2005 International Nuclear Atlantic Conference - INAC 2005 Santos, SP, Brazil, August 28 to September 2, 2005 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 85-99141-01-5
HEAVY METAL ANALYSIS IN GROUNDWATER SAMPLES BY SR-TXRF Silvana Moreira1, Maria Ficaris1, Ana Elisa S. de Vives2, Orghêda L. A. D. Zucchi3, Virgílio F. Nascimento Filho4 1
Depto. de Recursos Hídricos – Faculdade de Engenharia Civil, Arquitetura e Urbanismo (FEC) Universidade Estadual de Campinas (UNICAMP) Avenida Albert Einstein, 951 - Caixa Postal 6021 13083-852 Campinas, SP
[email protected] 2
3
4
Faculdade de Engenharia, Arquitetura e Urbanismo (FEAU) Universidade Metodista de Piracicaba (UNIMEP) Rodovia Santa Bárbara D´Oeste/Iracemápolis, km 01 13450-000 Santa Bárbara D’Oeste, SP
[email protected]
Faculdade de Ciências Farmacêuticas de Ribeirão Preto (FCFRP) Universidade de São Paulo (USP) Avenida do Café, s/n 14040-903 Ribeirão Preto, SP
[email protected]
Lab. Instrumentação Nuclear - Centro de Energia Nuclear na Agricultura (CENA) Universidade de São Paulo (USP) Avenida Centenário, 303 - Caixa Postal 96 13400-970 Piracicaba, SP virgilio @cena.usp.br
ABSTRACT In order to obtain information about levels of heavy metals in groundwater, analysis were carried out on samples from monitoring and supplying wells located in Campinas, São Paulo State, Southeastern Brazil. The analytical technique used was Synchrotron Radiation Total Reflection X-Ray Fluorescence (SR-TXRF) and all the measurements were performed at Synchrotron Light Source Laboratory, using a white beam and a Si(Li) detector in total reflection condition. The determined elements were Al, Cr, Mn, Fe, Ni, Cu, Zn, Ba and Pb. The results were compared with the maximum allowed values (MPV) established by the Brazilian Health Department. The detection limits obtained varying from 0.10 up to 8 µg.L-1 were in agreement with the values presented by others analytical techniques.
1. INTRODUCTION The number of wells in Brazil is every time larger, in spite of not disposing of the exact amount, it is considered that approximately 10,000 wells for supplying are perforated per year in the country1. In the São Paulo State, in 2001, they were sent 4 thousand of grants, which 2 thousand were licenses of well perforations2. Only in the São Paulo State are 308 municipal districts totally provisioned by underground waters3; due to this scenery, it is possible to have the vision of the great importance of this resource in the economic, social and health areas.
The pollutants, in a general way, reach the superficial waters directly, the ones which if auto debug with relative facility, mainly when the pollutants cited are degraded bio-chemically, but the underground waters, although more protected, are vulnerable to the polluted charges that reach them for infiltration, through the land. The inadequate disposition of urban and industrial solid residues in the soil increases the possibility of contamination of the underground water resource; wells bad built, wells abandoned without appropriate cover are also examples of pollution causes, that can be aggravated by resulting problems of the industrialization and of the uncontrolled urbanization, for the development of predatory agricultural activities and the intensive use of modern chemical input. The aim of this paper is to use the SR-TXRF for the quantitative analysis of underground water samples with the purpose of verifying the presence of heavy metals. The results were compared with the values limits established (Decree 1469 - December 29, 2000) of the Brazilian Health Ministry4. 2. MATERIALS AND METHODS 2.1. Instrumentation All the measurements were accomplished in X-ray Fluorescence beamline at the Synchrotron Light Source Laboratory, in Campinas, SP, South-east Brazil. For the sample excitation a white beam (polychromatic) of synchrotron radiation under total reflection geometry was used and a Si(Li) semiconductor detector (165 eV at 5.9 keV) for detection. 2.2. Samples: Collection, Treatment and Preparation For the sampling of the monitoring wells it is necessary to purge the water of the wells and to wait for approximately 1 day until collect the underground water sample, in agreement with NBR 138955 and the Guides for sampling and preservation of water samples6. The collections of the supplying wells were performed in Campinas and region around, São Paulo State. In this case, the collection was made through the opening of existent faucet in the exit of the well, being been the careful of verifying before if the well was in operation, case was, the collection was made soon after, otherwise, it let to slip water of 15 to 20 minutes so that the water stagnated could be removed. After the collection, the samples were acidified and maintained in refrigeration for posterior analyses. In the sample preparation 1 mL of each sample was taken, being added 100 µL of Ga solution (concentration of 102.5 ng.mL-1), used as internal standard, to follow a 5 µL was putted on the Perspex sample disks for posterior evaporation under infrared lamp7, and after analyzed for 100 s. 2.3. Quantitative Analysis and Detection Limits The concentration of the element of interest was calculated using the equation:
INAC 2005, Santos, SP, Brazil.
Ci =
Ii C p ⋅ I p SR
(1)
where: Ci and Cp = concentrations of the element i and the internal standard; SR = relative sensitivity (in relation to the element used as internal standard); Ii and IP = intensities of the characteristic X-rays and the internal standard. The detection limits DLi for each element i is directly related with the background intensity Ii(BG), in agreement with the equation8:
DLi = 3
I i ( BG ) C P t I PSR
(2)
where t = measuring time, in seconds. 3. RESULTS AND DISCUSSION 3.1. System Calibration and Detection Limits For the system calibration were prepared ten standard solutions containing Ga as internal standard, five for each series K and L. The standards were irradiated by 100 s and the obtained spectra were fitted with the use of the software Quantitative X-Ray Analysis. The experimental sensitivity for each element contained in the standard solutions was determined and so the sensitivity curves were fitting (equations 3 and 4) for elements of interest, including those for which standards are not available. K Series: S R = exp (−12.35 + 5.19.10 −1 Z + 5.16.10 −3 Z 2 − 2.92.10 −4 Z 3 ) R 2 = 0.9946
(3)
L Series: S R = exp (−12.70 + 1.71.10 −1 Z + 1.83.10 −3 Z 2 − 2.60.10 −5 Z 3 ) (4) R 2 = 0.9912 Using the equations 3 and 4 with the data of the background intensities, the detection limits were calculated for a 100 s measuring time and extrapolated for 1000 s (Table 1). Table 1. Detection Limits (µg.L-1) for 1000 s counting time.
Element DL
Al 7.72
Si 7.91
S 3.37
Cl 1.83
K 0.8
Ca 0.51
Ti 0.21
Cr 0.14
Mn 0.13
Element DL
Fe 0.12
Ni 0.1
Cu 0.14
Zn 0.25
Ga 0.32
Br 0.53
Sr 1.37
Ba 0.51
Pb 0.58
INAC 2005, Santos, SP, Brazil.
3.2. Results for Groundwater Analysis of Landfill Pirelli
Tables 2 and 3 show the results of the analysis performed in groundwater samples of Pirelli landfill collected in March and June, 2003, respectively, in rainy and dry seasons. Table 2. Metal concentrations in groundwater samples of landfill Pirelli, Campinas. Samples collected in March, 2003.
Concentrations (µg.L-1) Sample Al Cr Mn Fe Ni Cu Zn Ba Samples collected in March, 2003. P53 35 22 83 152 141 3269 664 22883 P55
