Chromium levels in soils and vegetables from Timis County Romania

Transcription

1 Volume 16(2), , 2012 JOURNAL of Horticulture, Forestry and Biotechnology Chromium levels in soils and vegetables from Timis County Romania Despina -Maria Bordean 1 * 1 Banat s University of Agricultural Sciences and Veterinary Medicine from Timisoara, Timişoara 119, Calea Aradului, Romania *Corresponding author. despina.bordean@gmail.com Abstract This work is aimed to evaluate chromium content in two common garden vegetables (green garlic and green onion) cultivated in Timis County, Romania. Determination of chromium content in soil and raw vegetables were performed using FAAS. All experiments and analyses were carried out in triplicate. The studied areas presented normal levels of chromium, exception Timisoara where the average value of the chromium concentration is exceeding the normal value (30 mgkg -1 ), but it s under the warning threshold (100 mgkg -1 ). The highest content of chromium was found in Allium sativa samples, while Allium cepa is accumulating less chromium. According to the principal component analysis mathematical model, it s possible to conclude that soil ph is influencing the accumulation of chromium in plants. Key words soil, chromium, Allium sativa, Allium cepa L., principal component analysis Minerals have an important role for the normal functioning of all biochemical processes in the body. Chromium (Cr) is the 21st most abundant element in the earth's crust [22]. By definition an essential mineral is a mineral required for supporting adequate growth, reproduction and health throughout the life cycle, when all nutrients are optimal [26]. According to this definition chromium is a trace mineral required by human health, due to its involvement in the synthesis of fatty acids and cholesterols, metabolism of carbohydrates, proteins, lipids and with role to facilitate the action of insulin [17, 24] its ability to regulate glucose, preventing hyperglycemia or diabetes [3]. Chromium occurs in nature in bound forms that constitute mg/kg of the earth's crust [20]. The total forms of chromium in some natural sources are presented in table 1. Parameter Total Chromium Concentration in Natural Substances [7] Reported Average Range References Units Table 1 Universe ppm 15 [36] Earth Crust mg/kg 100 [12,33] Limestone mg/kg 10 <1 120 [1, 35] Sediments mg/kg 72 [30] World Soil mg/kg 200 [15] U.S.A. Soil mg/kg [1, 31] Ground Water µg/l [1] Ocean Water µg/l [4, 5, 10] Arctic air pg/m [37] Indoor(tobacco smoke) ng/m3 ~1000 [37] Human Blood mg/dl [11] Human Liver ppm [11] Food: Milk and diary products mg/kg 0.06 [5] Meat mg/kg 0.07 [5] Continental Vegetation Annual Growth Ash - Dry Phytomass - Live Phytomass mg/kg [9] 106

2 Forms of Soil Chromium. Chromium exists in soils predominantly in the +3 and +6 oxidation states. The intermediate states of +4 and +5 are metastable and rarely encountered [38]. A number of soil processes and environmental factors may affect the form and biomobilization potential of chromium [2, 28]. In soils, Cr is present mostly as insoluble chromium hydroxide aqueous solution (Cr (OH) 3 aq) or as Cr (III) adsorbed to soil components [21]. The availability of soil chromium to the plant depends on the oxidation state of Cr, ph, and the presence of colloidal binding sites and Cr-organic complexes that would influence its total solubility. Chromium (III) is largely present in soil as relatively unavailable, insoluble oxides of Cr and Cr-Fe or can also exist as a substitute for Al (III) in the [AlO 6 ] groups of aluminosilicates [16]. The solubility of Cr (III) in soil is dependent on ph (Palmer and Wittbrodt, 1991) and decreases dramatically at ph > 4.5 [16]. The Cr(III) adsorption to humic acids renders it insoluble, immobile and unreactive; this process is most effective within the ph range of 2,7 4,5 [19 cited by 21]. Cr (III) is hydrolyzed with increasing ph. The most important species are CrOH 2+, [Cr (OH) 3 ]) 0, and [Cr(OH) 4 ] -, with [Cr(OH) 2 ] - occurring in a significant proportion only in the narrow ph range between 6.27 and At ph > 8.5, chromium (III) can form stable complexes with oxalate, citrate, malate, EDTA, DTPA and polymers. These complexes form slowly, and once formed, are difficult to break. The presence of organic complexes can significantly influence the concentration of total dissolved Cr (III) in the soil solution [16, 29]. Chromium (VI) is more soluble than Cr (III). Chromate, [CrO 4 ] 2-, which is the predominant form at ph > 6, exists in ph-dependent equilibrium with other forms of Cr (VI), such as [HCrO 4 ] - and dichromate [Cr 2 O 7 ] 2- [16, 29]. As a consequence, the intensity of adsorption will depend on the type and quantity of soil components, as well as ph and the presence of competing ligands such as phosphate. The availability of soil Cr to the plant depends on the oxidation state of Cr, ph, and the presence of colloidal binding sites and Cr-organic complexes that would influence its total solubility [29]. Material and Methods The study was performed on soils and vegetables sampled from Timis County (Timisoara, Sanmihaiul Roman, Dumbravita and Giroc). From all four locations were sampled fresh green vegetables, Allium cepa L and Allium sativa. Samples collection and preparation Soil Soils were sampled at 0 to 20 cm from the same place from where the plants were sampled. Soil sampling was done according to the recommendations of the Ministry of Agriculture, Food, and Forests Order nr. 223 updated and published in Romania s Official Monitor nr. 598/13 august 2002 [27]. The collected soil samples were dried two days and sieved and the impurities removed. The surface soil samples were analyzed using the procedure recommended by SR ISO: [34]. Plants All the collected plant samples were cleaned of the impurities washed with double distilled water to remove dust and pollutants. After washing, the plants (roots and leaves) were cut in small slices and were oven dried at 105 C to constant weight. After that, the dried samples were ground and stored at room temperature till analysis. Analytical determinations ph analysis: Soil samples ph were measured potentiometrically using an electronic ph meter with appropriate electrode in a soil/water slurry (1:2,5 - soil: water). Atomic Absorption Spectrometry analysis: After complete burning, 0.5 N nitric acid solution was added up to 50 ml. The solutions obtained were used for total chromium content determination by Flame Atomic Absorption Spectrometry (FAAS) in University Food Analysis Research Test Laboratory. The standard solutions (1000 mg/l) were analytical grade from Riedel de-haen (Germany) The nitric acid 65% solution used was of ultra pure grade (Merck, Germany). All solutions were prepared using deionised water. Analyses of chromium content were made with ContrAA-300, Analytik-Jena device, by FASS in air/acetylene flame [13, 18]. The device working parameters (air, acetylene, optics and electronics) were adjusted for maximum absorption for chromium. All analyses were made in triplicate and the mean values were reported. Statistical analysis The data were statistically analyzed using two statistical packages: MVSP 3.1 and PAST 2.14 [14]. Principal Components Analysis (PCA) is a mathematical model that permits to identify patterns in data by expressing the data to highlight their similarities and differences [32, 14]. Cluster Analysis is a statistical method that groups data objects based on information found in the data that describes the objects and their relationship [8]. Results and Discussions The chromium composition of the studied soil (mgkg - 1 ) and plant (mgkg -1 fresh matter) samples are presented in Figure 1. Each value in the graphics is an average of 3 replicates. 107

3 Fig. 1. Representation of soil ph and chromium content in soils and plants samples Legend: Soil ph; Soil Cr - Soil chromium contend (mgkg -1 ); Soil NV- Normal Values of chromium content in soil (mgkg -1 ); Cr contend in Allium sativa (mgkg -1 fresh matter); Cr contend in Allium cepa L.; MRL maximum recommended limits for vegetables The highest contend of chromium were detected in the soil samples from Timisoara areas (35.72 mgkg -1 ), value that is exceeding the normal value for chromium (30 mgkg -1 dry weight), but it is under the warning threshold (100 mgkg -1 dry weight). The concentration of total chromium in plant samples is under the maximal recommended limit (2.3 mg/kg). The maximal limit is recommended by FAO/WHO, 2001 [23]. Fig. 2. Clusters representation of chromium contend of studied areas samples The Cluster Analysis (Figure 2) was performed using transposed square-root transformed data to normalize the results using average distance to identify the nearest neighbour. The patterns of similarities between the studied locations: Sanmihaiul Roman - Dumbravita (Dissimil ) and Node 1- Giroc (Dissimil ) reveal the rural background with lower anthropogenic pollution, while Timisoara (urban location) is presenting a different graphical and mathematical fingerprint (Dissimil.0.253). PCA (Figure 3) is bringing new information regarding the chromium loadings in soil and plant samples. The correlation variance on PC1 is % and on PC2 108

4 24.33 %, PC % which is recommending PC1 as most significant axis to represent the eigenvalues. Fig. 3. Scatter representation of PCA using PC1 axis The Principal Components Analysis of the data presents the levels to which the accumulation of Cr in the product samples was influenced by the Cr soil content (Figure 3). As shown in Figure 3, the highest accumulations of Cr have occurred in Allium sativa samples. Allium sativa is accumulating more chromium then Allium cepa L. As we can observe from Figures 1 and 3, the lowest chromium contend is in the area of Giroc village, the area with the lowest ph of soil as well as the lowest soil and vegetables chromium content. According to the Figure PCA we can conclude that soil ph is influencing the accumulation of chromium in plants, observation confirmed by various literature data. According to Cary et al, 1977 R., the reduction of Cr(VI) to Cr(III) by organic matter is more rapid in acid than in alkaline soils [6 cited by 16]. Conclusions The results indicates that the studied vegetables present normal level of chromium, even if in some areas chromium content in soil, might exceed the normal values. As chromium is an essential trace element consumers could be influenced to consume vegetables that have the capacity to accumulate more chromium. It is suggested that regular monitoring regarding the soil chromium concentration should be encouraged to avoid possible increasing of chromium soil contend. Acknowledgements We are grateful to WEBOMATIK RO S.R.L. for permission to use statistical package MVSP 3.1 and technical assistance. References 1.Allard, B Groundwater, in Aalbu, B. and Steinnes, E., Eds., Trace Elements in Natural Waters, CRC Press, Boca Raton, FL, p ; 2.Allaway, W.H Soil and plant aspects of the cycling of chromium, molybdenum and selenium, Int. Conf. on heavy metals in the environ. T.C. Huthchinson (et al.) eds. Symposium proceedings vol. 1. Toronto, Canada Oct p ; 3.Balk EM, Tatsioni A, Lichenstein AH, Lau J, Pittas AG Effect of chromium supplementation on glucose metabolism and lipids: a systematic review of randomized controlled trials, Diabetes Care. 2007;30(8): Diabetes Care Aug; 30(8), p ; 109

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