Elemental Analysis of Environmental Samples by Atomic and Nuclear Methods

ELEMENTAL ANALYSIS OF ENVIRONMENTAL SAMPLES BY ATOMIC AND NUCLEAR METHODS

C. STIHI A. GHEBOIANU I.V. POPESCU C. GHEBOIANU “Valahia” University, Târgovişte M. FRONTASYEVA O. CULICOVA JINR-FLNP Dubna, Moscow Region, Russia

Abstract The aim of this work is to demonstrate the applicability of different atomic and nuclear method for environmental monitoring. In the frame of research project “Heavy metal pollution of the Dambovita county, Romania studied by nuclear and related analytical techniques” between Joint Institute for Nuclear Research, Dubna (JINR) and Valahia University of Targoviste, Romania-Multidisciplinary Research Institute for Science and Technologies (ICSTM-UVT), we begin to _onitories the heavy metal pollution of Dambovita county by elemental analysis using Neutron Activation Analysis (NAA) method complementary with Inductively Coupled Plasma (ICP) method. The analyzed samples are mosses collected from different points of Dambovita County with different sources of pollution.

1. Introduction The main sources of pollutants in the atmosphere are industrial processes, thermal power stations, domestic heating systems and roads. All of these sources are present in the territory of Dâmboviţa County. The main polluting regional industries are: stainless steel works (Târgovişte), cement and related materials production (Fieni), glass and lighting sources production (Târgovişte, Fieni), chemicals materials production (Târgovişte, Doiceşti), coal mining and thermal power station (Doiceşti), oil exploration (Târgovişte, Moreni, Găieşti). Mosses are particularly effective biomonitors [1] of atmospheric heavy metal contamination because of their bioaccumulative properties. These plant groups are amenable to biomonitoring because they are widespread, easy to handle and they lack a cuticle and root system thus reflecting directly atmospheric heavy metal deposition. It is important during metal biomonitoring programmes that background concentrations are established. In the frame of research project “Heavy metal pollution of the Dâmboviţa county, Romania studied by nuclear and related analytical techniques” between Join Institute for Nuclear Research, Dubna (JINR) and Valahia University of Târgovişte, Romania-Multidisciplinary Research Institute for Science and Technologies (ICSTM-UVT), we begin to monitorise the heavy metal pollution of Dambovita county by elemental analysis using Neutron Activation Analysis (NAA) method complementary with Inductively Coupled Plasma (ICP) method.

2. Experimental methods 2.1. Neutron activation analysis (NAA) Neutron Activation Analysis (NAA) is a nuclear method of determining the concentrations of elements in a wide variety of materials. The sample is first made radioactive by bombardment with neutrons, then the radioactive isotopes created are identified and the element concentrations are determined by the gamma-rays they emit. NAA is capable of detecting many elements at extremely low concentrations. In Dubna, pulsed fast reactor IBR-2, equipped with pneumatic system REGATA for instrumental NAA [2, 3], provides activation with thermal, epithermal and fast neutrons. Epithermal NAA (ENAA) is a useful extension of instrumental NAA in that it enhances the activation of a number of trace elements relative to the major matrix elements. Epithermal is taken to be neutrons with energies from the Cd “cut-off” of 0.55 eV up to approximately 1 MeV. In general, the activation cross sections of the matrix elements of environmental samples are inversely proportional to the neutron energy (1/v low). The trace elements also follow this general trend but many of them (rare earth elements in particular) have large activation cross section (resonance integrals) at specific energies in the epithermal energy region. Samples are irradiated with epithermal neutrons in transport containers made of polyethylene, teflon and aluminum. The irradiation time of a polyethylene container is limited by radiation and temperature resistance of polyethylene and is equal to 30 minutes, both at 2 MW power of the reactor. A teflon container is used for irradiation up to 5.0 h. Aluminum containers are used for longer irradiation. The internal volume of the polyethylene container is equal to approximately 4 cm3, and the volume of the aluminum container is 1.5 times lager. Personal computer controls the pneumatic transport system and amplitude spectrometers. All units of gamma-spectrometers and counting electronics are made in JINR. The software developed at FLNP- JINR for peak search, peak fitting and nuclide identification routine was used for processing the amplitude spectra. 2.2. Inductively Coupled Plasma (ICP) analysis Inductively Coupled Plasma (ICP) method is based on the fact that the atoms and ions produced in the plasma are excited and emit light. The intensity of light emitted at wavelengths characteristic of the particular elements of interest is measured and related to the concentration of each element from samples. The ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy) spectrometer [4], which will be use by us, is a Baird ICP2070 – Sequential Plasma Spectrometer (figure no. 1) that consists of a sample introduction system, a plasma torch, a plasma power supply and an optical measurement system.

Fig. no. 1. A schematic diagram of ICP spectometer The sample must be introduced into plasma in a form that can be effectively vaporized and atomized (small droplets of solution, small particles of vapor). The plasma torch confines the plasma to a diameter of about 18 mm. Atoms and ions produced in the plasma are excited and emit light. The intensity of light emitted at wavelengths characteristic of the particular elements of interest is measured and related to the concentration of each element from samples. Baird ICP2070 – Sequential Plasma Spectrometer use as a plasma gas Argon and the plasma is sustained in a quartz torch and the plasma is generated using a radio frequency generator at 40.68 MHz. Temperatures of 5000-9000K have been measured in the plasma. The detection systems used are a sequential monochromator with a wavelength range (160-800) nm. The optical emission spectra are made using a personal computer. 3. Experimental results Instrumental neutron activation analysis (NAA) at the reactor IBR-2 in Dubna – activation with epithermal neutrons allowed determination to following elements: Al, Ag, As, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Fe, Gd, Hf, I, K, La, Lu, Mg, Mn, Mo, Na, Ni, Sb, Sc, Se, Sm, Ta, Tb, Th, U, V, W, Yb, Zn, and Zr. The sampling locations are presented in the map from figure no. 2, and the collected samples are presented in table no. 1. Application of NAA multi-elemental method allowed a preliminary estimation of current contribution from different regional industrial pollution sources to the heavy metal pollution. Data processing of the results of measurements after irradiation of samples at the IBR-2 reactor is now in progress. 4. Conclusions and discussions Instrumental neutron activation analysis (NAA) is continuing to be the most sensitive method for multi-element analysis along with the relatively new analytical techniques: inductively coupled plasma atomic emission spectrometry (ICP-OES). Each of these techniques has their own merits and problems. A comparison of precision and detection limits for elements to be determined by different methods should be made with “real” samples as the result of the analysis depends strongly on the element composition of the sample. The results presented in this paper are preliminary results, NAA measurements results will be follow by ICP measurements of the same samples at Valahia University of Târgovişte.

Fig. no. 2 Dâmboviţa County map with samples localisation

The authors of the project expect continuation of the given project to complete the whole study in the Dâmboviţa county of Romania. The results from this study will be used for establishing correlation between environmental and epidemiological data in the examined area. Samples No. Collecting Place Map Localization RO-UVT-1 Şaua Strungă Near 9 RO-UVT-2 Moroieni 1 RO-UVT-3 Padina 2 RO-UVT-4 Şaua Strungă Near 9 RO-UVT-5 Vf. Omu Near 2 RO-UVT-6 Moroieni 1 RO-UVT-7 Moroieni 1 RO-UVT-8 Padina 2 RO-UVT-9 Moroieni 1 RO-UVT-10 Padina 2 RO-UVT-11 Doiceşti 3 RO-UVT-12 Fieni 4 RO-UVT-13 Doiceşti 3 RO-UVT-14 Pucioasa 5 RO-UVT-15 Pucioasa 5 RO-UVT-16 Brăneşti 6 RO-UVT-17 Priseaca 7 RO-UVT-18 Ungureni 8 RO-UVT-19 Ungureni 8 RO-UVT-20 Priseaca 7 RO-UVT-21 Priseaca 7 RO-UVT-22 Hotel Peştera 9 RO-UVT-23 Hotel Peştera 9 RO-UVT-24 Hotel Peştera 9 RO-UVT-25 Hotel Peştera 9 RO-UVT-26 Babele Near 2 RO-UVT-27 Mircea Vodă 13 RO-UVT-28 Tărtăşeşti 17 RO-UVT-29 Titu 14 RO-UVT-30 Răcari 16 RO-UVT-31 Conţeşti 15 RO-UVT-32 Ilfoveni 12 RO-UVT-33 Târgovişte Nord 11 RO-UVT-34 Ciubul cu Dor 18 RO-UVT-35 Târgovişte Nord-Vest 10 RO-UVT-36 Titu 14 RO-UVT-37 Târgovişte Nord 11 RO-UVT-38 Cuibul cu Dor 18

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