IMPORTANCE OF INAA IN ENVIRONMENTAL RESEARCH
Emine OLMEZ (EGILLII*. Ilhan OLMEZ**
*QNAEM, Industrial Applications Department, P.O.B.l, Ataturk Havalimani, 34831, Yesilkoy-Istanbul/TURKEY.
* * TUBITAK-MAM, Materials & Chemicals Technologies Res.Ins.,P.O.Box 21, 41470,
Gebze-Kocaeli/TURKEY
ABSTRACT
In studies of origin and fates of trace elements, it is advantageous to be able to analyze samples for a wide spectrum of elements with a high sensitivity and accuracy. This condition is best satisfied with instrumental neutron activation analysis (INAA) since it is one of the most sensitive, selective, and reliable multi-element analysis techniques available. In spite of these advantages in environmental studies, use of the technique has been generally limited because of the unavailability of research reactors and experienced researchers.
Trace element concentrations on airborne particles have provided invaluable information about the locations and contributions of different types of pollution or natural sources at a given receptor site. Examples of these atmospheric signatures include V, Ni and some rare earth elements (REE) as indicators of oil combustion; Pb and Br for motor vehicles in urban areas; and S, Se, and As for coal-fire power plants. It has been shown that “marker trace elements” can be very effective tools in source attribution in groundwater as well as in atmospheric studies.
INTRODUCTION
Studies that may lead to the development of emission inventories or to an assessment of environmental impact and public health risks, the use of a sensitive, reliable and accurate analytical methodology is essential. This is especially critical when performing analysis at nanogram (ng) and sub-nanogram levels. The analysis of most of the toxic metals in source materials and emissions are particularly difficult due to both the low concentrations and their unique physical and chemical properties involved. In that respect dependence of Neutron Activation Analysis (NAA) upon nuclear properties of elements rather than their electronic properties, provides a unique advantage over most of the other analytical techniques.
Pollution source attribution studies are carried out based on two different approaches; Dispersion Modeling and Receptor Modeling. In Dispersion Modeling environmental impact assessments are based on the data, on the composition of raw material, amount consumed, prevailing wind directions, estimated impact distance, regions,etc. However, actual emission characteristics, atmospheric transformations, reactions, wet and dry depositions, differences in atmospheric transport properties of species etc. are not considered. Therefore source characteristics can change by time and distance.
In Receptor Modeling on the other hand, composition of samples (air, water, e.g.) that actually influences a specific location with its people, habitat, ecology, are identified. This knowledge along with meteorological and statistical methods, source composition libraries and marker systems for each source (both natural and anthropogenic) is used for source identification, determination of strengths and source contributions.
The most critical requirements of this successful approach is the need for the determination of as many trace elements as possible, sometimes using samples as small as few micrograms for optimal resolution and fits in the models. Therefore, the non-destructive nature of NAA is the analytical technique of choice not only because of its multi-element and other characteristics but also it does not require pre-irradiation preparation of samples such as dissolution and/or digestion.
Some of the examples of studies that had significant contribution to environmental science in general due to the use of INAA are given below:
• Regional Pollution Studies,
Traditionally coal is known to be the "dirtiest" fossil fuel and inspite of the advanced emission control technologies its combustion products continuos to have a major negative impact on the environment. In addition to greenhouse gasses such as CO2 and acid precursors, (SO2, NOx), main portion of the toxic metals found in the atmosphere is result of emissions from coal-fired power plants, industries using coal, home heating, etc.
In countries such as Turkey, extensive usage of low quality lignites, increases the environmental and health impacts of coal related emissions. Also current coal cleaning combustion and emission control technologies may not be applicable to these kind of coals and national strategies should be established based on the type and quality on the coal consumed. Having this in mind, in this study five different coals representing the most common lignites used in Turkey, and their ashes were characterized with respect to their trace element concentrations to established a base line for understanding their combustion properties as well as environmental impacts. All of these samples were analyzed by instrumental neutron activation analysis (INAA), using TR-2 Reactor at £ekmece Nuclear Research and Training Center and TRIGA MARK-II Research Reactor at Istanbul Technical University-Nuclear Energy Institute.
Arsenic and selenium, among other possible sources, are mainly emitted from coal-fired power plants, and other processes utilizing coal. In ambient air their ratios (As/Se) is found to be less than 1, except areas influenced by specific point sources, such as Cu smelters. However, in long term atmospheric particulate studies in Turkey (Gullu,1996; Karatas,1999), the annual average of this ratio is found to be much higher than unity, reaching hundreds in certain days. This finding is rather unique and provides a robust marker for air masses influenced by the coal- related emissions in Turkey. Since atmospheric pollution is not limited within national
boundaries, it is rather critical to identify regional markers in order to assess the impact of trans boundary long-range transport.
Elements which are highly enriched in atmosphere (Zn, Mo, In, Zn, Cl, As, Au, Cd, Hg, Br, Sb, and Se) are mostly volatile and are found in the atmosphere at elevated concentration levels due to antropogenic activities. Their impact area ranges from regional to global. Depending upon the type and the characteristics of their emission sources, most of the highly enriched elements are released to the atmosphere as fine particles or gasses. As gasses, some element’s atmospheric residence times may be on the order of several years. Particulate forms of these elements have much shorter atmospheric residence times, but are useful as conservative markers for various industrial processes as listed in Table 1.
Table 1. Sources of atmospheric particulates and their elemental markers (compiled from the findings of Olmez and Gordon,1985; Olmez et al.,1988; Rahn and Lowenthal,1984; Small et al.,1981; Huang et al.,1994; Egilli,1999; Olmez et al.,1997).
Source Marker Elements
Crustal Material Sc, Al, REE*
Marine Aerosols Na, Cl
Coal Combustion As, Se, Hg
Oil Combustion V, La, La/Sm
Refineries La, La/Sm
U.S.Regional Se, Sb, As
Canadian Regional V, Na, Cd, Cl
Turkish Regional As, As/Se,
Motor Vehicles Br, Zn, Sb
Wood Burning K
Incinerators Na, K, Cl, In, Hg
Industrial Urban Areas V, Zn, Se, Mo, Sb Iron/Steel Works Fe, Zn, Se, Mo, Sb
Ni, Cu Smelters Hg, As, As/Se
Zn, Cd, Pb Smelters In, As, As/Se, Co, Cd, Cr
Aluminum Plant Al, Mg, Hg
Paint Ba, Ti
Precious Metals Au, Cr, Mo
• Atmospheric Signatures for Oil-Fired Power Plants and Refineries
The requirements for tracer on a regional scale are more stringent than for those used on a urban scale. During transit over hundreds of kilometres tracer particles and gases are subject to wet and dry deposition, chemical reactions, and processing by clouds and fogs; such processes can fractionate materials making up the tracer signature. Thus, there is an intense search for tracer that resist modification (robust tracer).
About half of the REEs are usually observed by INAA of atmospheric particulate matter and source materials such as soil, coal, and fly ash (Kowalczky et al.,1982; Germani et al.,1980). Although a basic concept of receptor modelling is that the more species observed, the greater the chance of identifying some associated with certain sources or regions, the REEs have largely been ignored. The REEs are chemically so similar to each other and to other lithophile elements that they are not expected to be fractionated by most environmental and combustion processes.
In our studies, on emission characteristics of several point sources and ambient aerosols around Philadelphia and Camden NJ/(USA), we have observed some discrepancies with the crustal REE pattern from examination of a new source-composition library and new data on ambient particles. The REE pattern for particles released by coal-fired plants is approximately the same as the crustal pattern, but patterns for oil-fired plants and refineries are strongly depleted in heavy REEs. Refineries and oil-fired plants have recently become major sources of REEs. Concentrations of REEs in crude oil are so low that they are difficult to measure, even by INAA. The probable source of the REE is zeolite cracking catalysts, which have come into wide use over the past 30 years and which typically contain 1 to 3% of mixed REE oxides (Wallace, 1981). Many changes have occurred in the oil industry in response to oil crises, requirements for low sulfur fuels in metropolitan areas, and replacement of alkyl Pb in gasoline by aromatics. Refiners have had to produced different mixes of products with certain compositions, increasing needs for cracking and reforming of hydrocarbon molecules at the same time that properties of zeolite catalysts were being improved. Most petroleum products now contain some components that have been subjected to the catalysts.
Rare earth ratios are probably better for long-range tracing of oil emissions than V and Ni concentrations because the ratios of rare earths on fine particles are probably not influenced by deposition and other fractionating processes. Emissions from oil-fired plants can be differentiated from those of refineries on urban scale by the much smaller amounts of V in the latter.
• Groundwater Studies
A simple Receptor Modeling approach has been developed and applied to groundwater pollution studies. Groundwater and source materials from one coal, five oil-fired power plants, and one coal-tar deposit site have been analyzed by INAA for more than 20 minor and trace elements. In one of the oil-fired power plants, trace element patterns indicated a leak from the
hazardous waste surface impoundments due to the failure of a hypolon liner. Also the extent and spatial distribution of groundwater contamination have been determined in a coal-tar deposit site.
It has been shown that “marker trace elements” can be very effective tools in source attribution in groundwater as well as in atmospheric studies (Olmez,1989). The success of this new approach in groundwater studies can be outlined as follows: unlike organic compounds, inorganic elements carry exactly the same signatures as the source material regardless of the distance between the source and the monitoring wells. Most of the organic compounds are so chemically active that they change their chemical composition completely after they travel through just a few centimeters of soil. Also, routine analytical techniques used in groundwater contamination are not sensitive enough to detect marker elements at 10-9 or, in certain cases, even 10-12 g levels. Although INAA is one of the most sensitive analytical techniques available in environmental studies, it is not widely available to the research community as other techniques. After the marker element methodology has been established by INAA, however, other common analytical techniques can be utilized, e.g., by preconcentration of samples with respect to the marker elements which are specific to that or similar sites.
REFERANCES
1. D.N.Wallace, In Industrial Applications of Rare Earth Elements, K.A.Gschneidner, Jr., Ed., ACS Symp. Ser., 164, 101, (1981).
2. E. Egilli, Evaluation of Coal related Emissions on Air Quality By Means of Trace Elements Determined by NAA, Ph.D. Thesis, ITU-NEE, (1999).
3. M.A. Germani, M. S. Germani, I. Gokmen, A. D. Sigleo, G. S. Kowalczyk. I. Olmez. A. M. Small, D. L. Anderson, M. P. Failey. M. C. Gulovali, C, E. Choquette, E. A. Lepel. G. E. Gordon and W. H. Zoller, “Concentrations of Elements in the National Bureau of Standards” Bituminous and Subbituminous Coal Standard Reference Materials Anal. Chem., 52, 240, (1980).
4. G. Gullu, Long Range Transporte of Aerosols, Ph.D. Thesis, Environmental Engineering, METU, Ankara, (1996).
5. D. Karatas, Determination of the Europian Contribution on the Aerosol Composition in the Black Sea Basin and Investigation of Transport Transport Mechanisms, Ph.D. Thesis, Depart. of Chemistry, METU, Ankara, (1999).
6. G.S. Kowalczyk, G.E. Gordon, S.W. Rheingrover, Environmental Sci. Technol., 16, 79, (1982).
7. X. Huang, I. Olmez, N.K.Aras, and G.E.Gordon, Elemental Emissions from Recent
Model Motor Vehicles: Potential Marker Elements and Source Composition Profile, Atmospheric Environment, 28, 1385-1391, (1994).
8. I. Olmez, and G.E.Gordon, Rare Earths: Athmospheric Signatures for Oil-fired Power Plants and Refineries, Science, 229, 966-968, (1985).
9. I.Olmez, A.E.Sheffield, G.E.Gordon, J.E.Houck, L.C.Pritchett, J.A.Cooper, T.G.Dzubay, and R.I.Bennett, Composition of Particles from Selected Sources in Philadelphia for Receptor Modelling Applications, Journal of Air Pollution Control Association, 38, 1392
1402, (1988).
10. I. Olmez, G. Gullu, M. Ames, X. Huang, S. Keskin, J. Che, A. Wakefield, J.K. Gone, J. Beal, Upstate NewYork Trace Metals Program, 2, Trace Metals, M.I.T. Report, MITNRL-064, (1997).
11. I. Olmez, Trace Element Signatures in Groundwater Pollution, Receptor Models in Air Resources Management, J.G.Watson, (1989).
12. K.A.Rahn, and D.H.Lowenthal, Elemental Tracers of Distant Regional Pollution Aerosols, Science, 223, 132-138, (1984).
13. M.Small, M.S.Germani, A.M.Small, W.H.Zoller, and J.L.Moyers, Airborne Plume Study of Emissions from the Processing of Copper Ores in Southeastern Arizona, Environmental Science Technology, 15, 293-299, (1981).
