Nutritional Value and Risk Assessment of Toxic Heavy Metals of Selected Fish Species from Freshwater Ecosystems in Ethiopia

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Date

2019-09

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Addis Ababa University

Abstract

One of the traditional sources of animal protein of the developing world is through livestock rearing. Unfortunately, the livestock production is under increasing pressure from the combined effects of human population growth, shortage of grazing land and expantion desertification. Therefore, it is important to look for fish, which is the cheap source of animal protein and an important source of high quality protein as it contains large amounts of essential amino acids. In addition, fish contains crude lipids, which supply the body with energy as well as omega-3 fatty acids- the healthy fats that playa role in regulating blood cholesterol and supporting proper brain functioning. Moreover, fish is rich in iron, zinc, magnesium, and copper. Despite this fact, biochemical composition and toxic metal accumulation of different fish species from various freshwater ecosystems had gained little emphasis in Ethiopia. Therefore, the present study was conducted to evaluate the nutritional quality, health benefits and toxic heavy metal risk assessment of selected fish species collected from four freshwater ecos ystems in Ethiopia. In this study, a total of 80 (40 females and 40 males) fish samples of two freshwater fish species, namely African catfish and Nile tilapia (C gariepinus and 0. niloticus) were collected from four freshwater bodies of Alwero River, Abay River, Lake Hawassa and Lake Ziway found in Ethiopia. The fish samples were transported to the Center for Food Science and Nutrition, Addis Ababa University for further analysis. Proximate analysis of the fish samples was done by Association of Official Analytical Chemists (AOAC) method. Minerals in fish samples were determined by Atomic Absorption Spectrophotometry (AAS). Heavy metals were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) with following a microwave digestion procedure. The analysis of the proximate composition of both fish species (male and female) from all sampled sites for maximum and minimum dry matter content for male and female were respectively 7.96% and 11.76% (p < 0.05); 7.06% and 12.00% (p<0.05). Dry matter fish muscles content showed a variation among fish species and sites offish collection in lakes and rivers. Even though sex has no significant (p>0.05) effect on dry matter content, female fish had higher (7.06 - 12.00% dry weight (DW) as compared to male fish (7.96 - 11.76%). The dry matter contents in the gill tissues of 0. nilolicus and C gariepinus male fishes were in the range of 6.62 to 10.66% and for female fishes were in the range of6.80 to 9.11 % in DW and sex has no significant (p>0.05) effect on dry matter content of gill tissues from all sampled sites.The results on the proximate composition of 0. niioticlIs fish muscle from all sampled sites for the maximum and minimum protein, fat, ash and carbohydrate contents were 15.22% and 12.44% (p < 0.05); 2.76% and 2.15% (p > 0.05); 106% and 0.65% (p > 0.05); 5.47% and 1.55% (p< 0.05). For C. gariepinlls maximum and minimum protein, fat, ash and carbohydrate contents were 20.23% and 10.75% (p< 0.05); 4.62% and 2.11% (p < 0.05); 1.55% and 109% (p > 0.05); 2.53% and 0.28% (p< 0.05) , respectively. The analysis of the proximate composition revealed that fat and ash content of the fish species ranged from 2.69 to 4.60 and 0.65 to 152 g/IOOg wet weight (WW), respectively. The lowest moisture was detected in C. gariepinlls from Lake Ziway (71.11 %) with high fat content (4.62 %). The protein content ranged from 12.44 - 15.22% and 10.75 - 20.23% for 0. niloticlIs and C. gariepinus from all fresh water bodies, respectively. The difference in fat content was the major cause for the change in caloric values for C. gariepinus fish tissue ranged from a 6199 -12206 kcalllOOg (260.36-512.65 kJ) followed by 0. niloticus ranged from 69.75-82.16 kcal 1l00g (292.95-345.07 kJ) from all fresh water bodies. Sexes were not significant (P > 0.05) influence in terms of the four proximate compositions (protein, fat, ash and caloric values) measured in muscle tissues of 0. niloticlIs and C. gariepinus collected from all sample sites. Five essential mineral elements Fe, Ni, Cu, Mn, and Zn and seven toxic heavy metals (Hg, Sn, Pb, As, B, Cd and Cr) were analyzed for each of the fish species in muscle and gill tissues from four different freshwater bodies. Iron, zinc, copper, nickel and manganese contents were in the range of33.54 to 122.29 mg/kg, 20.21 to 47.43 mg/kg, 0.75 to 10.87 mg/kg, 0.16 to 1.16 mg/kg and 2.48 to 69.82 mg/kg DW, respectively. The result showed that iron and z inc were the most abundant minerals detected in gill and muscle tissues. Toxic heavy metal concentration were assessed in gill and muscle tissues of C. gariepinlls and 0. niloticlis collect from Alwero River, Abay River Lake Hawassa and Lake Ziway. In gill tissue, the highest accumulated heavy metals were Cd (0.58 mg/kg DW) and Pb (4.56 mg/kg DW) and were observed in 0. niloticlIs species in all water bodies. The highest concentrations of Sn (222.89 mg/kg DW) and Hg (14.52 mg/kg DW) were observed in gills and muscle of 0. niioticlIs from Lake Ziway and Alwero River, respectively, while the highest concentrations ofCr (4.95 mg/kg DW) and As (30.92 mg/kg DW) were observed in gills and muscle of C. gariepinlls from Lake Ziway, respectively. A surprisingly too high As content was 30.92 mg/kg DW in muscle tissue ofC. gariepinus from Abay River and Hg content was 14.52 mglkg DW in muscle tissue of 0. niloticlIs from Lake Ziway, may be due environmental contaminants from municipal, agricultural and industrial sources may enter the food chain, accumulate in fish muscles. Those two fish species from Abay River and Lake Ziway are limiting its consumption for infant and pregnant women. However, the estimated daily intakes of all metals were below the acceptable daily intake (ADI) and oral reference dose (RID) set by international guideline. The target hazardous quotient (THQ) and hazard index (HI) values were «1) for all examined metals in both species in all sampled sites. There are no risk for consumptions of 0. niloticlIs and C. gariepinlls muscle meat for consumers. Therefore muscles of studied both fish species should be safe for utilization in human diet from those regions in Ethiopia.

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