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Determination of the levels of some heavy metals in African pear (dacryodes edulis) marketed in Lagos metropolis, Nigeria Akinola, M. O.; Adenuga, A. A. Environmental Biology Laboratory, Department of Cell Biology & Genetics. University of Lagos, Akoka, Yaba, Lagos, Nigeria Code Number: ja08005 ABSTRACT This paper presents the assessment of Pb, Cd and Zn concentrations in the African pear (Dacryodes edulis) sold in eight popular markets in Lagos metropolis, Nigeria. The concentrations of these metals ranged from 0.01±0.002µg/g to 3.00±1.00µg/g with Pb having the highest concentration of 3.00±1.00µg/g.There was significant difference in the level of Pb in the fruits sold at Ikeja and other markets in March (P<0.05). The washed samples revealed that metal pollutants can exist as superficial contaminants on the surface of the fruit wall which is the edible portion. And so if the fruit is thoroughly washed, it may increase its safety for dietary consumption. The presence of these heavy metals in the fruits confirms that (i) the sources of the fruits before they get to the markets are polluted and (ii) the exposure of the fruits to all types of gaseous emissions from vehicles, industries and domestic wastes at the markets. The concentrations of the heavy metals detected in the fruits were lower than their maximum permissible concentrations except for lead with a concentration of 3.00±1.00µg/g in fruits purchased at Ikeja in March. However, precautions need to be taken by both growers and sellers to ensure that the concentrations of these heavy metals in the fruits are not increased before they get to the consumers. @ JASEM There is no doubt that a large amount of waste substances, effluents, chemicals and energy are introduced into the environment through several sources (Kabata-Pendias and Pendias, 1992; Ademoroti, 1996; Paivoke, 2002). Some of these substances contain heavy metals such as cadmium, lead, mercury which are known to be toxic with no beneficial effects to man and wildlife (Tyler, 1981; Borgmann, 1983). Heavy metals have the ability to accumulate in living organisms and at elevated levels they can be toxic to living organisms. Elevated levels of copper have been reported to cause brain damage (DWAF, 1981). Lead and cadmium poisoning has also been reported in Japan in which many lives were lost and many more developed bodily abnormalities (Yamagata and Montague, 1970; Nogawa, 1980). Alarming concentration of heavy metals have been reported in top level carnivores such as tuna, marlin and swordfish (Montague and Montague, 1971). It is therefore of great concern and immense importance that the concentrations of heavy metals in foods are investigated. This is to ascertain that their concentrations are not high to levels that can be dangerous to humans. Heavy metals find their way into plants either from contaminated soil or through foliar absorption during exposure of plants to substances containing heavy metals in the environment. The fruits of D. edulis is relished by many Nigerians and it is usually eaten along with roasted or boiled maize. The outer portion of the fruits is eaten after being roasted. It produces a sort of butter like taste because the fruit wall is high in oil. The fruits come from different sources and farms to the different markets in Lagos metropolis, the commercial and business nerve centre of Nigeria. Large scale commercial farming is not common in Lagos State and majority of the foods are normally harvested and brought to the State from other States for sale. So the fruits of this plant is one of such foods that are brought to the State and the growers depend on it not only as source of food but also for money. It is therefore important to know the levels of these metals in the fruits since they are known to be lethal to living organisms including human beings when present in elevated concentrations. Furthermore, lead, cadmium and zinc are investigated in this study because they are constituents of effluents, gaseous emissions, industrial and domestic wastes. These substances can be accumulated in the shoot and roots of plants at low, medium or high levels ( Verma and Dubey, 2003; Yang et al., 2003; Chandra and Kulshrestha, 2004; Adeyeye, 2005). This study therefore aims at finding out by determining the concentrations of lead, cadmium and zinc in the fruits of this plant sold in eight different markets in Lagos metropolis. MATERIALS AND METHODS Fruit Collection Substantial amounts of the fruits of the African pear (Dacryodes edulis ) were bought from eight different markets (Oshodi, Mile 12, Bariga, Sabo-Yaba, Ikeja, Agege, Mushin and Oyingbo) in Lagos metropolis. The fruits were put in polythene bags, labelled properly, and taken to the laboratory for appropriate analysis. Fruit Sample Preparation The fruit samples were scrapped to separate the tissue from the seed. The tissue was then ovendried at 70oC until a constant weight was achieved. The dried tissue was milled to pass through a 2 mm mesh sieve and kept for digestion. Sample digestion Most samples require digestion before analysis so as to reduce organic matter interference by destroying all or most of the organic matter present in the sample and to convert all the metals present in the sample into such a form that they can be analyzed by the AAS. Fruit Sample Digestion Sub-samples of the milled sample were dry-ashed. Dry-ashing of the tissue was carried out by placing 1 g of the finely ground material in a silica dish and placed in a muffle furnace where it was burnt to ash at 550oC for 4 hours. It was then cooled and ash dissolved in 5ml of 2N HNO3, filtered into a 50ml volumetric flask and diluted to volume with distilled water. A blank was also prepared following the same procedure but the fruit sample was not added. Determination of heavy metals in the fruit samples The sample digests of the fruits were analyzed in three replicates for lead, cadmium and zinc by RESULTS AND DISCUSSION The concentrations of heavy metals in the fruits at the different periods of sampling are shown in Table 1. These results clearly show that Pb (3.00±1.00µg/g) was more in the fruits than Cd (0.15±0.01µg/g) and Zn (1.5±0.10µg/g) which are highest concentrations of these metals recorded in this study. This is because lead is easily absorbed and accumulated in different plant parts (Sharma and Dubey (2005). Moreover, the presence of these heavy metals in the fruits may mean that the shoot part contains higher concentration than the roots as reported for some plants by Akinola and Ekiyoyo (2006); Yang et al., (2003). It could also mean that quite a large amount of atmospheric emissions from machines or vehicles might have deposited on the fruits during transportation and/or where they were displayed for sale in the open markets along the roadside. These gaseous emissions contain lead which comes from leaded gasoline which is still very much in use in Nigeria. Generally, low concentrations of the heavy metals in the fruits were recorded in this study. It may be that the concentrations, of the heavy metals in the soils where this crop plant was cultivated, were low. Low concentration of lead, cadmium and chromium has been recorded in soils in Nigeria (Akinola and Ekiyoyo, 2006; Adeyeye, 2005). Nevertheless Table 1 shows that the concentration of lead (Pb) (3.00±1.00µg/g) in the fruits bought at Ikeja market indicated that the fruits were polluted with lead when compared with the maximum permissible concentration for lead in food (FAO/WHO, 1984). This is because there are many different industries located in and around Ikeja which could produce emissions that contain Pb and moreover the market is exposed to emissions from several vehicles which use leaded fuel. This makes the fruits which are usually uncovered susceptible to atmospheric deposition of lead. The concentrations of Cadmium and Zinc in the fruits Atomic Absorption Spectrophotometry (AAS) equipment (Buck scientific model 200A) as done by Ebdon et al, 1998. The flame type used for all the analysis was air-acetylene. Suitable working blanks were prepared from the solutions used in digesting the samples. Necessary dilutions were made using distilled water so as to bring the concentrations of the metals into suitable concentration range. Readings were then taken from the equipment. The results given by the AAS were converted into the actual concentrations of the metals in the sample using the following equation: Concentration (µg/g) = C X E S Where C is the concentration reading, E is extract volume which represents the final volume of digest used and S is sample weight used during digestion. bought from the eight markets at the different periods were lower than the maximum permissible concentrations Table 1. This means that such fruits are safe for dietary consumption but an accumulation in the bodies of the consumers over a long period of time is of major concern as it can result to serious health implications. Accumulation of lead in edible aquatic plants (Kumar et al., 2002) in soil and vegetation (Fatoki, 2003) and in animals (Salanki et al., 2003; Wilkinson et al,. 2003; Metcheva et al., 2003) has been reported. Lead has been found to be toxic to the red blood cell, kidney, nervous and reproductive systems (Taupeau et al., 2001). Excess of Cadmium has been reported to cause renal tubular dysfunction accompanied by osteomalacia (bone softening) and other complications which can lead to death (Yamagata and Shigemastu, 1970; Nogawa, 1980; Laws, 2000). High concentration of Zinc can result to damage of the pancreas, disruption of protein metabolism and arteriosclerosis (Anonymous, 1991). All the above mentioned health problems associated with these heavy metals are indications of the need to continually monitor, control and take necessary policy decisions so as to limit and ultimately prevent these avoidable health problems. The unwashed samples contained higher concentrations of the heavy metals than the washed samples Table 2. A high percentage of lead and cadmium was washed off from the fruit wall. For example, more than 50 to over 80 percent of lead and more than 30 to over 60 percent of cadmium were washed off from the fruit wall (Table 3) whilst low percentage of zinc was removed . This is an indication that quite a large amount of atmospheric emissions from machines and vehicles deposit only on the plants as artificial contaminants. Therefore the usual practice of thoroughly washing vegetables and fruits before consumption is indeed good and can help remove a substantial quantity of contaminants from getting to the body of their consumers. This is indeed a good continual ingestion and accumulation of heavy way of avoiding health problems and reducing metals in foods. Acknowledgement: The first author is grateful to Ocean Energy Nig. Ltd for the financial support towards the preparation of this manuscript during his sabbatical leave at the University of Wales, Bangor, United Kingdom. REFERENCES
Copyright 2008 - Journal of Applied Science and Environmental Management The following images related to this document are available:Photo images[ja08005t2.jpg] [ja08005t3.jpg] [ja08005t1.jpg] |
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