Copper and zinc content in soil and their accumulation in some agricultural products in Ha Mo co-operative, Dan Phuong district, Ha Noi

JOURNAL OF SCIENCE OF HNUE Chemical and Biological Sci., 2012, Vol. 57, No. 8, pp. 66-71 This paper is available online at COPPER AND ZINC CONTENT IN SOIL AND THEIR ACCUMULATION IN SOME AGRICULTURAL PRODUCTS IN HA MO CO-OPERATIVE, DAN PHUONG DISTRICT, HANOI Vu Van Hien Faculty of Biology, Hanoi National University of Education Abstract. Analytical results of Cu and Zn content in 20 soil and 20 pricipal agricultural products samples collected in Ha Mo Co-operative, Dan Phuong District, Hanoi, in 2009 and 2010 indicate that the average total Cu content in the examined soil is 32.12 mg/kg−1 and average available Cu content is 12.84 mg/kg−1. The average total Zn content is 90.18 mg/kg−1 and average available Zn content is 13.01 mg/kg−1. The Cu and Zn content in the soil samples is within permissible limits of heavy metal in agricultural soils by Vietnamese standards. The amount of Cu in rice grain, cabbage leaves and tomato and cucumber fruit was found to be 2.81 mg/kg−1 and respectively 0.75 mg/kg−1, 1.13 mg/kg−1 and 0.79 mg/kg−1 fresh weight. The amount of Zn in rice grain, cabbage leaves and tomato and cucumber fruits was found to be 20.22 mg/kg−1 and respectively 1.29 mg/kg−1, 3.60 mg/kg−1 and 1.81 mg/kg−1 fresh weight. The Cu and Zn content in these four agricultural products was found to be below the limit set by FAO/WHO. Keywords: Copper, zinc, soil, rice grain, cabbage, tomato, cucumber. 1. Introduction In areas which experience a tropical climate with torrential rains and high temperatures, agricultural soils have a low organic matter content due to increased mineralization of organic matter after cultivation, tillagemethods which physically disrupt the soil surface and erosion of top soil. Consequently, these soils benefit from an application of organic matter to improve their quality and fertility. Organic fertilizers, organic residues, municipal refuse, sewage sludge, animal waste are organic materials which are commonly applied to improve the soil’s physical, chemical and biochemical properties. However, repeated applications of organic residues can result in an accumulation of heavy metals in the soil [7, 8]. Received August 16, 2012. Accepted September 17, 2012. Contact Vu Van Hien, e-mail address: hienvv@hnue.edu.vn 66 Copper and zinc content in soil and their accumulation in some agricultural products... Copper and zinc are two essential trace elements that are required for plant growth, functioning as an activator of enzymes such as carboxy peptidase, carbonic anhydrase, aldolase, phosphatase, xytocromoxydase and DNA polymerase. Copper and zinc are also toxic to humans when high levels are ingested and an excess of copper and zinc interferes with plant growth. It is important to monitor copper and zinc content in soil to avoid marketing food products which contain dangerous amounts of these heavy metals [10]. This article presents the results of a study done to determine the copper and zinc content of soil and four agricultural products grown in Tan Lap Co-operative, Dan Phuong District, Hanoi. 2. Content 2.1. Materials and methods * Sampling and preparation of soil Soil samples were obtained from four fields, each used to grow exclusively rice, cabbage, tomatoes and cucumbers. The soil samples were taken at five randomly selected sites within each field. Soil samples (0 - 20 cm in depth) were taken using an auger 5 cm in diameter, placed in polyethylene bags, packed in a insulated box and transported to the laboratory where they were air dried, ground and passed through a 2 mm mesh sieve to be used for analyses. Five agricultural product samples were collected from each field. * Analytical methods [5] Particle size was determined using the pipette method. Organic carbon in the soil was determined using the Walkley - Black method. This involved a wet combustion of the organic matter with a mixture of potassium dichromate and sulphuric acid. After reaction the residual dichromate was titrated against ferrous sulphate with barium diphenylamine sulphonate. Soil pHwas potentiometricallymeasured in a water:soil solution ratio of 1:2.5 using a glass electrode. Total nitrogen was measured using the Kjeldalh method. The soil samples were digested in sulphuric acid and organic nitrogen was converted to ammonium sulphate. The solution was then made alkaline and NH3 distilled. The evolved ammonia was trapped in boric acid and titrated with standard acid. Total phosphorus was determined using the spectrophotometer method. The soil samples were digested in a mixture of pecloric and sulphuric acid. Total potassium was determined using a Flamephotometer. The soil samples were combusted and dissolved by an HF and HClO4 mixture according to M. Jackson. Available phosphorus was fractionated using 0.1 N HCl and 0.03 M NH4F in a 1:7 soil:liquid mixture. Available phosphorus in the extract was determined colorimetrically with ascorbic acid as the reducing agent. Available potassium in soil was extracted using 1 M ammonium acetate (pH = 7.0). Available potassium in the extract was determined using the Flamephotometer. 67 Vu Van Hien Exchangeable bases were extracted using 1 M ammonium acetate (pH = 7.0). Ca and Mg in the extract were measured using Atomic Absorption Spectrophotometer. Cation exchange capacity (CEC) was determined using the stream distillation and titration method.Soil samples used to measure total content of Cu and Zn were digested in a mixture of HNO3 and HCl at a ratio 3:1. Available Cu and Zn in soil were extracted using 0.43 M HNO3. Agricultural product samples that were used for measuring Cu and Zn content were digested using 65% HNO3. Cu and Zn content in soil and agricultural products samples was determined using an Atomic Absorption Spectrophotometer (AAS). * Statistical analysis Excel and Statistic programs for Windows 5.0 were used to evaluate the analytical results of Cu and Zn content in the soil and in agricultural products. 2.2. Results and discussion 2.2.1. Main properties of the soil The soil examined is alluvial soil of the Red River Delta. Because of the variation in available water, alluvial soil of the Red River Delta has different textures in terms of profile and surface. In some provinces, interposed layers of clay, silt sand can be found. Soils near rivers at higher elevations and have a sandy texture while soils far from rivers have a finer texture [4]. The main properties of the study soil are shown in Table 1. Table 1. Main characteristics of the soil of study site Properties Average Properties Average Sand (%) 0.8 Total P (%) 0.12 Silt (%) 42.7 Total K (%) 1.69 Clay (%) 35.3 Available P (mg/100) 4.7 Colloid (%) 21.2 Available K(mg/100) 7.06 OM (%) 2.18 Ca2+ (meq/100) 6.88 pH 7.1 Mg2+(meq/100) 2.34 Total N (%) 0.14 CEC (meq/ 100) 14.80 As shown in Table 1, the study soil has a relatively high percentage of silt and clay at 42.7% for silt and 35.3% for clay. The soil has an average organic matter content of 2.18%. The reaction of the soil solution is neutral (pH = 7.1). According to a 2004 Vietnam soil quality standard report, the study soil has an average total nitrogen content [12]. Total phosphorus and potassium content is relatively high at 0.12% and 1.69%, respectively. 2.2.2. Copper and zinc content in soil Cu and Zn content in soil depends on chemical composition of parent rock, mechanical composition and organic matter content of soil. The greater the organic matter content in soil, the higher the Cu and Zn content. 68 Copper and zinc content in soil and their accumulation in some agricultural products... Applyingmanure, compost and various organic fertilizers to soils not only increases the content of microelements such as nitrogen, phosphorus, potassium, it also increases Cu and Zn content. The availability of Cu and Zn in the soil depends on the soil pH. In acidic soils, the availability of Cu and Zn is higher than in alkaline soils because in alkaline soils Cu2+ and Zn2+ are converted to insoluble Cu and Zn hydroxide. It is also the case that, in general, the higher the organic matter content of soil, the lower the availability of Cu and Zn because copper and zinc cations (Cu2+ and Zn2+ ) react with humus acid to form an insoluble complex: Humic acid + Cu2+ → Humate–Cu + 2H+. The Cu and Zn content in the study soil is shown in Table 2. Table 2. Copper and zinc content in soil (mg/kg −1) Elements Interval of variation Average Cv % Total Cu 26.22 - 39.05 32.12 ± 1.28 17.81 Available Cu 9.42 - 16.21 12.84 ± 0.60 20.92 Total Zn 67.52 - 108.90 90.18 ± 4.28 21.23 Available Zn 8.53 - 23.82 13.01 ± 0.71 24.41 Table 2 shows that the total content of Cu in the study soil ranges from 26.22 mg/kg−1 to 39.05 mg/kg−1 with an average of 32.12 ± 1.28 mg/kg−1. It also shows that the total Cu content in the soil varies widely; the coefficient of variation is 17.81%; the available Cu content in soil ranges from 9.42 mg/kg−1 to 16.21 mg/kg−1. Compared to total Cu content, the available Cu content varies more widely, the coefficient of variation exceeding 20%. The analytical results show that the total Zn content in the study soil varies from 67.52 mg/kg−1 to 108.90 mg/kg−1 with an average of 90.18± 4.28 mg/kg−1. The available Zn content ranges between 8.53 - 23.82 mg/kg−1 with an average of 13.01 mg/kg−1. It is observed that Zn content in soil varies more widely when compared to with Cu content. It is observed that available Cu and Zn content does not directly correlate to total Cu and Zn content. This is due to agricultural practices such as irrigation and the application of fertilizers during the growing season. A 2002 Vietnam soil quality standard report shows the critical level of total Cu content to be 50 mg/kg−1 and for total Zn 200 mg/kg−1 [11]. With reference to these levels, the study soils do not contain a dangerously high level of Cu or Zn. 2.2.3. Accumulation of copper and zinc in some agricultural products The absorption and accumulation of Cu, Zn in plants depends on soil properties such as pH, cation exchange capacity, organic matter content, in addition to Cu, Zn soil content. The accumulation of Cu, Zn in plants also varies with plant species. Other factors affecting the accumulation of Cu, Zn in plant depends are meteorological and hydrological 69 Vu Van Hien conditions. Some studies have shown that pants accumulate more Cu, Zn in years of abundant rainfall than they do in years of little rain and high temperatures [1, 9]. The quantities of Cu and Zn accumulated in some principal agricultural products in Ha Mo Co-operative, Dan Phuong District, Hanoi, are shown in Table 3. Table 3. Copper and zinc content in four principal agricultural products (mg/kg−1 fresh weight) Elements Rice grain Cabbage leaves Tomato fruit Cucumber fruit Interval of variation 2.13 - 3.49 0.61 - 1.04 0.92 - 1.58 0.65 - 1.12 Cu Average 2.81 ± 0.22 0.75± 0.04 1.13± 0.07 0.79± 0.05 Cv% 17.51 10.91 14.43 15.25 Interval of variation 17.96 - 24.79 0.89 - 2.18 2.07 - 4.46 1.16 - 2.19 Zn Average 20.22 ± 1.67 1.29± 0.11 3.60± 0.32 1.81± 0.11 Cv% 17.60 19.07 19.57 13.42 Of the four agricultural products examined in this study, rice grain was found to have the highest Cu content, this content ranging between 2.13 - 3.49 mg/kg−1 with an average of 2.81 ± 0.22 mg/kg−1. The lowest level of Cu was found in cabbage leaves with Cu levels varying from 0.61 mg/kg−1 to 1.04 mg/kg−1 with an average 0.75 ± 0.04 mg/kg−1. The average Cu content in tomato fruit is 1.13± 0.07 mg/kg−1 and in cucumber fruit is 0.79 ± 0.05 mg/kg−1. The Cu content of the study products has a coefficient of variation that ranges between 10 - 20 %. Similar to Cu content, the highest Zn content is observed in rice grain (17.96 mg/kg−1 - 24.79 mg/kg−1 with an average of 20.22 ± 1.67 mg/kg−1). The Zn content in cabbage leaves varies from 0.89 mg/kg−1 to 2.18 mg/kg−1 with an average of 1.29 ± 0.11 mg/kg−1. The lowest level of Zn content is observed in cucumber fruit (1.81 ± 0.11 mg/kg−1). The Zn content in the agricultural products of this study has a wider variation than that of Cu content. However, the coefficient of variation is still in the medium range (10 - 20%). It is recognized that the Cu and Zn content in the agricultural products of this study are below the limit as set by FAO/WHO standards [2, 3]. 3. Conclusion This study shows that: The average total Cu content in the study soil is 32.12 mg/kg−1 and the average available Cu content is 12.84 mg/kg−1. The average total Zn content is 90.18 mg/kg−1 and the average available Zn content is 13.01 mg/kg−1. The Cu and Zn content in the study soil are within the levels permitted by Vietnam in agricultural soils. The amount of Cu found in rice grain, cabbage leaves, and tomato and cucumber fruits is 2.81 mg/kg−1 and respectively 0.75 mg/kg−1, 1.13 mg/kg−1 and 0.79 mg/kg−1 fresh weight. The amount of Zn found in rice grain, cabbage leaves, tomato and cucumber fruits is 20.22 mg/kg−1 and respectively 1.29 mg/kg−1, 3.60 mg/kg−1 and 1.81 mg/kg−1 70 Copper and zinc content in soil and their accumulation in some agricultural products... fresh weight. The Cu and Zn content in these four agricultural products was found to be below the limit set by the FAO/WHO. REFERENCES [1] Chen Z.S., 2002. Relationship between heavy metal concentrations in soils of Taiwan and uptake by crops, [2] EC, European Commission Directive No. 4667/2001 (March 8, 2001). Highest permissible concentrations of different substances in foodstuff. Ro 466 - SV- 01-04-2005 - 011.001-1. [3] FAO/WHO, Joint FAO/WHO, 2006. Food Standards Programme. Codex Alimentarius. Commision 29th Session, Geneva 3-7, Report ALINORM 06/29/41/2006. [4] National Institute for Soils and Fertilizers, Department of Science, Technology and Product quality, 2002. The basic information of main soil units of Vietnam. The World Publishing House, pp. 56-75 (in Vietnamese). [5] National Institute for Soils and Fertilizers, 1998. Mannual for soil, water, fertilizer and plant Analysis. Agriculture Publishing House, Hanoi (in Vietnamese). [6] Pendias A.K. Pendias H., 2001. Trace elements in soils and plants. CRC Press Boca Raton London, New York W.C. [7] Petruzelli G, 1989. Recycling wasters in agriculture: heavy metal - bioavailability. Agric. Ecosyst. Environ. 17: pp. 493-503. [8] Smith J.L.,Papendick R.I., Bezdisek D.J., Lynch J.M., 1992. Soil organic matter dynamics and residue management. In Meting FB (ed) soil microbialecology: Application in agricultural and environmental management. Marcel Dekker New York, pp. 65- 94. [9] Spurgeon D.J. Hopkin S.P., 1996. Effect of variation of the organic matter content and pH of soil on the availability and toxicity of zinc to the earthworm Eisenia fetida. Pedobiologia 40: pp. 80-96. [10] Tiller K.G., 1989. Heavy metal in soil and their environmental significance. Adv. Soil Sci. 9: pp. 113-142. [11] Vietnam Standard 7209: 2002. Soils quality - Critical level of heavy metals in the soils of Vietnam (in Vietnamese). [12] Vietnam Standard 7373, 7374,7375:2004. Soils quality - Index values of total nitrogen, phosphorus and potassium content in the soils of Vietnam (in Vietnamese). 71