Res.J.Chem.Sci.___________________________________Research Journal of Chemical Sciences Vol. 1(4), 98-108, July (2011) ISSN 2231-606X International Science Congress Association 98 Zinc Speciation in Maize and Soils \n  \r   Department of Pure and Applied Chemistry Bayero University, Kano - NIGERIA Department of Applied Science College of Science and Technology Kaduna Polytechnic, Kaduna – NIGERIA Available online at: www.isca.in (Received 25th May 2011, revised 5th June 2011, accepted 14th June 2011)AbstractThe levels of trace elements in food and agricultural samples have been shown to influence human and plant metabolism. The study of heavy metal speciation is of interest for the evaluation of their mobility, bioavailability and ecotoxicity. In this study, the zinc concentrations of the cereal and soil samples were determined using flame atomic absorption spectrometry (FAAS). The soil samples related to the cereal were digested and extracted using different digestion and extraction reagents. The results indicate that the soil samples collected from various locations, contain varying amounts of the metal, and it was distributed between Residual, Oxide, and Carbonate fractions. The results of the study also showed that the lowest value of total Zn concentration in soil was in sampling points KC1 (1.49 mg/kg) and the highest value was in the sampling points KK5 (207.2 mg/kg) and MD5 (207.2 mg/kg). It was found out that in all the sampling locations, the Zn concentration is within the tolerable range (10 – 300 mg/kg). The relationship between the cereal Zn and soil-extractable Zn concentrations was significant (P 0.05). Keyword:Speciation, zinc, soil, cereal, flame atomic absorption spectrometry. IntroductionZinc is essential for the function of more than 300 enzymes, phosphates, alcohol dehydrogenase, Superoxide dismutase, carboxypeptidase, – aminolevulinic acid dehydratase, carbonic anhydrase, and deoxyribonucleic acid polymerases. Severe zinc deficiency in animals has been associated with reduced fertility, fetal nervous system malformations and growth retardation in late pregnancy. Zinc contamination in soils and vegetation is derived from several anthropogenic activities. Soils are the receptacles for metals released from industrial activities, municipal waste sludge, urban composts, road traffics, atmospheric deposits and agro-chemicals. Heavy metals are persistent in the environment and are non-biodegradable thus readily accumulate to toxic levels. The heavy metal content alone does not provide predictive insights on the bioavailability, mobility and fate of heavy metal contaminants . It is the chemical form or species of the heavy metal that is a factor in assessing their impacts on the environment because it is their chemical forms that control its bioavailability or mobility. The approach to soil speciation is to separate the soil into different chemical reagents or solvent fractions and analyse in each fraction the amount of element combined or associated with each fraction or phase. Research on nutrient intake have shown that low dietary Zn poses a potential nutritional problem. Therefore, the accurate Zn determination in food and soil is very important. This study reports Zn concentrations in maize and soil samples by flame atomic absorption spectrometry (FAAS). Res.J.Chem.Sci.______________________________________________Research Journal of Chemical Sciences Vol. 1(4), 98-108, July (2011) ISSN 2231-606X International Science Congress Association 99 Material and MethodsThe soil samples were dissolved by using the chemical reagents such as mixture of HNO/H, (COOH), NaEDTA and CHCOOH. The relation between the maize contents and the Zn contents of soil extracts was also investigated. In the digestion and extraction procedures, concentrated HNO, H, 1.0M (COOH), 0.05M NaEDTA and 1.0M CHCOOH were used. Stock solution of Zn (1000mg/L) was prepared by dissolving Zn (NO in 1.0mol/L nitric acid. Preparation of Samples: The study covered seven agricultural sites in Kaduna, Nigeria (fig. 1). The sites are: Nasarawa (NS), Sabon Tasha (ST), Unguwar Muazu (UM), Tudun Wada (TW), Kakuri (KK), Mando (MD) and Kabala West (KB). The samples were collected during the harvest season (Oct – Nov., 2008, 2009 and 2010). The soil samples were collected from different areas enumerated at a depth of 10cm below the surface10. The maize sample (maize) were collected at each of the locations. Kachia, a town situated about 130km away from Kaduna was taken as control. The sample was washed with water and was allowed to dry on filter papers. Both samples were dried at 85ºC. All the analyses were carried out in the analytical laboratory of the department of Applied Science, College of Science and Technology, Kaduna Polytechnic, Kaduna-Nigeria. Wet Ashing of Maize: 5g of oven dried crushed and sieved maize sample was weighed into an evaporating dish and ashed at 480ºC for 4 hr. 10cm³ of a mixture of nitric acid – hydrogen peroxide (2+1) was added to the ashed sample and dried with occasional shaking on a hot plate and cooled, 4cm³ of 1.5 mol/dm nitric acid was then added and centrifuged. The digest was diluted to 60cm³ of water and filtered. This was analyzed for Zn using FAAS model 8010 Young Lin. A blank digest was carried out in the same way. Digestion of Soil: Soil pH was measured (1:5, w/v) using microprocessor pH meter model, pH 210. 10cm³ of mixture of nitric acid – hydrogen peroxide (2+1) was added to 5g of soil sample and dried with occasional shaking on a hot plate and cooled, 4cm³ of 1.5 mol/dm nitric acid was added and centrifuged and diluted to 60cm³ with water and was filtered. The clear digest was analyzed for Zn using FAAS model 8010 Young Lin. A blank digest was carried out in the same way. Extraction of Soil: Soil extracts were obtained by shaking separately, 5g of soil samples with 10cm³ of 0.05Mol/dm NaEDTA (for carbonate and organically bound phases), 0.1Mol/dm oxalic acid (for oxide phases), and 1.0Mol/dm acetic acid (for carbonate phases). The mixture was evaporated with occasional shaking on a hot plate. 4cm³ of 1.5mol/dm nitric acid was added to the remainder and centrifuged. This is referred to as hot extraction. The digest was diluted to 60cm³ and analysed for Zn using FAAS model 8010 Young Lin. A blank digest was carried out in the same way. Results and DiscussionZn content in Samples: The Zn content for the samples collected from the eight different locations at Kaduna, Nigeria is shown in Tables 1 to 8. The results of the Zn concentrations from each location indicate higher concentrations of the metal in maize samples than the soil samples and in agreement with results from other investigators11-12. The lower Zn concentration for some soil sites compared to others could be due to the lesser impact of anthropogenic sources11. Similar findings were observed by other investigators13. The higher Zn values obtained for the maize samples could be attributed to the various agricultural practices14. The pH of the soil samples from the various locations is acidic. Similar results were also reported by many authors14-16. Res.J.Chem.Sci.______________________________________________Research Journal of Chemical Sciences Vol. 1(4), 98-108, July (2011) ISSN 2231-606X International Science Congress Association 100 Metal Speciation: The distribution of Zn in soil samples from the various locations showed that the metal exist in three operationally defined geochemical fractions; the residual, oxide and carbonate (Table 1 – 8). The concentration of the metal bound to oxide is generally higher than the carbonate or residual, except in Nasarawa (NS), where the carbonate is higher compared to the other two fractions. The predominance of the oxide fraction in these areas is in agreement with the result as reported by other investigators11,17. The dominance of the metal concentration in the carbonate fraction from NS is in agreement with the results of other investigators10. In case of total Zn concentration in the soil, the lowest value was in point KC1 and the highest was in sampling points KK and MD. In all the sampling locations, the Zn concentration is within the range (10–300mg/kg) as reported18. The (COOH)extractable, CHCOOH extractable, EDTA extractable and HNO/HO extractable Zn have been considered as available Zn18. These Zn species should measure available concentration of Zn in the soils from the various locations19. The results of correlation calculations (Table 9) show that the HNO/H, EDTA, (COOH) and CHCOOH extractable and total Zn content in maize positively and significantly correlate with each other at 0.05 and 0.01 levels. Hence it could be deduced that the various reagents used were efficient for the extraction of this metal from the soil at these levels. ConclusionsDifferent selective chemical reagents and the modified sequential extraction procedures used in this work were found useful in determining the mobility and chemical forms of Zn in soil. The results obtained show that the metal is distributed between Residual, Oxide and Carbonate fractions. 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