Bioaccumulation of Some Heavy Metals in Tissues and Head of Commercial Nile Fish in Sudan

H. A. Elagba Mohamed

Bioaccumulation of Some Heavy Metals in Tissues and Head of Commercial Nile Fish in Sudan

H. A. Elagba Mohamed

Natural History Museum, Faculty of Science, University of Khartoum, P.O. Box 321, Khartoum, Sudan

Author

Correspondence author
International Journal of Aquaculture, 2014, Vol. 4, No. 20 doi: 10.5376/ija.2014.04.0020
Received: 07 Apr., 2014 Accepted: 18 May, 2014 Published: 24 Jun., 2014

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Preferred citation for this article:

Mohamed, 2014, Bioaccumulation of Heavy Metals in Muscle Tissues and Head of Some Commercial Nile Fish in Sudan, International Journal of Aquaculture, Vol.4, No.20: 118-122 (doi: 10.5376/ija.2014.04.0020)

Abstract

The concentration of heavy metals was determined in tissue and head of the Nilefish: Barbus bynni, Labeo niloticus, Marcusenius cyprinoides, Mormyrus niloticus, Clarias lazera, Mormyrops anguilloides and Protopterus annectens. Tissue and head contained (14.3 to 14.7 µg/100g) of (Be). The range of (Mo) was (3.5 to 16.25 µg/100g) in the tissue, high in M. anguilloides and low in P. annectens. The head of C. lazera contained the maximum level of (53.55 µg/100g). The level of (Ba) in the tissues was (22 µg/100g) in L. niloticus and C. lazera and (67.3 µg/100g) was detected in head of C. lazera. A level of (18.8 µg/100g) of (Si) was found in tissue of M. niloticus, and (23.5 µg/100g) in head, while B. bynni contained (26.75 µg/100g) in tissue. The range of (Mn) in tissue was (16.8 to 38.5 µg/100g), high of L. niloticus, and (41.5 to 89.85 µg/100g) in head, high in C. lazera and M. niloticus. Low level was found in both tissue and head of P. annectens. The range of (B) in the tissue was (62.25 to 80.8 µg/100g) maximum in M. anguilloides and minimum in P. annectens. The range in head was (74.4 to 91.25 µg/100g), maximum in M. niloticus and minimum in M. anguilloides. The present results revealed significant differences (p < 0.05) in the distribution of heavy metals between tissue and head. The head contained higher concentrations of Mo, Ba, Mn and B in all species. Boron was the most common heavy metals in both tissue and head followed by Mn, Ba and Mo. Bioaccumulation of heavy metals vary in different species. Protopterus annectens contained the least levels in both tissue and head. Bioaccumulation of heavy metals in fish can be considered as an index of pollution in the aquatic bodies. Regular monitoring of heavy metals in theNile and fish should be done to ensure continuous safety of food.

Keywords

Aquatic pollution; Head and muscle tissues; Nile fish; Heavy metals

Heavy metals are serious pollutants in natural environment due to toxicity, persistence and bioaccumulation problems (Tam and Wong, 2000). All heavy metals are potentially harmful to most organisms at some level of exposure and adsorption (Yilmaz et al., 2003; Marcovecchio 2004). High concentration of heavy metals can result in poor water quality and low productivity of aquatic ecosystems (FAO, 1992; Wegwu and Akaninwor, 2006).

The development in industrialization and technological advances in agriculture, has introduced various pollutants into the aquatic ecosystems, which serves as the ultimate sink for most metals (Ogbeibu and Ezeunara, 2002). Waste water streams containing heavy metals are produced by many manufacturing processes and find their way into the environment (Ogbeibu and Ezeunara, 2002). Some research findings have shown that heavy metals in aquatic environment could accumulate in biota especially fish, the most common aquatic organisms at higher tropic level (Olaifa et al., 2004; Wariaghli et al., 2013). Bio-accumulation in fish has been reported by many researchers (Papagiannis et al., 2004; Yilmaz et al., 2007; Christopher et al., 2009; Njogu et al., 2011). Other factors for bioaccumulation has been reported to depend upon the rate of uptake through gut from food and the rate of excretion (Huang, 2003), species differences as well as feeding habitat and trophic status of the fish.

Most heavy metals have no beneficial functions to the body and can be highly toxic. If enter the body through inhalation, ingestion and skin can accumulate in the body tissue faster than the body’s detoxification pathways and disposition (Ekpo et al., 2008). High concentration exposure, overtime, can reach toxic concentration at low levels (Ploetz et al., 2007; Akan, et al., 2009). Fish is a valuable and cheap food item and source of protein to man. Concern about heavy-metal contamination of fish has been motivated largely by adverse effects on humans, given that fish consumption primary route of heavy metal exposure (Nsikak et al., 2007).

Since there is no formal control of effluents discharged into the Nile, it is important to monitor the levels of metals contaminants in the Nile fish and assess the suitability for domestic uses. In order to effectively control and manage water pollution due to heavy metals, it is important to have a clear understanding of the distribution and profiles of heavy metals in the biota (Sabo et al., 2008).

Therefore, the present work aimed to determine the profile of some heavy metals (Beryllium, Be, Molybdenum, Mo, Barium, Ba, Silica, Si, Manganese, Mn and Boron, B) in muscle tissues and head of seven common Nile fish (Barbus bynni, Labeo niloticus, Mormyrops anguilloides, Marcusenius, and to evaluate the hazards and toxicity to fish population and consumers in general. The heavy metals are not destroyed by humans (Castro-Gonzeza and Méndez- Armentab, 2008). Instead, tend to accumulate in the body and can be stored in soft and hard tissues such as liver, muscles and bone and threaten the health of humans (Adham et al., 1999; Olaifa et al., 2004; Ploetz et al., 2007; Paulami and Banerjee, 2012). Due to toxicity and accumulation in the biota, determinating the levels of these heavy metals in fish species have received considerable attention in different countries (Mohamed and Gad, 2008; Klavins et al., 2009; Ozturk et al., 2009; Olowu et al., 2010; Ambedkar and Muniyan, 2011; Wariaghli et al., 2013).

1 Material and Methods

1.1 Samples collection

Ten fresh and mature specimens (250-330 mm/length and 500-850g weight) of each of seven commercial fish from the Nile namely: Barbus bynni, Labeo niloticus, Marcusenius cyprinoides, Mormyrus niloticus, Clarias lazera Mormyrops anguilloides and Protopterus annectens were purchased from the local fish market in Khartoum. All specimens were previously collected from Jabel Aulia area on the White Nile water and broughtin ice container to thelabratory. Each fish was skinned, gutted, washed and the whole head of each specimen was carefully separated. The edible portion of the muscles was also removed. Samples were taken separately from muscles and head because most of Sudanese people along the Nile eat fish heads. Both muscles and heads were freeze dried to constant weight using Freeze Dryer model 230 to -40°C. The dried samples were ground to a fine powder and used for analysis.

1.2 Chemical analysis

The concentration of heavy metals was determined in the dried samples after acid digestion by Atomic Absorption Spectrophotometer (APHA, 1998). About 4g of the each sample were kept in muffle furnace on a hot plate at 550ºC for 3 hours to obtain the ash. Ash was dissolved in 10 ml of 20% HCl then filtered in a 100ml volumetric flask and the volume was completed with distilled water to 50ml. All determinations in muscles and heads of each species were done in triplicates and calculated as mean content in (μg/100g dry weight). Data analysis was conducted using the Statistical Package for Social Science (SPSS, version 16, 2011). The result is considered significantly different when p < 0.05.

2 Results and Discussion

The result of accumulation of heavy metals in muscles and heads of the seven species of the Nile fish are presented in (Figure 1 & Figure 2). Both muscles and heads of the analyzed fish contained almost same levels of being with a range of 14.3 to 14.7 µg/100g. The range of Mo in the muscles was 3.5 to 16.25 µg/100g, high in M. anguilloides and low in P. annectens (Figure 1), while the head of C. lazera contained an average level of 53.55 µg/100g, (Figure 2). Ba level in the muscles was high in L. niloticus and C. lazera with average value of 22 µg/100g. An average maximum level of 67.3 µg/100g was also detected in the head of C. lazera. Mormyrus niloticus contained minimum average level of 18.8 µg/100g of Silica in the muscles, and maximum average level of 23.5 µg/100g in the head, while B. bynni contained 26.75 µg/100g in the muscles. A range of Mn 16.8 to 38.5 µg/100g was detected in muscles, high in L. niloticus, and of 41.5 to 89.85 µg/100g in was detected in head, high in C. lazera and M. niloticus, while low average level of Mn,16.8 µg/100g, was found in muscles and 41.5 µg/100g in head of P. annectens. The range of B in muscles was 62.25 to 80.8 µg/100g, maximum in M. anguilloidesand minimum in P. annectens, while the range in head was 91.25 µg/100g in M. niloticusand 74.4 µg/100gin M. anguilloides.

Figure 1 The concentration of heavy metals in muscles of seven commercial Nile fish

Figure 2 The concentration of heavy metals in heads of seven commercial Nile fish

Results from this study revealed significant differences (p<0.05) in the distribution of heavy metals between muscles and head of the studied species of fish. The head concentrates higher levels of Mo, Ba,Mn and B in all species of fish than the muscles. Ahmed et al., (2010) also observed more concentration of minerals and heavy metals in head of of fish species. Accumulation of different heavy metals depends on many factors such as the physiological needs, feeding habits and genetic composition, sex of each fish species and the biochemical significant role of each metal (Kamaruzzaman et al., 2010). Bo was the most common heavy metals in both tissue and heads followed by Mn, Ba and Mo. The level of Be and Si was not significantly (P>0.05) different between the tissues and heads of all species. Protopterus annectens was observed to contain the least level of most of heavy metals in both tissues and head compared to the other species. The main reason could be the different habits and habitat of P. annectens because the fish is found in marginal swamps and backwaters of rivers and lakes. It normally lives on flood plains, and when these dry up it secretes a thin slime around itself which dries into a cocoon. So the fish is not continuously exposed to pollutants in the Nile like other species.

Generally, heavy metal concentrations in the muscles of freshwater fish vary considerably among different studies (Papagiannis et al., 2004; Yilmaz et al., 2007; Ahmed et al., 2010; Njogu et al., 2011; Opaluwa et al., 2012; Mohammed and Osman, 2014), possibly due to differences in metal concentrations and chemical characteristics of water from which fish were sampled, ecological needs, metabolism and feeding patterns of fish, and also the season in which studies were carried out. The variation in metal concentrations could also be due to the presence of major sources of metal pollution, intensive human activity and discharge of municipal waste and industrial effluents.

Fish are often at the top of the aquatic food chain and have the tendency to concentrate large amount of some heavy metals from the water (Mansour and Sidky, 2002). Bioaccumulation of heavy metals is toxic to fish (Chattopadhyay et al., 2002; Ayotunde and Offen, 2012). Be and Ba are considered as potential toxic metals. Soluble Ba compounds are poisonous due to release of the soluble Ba ions. The health risk limits established (HRLs) were 2.0 and 0.00008 mg/L for barium and beryllium, respectively (WHO, 1985). Manganese is an essential element and shows relatively low toxicity to aquatic biota. It is rarely found at concentration above 1mg/L in natural freshwater (Hellawal, 1986). The concentration of Mn in water can increase due to the influence of industrial wastes on the Nile. Adverse sublethal effect on fish occurs at Mn concentration of 0.278 g/L. These metals may alter the biochemical parameters in both blood and other organ tissues and affect the physiological activities and development of the fish (Bogut, 1997; Mohamed and Gad, 2008). Metal stresses were reported to cause reproduction failure and losses in fish populations (Adham et al., 1999; Saeed and Shaker, 2008). The gills serve as respiratory organs through which ions are absorbed (Khan et al., 2011). Fish can absorb metals from both the surrounding water and from their contaminated food and bioaccumulate them in their tissue. Some metals are essential, but at high concentrations, they can be toxic to fish, cause mortality, growth retardation, and reproductive impairment (Adham et al., 1999; Saeed Shaker, 2008). Even If the minerals contents is lower than threshold values indicated by WHO (1996), contamination of aquatic ecosystems should be expected through bioaccumulation. Bioaccumulation of metals in fish can be considered as an index of metal pollution in the aquatic bodies (Javed and Hayat 1998; Tawari-Fufeyin and Ekaye, 2007; Karadede-Akin and Unlu, 2007; Authman, 2008), that could be a useful tool to study the biological role of metals present at higher concentrations in fish (Dural et al., 2007; Anim et al., 2011).

3 Conclusion

Results from this present study showed that accumulations of heavy metals metals vary between the studied species of the Nile fish, and also in different fish organs. The head bioaccumulated more metals than the muscle muscles.This can be due to the presence of gills that are in constant contact with the contaminated water. Although the results do not indicate a manifestation of toxic effects, the deleterious effects could possibly manifest after a long period of consumption of fish with trace metal contamination. Knowledge of heavy metal concentrations in fish is important with respect to nature of management and human consumption of fish. Regular monitoring of heavy metals in the Nile and fish should be done to ensure continuous safety of food and laws should be enforced to protect the aquatic ecosystems.

References

Ahmed A.,Dodo A.,Bouba A.M., and Clement S., 2000, Minerals and heavy metals in water, sediments and three fish species (Tilapia nilotica, Silurus glanis and Arius parkii) from Lagdo Lake, Cameroun, Journal of Fisheries International, 5(3): 54-57

Adham K.G., Hasan I.F., Taha N., and Amin Th., 1999, Impact of hazardous exposure to metals in the Nile and Delta Lakes on the Catfish, Clarias Lazera, Environmental Monitoring and Assessment, 54(1): 107-124
http://dx.doi.org/10.1023/A:1005898430980

Akan J.C., Abdulrahman F.I., Sodipo O.A., and Akandu P.I., 2009, Bioaccumulation of some heavy metals of six fresh water fishes caught from Lake Chad in Doron Buhari, Maiduguri, Bornno State Nigeria, Nigerian Journal of Applied Sciences and Environment Management, 4: 103-114

Ambedkar G., and Muniyan M., 2011, Accumulation of metals in the five commercially important freshwater fishes in Vellar River, Tamil Nadu, India, Archives of Applied Science Research, 3(3): 261-264

Anim A.K., Ahialey E.K., Duodu G.O., Ackah M., and Bentil N.O., 2011, Accumulation profile of heavy metals in fish samples from Nsawam, along the Densu River, Ghana,Research Journal of Environment and Earth Science, 3: 56-60

APHA, 1998, American Public Health Association Standard methods for the xamination of water and wastewater (20^th ed). New York, American Public Health Association. Washington, D.C

Authman M.M.N., 2008, Oreochromis nilotica as a biomonitor of heavy metals pollution with emphasis on potential risk and relation to some biological aspects, Global Veterinaria, 2(3): 104-109

Ayotunde E.O., and Offen B.O., 2012, Heavy metals profile of water, sediment and freshwater catfish Chrysichthys nigrodigtalus (Siluriformes, Bagridae) of Cross River, Nigeria, Revista de Biologia Tropical, 60(3): 12-20

Bogut I., 1997, Water pollution by heavy metals and their impact on fish and human health, Hrvatske Vode, 5: 223-229

Castro-Gonzeza I.M., and Méndez-Armentab M., 2008, Heavy metals: Implications associated to fish consumption,Environmental Toxicology and Pharmacology, 26: 263-271
http://dx.doi.org/10.1016/j.etap.2008.06.001

Chattopadhyay B., Chatterjee A., and Mukhopadhyay S.K., 2002, Bioaccumulation of metals in the East Calcutta wetland ecosystem, Aquatic Ecosystems Health Management, 5: 191-203
http://dx.doi.org/10.1080/14634980290031848

Christopher E., Vincent O., Grace I., Rebecca E., and Joseph E., 2009, Distribution of heavy metals in bones, gills, livers and muscles of (Tilapia) Oreochromis niloticus from Henshaw Town Beach Market in Calabar, Nigeria, Pakistan Journal of Nutrition, 8(8): 1209-1211

Dural M., Goksu M.Z., and Ozak A.A., 2007, Investigation of heavy metal levels in economically important fish species captured from the Tuzla Lagoon, Food Chemistry, 102: 415-421
http://dx.doi.org/10.1016/j.foodchem.2006.03.001

Ekpo K.E., Asia I.O., Amayo K.O., and. Jegede D.A, 2008, Determination of lead, cadmium and mercury in surrounding water and organs of some species of fish from Ikpoba river in Benin city, Nigeria, International Journal of Physiological Sciences, 3: 289-292

Food and Agriculture Organization (FAO), 1992, Report of the third Session of Working Party on Pollution and Fisheries, Accra, Ghana, 25-29^th Nov., 1991, FAO Fisheries Report, 471: 43

Helawell J.M., 1986, Biological Indicators of Freshwater Pollution and Environmental Management, Elsvier Applied Science Publisher, London
http://dx.doi.org/10.1007/978-94-009-4315-5

Huang B.W., 2003, Heavy metal concentrations in the common benthic fishes caught from the coastal waters of Eastern Taiwan, Journal of food and drug analysis, 11(4): 324-330

Javed M., and Hayat S., 1998, Fish as a bioindicator of freshwater contamination by Metal, Pakistan Journal of Agriculture, Science, 35: 11-15

Kamaruzzaman Y.B., Ong C.M., and Rina Z.S., 2010, Concentration of Zn, Cu and Pb in some selected marine fishes of the Pahang coastal waters, Malaysia,American journal of applied sciences, 7(3): 309- 314
http://dx.doi.org/10.3844/ajassp.2010.309.314

Karadede-Akin H., and Unlu E., 2007, Heavy metal concentrations in water, sediments, fish and some benthic organisms from Tigris river, Turkey, Environment Monitoring and Assessment, 131: 323-337
http://dx.doi.org/10.1007/s10661-006-9478-0

Khan B., Khan H., Muhammad S., and Khan T., 2011, Heavy metal concentration trends in three fish species from Shah Alam River (Khyber, Pakhtunkhwa Province, Pakistan), Journal of Natural and Environmental Sciences, 3(1): 1-8

Klavins M., Potapovics O., and Rodinov V., 2009, Heavy metals in fish from Lakes in Latvia: Concentrations and trends of changes, Bulletin of Environmental Contamination and Toxicology, 82: 96-100
http://dx.doi.org/10.1007/s00128-008-9510-x

Mansour S.A., and Sidky M.M., 2002, Ecotoxicological studies, 3: Heavy metals contaminating water and fish from Fayoum Governorate, Egypt, Food Chemistry, 78(1): 15-22
http://dx.doi.org/10.1016/S0308-8146(01)00197-2

Marcovecchio, J.E., 2004, The use of Micropogonias furnieri and Mugil liza as bioindicators of heavy metals pollution in La Plata River Estuary, Argentina, Science of the Total Environment, 323: 219-226
http://dx.doi.org/10.1016/j.scitotenv.2003.09.029

Mohamed E.A.S., and Gad N.S., 2008, Environmental pollution-induced biochemical changes in tissues of Tilapia Zilli, Solea vulgaris and Mugil capito from Lake Qarun, Eygpt, Global Veterinaria, 2(6): 327-336

Mohammed E.H.A., and Osman A.R., 2014, Heavy metals concentration in water, muscles and gills of Oreochromis niloticus collected from the sewage-treated water and the White Nile, International Journal of Aquaculture, 4(06): 36-42

Njogu P. M., Keriko J. M., Wanjau R. N., and Kitetu J. J., 2011, Distribution of heavy metals in various lake matrices; water, soil, fish and sediments: A case study of the lake Naivasha Basin, Kenya, Journal of Agriculture, Science and Technology, 13(1): 17-24

Nsikak U.B., Joseph P.E., Akan B.W., and David E.B., 2007, Mercury accumulation in fishes from tropical aquatic ecosystems in the Niger Delta, Nigeria, Current Science, 92: 781-785

Ogbeibu A.E., and Ezeunara P.U., 2002, Ecological impact of brewery effluent on Ikpoba River using the fish communities as bioindicators, Journal of Aquatic Research, 17: 35-44

Olaifa A.K., Adelaja A.A., and Owolabi A.G., 2004, Heavy Metal contamination of Clarias gariepinusfrom a lake and fish farm in Ibadan, Nigeria, African Journal of Biomedical Research, 7: 145-148

Olowu R.A., Ayejuyo O.O., Adewayi G.O., Adejoro I.A., Denloye A.A.B., Babatunde A.O., and Ogundajo A., 2010, Determination of heavy metals in fish tissues, water and sediment from Epe and Badagry Lagoons, Lagos, Nigeria, E-Journal of Chemistry, 7(1): 215-122
http://dx.doi.org/10.1155/2010/676434

Ozturk M., Ozozen G., Minareci O., and Minareci E., 2009, Determination of heavy metals in fish, water and sediment of Avsar Dam Lake in Turkey, Iran Journal of Environmental Health Science and Engineering, 6(2): 73-80

Opaluwa O.D., Aremu M.O., Ogbo L.O., Magaji J.I., Odiba I.E., and Ekpo E.R., 2012, Assessment of heavy metals in water, fish and sediments from UKE Stream, Nasarawa State, Nigeria, Current World Environment, 7(2):213-220
http://dx.doi.org/10.12944/CWE.7.2.04

Papagiannis I., Kagalou I., Leonardos J., Petridis D., and Kalfakaou V., 2004, Copper and zinc in four freshwater fish species from Lake Pamvotis (Greece), Environment International, 30: 357-362
http://dx.doi.org/10.1016/j.envint.2003.08.002

Paulami M., and Banerjee S., 2012, Fate of metals in fish under variable sewage input in fish ponds, International Journal of scientific Research Publications, 2(6): 1-13

Ploetz D.M., Fitts B.E., and Rice T.M., 2007, Differential accumulation of heavy metals in muscles and liver of a marine fish (King Mackerel, Scomberomorus cavalla, Cuvier) from the Northern Gulf of Mexico, USA, Bulletin of Environment Contamination and Toxicology, 78: 134-137
http://dx.doi.org/10.1007/s00128-007-9028-7

Sabo A., Nayaya A.J., and Galadima A.I., 2008, Assessment of some heavy metals in water, sediment and freshwater mudfish (Clarias gariepinus) from River Gongola in Yamaltu-Deba, Gombe, Nigeria, International Journal of Applied Sciences, 2: 6-12

Saeed M.S., and Shaker M.I., 2008, Assessment of heavy metals pollution in water and sediment and its effect on Oreochromis niloticus in the Northen Delta lakes Egypt, 8^th International Symposium on Tilapia in Aquaculture, Egypt: 475-490

SPSS, 2011, Statistical Package for Social Science, Version 16.0, Marija Journal of Neruris SPSS Inc, Chicago, Illinis

Tam N.F.Y., and Wong Y.S., 2000, Spatial variation of heavy metals in surface sediments of Hong Kong mangrove swamps, Environmental Pollution, 110: 612-622
http://dx.doi.org/10.1016/S0269-7491(99)00310-3

Tawari-Fufeyin P., and Ekaye S.A., 2007, Fish species diversity as indicator of pollution in Ikpoba river, Benin City, Nigeria, Review of Fish Biology and Fisheries, 17: 21-30
http://dx.doi.org/10.1007/s11160-006-9015-9

Wariaghli F., Tigillimann A., El Abidi A., El Hamri H., Fekhaoui M., and Yahyaoui A., 2013, Evaluation of the degree of heavy metals contamination in the Sebou Estuary and in Moulay Bousselham reserve, International Journal of Aquatic Science, 4(2): 69-82

Wegwu M.O., and Akaninwor J.O., 2006, Assessment of heavy-metal profile of the New Calabar River and its impact on juvenile Clarias gariepinus, Chemical Biodiversity, 3: 79-87
http://dx.doi.org/10.1002/cbdv.200690010

WHO, 1985, World Health Organization guidelines for drinking water quality (ii): Health Criteria and supporting information WHO, Geneva, Switzerland

WHO, 1996, World Health Organization guideline values for contaminants in water: Guidelines for Drinking-Water Quality–Second Edition-Volume 2-Health Criteria and Other Supporting Information 971 pp

Yilmaz, A.B., 2003, Levels of heavy metals (Fe, Cu, Ni, Cr, Pb and Zn) in tissues of Mugil cephalus and Trachurus mediterraneus from Iskenderun Bay, Turkey, Environmental Research, 92: 277-281
http://dx.doi.org/10.1016/S0013-9351(02)00082-8

Yilmaz F., Ozdemir N., Demirak A., and Tuna A.L., 2007, Heavy metal levels in two fish species Leuciscus cephalus and Lepomis gibbosus, Food Chemistry, 100: 830-835
http://dx.doi.org/10.1016/j.foodchem.2005.09.020

International Journal of Aquaculture

• Volume 4

View Options
. PDF(1350KB)
. FPDF
. HTML
. Online fPDF
Associated material
. Readers' comments
Other articles by authors
. H. A. Elagba Mohamed