MenuISSN (0970-2083)
ISSN (0970-2083)
Department of Chemical and Petroleum Engineering University of Uyo, P.M.B. 1017, UYO Akwa Ibom State, Nigeria
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Atomic Absorption Spectrophotometry, Trace Metals, Food Drinks.
The relevance of food composition data in nutrition planning and provision of basic research data for epidemiological studies have been highlighted by Bruce and Bergstrom (1983). The quantity and quality of data available is however recognized to be limited (Bressani 1983). Heavy metal composition of foods is of interest because off their essential or toxic nature. For instance, iron, zinc, copper, chromium cobalt and manganese are essential, while lead, cadmium, Nickel and Mercury are toxic at certain levels (WHO 1973). The composition of various metals in different food drink of various countries have been the subject of many studies (Drury and Hammond, 1979) such data are not readily available for most foods processing companies of less-developed countries such as Nigeria (Veenamani et al 2005) where food drink composition data are basically on proximate composition and other nutrients (US Department of Health, Education and Welfare 1990). The present study focuses on heavy metal contents of selected Nigeria food-drinks (as is the case in Nigeria) in general and Port Harcourt city in particular. Indeed in many other African Countries, food-drinks make up a significant proportion of daily food intake. Muscle (1976) report that, in Germany and other parts of Europe food-drink contribute 43, 36 and 319 of the total lead, cadmium and mercury respectively in the diet.
The present study provides a more detailed determination of the contents of cadmium, cobalt, chromium, copper, iron, nickel, lead and zinc in various classes and brands of food-drinks in Port Harcourt market.
Four types (or brands in some cases) of each class of food (Table 1) were obtained from local markets in Port Harcourt, Nigeria. The selections were done to reflect the common types consumed by different class of people. We toxidation methods processed sample for analysis. 100cm3 of each sample were processed for analysis with little concentrated nitric acid in an evaporating dish on a regulated hot-plate. Thereafter distilled water were added to make up to the mark. The sample solutions were subsequently analyzed for the metals using an air-acetylene flame atomic absorption spectrophotometer (Buck scientific 200A model) by the standard calibration technique.
Table 1 Classes and brands of beverages and food drinks used for the study
Appropriate quality assurance procedures and precautions were carried out to ensure reliability of the results. Samples were generally carefully handled to avoid contamination. Glassware was properly cleansed and the reagents (nitric acid and distilled water) were of analytical grade. Reagent blank determinations were used to correct the instrument readings. Calibration standards were made by dilution of the High purity commercial BDH metal standards for atomic absorption analysis. A recovery test of the total analytical procedure was carried out for some of the metals in selected samples by spiking analyzed samples with aliquots of metal standards and then reanalyzing the samples. Acceptable recoveries of 90 and 92% were obtained for lead and cadmium respectively.
The mean (standard deviation) and range of the concentrations of the metals in the various classes of food drinks analyzed are given in Table 2 and 3 respectively. The levels of the toxic metals, cadmium and Lead, were generally low, being much less than or just about 0.5ppm in almost all samples Fig. (1) while that of Cu and Fe are slightly high (Fig 2 and 3) Non-alcoholic wine and fruit juice showed high level of iron-content. Generally most elements showed a level lower than 1ppm. The levels of the various metals are mostly below the safe limits specified for food-drinks in Port Harcourt, which are essentially adopted from international food standard. It is therefore important that food-processing companies step down the contents of such heavy metals as Fe, Cu and Zn that is quite high and have cumulative poisonous effect on human lives and for other health reasons.
Fig. 1 Histogram of time Vs Concentration. Relationship
Fig. 2
Fig. 3
Table 2 Mean level (±SD) of the heavy metals in the beverages (mg/L)
Table 3 Range of concentrations of heavy metals in the food-drink (mg/L)
Table 4 Nigerian standard for some metals in some beverages (mg/L)
The study shows that the levels of the eight heavy metals studied are generally within safe limits except for cupper, iron and in few cases Zn and compare well with levels in similar foods from other parts of the world. The nutritive value of such foods could be lower than required such that it can pose some health problems. Hence, the need for food processing industries to maintain recommended standards in all food at all times.
The authors wish to thank Mr. O. J. Donald, Laboratory Technologist and Mr. T. O. Braide, the Head of Department of Chemistry, Rivers State College of Education, Port Harcourt for allowing us to use the atomic absorption spectrophotometer, and the encouragement during the practical period.
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