HEAVY METAL CONCENTRATIONS IN TISSUES OF COMMERCIALLY EXPLOITED FISH (Oreochromis niloticus baringoensis, Protopterus aethiopicus, Clarias gariepinus) FROM LAKE BARINGO, KENYA

Studies have shown that elevated heavy metal concentrations in water and sediments may be biomagnified along the aquatic food chains/webs and eventually affecting human health through the consumption of metal-contaminated water and/or fish from such water bodies. This study was conducted to assess the concentration of heavy metals in the tissues of Oreochromis niloticus baringoensis, Protopterus aethiopicus and Clarias gariepinus fish species of Lake Baringo and compare the results with WHO guideline values. Water and fish samples were collected from five selected sites in six sampling occasions and the analyses for heavy metals (i.e. Cu, Hg, Cd, Pb) in fish and water samples was done using the Atomic Absorption Spectrophotometer at Nakuru Water and Sewerage Company Laboratory. There was a significant difference in physical chemical parameters from all sites in Lake Baringo except for temperature. Copper, Cadmium and mercury were available in measurable quantities in water samples but lead was below detection limit (<0.026). There was no significant difference in heavy metal concentration in all the tilapia (F=0.88, P=0.44), lungfish (F=0.99, P=0.43) and catfish (F=0.09, P=0.70) samples collected from different sampling sites. The pooled heavy metal concentration levels recorded in fish for Copper, Cadmium and Zinc was 0.473±0.125, 3.565±0.063 and 24.398±3.262 respectively. Therefore the heavy metal concentration in fish decreased in the sequence Zinc>Cadmium>copper. Lead and Mercury concentrations in fish samples were below the limits of instrument detection. Copper, Lead and Mercury concentration in fish were below WHO guideline values thus posing more of an environmental than human health concern. However, Cadmium and Zinc concentration was above WHO guideline values thus posing a human health concern. Regular monitoring of the Lake Baringo water quality is therefore necessary to record any variation in the water quality and heavy metal concentration in fish in order to curb heavy-metal related health effects arising from consumption of heavy metal contaminated fish.

Background Information
Heavy metals in the aquatic ecosystems are of global concern due to their bioaccumulation, biomagnification ability and toxicity in low concentration thus posing potential negative impacts to the environment and human health. Heavy metals are released to the environment from anthropogenic activities such as metal production, agricultural activities, mining and industrial development. These metals are also as a result of natural geochemical processes such as volcanic eruptions and forest fires. The continued increase in human population has amplified the release of heavy metals in lakes (Storelli, 2008).

Heavy metals have wide environmental dispersion (Ishaq, 2011), with the tendency to accumulate in selective tissues (Bezuidehout et al,1990), of the living organisms and have overall potential to be toxic even at relatively low levels of exposure (Hu, 2002). In the aquatic ecosystem, heavy metals may bioaccumulate in various organs of aquatic organisms, especially fish, which in turn may enter the human metabolism through consumption causing serious health hazards (Shrivastava, 2011). Heavy metals enter the fish through gills, skin, oral in food and water. In the fish body, the metal is transported through the blood stream and either stored, transformed or eliminated in the liver, kidney or the gills (Ishaq, 2011)

Fish consumption can be an important route of human exposure to a variety of heavy metals such as mercury, lead, cadmium and copper as fish is often at the top of aquatic food chain and may, therefore, concentrate large amounts of some heavy metals from the water (Storelli, 2008). Globally, fish is preferred as an important source of proteins, minerals, vitamins and polyunsaturated fatty acids (PUFAs), especially omega-3 PUFAs. Fish consumption reduces the risk of coronary heart disease, decreased mild hypertension and prevents certain cardiac arrhythmias (Mozaffarian , 2006).

Human health effects from heavy metal contaminated fish are an issue of global concern. Such a case has been documented in Japan where major factories discharged their waste into water bodies resulting into contamination of fish thereby causing adverse effects on human health. This led to the outbreak of the Minamata disease in 1956 around Minamata Bay, in Kumamoto prefecture (Museum, 2007). Minamata disease was as a result of consumption of methylmercury- contaminated seafood. This disease affects the central nervous system resulting into ataxia, hearing impairment, narrow vision and speech impediments. Cases of congenital Minamata were also recorded as a result of methylmercury poisoning of the fetus via the placenta due to consumption of contaminated seafood by the mother (Kurland et al, 2001).

The increase in industrial activities and urbanization in Africa has lead to a massive increase of heavy metals in the natural environment. Anthropogenic activities releasing heavy metals include leather tanning, electroplating, and combustion of leaded petrol, intensive agriculture and sludge dumping (Alo, 2006). Heavy metals have been recorded in Ogu River, Nigeria (Farkas & Adelowo, 2007), Lake Kariba, Zimbabwe (Berg et al, 1995) and Nasser Lake (Rasheed, 2008).

Kenyan aquatic ecosystems have been reported to have high concentration of heavy metals, both in fish and water (Campbell et al, 2003; Mwashote, 2003;Muiruri et al, 2013). Lake Baringo is a fresh water lake in the Rift Valley that supports a variety of fish populations, providing subsistence food to the local communities, as well as, a source of income. The fish community of Lake Baringo comprises of seven species with the endemic Baringo Tilapia (Oreochromis niloticus baringoensis) being the predominant species that contribute greatest to the commercial fishery and highly regarded for their nutritional value. The other fish species, in the order of their commercial importance, include Lungfish (Protopterus aethiopicus), African sharptooth Catfish (Clarias gariepinus), barbus (Barbus gregorii), Redeye Labeo (Labeo cylindricus), Line-spotted barb (Barbus lineomaculatus) and Aplocheilichthys species (Hickley et al., 2004).

The Lake Baringo water catchment areas have been intensely degraded through deforestation and conversion into agricultural farms (Hickley et al., 2004). Owing to the numerous anthropogenic activities on the catchment areas, the water quality of the feeder rivers may be impaired due to high concentrations of dissolved organic and inorganic substances such as heavy metals and potassium, magnesium, sulphate and chlorine (Odada, 2005). Apart from the inflowing rivers, other possible sources of heavy metals in Lake Baringo include tourism activities particularly the use of boats to ferry tourists to various destination points on the lake and rapid urbanization of the surrounding areas of the lake. The study, therefore, specifically identified the potentially toxic heavy metals in Lake Baringo, quantified their concentrations in water and commercially exploited fish species at various points on the lake and determined whether these heavy metal levels in selected fish species are within WHO guideline values.

Statement of the Problem
The rapid increase in human population around Lake Baringo drainage basin, growing at a rate of 2.65% per annum, has increased the demand for fish from Lake Baringo. The exploited fish species given their position in the aquatic food chain have the potential of accumulating substantial amounts of heavy metals in the soft and hard tissues thus posing health risks to fish consumers. Most of the fish for subsistence consumption hardly go through health inspectors and, therefore, a high likelihood that a greater portion of the population within the Lake will be affected if they consume metal-contaminated fish. Heavy metals are of particular concern because of their environmental persistence, toxicity at low concentration and the ability to bioaccumulate along the food chain. Heavy metals are also potent neurotoxicants and can adversely affect the developing brain of fetus, infants, and young children. Heavy metals can also lead to cardiovascular, reproductive and renal effects in chronic exposures. The study therefore, assessed concentrations of mercury, lead, Zinc, cadmium and copper, specifically, in tissues of commercially exploited fish and compared the study values with WHO guideline values.

Broad objective
To contribute to the understanding of the level of heavy metal concentrations in tissues of commercially exploited fish species (Oreochromis niloticus baringoensis, Protopterus aethiopicus, Clarias gariepinus) of Lake Baringo, Kenya.

Specific objectives
1. To characterize the physical chemical parameters (pH, temperature, conductivity, dissolved solids and salinity) of water Lake Baringo.

2. To determine the concentrations of selected heavy metals (Copper, Mercury, Cadmium, Zinc and Lead) in water samples taken from different sampling points in Lake Baringo.

3. To determine the concentrations of the selected heavy metals (Copper, Mercury, Cadmium, Zinc and Lead) in tissues of selected fish species (Oreochromis niloticus baringoensis, Protopterus aethiopicus, Clarias gariepinus) of Lake Baringo.

Research questions
1) Is there is any variation in physical chemical parameters in Lake Baringo?

2) Is there significant difference in concentrations of selected heavy metals in water samples collected from different sites in Lake Baringo?

3) Is there variation in concentrations of selected heavy metals in tissues of the selected fish species obtained from Lake Baringo?

Lake Baringo is a Ramsar site in Kenya that is under threat of heavy metal pollution from agricultural activities, waste from surrounding urban centres and human settlements within the lake’s catchment area. Tourism activities such as the use of motor boats lead to oil pollution which partly contributes to the heavy metal contaminants into the lake. Increased human population around Lake Baringo has resulted to an increase in demand for fish as a source of food. The major commercially exploited fish in Lake Baringo include, Oreochromis niloticus baringoensis, Protopterus aethiopicus and Clarias gariepinus, which form an important staple food as a source of proteins, minerals, vitamins and polyunsaturated fatty acids to the local community. These fish species may form an important route of human exposure to a variety of heavy metals such as mercury, lead, cadmium and copper as fish is often at the top of aquatic food chain and may, therefore, concentrate large amounts of some heavy metals from the water. Consumption of heavy metal- contaminated fish can lead to various health risks such as cancer, neurological, cardiovascular, renal and gastrointestinal complications. Human health is therefore more likely to be negatively affected through consumption of metal-contaminated fish which justifies this study. Determining heavy metal concentration in the fish tissues will serve an important function as an early warning indicator of heavy metal contamination of Lake Baringo ecosystem. The study findings are important for continuous monitoring of contaminants in Lake Baringo and form a baseline for further assessment of human health risks from heavy metal poisoning.

Scope of the Study
The study was part of an extensive research in Lake Baringo, “An assessment of heavy metal concentrations in water, sediments and fish tissues of commercially exploited fish species in Lake Baringo, Kenya”. The study was limited to the major commercially exploited fish species of Lake Baringo, that is, Oreochromis niloticus baringoensis, Protopterus aethiopicus and Clarias gariepinus. The samples were collected from 5 sampling sites (S1-Kampi ya Samaki discharge point; S2-Endau River discharge point; S3-Salabani discharge point; S4-Molo River discharge point, and; S5-Ol- Kokwar). A total of 40 samples (2 replicates X 5 sites X 4 sampling occasions), for both water and fish, were collected by the end of the study. The physical- chemical parameters, that is, (temperature, conductivity, and dissolved oxygen) were measured insitu. Heavy metal concentration in fish tissues and water was determined. The fish heavy metal concentration was compared with the WHO guideline values to determine the safety of the fish for human consumption.

Definition of Terms
Acquired ataxia- refers to a collection of disorders, including the loss of balance and physical coordination leading to difficulty walking, speaking and poor vision due to damaged cerebellum or other parts of nervous systems. These disorders are as a result of nutritional intake of heavy metal-contaminated food (WHO, 2010).

Bioaccumulation- the process by which the heavy metal concentration in fish attains a point that surpass that in water as a consequence of heavy metal uptake via every probable way of chemical contact, for instance, nutritional assimilation, movement across the respiratory surface, absorption through the skin and inhalation (Jezierska, 2006).

Bioconcentration- the process whereby heavy metal concentration in an aquatic fish surpass that in water as an outcome of contact with waterborne chemical assimilation from the water through the respiratory surface, for instance, gills and the skin (Jezierska, 2006).

Biomagnification- this is a scenario whereby, heavy metal concentration increases along a food chain as a result of persistence (not easily broken down by environmental processes) or low rate of internal degradation (Babatunde et al, 2012).

Heavy metal- a metallic substance with high atomic weight such as mercury, chromium, cadmium and lead that can damage living things at low concentration and tend to accumulate in the food chain (USEPA, 2000).

Methylation- this is the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group and leads to modification of heavy metals (Farkas & Adelowo, 2007).

Necrosis- this is a disorder due to heavy metal toxicity that involves the death of body tissues that is not reversible and occurs when there is no enough blood flowing to the tissues (Hu, 2002).

Osteomalacia- this is a muscle-skeletal disorder whereby the bones become very soft and more likely to bow and fracture and results from defect in the bone-building process especially due to heavy metal toxicity(WHO, 2010).

Osteoporosis- this is a skeletal problem whereby the bones become fragile and more likely to fracture. Bones become less dense by loss of density which is a measure of calcium and minerals in the bone (Storelli, 2008).

Polyunsaturated fatty acids (PUFAS) - these are unsaturated fatty acid whose carbon chain has more than one double or triple valence bond per molecule. They are mainly found in fish (Storelli, 2008).

Toxicity-this refers to the quality or relative degree of a heavy metal being toxic or poisonous to living things. Heavy metal toxicity can result in considerable human mortality and morbidity (Mozaffarian, 2006)

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