloticus> Tilapia zilli> Oreochromis niloticus. (considering the examined only). The accumulation order may not be dependent on the body weight of the fish since Clarias gariepinus which has the small body weight showed the highest sequestration of these heavy metals. The feeding habit and migratory nature of the specie involved may account for the metals accumulated. Aladja River is within the Niger Delta region of Nigeria which has vast interwoven water bodies, therefore, the fish species must have travelled long distances accumulating various contaminants before been caught. Oyewale and Musa's work 2006, on the pollution assessment of the lower basin of lakes Kainji and Jebba in the northern part of Nigeria showed lower heavy metals levels like Pb, Cr, and Ni etc when compared with the present study. Anthropogenic pressure may be the likely reason for the higher levels of these heavy metals seen in the fish parts as Niger Delta is characterized by higher industrialization and oil exploration activities than Kainji and Jebba in Northern Nigeria. When our result is placed side by side with the Cu,Zn,Pb and Cd levels in muscles in Australia commercial fish, USA Portsmouth seafish, Greece sea fish(from both polluted and unpolluted area),Israel Haife Sea fish, West Malaysia coastal fish, Swedish EPB Lake Fish etc, it is evident that our result is very high [17,33,25,26]. This means that the pollution status of the fish immediate environment can accentuate its metal accumulation. This agrees with our previous report that fish species from crude oil polluted water has high metal levels in their parts . Aladja River is part of Niger Delta water bodies which has been devastated by several years of crude oil spillages. Also uptake of metals by fish is influenced by species of fish and various environmental factors such as pH and temperature , metal release into any water system is an active biochemical and physiological process dependent on fish group, age, sex, position of fish relative to shoreline, water depth, salinity and pollutants interactions . The total amount of these heavy metals in the different types of fish were higher than the FAO/WHO recommended standard for fresh fish weight in mg/kg--[ Pb (0.20),Cd (0.05-0.20),Ni (0.10-0.90), Fe (1.00-4.50), Zn (5.00-10.00) and Mn (0.50-1.20)]. Comparing the results presented on the tables, it means that water pollutants affect aquatic or biological organism as against water itself. This is perhaps due to bioaccumulation.
The levels of heavy metals known to be associated with petroleum industry operations, including Pb, Ni, V, Cr, Cd, Zn and Fe, have been reported to exceed the threshold limits set by the WHO health-based guideline for drinking water in some water bodies in Warri, Niger Delta. [9,20]. The presence of heavy metals may also be attributed to effluents from other relevant occupational fields such as steel making, foundry work, thermal cutting, welding ,glass and ceramic production etc within the study area, other metal pollutants may infiltrate from the basement rock and agricultural practices, since rivers are wide open to flooding which carry various contaminants. The recent discovery of an illegal toxic waste dump site within the area reminiscent of 1988 toxic waste dump at Koko (a nearby town) by a foreign firm, could be another source of heavy metals in the water through seepage and run off. The physico chemical parameters of the Rivers such as temperature, pH, turbidity, Dissolved Oxygen; DO and Biochemical Oxygen Demand BOD measured were within acceptable limit that can support aquatic life. DO and BOD of 4.25 mg/l and 15mg/l respectively were indication of organic pollution of the River and most organic materials are associated with heavy metals .
Human consumption of contaminated fish with the potential for adverse health effects has been identified in Great Lakes region . A pair-matched study from Canada reported that fish eaters from this environment had relatively higher blood lead levels than non-fish eaters . A Michigan study reported that mean blood lead levels were significantly higher in fish eaters than among control group . In the Niger Delta there is high shipping traffic and seawater is visibly contaminated by waste including crude oil.
In the coastal states of Nigeria whole smoked fish is eaten with "kpokpo garri and tapioca" (local delicacies from cassava), it is feared that the people may continually be exposed to high intake of these heavy metals. The ingestion of smoked fish both as snacks and main diet amongst the Niger Delta people of Nigeria may account at least in part for the presence of various metals in a recent biomonitoring survey of blood samples of children . This also makes the hospitality industry where these fish are coveted delicacies unattractive as not only the local populace but the larger Nigerian people and visitors who may consume the fish to health hazards . Nursing mothers can pass these metals (especially lead) to their infants during gestation. These heavy metals present various toxicities in man. Cadmium is known to be one of most harmful heavy metals and is capable of inducing renal, hepatic and testicular injury . Long term exposure to chromium can cause kidney, liver and nerve tissue damage, many chromium compounds are carcinogenic . Evidence of manganese accumulation in certain fish species has been reported by Sharif et al. , its ingestion can cause sleepiness weakness and emotional disturbance. "Nickel-iron-hypothesis" suggests that [Ni.sup.2+] is the active agent in Ni toxicity and that its intracellular concentration is a major toxic determinant, irrespective of the Ni compound to which an organism is exposed . High iron content leads to primary heamochromatisis (genetic effect) or secondary hemochromatisis in severe cases and thalassaemia . Prospective lead studies of child development from 1980 to date show associations between low blood lead concentration and poor neurobehavioral development . Zinc toxicity results in vomiting and diarrhea. Compounds of vanadium are known to cause bronchiolar constriction, shortness of breath, conjunctiva irritation. The health effects of manganese exposure in humans are not well understood. Although dietary manganese is an essential nutrient, high intake of manganese have been shown to be toxic (Institute of Medicine Food and Nutrition Board 2002). Manganese is best characterized asneurotoxin, occupational exposures are associated with characteristic syndrome called manganism which involves both psychiatric symptoms and Parkinsonism features .
Educational authorities in Nigeria have been perturbed by what they described as progressive poor performance in mathematics and science related subject amongst students. It will be worthwhile to investigate the blood lead levels of these children and compare them with those who are of above performance in these subjects. Reports from tertiary health institutions tend to show an in crease in liver and kidney problems amongst the people.
Considering the crude oil pollution of the water ecosystem, it is possible the heavy metals including lead contaminate the fish that form the main source of protein for the local population in the Niger Delta. Taken together we report that heavy metal levels found in these fish species were higher than levels found in the water samples from Aladja River. Bioaccumulation may be responsible for this observation. In view of the ranking of heavy metal content this study suggest that the most toxic fish specie from the Aladja River near Warri, Niger Delta of Nigeria may be Clarias gariepinus.
We recommend further study that will account for the sources of these heavy metals, possible role of electronic waste and a follow up study of blood metal levels on Nigerians especially children in the Niger Delta region. This study is intended to draw the attention of health and environmental authorities on the need for appropriate regulatory framework.
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(1) Nduka John Kanayochukwu, (2) Orisakwe Orish Ebere and Okerulu Isaac Obi
(1) Pure & Industrial Chemistry Department, Nnamdi Azikiwe University, P.M.B. 5025, Awka, Anambra State, Nigeria.
(2) Toxicology Unit, Department of Clinical Pharmacy, Faculty of Pharmacy, University of Port Harcourt.
Nduka John Kanayochukwu, Pure & Industrial Chemistry Department, Nnamdi Azikiwe University, P.M.B. 5025, Awka, Anambra State, Nigeria.
Table 1: The concentration of metals mg/kg in muscles of different types of fish. Fish Specie V Mn Cd Cr Oreochromis niloticus 1.20 2.40 <0.01 0.01 Tilapia zilli 1.10 0.15 0.03 0.40 Serathrodon niloticus. 5.02 0.25 0.14 0.40 Clarias gariepinus. 4.86 1.50 0.20 0.80 Ethmaliosa timbriata. 3.14 3.00 0.10 0.42 Fish Specie Zn Ni Fe Pb Oreochromis niloticus 1.41 0.01 0.80 0.01 Tilapia zilli 1.04 6.82 1.97 0.60 Serathrodon niloticus. 3.80 4.86 2.84 0.15 Clarias gariepinus. 10.80 5.00 18.01 1.00 Ethmaliosa timbriata. 1.85 4.00 6.20 2.40 Table 2: The concentration of metals in mg/kg for soil, water hyacinth (WH) mg/kg and water (mg/L). Sample V Mn Cd Cr Soil sediment 1.04 4.95 0.97 5.00 WH 6.00 6.10 0.70 0.40 Water 0.98 <0.01 0.07 0.50 Sample Zn Ni Fe Pb Soil sediment 1.04 3.86 6.48 0.25 WH 10.50 0.09 9.63 0.30 Water 0.84 4.82 2.47 0.50