Sr and Pb isotopes as environmental indicators in environmental studies

Environment International 28 (2002) 147 – 151 www.elsevier.com/locate/envint

Sr and Pb isotopes as environmental indicators in environmental studies G. Charalampides a,*, O. Manoliadis b a

Laboratory of Applied Geochemistry, Department of Geotechnology and Environmental Engineering, Technological Educational Institute of Western Macedonia, Koila 50100, Kozani, Greece b Laboratory of Environmental Geotechnics, Department of Geotechnology and Environmental Engineering, Technological Educational Institute of Western Macedonia, Koila 50100, Kozani, Greece Received 11 July 2001; accepted 27 March 2002

Abstract An environmental indicator is a numerical or a descriptive categorization of environmental data with the primary purpose of assessing the affected environment. In these studies, two characteristic isotopes, namely Sr and Pb, were assessed of their ability to describe the affected environment in environmental studies by detecting trends of pollution over short as well as long time periods and by identifying sources of contamination. The ability of environmental indicators to serve as elements in summarizing the situation of the affected environment is discussed. An illustrative example is presented where lead isotopes are used to understand the source of pollution in Kozani, a small rural area in Greece. Conclusions are derived in terms of the source of the pollution in the specific area. D 2002 Elsevier Science Ltd. All rights reserved. Keywords: Environmental indicators; Lead and strontium isotopes

1. Introduction Environmental changes due to human activities cause increasing disturbances in nature and pose a threat to future life on Earth. Natural conditions and natural development in relation to man-made processes have to be clarified since the human influence on nature turns out to be a question of doubtful impact. Accordingly, the knowledge about chemical – biological processes in the environment is a prerequisite for a continued use of natural resources. The Earth in itself can be seen as a huge laboratory and archive in which a number of biological, chemical, and physical processes take place continuously and in which the results of the past are recorded for posterity. In order to make correct decisions in environmental questions, an understanding of the link between physical – chemical processes and cyclic problems is of a fundamental importance. Of special interest is the interdisciplinary research where geoscientific and biological problems are integrated (Manoliadis, 2001a). It is thus of great importance to increase the knowledge about processes *

Corresponding author. Tel.: +30-461-40161; fax: +30-461-39682. E-mail addresses: [email protected] (G. Charalampides), [email protected] (O. Manoliadis).

in nature and to what extent the anthropogenic activities affect the environment. Environmental indicators are used to characterize the affected environment (Manoliadis, 2001b) in order to: 

focus attention on key environmental factors, to serve as elements in summarizing the situation of the affected environment,  communicate information between same projects, and  to serve as a basis for the expression of impact by forecasting the difference between the pertinent index with the project and the same index without the project. 

Environmental indicators have been used for many decades (in Canter, 1996). For example, in the western United States, plants have been much used as indicators of water and soil conditions, especially since these conditions affect grazing and agricultural potentials (Odum, 1959). The use of vertebrate animals, as well as plants, as indicators of temperature zones, has also been practiced. Relative to pollution effects, an ‘‘indicator organism’’ is a species selected for its sensitivity or tolerance (more frequently to sensitivity) to various kinds of pollution or its effects—for example, metal pollution (Chapman, 1992).

0160-4120/02/$ - see front matter D 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 6 0 - 4 1 2 0 ( 0 2 ) 0 0 0 2 0 - X

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Environmental indicators have also been suggested as useful tools for monitoring the state of the environment in relation to sustainable development and associated environmental threats. Indicators, which would enable the measurement of environmental performance with respect to the level and changes of environmental quality, are being considered—the integration of environmental concerns in policies. However, the methodologies in using environmental indicators often do not identify the source of the pollutant, the route of local- or long-distance transport, and the related trends. In this paper, an attempt is made to describe the above issues as environmental indicators used as elements of more synthetic holistic environmental indices, which use isotopes to describe the affected environment. First, the reason of using isotopes as environmental indicators is discussed. Then, a case study of using isotopes to understand the pollution in Western Macedonia is presented followed by conclusions and recommendations.

2. Isotopes as environmental indicators Over the last decade, there has been an increased interest in the isotope technique as means of identifying the source of pollutant and route in environmental studies (e.g., Sr to measure the rates of weathering or determination of soil exchangeable cation loss). The reasons for selecting isotopes are the following: 









Isotopic techniques can be used for identification of sources of contamination in such components of the environment as top soil, vegetables, trees, and wild and domestic animals. There is a great potential in combining different parameters like soil, water, biological material, and isotopes for detecting environmental changes over short as well as long time periods. Sampling of the past is a difficult task but biological material, in combination with inorganic material, proves advantageous as environmental archives. The spread and variation in isotopic ratios make isotopes a powerful tool when it comes to detecting trends in the soil –vegetation system. Accessibility in understanding the deterioration mechanism of natural stone, as part of cultural heritage of mankind.

Particularly, the significance of using lead isotopic ratios could be summarized as follows:  

apportion sources of anthropogenic pollution, verify the pathways of pollution transport from source to a receptor,  determine lead concentration and its isotopic signature in pre-industrial and contemporary metallic lead and pewter, coal and lead ore from various mines,

 

petrol lead additives, fly ash, soils, etc. to characterize different possible sources of lead in man, detect the origin of toxic long-distance transported air pollutants, and determine historical changes in the magnitude of air contamination by lead due to local and international environmental policies.

Primarily, natural isotopes, particularly lead and strontium isotopes, have for decades been used in understanding and establishing theories about petrogenetical and petrochemical processes on Earth contributing to ore prospecting ˚ berg and Charalampides, 1986, 1988). methodology (e.g., A There were many researchers using isotopes as environmental indicators. Among the early works in using Sr are those of Graustein and Armstrong (1983) and Gosz et al. (1983), while more recent studies have been reported by Miller et al. (1993) and Blum et al. (1993). Sr isotopes of different organic and inorganic materials have been used for tracing the past and monitoring of processes in the present ˚ berg, 1995; A ˚ berg et al., 1998; Charalampides et al., (A 2000). Also, Sr isotopes from a number of soils and samples of coal-derived fly and bottom ashes were used as a tracer for detecting dispersion of lignite ashes on soils (Mattigod et al., 1990), while fly ash-derived strontium may readily be absorbed by agronomic and native plant species when incorporated in soil (Straughan et al., 1981). Another important natural isotope dealing with the matter discussed is lead, belonging to the group of the most heavy metals. Historically, lead was recognized as one of the first poisons of the environment, produced by mankind. This attracted a great interest in learning about lead sources, its behaviour in the air, water, and soil, and its toxicity and metabolism. Environmental contamination by lead has brought a lot of controversy both in the past and the present. Lead is emitted to the atmosphere through fine particles that can be transported within air masses on very long distances, e.g., from regions in mid-latitudes to the Arctic and Antarctica (Sturges and Barrie, 1989). This phenomenon, in addition to a great number of emission sources, has resulted in lead being not only a local air pollutant but also a pollutant on a global scale. Today, there is a global concentration background of this compound in the environment due to past anthropogenic activities. Therefore, there is a potential to distinguish sources of lead pollution in the atmosphere by examining the lead ˚ berg et al., isotope ratios (Sturges and Barrie, 1987; A 1999a). The pollution history of the atmosphere has also been discussed by means of Pb isotopes in biological – ˚ berg biogeochemical archives (Shotyk et al., 1996, 1998; A et al., 1998; Dunlap et al., 1999) and in lake sediments, peat deposits, and soil profiles (Renberg et al., 2000) and for Northern hemisphere by means of Pb isotopes in Greenland ice (Rosman et al., 1997). Anthropogenic activities have also been followed up by studying the lead isotopic variations in certain archives of the ancient as well

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¨ lander et al., 1993; Puchelt et al., as the modern human (O ˚ berg et al., 1998, 2001). 1993; Satake et al., 1996; A Furthermore, a sulfation process of natural limestones and dolomitic sandstones takes place during the deterioration of natural stones and thus part of our cultural heritage. This sulfation process is a mechanism in environments polluted with SO2, NO2, and O3. A potential environmental indicator tracing the above-described deterioration mechanism could be the carbon isotopes, indicating the sulfation of calcite in a limestone or carbonaceous sandstone. Thus, it is important to notice that this process gives a shift in carbon isotopes suggesting an exchange between CO2 carbon in air ˚ berg et al., 1995, 1999b). and calcite carbon in the rock (A Even oxygen isotopes have proved to be a good tool for the determination of the functioning of different aquifer systems by measuring the variations of d18O values in water, possibly suggesting variations in infiltration velocity (Bahir et al., 2001). Studies by Fontes (1976), Molinari (1977) and IAEA (1981) have shown that variations of oxygen isotopes and deuterium in natural waters can be used to trace their characteristic variations of physical and chemical properties, even in polluted environments, while Craig (1961). by examining the isotopic variations in meteoric waters, explains the regime of precipitation in Atlantic Ocean. In addition, isotopic hydrogeological data have been put forward by Aranyossi (1989) as an example of detecting environmental degradation. 2.1. Strontium and its isotopes Strontium does not belong to the major elements but substitutes for calcium and can thus be treated as an analog for this element. Strontium is naturally occurring with four isotopes: 84Sr (0.6%), 86Sr (9.9%), 87Sr (7%), and 88Sr (82.5%). All these isotopes of strontium are stable except for 87Sr, which is the radioactive daughter of 87Rb, that decays with a half-life of 4.88  1010 years. By convention, 87 Sr abundance in a sample is expressed relative to the abundance of the stable nonradiogenic isotope 86Sr. The spread and variation in 87Sr/86Sr ratio make strontium isotopes a powerful tool when it comes to detecting trends in the soil –vegetation system. There is also a great potential in combining different parameters like soil, water, biological material, and Sr isotopes for detecting environmental changes over short as well as long time periods. Sampling of the past is a difficult task but biological materials, in combination with inorganic material, prove advantageous as environmental archives. There is also possibility of using museum collections as environmental historic archives. Analyses of Sr isotope ratios for soil samples indicate that weathering is related to the size of the mineral grains, smaller grains have a lower Sr isotope ratio than larger ˚ berg, 1995). An explanation grains (Jacks et al., 1989; A may be that the greater surface-to-volume ratio of smaller grains results in a stronger weathering ability that in turn may give rise to a preferential leaching. In another study by

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˚ berg (1995), the barks of spruce, pine, and birch from two A areas were analyzed for Sr. The age of the trees is about 40 years. An advantage of analyzing tree material is the ability to determine the age of every growth ring. Over time, each growth ring becomes terminated and lignified, thereby preserving its Sr isotope ratio. Barks from spruce and pine gave similar values within each of the two areas and birch bark Sr isotope ratios were slightly displaced towards higher values, possibly due to the different root system of the birch. 2.2. Lead and its isotopes The element lead is naturally occurring with four isotopes: Pb (1.4%), 206Pb (24.1%), 207Pb (22.1%), and 208Pb (52.4%). The ratio between the different Pb isotopes varies in different geological environments because 206Pb and 207Pb are formed by the decay of 238U and 235U, while 208Pb is a product of the radioactive decay of 232Th. 204Pb is the only Pb isotope that is not formed by decay but can be seen as stable. The use of Pb isotopes in the sedimentary profiles— environmental archives—may show the level of pollution from mining activity at different places at different times during history. We know today how high the level of pollution is, but what was the level before, what was the spreading pattern, and how has it developed? An important tool that can be used for solving the paradox of the decreasing lead level in 20th century man, through the identification of the changing sources of lead in man, is the analysis of naturally occurring stable isotopes of lead. The isotopic ratios differ significantly among particular lead bearing ores, coals, lead additives to gasoline, and rocks and soils of various areas. These ratios can be used for distinguishing among the sources of lead in ancient and modern human populations and in the atmospheric aerosols deposited with annual ice layers in glaciers. The same isotopic techniques can be used for the identification of sources of contamination in such components of the environment as top soil, vegetables, trees, and wild and domestic animals. An interesting trend that has been observed for the 206 Pb/204Pb ratio during the period from 1992 to 1996 is ˚ berg et al., 1999a). the use of air filters in the Oslo area (A Although this ratio has been decreasing during 1992 and 1993, it started to increase continuously at the end of 1993 throughout 1996. The change of the 206Pb/204Pb ratio from the end of 1993 would indicate that although the impact of combustion of low-ended gasoline on the air concentrations of this element after 1993 was still high, other source or sources have become more feasible, for example, the combustion of wood may have become the source of lead contamination in the Oslo area. 204

3. Case study An example is given in the present study to illustrate the use of isotopes in understanding the pollution of a small

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Fig. 1. Mean distribution of 206Pb/207Pb ratios, indicating the clear intermediate position of atmospheric Pb and the value of wheat Pb of the Kozani area in ˚ berg et al., 2001). between the Pb ratios of Greek gasoline and those of lignites taken from the mining area of the Kozani – Ptolemais basin (modified from A

rural area in Western Macedonia, Greece. Data on a high particulate matter (< 10 Am) concentration day are collected in order to identify the possible contribution of different ˚ berg et al., 2001). A pollution sources using lead isotopes (A principal method used in this study is the analysis of the lead isotopic signature in different media, which is capable of being used to discriminate between different sources of pollution in the area of Kozani. Pollution by Pb is mainly due to industrialization, urbanization, and motorization. Because of the high emissions of this toxic element, large amounts of the compound accumulated in the soil reservoir and sediments, and adverse impact on the environment and human health still pose a serious threat to humans. The origin of lead measured in certain receptors and the source apportionment within the emission regions are very important to consider when discussing the emission reduction options in a certain region. It is, therefore, of great importance to elaborate techniques that will enable us to apportion the emission sources of lead and help explain the origin of lead measured in the region at issue. One of the most powerful of these methods is the use of the naturally occurring lead isotope system, as explained above. Eight samples of lignite were taken from two locations in the lignite mining area, that is ‘‘Northern Field’’ and ‘‘Sector 6’’ between Kozani and Ptolemais, West Macedonia and the air filters from the town of Kozani during selective meteorological conditions. After mining has been completed in one site, reclamation of land takes place with experimental farming. In one of the fields cultivated with wheat a mixed sample of the crop was taken to see if there was an impact of soil or at atmospheric transport. The air filters in Kozani are of a quite low 206Pb/207Pb ratio (1.12) and plot between the lignite and gasoline Pb (Fig. 1). The wheat sampled in a reclaimed experimental field between Kozani and Ptolemais has a 206Pb/207Pb ratio of 1.13, very close to that of the air filters, indicating that the major uptake of Pb is from the air rather than from the reclaimed soil of 1.20.

The 206Pb/207Pb signature in Greek gasoline is low (1.06; Kersten et al., 1997) and thus of Precambrian origin (Gulson, 1986), probably Australian. It is also low in comparison to the common European 206Pb/207Pb gasoline signature of about 1.10 (Kersten et al., 1997). A low 206 Pb/207Pb signature as that in Greek gasoline is therefore easy to trace in the environment and in particular when the background signature is much higher like in west and southeast Greece where the common 206Pb/207Pb signature is about 1.20 in relation to the 1.06 of Greek gasoline.

4. Conclusions Isotopes can be used as environmental indicators to describe the affected environment in environmental studies by detecting trends of pollution over short as well as long time periods and by identifying sources of contamination as well as routes for transports. Lignites in Kozani are of an average 206Pb/207Pb signature of 1.20 while the average of two locally sampled air filters has a value of 1.12 (Fig. 1). Current emission of pollutants in the area of Kozani is thus clearly characterized by gasoline Pb rather than contribution of Pb from the combustion of lignite in the local power stations. Since the Greek soil seems to be have a 206Pb/207Pb signature of 1.20 due to the sulfide mining during Hellenic– Roman time and later mining activities, the questions are how much of the Pb signature on the air filters is due to lignite burning in the power stations and how much comes from windblown dust of the same Pb isotopic ratio? The only source for lowering the Pb ratios to about 1.11, however, is the contribution from traffic and leaded gasoline.

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