Studies on distribution and fractionation of heavy metals in sediment of cau River, Vietnam - Van Dieu Anh

Journal of Science and Technology 54 (2A) (2016) 293-298 STUDIES ON DISTRIBUTION AND FRACTIONATION OF HEAVY METALS IN SEDIMENT OF CAU RIVER, VIETNAM Van Dieu Anh 1, * , Pham Ky Uoc 1 , Tran Thi Phuong Dung 1 , Fujii Shigeo 2 1 School of Environmental Science and Technology, Hanoi University of Science and Technology, Vietnam 2 Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192 Japan * Email: anh.vandieu@hust.edu.vn Received: 5 April 2016; Accepted for publication: 26 June 2016 ABSTRACT Cau River, one of the major rivers of Thai Binh River Systems, has been under pressure from discharge from the economic and social development activities of the region. Water and sediment samples will be collected along Cau River to determine the spatial variability of metal in Cau River. Sediments collected from Cau River were extracted sequentially to investigate the distribution and fractionation of metal in Cau River. Results showed that the presence of certain metals in water and sediment with the concentrations ranged in a wide variation. In water Cu (58-181 µg/L), Pb (0.6-1.85 µg/L), Zn (18.1-32.5 µg/L), Cd (0-0.02 µg/L), Ni (3.04-4.41 µg/L), Cr (2.72-5.07 µg/L); in sediment Cu (27.6-401 mg/kg), Pb (0-282 mg/kg), Zn (3.9-71.9 mg/kg), Cd (0.01-2.44 mg/kg), Ni (2.24-5.89 mg/kg), Cr (4.08-11.5 mg/kg). Sequential extraction for study the distribution of metal species in sediment showed that metal mainly concentrated immobile form of residues fraction, organic compound bound fraction and Fe-Mn oxide associated fraction. This dominant existence of metal result in the tendency of metal assimilation in sediment and low bioavailability. However, some toxic metals such as Cd, Cr found moderated soluble form must be studied more for their release to water phase and and bioaccumulation. Keywords: heavy metal, river sediment, fractionation, sequential extraction. 1. INTRODUCTION Heavy metal pollution in water environment has become a major concern due to their toxicity, persistence, and bioaccumulative nature. When metals enter the environment, they will distribute between the aqueous phase and the suspended sediments during their transport [1]. Metals tend to be assimilated in sediment. Hence sediment is always regarded as the potential reservoir for metals and plays an important role in adsorption of dissolved heavy metals. In turn, contaminated sediments also act as sources of heavy metals when released into the river water. Van Dieu Anh et al. 294 In sediments, heavy metals can be present in a number of chemical forms, and generally exhibit different physical and chemical behavior in terms of chemical interaction, mobility, biological availability and potential toxicity. It is necessary to identify and quantify the forms in which a metal is present in sediment to gain a more precise understanding of the potential and actual impacts of elevated levels of metals in sediments. Cau River one of the major river of Thai Binh River Systems has its catchment area of 6,030 km² and length of 290 km. Cau River flows through seven provinces of the Northern Vietnam including Hanoi. It has abundant water with average flow of 135 m 3 /s [2]. In recent years the water quality of the river has been declined due to pressure from discharge from the economic and social development activities of the region. The main sources of pollution discharging into the river include domestic waste water, industrial wastewater from specific industries such as mining and mineral processing, metallurgy, chemical production ... wastewater from agriculture and activities of the villages, such as the paper production villages, metal plating village, recycling waste villages Results of water quality monitoring showed the occurrence of heavy metals in water and sediment. However, studies related to heavy metals pollution in the Cau River only focus on total metal. Studies on the species of metal in sediment of Cau River are still limited. This study is carried out to determine of the spatial variability of metal in surficial sediment of Cau River and to investigate the distribution of metal in surficial sediment of Cau River. 2. MATERIALS AND METHODS Water and sediment samples were collected along Cau River. Sampling stations are showed in Fig. 1. At each sampling station, one (01) composite water sample of 2 litter and one (01) surficial sediment sample were collected. The water samples were collected by horizontal water sampler and then kept in plastic bottle brought to the laboratory stored in a refrigerator for analysis. The sediment samples were collected by using a grab sampler, sealed in clean polythene bags and brought to the laboratory stored at -30 0 C until analysis. Figure 1. Sampling map. 2.2. Sample treatment and analysis Studies on distribution and fractionation of 295 All chemicals used in treatment and analysis for metal determinations were obtained from Merck or equivalent grade. Deion water were used throughout the study. All the glassware and sample bottles were thoroughly cleaned and rinsed with 10% HNO3 and then deion water. 2.2.1. Sample pretreatment Water samples were filtered immediately after arrival the laboratory, then the filtrates were acidified with concentrated HNO3 to reduce the pH of the filtrates below 2.0. Sediment samples were air dried and grinded and then extracted metal by the suitable procedures. 2.2.2. Metal extraction procedures Microwave-assisted extraction procedure: Sediment sample (0.2 g) was weighed into the Teflon digestion vessel, 0.5ml of 30% mass/mass H2O2, 5 ml of 65 % mass/mass HNO3, and 1.5 ml of 37 % mass/mass HCl were added then the vessel were put in the reactor for digestion. The digestion program consisted of a multi-stage program with the power, maximum pressure to be reached and digestion time as follows: stage 1 (380 W; 20 psi; 5 min); stage 2 (380 W; 40 psi; 5 min), stage 3 (380 W; 80 psi; 5 min) and stage 4 (380 W; 140 psi; 105 min). After digestion, the vessels were cooled, the contents in the vessels were dissolved with 1 ml of HCl and transferred, and made up to volume in 50 ml calibrated flasks with de-ion water. Sequential extraction procedure: Metals in sediment samples were sequentially extracted according to scheme proposed by Tessier et al. [3] as in Figure 2. Figure 2. Flow chart for sequential extraction scheme of sediments [3]. 2.2.3. Analysis Concentration of metals in water filtrates and sediment extracts were quantified by ICP-MS. Van Dieu Anh et al. 296 3. RESULTS AND DISCUSSION 3.1. Concentration of metal in water and surface sediment of Cau River Table 1. Concentration of metal in water and sediment of Cau River Sample Cu Pb Zn Cd Ni Cr Concentration in water ( g/L) CR3 ND 0.59 24.0 0 4.41 3.77 CR5 ND 0.86 32.5 0.02 3.04 3.39 CR6 ND 1.10 18.1 0.01 3.80 5.07 CR7 58.6 0.97 21.2 0.01 4.06 2.72 CR8 181 1.85 29.9 0.01 3.54 4.00 CR9 87.7 1.23 25.7 0.02 3.76 4.15 CR10 80.9 1.09 26.0 0.01 3.50 2.96 Concentration in sediment (mg/kg) CR3 27.6 3.35 3.90 0.02 2.24 4.08 CR5 401 0.28 71.8 2.44 5.89 10.9 CR6 56.5 5.77 26.3 0.16 3.38 6.27 CR7 95.9 ND 69.0 0.26 5.74 11.5 CR8 94.0 283 9.43 0.06 5.47 7.52 CR9 121 5.53 13.3 0.07 5.45 7.42 CR10 40.02 3.68 6.41 0.01 3.43 5.12 ND: not detected Results for the concentration of metal in river water were Cu (58-181µg/L), Pb (0.6- 1.85µg/L), Zn (18.1-32.5µg/L), Cd (0-0.02µg/L), Ni (3.04-4.41µg/L), Cr (2.72-5.07µg/L). Comparison with nation technical regulation on surface water quality (QCVN 08-MT: 2015/BTNMT) all observed metals were below the permitted values except for Cu. In sediment, the total concentration of metal were Cu (27.6-401mg/kg), Pb (0-282mg/kg), Zn (3.9- 71.9mg/kg), Cd (0.01-2.44 mg/kg), Ni (2.24-5.89mg/kg), Cr (4.08-11.5mg/kg). The metal contamination in sediment was evaluated by and nation technical regulation on sediment quality (QCVN 43:2012/BTNMT). Cu and Pb were found exceeding the permitted values. Cu showed the highest concentration levels among metals in both of water and sediment samples. The concentrations of studied heavy metals in this study were found in the same range with the results of National Monitoring Program on Cau River in 2014 [2]. The high content of metals in sediment obatained in area near Thai Nguyen (CR5, CR6) and Bac Ninh (CR8) provinces where there is a concentration of mining and mineral processing, metallurgy, chemical production in Thai Nguyen and metal plating village, recycling waste villages in Bac Ninh. The concentrations of heavy metals in sediments were found considerably higher than those obtained in river water. Studies on distribution and fractionation of 297 It means that metal in water column might settle to sediment resulting in exposure risks to the benthic biota of the river. 3.2. Metal fractionation in sediment of Cau River Figure 3. Fractionation pattern of Cu, Pb, Zn, Cd, Ni, Cr in sediment of Cau River; F1: soluble fraction; F2: carbonate fraction; F3: Fe-Mn fraction; F4: organic fraction; F5: residual Fractionation pattern for each metal and sampling point are shown in Fig. 3. Results of the sequential extraction study reveal that for all metals the immobile species (F3, F4, F5) were predominant. Residues fraction (F5) accounted for the majority of Ni (56 – 71 %), Cr (63 % - 89 %) but observed the smallest in Cd (< 10 %). Metals found in residues fraction are expected to be chemically stable and biological inactive [4]. Considering that the metals under study were present mostly in the least mobilisable fraction, it is assumed that the metals in sediments are to great extent derived from geochemical background rather than anthropogenic inputs. The tendency of tightly bound to sediment of heavy metal was also found in many researches [5, 6]. For Cd, the very different fractionation patterns in various samples can be observed. This metal was mostly associated with Fe-Mn oxides. The next important phase of Cd was soluble fraction (10-25 %) and the soluble specie of Cd was found in high level at the sampling sites of CR6 (21 %), CR8 (15 %) and CR9 (25 %). Beside Cd, Cr was the second metal that had a high proportion of soluble form (4-17 %) and the high level of soluble Cr also observed at CR8 (16 %), CR9 (10 %) and CR10 (17 %). Cu showed a homogeneous distribution in all samples except for CR5. The most predominant specie of Cu was bound to organic matter (15-77%). The metals in the sediments are bound with different strengths to the fractions exhibiting different chemical interaction, mobility, biological availability and potential toxicity. Many studies [7, 8] applied risk assessment code (RAC), the percentage exchangeable form and carbonate form, to assess the capability of resolution metal in sediment to water column. RAC of Cu, Pb, Zn, Ni at all investigated sites were in the range of 1-10% reveals the low risk but RAC of Cd and Cr in many sites found in medium risk (11-35%). Thus, in Cau River sediments, Cd Van Dieu Anh et al. 298 and Cr were found medium risk of release to overlaying water, besides the two metals have high toxicity to ecosystem, so that they will raise potential and actual impacts to river environment. 4. CONCLUSIONS Concentrations of metals in sampling points distributed along Cau River indicated an elevated level with a wide range of variation. 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