Determination of the Levels of Some Heavy Metals in African Pear (Dacryodes Edulis) Marketed in Lagos Metropolis, Nigeria

JASEM ISSN 1119-8362 Full-text Available Online at J. Appl. Sci. Environ. Manage. March, 2008 All rights reserved www.bioline.org.br/ja Vol. 12(1) 33 - 37 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 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 many Nigerians and it is usually eaten along with substances, effluents, chemicals and energy are roasted or boiled maize. The outer portion of the introduced into the environment through several fruits is eaten after being roasted. It produces a sort sources (Kabata-Pendias and Pendias, 1992; of butter like taste because the fruit wall is high in Ademoroti, 1996; Paivoke, 2002). Some of these oil. The fruits come from different sources and substances contain heavy metals such as cadmium, farms to the different markets in Lagos metropolis, lead, mercury which are known to be toxic with no the commercial and business nerve centre of beneficial effects to man and wildlife (Tyler, 1981; Nigeria. Large scale commercial farming is not Borgmann, 1983). Heavy metals have the ability to common in Lagos State and majority of the foods accumulate in living organisms and at elevated are normally harvested and brought to the State levels they can be toxic to living organisms. from other States for sale. So the fruits of this plant Elevated levels of copper have been reported to is one of such foods that are brought to the State cause brain damage (DWAF, 1981). Lead and and the growers depend on it not only as source of cadmium poisoning has also been reported in Japan food but also for money. It is therefore important to in which many lives were lost and many more know the levels of these metals in the fruits since developed bodily abnormalities (Yamagata and they are known to be lethal to living organisms Montague, 1970; Nogawa, 1980). Alarming including human beings when present in elevated concentration of heavy metals have been reported concentrations. Furthermore, lead, cadmium and in top level carnivores such as tuna, marlin and zinc are investigated in this study because they are swordfish (Montague and Montague, 1971). It is constituents of effluents, gaseous emissions, therefore of great concern and immense industrial and domestic wastes. These substances importance that the concentrations of heavy metals can be accumulated in the shoot and roots of plants in foods are investigated. This is to ascertain that at low, medium or high levels ( Verma and Dubey, their concentrations are not high to levels that can 2003; Yang et al., 2003; Chandra and Kulshrestha, be dangerous to humans. Heavy metals find their 2004; Adeyeye, 2005). This study therefore aims at way into plants either from contaminated soil or finding out by determining the concentrations of through foliar absorption during exposure of plants lead, cadmium and zinc in the fruits of this plant to substances containing heavy metals in the sold in eight different markets in Lagos metropolis. environment. The fruits of D. edulis is relished by MATERIALS AND METHODS Fruit Sample Preparation Fruit Collection The fruit samples were scrapped to separate the Substantial amounts of the fruits of the African tissue from the seed. The tissue was then oven- o pear (Dacryodes edulis) were bought from eight dried at 70 C until a constant weight was achieved. different markets (Oshodi, Mile 12, Bariga, Sabo- The dried tissue was milled to pass through a 2 mm Yaba, Ikeja, Agege, Mushin and Oyingbo) in mesh sieve and kept for digestion. Lagos metropolis. The fruits were put in polythene bags, labelled properly, and taken to the laboratory Sample digestion for appropriate analysis. 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 *Corresponding author: Akinola, M. O. Determination of the Levels of Some Heavy MetalsiIn African Pear ………………….. 34 in the sample into such a form that they can be Atomic Absorption Spectrophotometry (AAS) analyzed by the AAS. equipment (Buck scientific model 200A) as done by Ebdon et al, 1998. The flame type used for all Fruit Sample Digestion the analysis was air-acetylene. Suitable working Sub-samples of the milled sample were dry-ashed. blanks were prepared from the solutions used in Dry-ashing of the tissue was carried out by placing digesting the samples. Necessary dilutions were 1 g of the finely ground material in a silica dish and made using distilled water so as to bring the placed in a muffle furnace where it was burnt to concentrations of the metals into suitable ash at 550oC for 4 hours. It was then cooled and ash concentration range. Readings were then taken dissolved in 5ml of 2N HNO3, filtered into a 50ml from the equipment. The results given by the AAS volumetric flask and diluted to volume with were converted into the actual concentrations of the distilled water. A blank was also prepared metals in the sample using the following equation: following the same procedure but the fruit sample Concentration (µg/g) = C X E was not added. S Where C is the concentration reading, E is extract Determination of heavy metals in the fruit volume which represents the final volume of digest samples used and S is sample weight used during digestion. The sample digests of the fruits were analyzed in three replicates for lead, cadmium and zinc by RESULTS AND DISCUSSION bought from the eight markets at the different The concentrations of heavy metals in the fruits at periods were lower than the maximum permissible the different periods of sampling are shown in concentrations Tables 1. This means that such Table 1. These results clearly show that Pb fruits are safe for dietary consumption but an (3.00±1.00µg/g) was more in the fruits than Cd accumulation in the bodies of the consumers over a (0.15±0.01µg/g) and Zn (1.5±0.10µg/g) which are long period of time is of major concern as it can highest concentrations of these metals recorded in result to serious health implications. Accumulation this study. This is because lead is easily absorbed of lead in edible aquatic plants (Kumar et al., 2002) and accumulated in different plant parts (Sharma in soil and vegetation (Fatoki, 2003) and in animals and Dubey (2005). Moreover, the presence of these (Salanki et al., 2003; Wilkinson et al,. 2003; heavy metals in the fruits may mean that the shoot Metcheva et al., 2003) has been reported. Lead has part contains higher concentration than the roots as been found to be toxic to the red blood cell, kidney, reported for some plants by Akinola and Ekiyoyo nervous and reproductive systems (Taupeau et al., (2006); Yang et al., (2003). It could also mean that 2001). Excess of Cadmium has been reported to quite a large amount of atmospheric emissions cause renal tubular dysfunction accompanied by from machines or vehicles might have deposited on osteomalacia (bone softening) and other the fruits during transportation and/or where they complications which can lead to death (Yamagata were displayed for sale in the open markets along and Shigemastu, 1970; Nogawa, 1980; Laws, the roadside. These gaseous emissions contain lead 2000). High concentration of Zinc can result to which comes from leaded gasoline which is still damage of the pancreas, disruption of protein very much in use in Nigeria. Generally, low metabolism and arteriosclerosis (Anonymous, concentrations of the heavy metals in the fruits 1991). All the above mentioned health problems were recorded in this study. It may be that the associated with these heavy metals are indications concentrations, of the heavy metals in the soils of the need to continually monitor, control and take where this crop plant was cultivated, were low. necessary policy decisions so as to limit and Low concentration of lead, cadmium and ultimately prevent these avoidable health problems. chromium has been recorded in soils in Nigeria The unwashed samples contained higher (Akinola and Ekiyoyo, 2006; Adeyeye, 2005).

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