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Nuclear Analytical Techniques applied to Element Analysis of the Danube Delta Lacustrine Sediments and Soil • L.C. Dinescu • Horia Hulubei National Institute of Physics and Nuclear Engineering, Magurele, Bucharest, Romania
SOME CHARACTERISTICS OF DANUBE DELTA • Three branches: Chilia, Sulina, Sf. Gheorghe • A plane formation with an W-E inclination of 0.006‰ and an area of 5640 km2 • 20.5% of Delta territory under the see level • The water surface: 80 - 90% • Sedimentation rates: 0.6 - 100 mm/y • Thickness of lacustrine sediments: 0.5 - 3 m • A special flora, fauna and morpho-hydrology (river banks, marine levees, wetland, lakes, streamlets, swamps).
Danube Delta schematic map showing the location of the investigated lakes.
LOCATION OF SELECTED SAMPLING POINTS • Lakes: Lung (3.6 km2), Mesteru (2.9 km2) and Furtuna (11.6 km2) in Western part of Delta in an active sedimentation zone • Lake Matita (6.44 km2): N - E of Delta in a low sedimentation zone • Channel Sontea - close to Furtuna lake • Caraorman Bar – S-E of Delta
Objectives The main purpose of this work was to uncover the existence of heavy metal pollution of the Danube Delta recent lacustrine sediments and soil.
EXPERIMENTAL SAMPLE COLLECTION • Sediment cores • Autumn 1996, core length: 0.6 - 1 m, • Hand corer, 5 cm diameter • Soil samples • Autumn 2001, Caraorman bar, at surface (5 cm thick) and about 30 cm depth
SAMPLE PREPARATION • The sediment cores were sectioned in slices of 1-2 cm thickness. • The obtained samples were dried at 105C for 2 h, then homogenized by grinding, sieved and weighed. • Soil samples - prepared as above • Aliquots were taken from each sample for elemental analysis by INAA, ENAA and TTPIXE; some selected samples were analyzed ICP-MS.
TECHNIQUES USED FOR ELEMENTAL ANALYSIS • Instrumental Neutron Activation Analysis (INAA) at NIPNE, Bucharest, Romania (L. Dinescu) • Epithermal Neutron Activation Analysis (ENAA) at JINR, Dubna - Russia (M. Frontasyeva) • Thick Target Proton Induced X-ray Emission (TTPIXE) at NIPNE, Bucharest (C. Ciortea) • Complementary method: Inductively Coupled Plasma–Mass Spectrometry (ICP-MS) at Norwegian University of Science and Technology, Trondheim, Norway (E. Steinnes)
Instrumental Neutron Activation Analysis (INAA) • 0.250-0.300 g of each sample and SL1, SL3 (IAEA Reference materials)-wrapped in polystyrene envelopes • Irradiation: 4 h in a wet vertical channel, at 1.4 x 1013 n cm-2 s-1 at the nuclear reactor VVR-S, NIPNE (Bucharest), Romania • Measurement: after 4 - 6 d and 20 - 25 d cooling times, for 1000 - 5000 s, with a HPGe detector having 1.9 keV (FWHM) at 1.33 MeV (60Co), and a relative efficiency of 30%, connected to a CANBERRA MCA; Software: OS/2 GENIE-PC for gamma spectra processing
Epithermal Neutron Activation Analysis (ENAA)– JINR, Dubna • The investigated samples and SD-M-TM and SL-1 IAEA standards were weighted and sealed into polyethylene bags, • Irradiation: 4 days with epithermal neutrons in Ch1 (Cd screened channel) of IBR-2 pulsate reactor at 1012 n. cm‑2 s-1. • Measurement: after 4 days during 45 min and after 14 days for 1.5 h. with a Ge(Li) detector having an energy resolution of 2.2 keV (1.33 MeV 60Co) and a relative efficiency of 18 %. • Software: VACTIVE and NEWMASS homemade programs have been used for acquisition and processing of experimental gamma-ray spectra.
Thick Target Proton Induced X-ray Emission (TT-PIXE) NIPNE, Bucharest • Aliquots from the investigated samples and SL1 were pressed into pellets of 8-12 mm diameter and 1-3 mm thickness. • A collimated beem of 3 MeV protons delivered by the 9 MV Van de Graaff tandem accelerator of NIPNE was used. The targets were oriented at 45° with respect to the beem direction and irradiated for a collected charge of 10 A. • Measurement: with a Ge(Li) detector having an energy resolution of 180 eV at 5.9 ke,V placed at 90 ° to the incident beem direction • Software: code LEONE for X-ray spectra processing
DATA FROM DIFFERENT ANALYTICAL TECHNIQUES Analyzed elements INAA: K, Na, Sc, Cr, Fe, Co, Zn, As, Br, Rb, Sb, Cs, Ba, Ta, Hf, Th, U, Sm, Ce, La, Tb, Yb, Eu, Lu ENAA: K, Na, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Br, Rb, Sr, Zr, Mo, Cd, Sb, Cs, Ba, La, Ce, Nd, Eu, Gd, Sm, Tb, Tm, Lu, Yb, Hf, Hg, Ta, W, Th, U TTPIXE: K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Br, Rb, Sr, Zr, Pb. ICP-MS: Be, Na, Mg, Al, P, S, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Ag, Cd, In, Sn, Sb, Cs, Ba, Ce, Pr, Sm, Hg, Tl, Pb, Bi, U
Intercomparison between INAA and ENAA data (L. Dinescu, O. Culicov, M. Frontasyeva, O. Duliu, J. Trace and Microprobe Techniques, 2003, 20 (4), 665-676) (Furtuna l., upper 20 cm): Sc, La, Tb, Yb, Th, Na, Rb,Cs, Ba, As, Sb, Cr, Fe, Co concentrations agreed within one SD, and Ce, Sm, Lu, Ca, Br, Ta concentrations agreed within two SD. ENAA showed the advantage fordetermination of REE A total of 41 elements, 18 of which additionally determined at JINR, allowed one to reveal almost all pollutant elements and to estimate the contamination level of the recent lacustrine sediments in the Danube D.
Depth Cr, mg/kg Zn, mg/kg Br, mg/kg cmINAA PIXE INAA PIXE INAA PIXE 0.5 95.5 89.0 169 185 13.6 11.9 2.5 93.8 91.9 159 168 12.4 17.1 4.5 121.0 85.0 194 173 14.2 11.2 6.5 103.0 99.7 171 183 12.7 12.1 8.5 111.0 98.3 170 158 10.5 16.2 11 107.0 79.7 146 130 13.3 16.4 15 89.4 97.3 118 128 11.9 16.8 19 81.2 89.6 107 118 13.1 10.5 Intercomparison between INAA and TTPIXE (sediment core from Furtuna L)
The data from INAA, ENAA and TTPIXE represent the total contents of the elements in samples and are therefore directly comparable; they are in good agreement for elements determined by these techniques. The ICP-MS data are based on the element fraction dissolved in nitric acid. Any form of the elements, bound to the surface of the soil or sediment particle, is soluble in concentrated nitric acid. So, they are likely to be better suited for disclosing any contribution of pollution in sediment or soil. A comparison of ICP-MS values with either NAA or TTPIXE for sediment samples below 20 cm depth indicate that the following percentages are dissolved by nitric acid: Ni, As, Br, Pb: >95%; Ca, Fe, Zn: 80-90%; Co, Cu, Mn: 70-80%; Sc, Cr, Rb: 50-60%. (L. Dinescu, E. Steinnes, O. Duliu, C. Ciortea, T. Sjobakk, D. Dumitriu, J.R.N.C., 2004, 262 (2): 345-354)
Vertical distribution of elements concentration in lake sediments Mesteru Lake:Cr, As,Sb by INAAHg, V, Zn, Ni, Caby ENAACd, Cu,Pb, Tl byICP-MS
Calculated ratios of Sb, Zn, As, Cu, Pb, Cd, Hf to Sc(Hf and Sc are native constituents of sediments)
DISCUSSION Based on the vertical distribution and calculated ratios, the following elements were identified as potential pollutants: Cu, Zn, As, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb,andBi. The surface enrichment factor was generally 1.3 - 3, but 5 for Cdand Hg. V and Ni do not show a surface enrichment. All the above elements are known as air pollutants. Caand Sr concentrations are markedly higher in the uppermost 15 cm. P, S, Mn, and U also show increased concentration in the near surface sediments. Most of the other elements (Na, Mg, Sc, Cr, Fe, Co, Rb, Cs, Ba, Hf, REE, Th) show a relatively uniform concentration distribution along the sediment core - typically for lithophilic elements. In some few cases, As, Cd, Cu, Cr, Mn, and Pbexceeded the minimum threshold of safety, defined by the Romanian legislation.
SOIL Zn, Ag, Cd, Sb, Hg, and Pb enriched in surface layer - components of the long range transported aerosols in atmosphere. On the other hand, Cu, Zn, Cd, and Ba - enriched in topsoil's due to the upward transport by plants. Enrichment factor: 1.5 – 3.1 for the most of the elements, except 8.3 for S. The low concentration values, compared to that obtained in lakes indicate that atmospheric deposition is of much less importance than riverine transport in contributing to the surface contamination of sediments in the Danube delta.
Time evolution • A steady increase of the elements concentration, starting with the beginning of 60’s until the end of 80’s, followed by a slow decrease after1990. • These variations generally reflect the history of the recent sediment pollution and can be correlated with the evolution of the industrial activity in Central and Eastern European Countries.
Concluding remarks The concentrations of 42 elements in all were determined by using four analytical methods: INAA, ENAA, TTPIXE and ICP-MS. The elements identified as potential pollutants are: Cu, Zn, As, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb, and Bi. The enrichment factor was generally 1.3 –3 for most of them, and 5 in the case of Cd and Hg; V and Ni do not show a surface enrichment. In some cases, the concentrations of As, Cd, Cu, Cr, Mn, and Pb exceeded “minimum thresholds of safety”, as defined by the Romanian legislation.
The vertical profiles of the remaining elements were characterized by a relatively uniform distribution along the cores. The concentration values of As, Sb, Hg, and Pb in three soil samples, have been much lower than those obtained in the lacustrine sediments the near-surface contamination of the lacustrine sediments was mainly by riverine transport.
This work was started in the frame of IAEA T.C. Project ROM/8/013 and supported in part by the Center of Excellence IDRANAP under ICA1-CT-2000-70023 Contract with the European Commission, and by the Ministry of Education and Research of Romania