1 Analysis of Water Quality and Sediment Composition In
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ANALYSIS OF WATER QUALITY AND SEDIMENT COMPOSITION IN THE PARAOPEBA AND DAS VELHAS RIVERS- BRAZIL M. A. R. V. VEADO*, G. PINTE**, A. H. OLIVEIRA*, G. REVEL** *Departamento de Engenharia Nuclear- UFMG Av. do Contorno 842, CEP 30110-060 – Belo Horizonte, Brazil E-mail: [email protected] , [email protected] **Laboratoire Pierre Süe, CEA-CNRS F-91191 Gif-sur-Yvette, Cedex, French E-mail: [email protected] ABSTRACT Instrumental Neutron Activation Analysis (INAA) and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) are used for analysis of the water and sediments in the DAS VELHAS and PARAOPEBA basin in State of Minas Gerais, south-east Brazil. Elemental concentrations of Fe, Co, Cr, Cu, As, Ni, Ba, Cs, La and Ce are measured in samples collected in different parts of this river, in a tributaries and in a region lake. The results indicate an increase in the concentration these polluting elements in an industrial discharge area. Pollution by metallic elements associated with mining region is clearly demonstrated Key words: : INAA - ICP-MS – Water analysis– Sediment analysis - River pollution beginning and ecological problems have been identified in I. INTRODUCTION rivers, lakes and reservoirs [1]. The Foundation for Environments of the state of Minas Gerais (FEAM) is responsible for the water quality The state of Minas Gerais is the fourth largest controls and monitoring in the Paraopeba and Das Velhas state of Brazil and the state itself is the world’s second river. The analysis method which has been utilized until now largest producer of minerals. Its many sources of is the Atomic Absorption Spectrometry (AAS) and that is freshwater provide near to 20% of electricity produced in sufficient for their controls efforts. Brazil. The Paraopeba and Das Velhas rivers runs through This research proposes two other more sensible a region which is rich by Fe, Al and Mn ores and flows analytical methods: Instrumental Neutron Activation into São Francisco river that is called in Brazil " The Analysis (INAA) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The INAA is a very accurate National Integration River " because it runs across four method for the analysis of solid samples and has been widely states and is used for navigation, recreation and electricity used for the analysis of water and sediment from freshwater production. Waste waters from about 70 great industries [2-8] The ICP-MS is a very fast method for the analysis of are generated in the Paraopeba basin. In the region of the liquid samples and it can analyze more than 100 samples Betim tributary alone there’s a concentration of 57 daily, and was recently used to determine the composition of industries. Several clandestine industries are discharged river water and sediment for routine trace analysis [9-12] into the Das Velhas river. These two methods are multi-elementary and allow high In spite of the environmental controls carried out sensitivity determination of traces of numerous elements. by the most important industries, this concentrations causes serious environmental pollution. This pollution is the largest governmental problem in Minas Gerais. Studies of freshwater ecosystems in Minas Gerais are just 1 II. EXPERIMENTAL PROCEDURES Water samples were collected near the river bank from a depth of 15 cm, placed in 125 ml Nalgene bottles and stored Study Area and Sampling: at 4°C. Temperature, pH and electrical conductivity were measured in each sites. We had not detected significant variations between the different areas. The average values of Water and sediment samples were collected from these parameters are: temperature = 25°C; pH = 7.2; approx. 200 km Paraopeba river and near the source of the electrical conductivity = 30 mS. The samples were taken in approx. 100 km long Das Velhas, river in January 1995. duplicate and half of them were acidified on site with 5 The sampling areas are indicated in Fig. 1. drops of ultrapur acid nitric (pH~2). This acidification is believed to reduce any sorption on the walls of the bottles [13-15]. The sediment samples were collected in a 20 ml polyethylene tube and also stored at temperature of 4°C. They were dried for a day at a temperature of 80°C prior to analysis. One sediment sample was collected per water sample. Neutron Activation Analysis (INAA): Water samples must be pre-concentrated before irradiation in order to perform neutron activation analysis. 10 ml samples were evaporated in the ultrapur-quartz ampoules, SUPRASIL, 80°C for 24 h and heat-sealed. The samples and standards were irradiated in Saclay’s OSIRIS nuclear reactor at a neutron flux of 1.4 1014 n cm-2 s-1 for 17 h. The g-rays subsequently emitted were counted for 8 hours, after a decay time of 10 or 20 days, with 100 cm3 coaxial HpGe PGT detector coupled to a 4096 pulse height analyzer. The computational K0 method [16] was used to determine the concentration of elements of interest. The sediment samples (150 mg) were irradiated in the OSIRIS nuclear reactor for 2 h. and counted for 4 h in the same conditions done for the water. To enable the techniques of INAA and ICP-MS to be compared, 20 ml of a 3:1 mixture of HCl and HNO3 was added to the irradiated sediment samples, the mixture evaporated at 80°C, diluted with 20 ml of 5% nitric acid and centrifuged. The liquid samples were counted for 4 hours. Inductively Coupled Plasma Spectrometry (ICP-MS): Measurements were carried out using the multi- element modes. An analytical program was established for both calibration and routine analysis. This program uses a series of automated operations to align the optics, select the analytical wavelength for the peaks and position the source at the entrance slit, in order to optimize the signal. The selected analytical wavelengths are the characteristic lines of the elements, which are free of spectral interference. and this avoids the necessities of the corrections at the concentration level of interest. The ICP-MS used in this study was a PQ 2- Plasma Quad with a Meinhard ultrasonic nebulizer. The data acquisition was controlled using PQ VISION software. The measurements were taken in duplicate, using the following operating conditions: - ICP-MS power: 1.35 KW; - Coolant Argon flow: 14 l/min; - Nebulizer Argon flow: 0.8 l/min; - Auxiliary Argon flow: 0.8 l/min; -Sample uptake rate: 0.6-1 ml/min. The instrument was calibrated with a commercial Fig.1. Location of study area and samples sites in solutions (SPEX) which contained standards prepared out of Paraopeba and Das Velhas rivers. 2 10 ppb multielementary and 1000 ppb Ca solutions. Blanks soluble chemical state [18,19], explaining the non increase were also used in order to enable an accuracy of 2-3%. of Fe and Cr concentration in the sediment at S4. The 250mg of sediment samples were digested Except for the rare earth elements, La and Ce, an with a solution of HNO3, HCl and HF under pressure in a increase of the concentration of the other elements analyzed stove at 110 oC for 12h, followed by other sequence acids is shown in the water samples from S5 to S6. This is in spite attacks for total digestion [17]. The internal standards of of the points of collection S5 and S6 being located before water and sediment samples were 10 ppb solution of In, and after the barrage of the Electric Company of Minas Re, and Be. Gerais –CEMIG. The point of collection S6 receives a very The elements Fe, Cr, Co, La and Ce were important contribution from the polluted waters of Betim analyzed by the INAA method and the elements Ni, Cu, river. This same phenomenon is the inverse of the results Ba, Cs, were analyzed for ICP-MS, because it had already obtained in the sediment samples, reinforcing the conclusion been demonstrated they were the most indicated method above. for studies of these elements in this particularly rich ores The lake shown, near to Paraopeba river, in the fig region[17]. 1, is placed 3 km from the margins of the river. There were analyses made in samples of water and sediment in 3 points taken in a triangular distance. The results are shown in the III. RESULTS AND DISCUSSION table 2 for the same elements considered in the study. These analyses were taken as comparative parameters for the The INAA and ICP-MS detection limits in our results from the river and the lake which don’t receive any analysis are indicated in table 1. The background were influence from the Paraopeba river. considerate as limit for sediment samples which were This comparison allows us to judge the pollution directly irradiated in reactor. For the water samples, the introduced by the industries in the course of the Betim and evaporated waters in ultrapur-quartz ampoules were Paraopeba rivers. It is observed that the results obtained in irradiated. Blank quartz ampoule irradiated along side the three points of lake are very close to an unpolluted water samples is given as a limit for INAA method. For region, which reinforces the significant differences of the ICP-MS, the limits obtained are practically identical in concentration results in the lake and in the pollution sites of water and sediment samples which are the introduced the Paraopeba river. same blanks in samples for dilution. RESULTS OF DAS VELHAS RIVER: TABLE 1. Detection limits, ppb, for the dosage of elements The concentration results are shown in figures 10 to 11, for water samples. The increase in concentration Element INAA ICP-MS Element INAA ICP-MS beginning in S3, confirms a significant source of pollution of Cr 0.40 0.53 As 0.01 0.40 industrial mining area, near Itabirito city.