Journal of Environmental Research And Development Vol.10 No. 02, October-December 2015

Transcription

1 TRACE ELEMENTAL ANALYSIS OF SOIL SAMPLES USING PARTICLE INDUCED X-RAY EMISSION TECHNIQUE Kumar M. R., Sarita P. 1, Naga Raju G. J.* 2 and Reddy S. B Department of Physics, GIT, GITAM University, Visakhapatnam, Andhra Pradesh (INDIA) 2. Department of Physics, UCEV, JNTUK, Vizianagraram, Andhra Pradesh (INDIA) 3. Swami Jnanananda Laboratories for Nuclear Research, Andhra University, Visakhapatnam, Andhra Pradesh (INDIA) Received July 10, 2015 Accepted October 14, 2015 ABSTRACT Trace elemental analysis was carried out in the soil samples collected from in and around Visakhapatnam using Particle Induced X-ray Emission technique (PIXE). PIXE is a powerful tool for the study of environmental pollution because it is non-destructive and provides quantitative information on nearly all trace elements. A 2MeV proton beam was used to excite the samples. The present experiments were carried out using 3MV tandem pelletron accelerator at Institute of Physics, Bhubaneswar, India. The elements Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr and Pb were identified and their relative concentrations were determined. The high levels of some elements observed in the study areas when compared to the control area is attributed to automotive exhaust and industries in the vicinity. Key Words : PIXE, Trace elements, Soil pollution, Automobile exhaust, Environmental pollution INTRODUCTION Some of the mineral elements are present in minute amounts in plant and animal tissues and in environmental samples. Earlier, it was very difficult to measure their precise concentrations because of the non-availability of sophisticated analytical methods. They were therefore described as occurring in traces, hence the term trace element. With the invention of many modern analytical techniques like Atomic Absorption Spectrometry (AAS), Instrumental Neutron Activation Analysis (INAA), Rutherford Back Scattering (RBS), X-ray Fluorescence (XRF), Energy Dispersive X-ray Fluorescence (EDXRF), Auger Electron Spectroscopy (AES), Particle Induced Gamma ray Emission (PIGE), Particle Induced X-ray Emission (PIXE), Wavelength Dispersive X-ray Fluorescence (WDXRF) etc., it has become possible to estimate the concentrations of trace elements in parts per million (ppm) and parts per billion (ppb) levels 1. These analytical techniques have the capability to measure all the trace elements *Author for correspondence 298 present even in the smallest sample with great precision and accuracy. The term trace is traditionally followed though it has become scientifically obsolete owing to the availability of improved techniques. Among all the afore-mentioned techniques, PIXE technique has its own advantages over the other techniques. From analytical point of view, techniques for the identification of trace elements and evaluation of their concentrations are categorized into destructive and nondestructive techniques. Chemical analysis and AAS are the two well-known methods under the former category. Generally, these methods require large amounts of sample and are tedious as they involve element-by-element analysis. The latter include the techniques INAA, XRF, EDXRF, AES, RBS, WDXRF, and PIXE. Non-destructive techniques include both atomic and nuclear processes. Since the cross-section for inner-shell ionization exceeds the typical cross-section for nuclear reactions by several orders of magnitudes, inner-shell ionization processes are preferably used for the analysis of trace elements.

2 Both PIXE and XRF are methods based on X-ray emission and have several features in common. From sensitivity point of view, PIXE has certain superiority. Moreover, the bremsstrahlung produced in PIXE is a secondary effect whereas in the case of electron microprobes and XRF, it is a primary contributor and the principal source of photon background against which the characteristic X-rays of elemental constituents must be distinguished and hence is also the principal determinant of detection limits. The low bremsstrahlung in PIXE enables ppm sensitivities, making it superior to its sister techniques. Particle Induced X-ray emission (PIXE) was first demonstrated by Johansson et al. 2 in It is a powerful and relatively simple analytical technique that can be used to identify and quantify trace elements. A high signal to noise ratio allows trace impurity detection down to 1 ppm or less. PIXE technique has rapidly gained acceptance as a valuable analytical tool, because of the ever-increasing need for elemental analysis of very small amounts of sample. Moreover, it offers a further advantage of the very short time needed for a complete analysis. Due to its high sensitivity and multielemental analysis capability, PIXE has found application in the trace elemental analysis of samples from almost every conceivable field of scientific or technical interest. 3-8 AIMS AND OBJECTIVES In view of the afore-mentioned advantages of PIXE over the other techniques, it is chosen in the present work to determine trace elemental concentrations in soil samples collected from in and around Visakhapatnam, A.P., India. MATERIAL AND METHODS Sampling areas and sample preparation The soil samples were collected from six locations of Visakhapatnam : (i) MVP colony (ii) Gajuwaka (iii) NAD Kotha Road (iv) Bharat Heavy Plates and Vessels (BHPV) area (v) Port area and (vi) Mudasarlova. The samples were collected from the superficial layer of the soil i.e, the uppermost 3 cm. For each site the soils were collected from three 299 points a few meters apart from each other and then mixed in order to prepare homogeneous samples. The polythene bags used for sample collection were cleaned by soaking in dilute nitric acid and then rinsing with double distilled water. The soil samples were oven dried at 60 0 C and then homogenized in an agate mortar. A quantity of 150 mg of each powdered sample was mixed with pure graphite powder in the ratio of 1:1 by weight. The purpose of mixing graphite powder was to monitor the beam current. The mixture was homogenized and the resulting sample weighing 300 mg was pressed into a pellet of 12 mm diameter using a 10 ton hydraulic press. The pellets were then used as targets for the PIXE experiment. Experimental details Present experiments were carried out using a 3 MV Pelletron Accelerator facility at the Institute of Physics, Bhubaneswar, Orissa, India. Protons with 2 MeV energy were used to excite the samples. The samples were mounted on an aluminium target holder (a ladder arrangement). Then, the target holder was inserted into the scattering chamber and the irradiation was carried out in vacuum conditions. A collimated proton beam of 2 mm diameter was made to fall onto the sample. The beam current was kept at 20 na. The samples to be excited on the target holder were positioned in the scattering chamber at an angle of 45 o with respect to the direction of the proton beam. The position of the sample relative to the beam direction was adjusted properly by viewing through a window provided in the scattering chamber. A high resolution Si (Li) detector (160 ev FWHM at 5.9 kev energy) was employed in the present experiments to record the x-ray spectrum. The detector was placed at an angle of 90 0 with respect to the beam direction. The output of the Si (Li) detector was coupled to data acquisition system. The PIXE spectra of soil samples collected from different areas are shown in Fig. 1. The spectrum of each sample was recorded for a sufficiently long time so as to ensure goods statistics. During the irradiation of each sample, the total charge collected and the average beam current were noted.

3 Fig. 1 : PIXE spectra of the soil samples collected at different areas Data analysis The Guelph PIXE (GUPIX) software package 9 was used to analyze the spectra utilizing a standard Marquardt non-linear least square fitting procedure. This package has provision to identify different elements present in the 300 sample and to estimate their relative intensities. Using this GUPIX software package, the X-ray intensities of different elements were converted into the respective concentrations using a standardization technique involving fundamental parameters,

4 predetermined instrument constants and input parameters such as solid angle, charge collected, etc. Quantitative results for the identified trace elements are furnished in Table 1. Comparing the concentration of yttrium obtained in the present work with the known concentration of yttrium added to the sample, the reliability of the input parameters was checked. The accuracy and reliability of the present experimental set-up and use of 301 GUPIX software package in the data analysis was checked by the analysis of International Atomic Energy Agency (IAEA) certified reference material- animal blood (Sample No A-13) and National Institute for Standards and Techniques (NIST) certified reference materials bovine liver (Sample No. 1577b) and apple leaves (Sample No. 1515) in the same experimental conditions as that of the samples Table 1 : Concentrations of elements (µg/g) in soil samples collected at different areas Elements ND: Not Detected MVP Colony Gajuwaka RESULTS AND DISCUSSION NAD Kotha Road In the present work, trace elemental analysis was carried out in the soil samples collected from different areas of Visakhapatnam. The elements Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr and Pb were identified and their concentrations were determined for each sample. The soil sample collected from MVP colony area is taken as control because this area is a totally residential area and faraway from industries. From Table 1, it can be seen that the concentrations of elements K, Ti, Cu, Br and Pb are higher while the concentrations of BHPV Port area Mudasar -lova Cl 1730± ± ± ± ± ±1023 K 466±53 839± ± ± ± ±124 Ca 1271±99 191± ± ± ± ±61 Ti 74±7 206±8 313±23 681± ±99 385±19 V 3±3 9±5 8±6 26±7 28±19 ND Cr 18±3 21±3 92±8 78±5 53±7 1±7 Mn 541±47 85±10 182±26 249±18 325±31 179±46 Fe 5175± ± ± ± ± ±163 Co 197±34 180±30 409±17 340±51 570±88 204±98 Ni 45±17 13±17 70±34 66±22 43±42 ND Cu 39±6 51±5 52±9 51±7 97±15 28±11 Zn 366±35 165±9 112±13 141±11 183±19 81±12 Br 9±7 32±8 38±18 1±14 8±26 ND Rb 38±10 30±10 60±21 103±18 255±35 67±24 Sr 64±13 30±10 118±22 74±14 139±27 72±23 Pb 153±23 403±28 377±52 146±31 242±61 182±36 the elements Cl, Ca, Mn, Ni, Zn and Sr are lower in the soil samples collected from Gajuwaka compared to control area. High concentrations of Pb and Br can be attributed to the automotive exhaust and industrial sources in the vicinity of Gajuwaka. The concentrations of most of the elements (Cl, K, Ca, Ti, Cr, Fe, Co, Ni, Cu, Br, Rb, Sr and Pb) in the soil samples collected from NAD Kotha Road area are higher than in the control area. These higher levels may be due to heavy traffic and due to the presence of small scale industries in this area. The concentration of the trace elements Cl, K, Ca, Ti, V, Cr, Fe, Co and Rb are found to be

5 higher in the soil samples of BHPV area while the levels of Mn, Zn and Pb are low. The concentrations of the elements Cl, K, Ca, Ti, V, Cr, Fe, Co, Cu, Rb, Sr and Pb in the soil samples of Port area are very high compared to all other samples. These high levels may be due to the handling of cargo in the port region. The vehicular traffic is also high in this region. The increase in K, Ca, Pb levels and the decrease in Mn, Zn levels observed in the soil samples of polluted areas when compared to the control area are in agreement with the results reported by Khamparia et al. 13, in their work on the effect of cement dust pollution on soil health. The concentrations of the elements obtained from the sediment sample collected from Mudasarlova reservoir are presented in Table 1. The concentrations of Cl, K, Ca, Ti, Fe, and Rb are higher while Cr, Mn, Cu and Zn are lower when compared to control area CONCLUSION PIXE, a well established method for elemental analysis was used in this work to identify and quantify trace elements in the soil samples collected from different areas of Visakhapatnam, India. The elements Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr and Pb were identified and their concentrations were determined. Variations were observed in the levels of most of the trace elements in the soil samples collected from the six environmentally different sites. The observed elemental concentrations are in accordance to the proximity of these sites to industries and vehicular traffic. These results once again indicate that the main sources of pollution in Visakhapatnam are the emissions from industries and vehicles. ACKNOWLEDGEMENT Authors are thankful to authorities and staff of Ion Beam Laboratory, Institute of Physics, Bhubaneswar, India for providing the Pelletron accelerator facility and for rendering technical assistance. REFERENCES 1. Keen C. L., Jue T., Tran C. D., Vogel J., Downing R.G., Iyengar V. and Rucker R.B., Analytical methods : Improvements, 302 advancements and new horizons, J. Nut., 133(5), 1574S-1578S, (2003). 2. Johansson T. B., Akselsson R. and Johansson S. A. E., X-ray analysis : Elemental trace analysis at the g level, Nucl. Ins. Meth. P., 84(1), , (1970). 3. Sarita P., Naga Raju G.J. and Bhuloka Reddy S., Studies on changes in trace elemental content of serum of uterine cervix cancer patients using PIXE, J. Rad. Nucl. Chem., 302(3), , 4. Sarita P., Naga Raju G. J., Kumar R. M., Naidu B. G., Rautray T. R. and Bhuloka Reddy S., Serum trace elemental content of tongue cancer patients using particle induced x-ray emission technique, Adv. Sci. Lett., 20(3-4), , 5. Sarita P., Naga Raju G. J., Kumar R. M., Pradeep A. S. and Bhuloka Reddy S., Analysis of blood serum of lung cancer patients using particle induced X-ray emission, J. Rad. Nucl. Chem., 297(3), , (2013). 6. Ravi Kumar M., Sarita P., Naga Raju G. J. and Bhuloka Reddy S., Trace element accumulation in the leaves of Azadirachta india and Pongamia glabra collected from different environmental sites, J. Environ. Res. Develop., 7(3), , (2013). 7. Naga Raju G. J., Sarita P., Chandra Sekhara Rao J., Rao K. C. B. and Bhuloka Reddy S., Correlation of trace elemental content in selected anticancer medicinal plants with their curative ability using Particle Induced X-ray Emission (PIXE), J. Med. Plan. Res.,7(16), , (2013). 8. Chaves P. C., Taborda A., de Oliveira D. P. S. and Reis M. A., CdTe detector based PIXE mapping of geological samples, Nucl. Ins. Meth. Phys. Res. Sect. B., 318(1), 37-41, 9. Campbell J. L., Boyd N. L., Grassi N., Bonnick P. and Maxwell J. A., The Guelph PIXE software package IV, Nucl. Ins. Meth. Phys. Res. Sect. B., 268(20), , (2010). 10. Sarita P., Naga Raju G. J., Pradeep A. S., Tapash R. R., Bhuloka Reddy S. and

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