Current issues in establishing geochemical background of trace elements

Transcription

1 Geochemistry and the Environment Division Institute of Chemistry Jan Kochanowski University in Kielce Current issues in establishing geochemical background of trace elements Agnieszka Gałuszka & Zdzisław M. Migaszewski

2 Outline of the talk Defining geochemical background Importance of the knowledge of geochemical background of trace elements Methods of establishing geochemical background the pros and cons Tasks for the future

3 Defining geochemical background Historical use of the term geochemical background in exploratory geochemistry and geochemical prospecting Hawkes, Webb (1962): the normal abundance of an element in barren earth material a lack of anomaly GEOCHEMICAL PROSPECTING IS A SEARCH FOR POSITIVE ANOMALIES

4 Element concentration Distance Positive anomaly Geochemical background Negative anomaly

5 Defining geochemical background Environmental approach: Geochemical background ( ) is a relative measure to distinguish between natural element or compound concentrations and anthropogenically-influenced concentrations in real sample collectives a lack of man-made pollution (Matschullat et al., 2000)

6 Element concentration Distance Positive anomaly Geochemical background Negative anomaly Pollution source

7 Geochemical background types in environmental approach Geochemical background Preindustrial background Anthropogenic background Natural background Ambient background Area background Taken from: Reimann, Garret, 2005; Gałuszka, 2007

8 Related terms Threshold value the concentration above which all values are considered anomalous = the upper limit of geochemical background range Baseline the present concentration of a given substance in a given environmental sample, measured to find any possible changes of concentrations in the future

9 Environmental issues What is pollution? Pollutant is a substance present in greater than natural concentrations as a result of human activity and having a net detrimental effect on its environment (Spellman, 1999) NATURAL CONCENTRATIONS = GEOCHEMICAL BACKGROUND

10 How do humans change the environment? Anthropocene the current interval of time, dominated by human activity (Crutzen, 2002) The begining: Early agricultural practice (8,000 years ago) Industrial Revolution (about 1760) 1800 (human population hits 1 billion and started to grow at an alarming rate) Postwar Great Acceleration (marked by radionuclides derived from atomic detonations)

11 How do humans change the environment?

12 Trace elements in the environment Natural sources of trace elements Concentrations of trace elements measured in + environmental samples Anthropogenic sources of trace elements

13 Anthropogenic trace element input The main anthropogenic sources of trace elements: Industry (mining, metallurgic, chemical etc.) As, Cd, Cr, Cu, Hg, Ni, Mn, Pb, Zn Power generation As, Cd, Hg, Pb Traffic Cd, Mo, Ni, Os, Pb, Pt, Sb, V, Zn Agriculture As, Cd, Mn, V, Zn Waste management Cd, Cu, Hg, Mn, Ni, Pb, V, Zn

14 Anthropogenic influence assessment Geochemical calculations Enrichment factor (EF) = A e B c B e A c A e element concentration in environmental sample B e reference element concentration in environmental sample A c Clarke value or average shale value of the element B c Clarke value or average shale value of reference element EFs close to unity point indicate crustal origin whereas those greater than 10 are considered to be non-crustal source

15 Anthropogenic influence assessment Reference (conservative) elements Si indicator of amount and distribution of element-poor quartz Al indicator of Al silicates, used to account for granular variations of element-rich fine silt and clay size Alsilicates Fe indicator of element-rich Fe-bearing clay minerals, Ferich heavy minerals and hydrous Fe oxides Sc indicator of Sc structurally combined in clay minerals Cs indicator of Cs structurally combined in clay minerals and feldspars Li indicator of Li structurally combined in clay minerals and micas

16 Example of the use Shazili et al. (2007): Interpretation of anthropogenic input of metals in the South China Sea bottom sediments of Terengganu (Malaysia) coastline using Al as a reference element. Aquatic Ecosystem Health & Management 10/1: Enrichment factor (EF) values using Al as a reference element were determined and showed that sampling sites of the major rivers of Terengganu were anthropogenically influenced by Pb and Cd. Sources of pollution are probably sewage, agricultural wastes and atmospheric deposition of Pb from the use of leaded petrol

17 Anthropogenic influence assessment Geochemical calculations Contamination Factor (CF) = C i mean content of element in samples taken from at least 5 sampling sites (μg g -1 dw) C n pre-industrial concentration of element CFs values below 1 indicate low contamination, in the range of 1-3 moderate contamination, 3-6 considerable contamination, >6 very high contamination C i C n

18 Example of the use Hoda et al. (2009): Heavy Metals Contamination in Sediments of the Western Part of Egyptian Mediterranean Sea. Australian Journal of Basic and Applied Sciences 3(4): According to the values of contamination factors (CFs), sediment samples of the western part of Egyptian Mediterranean Sea were classified to be low contaminated by Cr, Cu, Mn, Ni, Zn and moderately polluted by Pb

19 Anthropogenic influence assessment Geochemical calculations Pollution load index (PLI) (Tomlinson, 1980) The PLI is obtained as a concentration factor (ConcF) of each element with respect to the background value: PLI = n (ConcF 1 ConcF 2 ConcF n ) where: Concentration of the element in the sample ConcF = Background concentration The PLI represents the number of times by which the element content in the sample exceeds the background concentration

20 Example of the use Galán et al. (2002): Residual pollution load of soils impacted by the Aznalcóllar (Spain) mining spill after clean-up operations. The Science of the Total Environment 286 (1-3): The soils affected by the Aznalcóllar mining spill contained a significant residual contamination, especially in the vicinity of the river bed (pollution load indices = 3-9). Within profiles the PLI values of the samples decreased with depth, as the source of pollution was deposited on the soil surface during the flood

21 Anthropogenic influence assessment Geochemical calculations Geoaccumulation index (I geo ) I geo = log 2 C e 1.5 GB C e concentration of the examined element in the sample GB geochemical background concentration According to I geo values, there are 7 classes of the sample pollution, varying from 0 (unpolluted) to 6 (extremely polluted)

22 Example of the use Loska et al. (2004): Metal contamination of farming soils affected by industry. Environment International 30(2): The index of geoaccumulation was applied in the study of trace element concentrations in soils from Suszec commune (southern Poland). The results showed contamination of soils with Cd, Pb, As, Hg and Sb

23 Anthropogenic influence assessment 10 μm SEM image of technogenic particles on pine needle surface, southern part of Magurski National Park

24 Anthropogenic influence assessment Isotopic fingerprint Soil S in precipitation Pine needles Industrial particles

25 Anthropogenic influence assessment Geochemical tracers Geochemical tracers are used to assess anthropogenic influence, mainly on waters Examples of geochemical tracers: Boron and its isotopes Strontium isotopes Lead isotopes Rare earth elements (REEs) (e.g. gadolinium, cerium) gadolinium

26 Soil horizon/subhorizon Factors influencing concentrations of substances geochemical variability µg kg -1 Concentrations of Σ17 PAHs in soil profile at in Wymysłów Psarska Mt. (Holy Cross Mts) in 2001

27 Natural geochemical variability Mercury and lead concentrations in soil profile at Psarska Mt. Soil horizon/ subhorizon Ol Ofh ABC BC R Year Hg (μg kg -1 ) Pb (mg kg -1 ) <5

28 Trace element concentrations in various environmental samples As in water: 60 g L -1 As in soil: 171 mg kg -1 As in sediment: 1138 mg kg -1 As in pyrite: 9666 mg kg -1

29 Why is the knowledge of geochemical background so important? In exploratory geochemistry and geochemical prospecting: it enables to indicate anomallies which are crucial in searching for new mineral deposits In environmental sciences: it defines concentration above which substances are regarded pollutants; it is used to establish quality criteria for soils, waters and sediments In other areas: health sciences, forensic sciences, land use management etc.

30 Methods of establishing geochemical background Direct (geochemical) Indirect (statistical) Integrated

31 Direct methods Historical approach archival samples collected before Industrial Revolution or samples dated as representing pre-industrial period Contemporary approach samples collected in relatively pristine areas, not heavily influenced by anthropogenic activity MEASURED CONCENTRATIONS = GEOCHEMICAL BACKGROUND

32 Advantages and disadvantages of direct methods + The values of geochemical background are easy to establish (means or medians of the results are commonly used) + The original results do not require any data processing Subjective sample/study area selection criteria High costs Heavy laboratory workload The neccessity of expert knowledge

33 Indirect methods Are based on statistical techniques (computational and graphical), which aims at eliminating the outliers from statistical population distribution Background is represented by non-anomalous concentrations Traditional formula: Range of Mean 2 geochemical background = standard deviations

34 Example of indirect methods: Pb in the O soil horizon from the Holy Cross Mts

35 Pb in O horizon (mg kg -1 ) 4-σ outlier test Mean = 60 mg kg -1 4 = 244 Geochemical background: Mean 2 = mg kg Sample #

36 Pb in O horizon (mg kg -1 ) Iterative 2-σ technique Mean = mg kg -1 2 = Geochemical values background: 5-81 mg kg Sample #

37 Pb in O horizon (mg kg -1 ) Pb in O horizon (mg kg -1 ) Calculated distribution function Geochemical background: 5-79 mg kg Sample Sample # #

38 Tukey boxplots Reimann et al. (2005): Background and threshold: critical comparison of methods of determination. Science of the Total Environment 346: 1-16

39 Cumulative Distribution Function The histogram and cumulative distribution function curve for arsenic in topsoils (Geochemical Atlas of Europe 2005, the Association of the Geological Surveys of the European Union)

40 Advantages of indirect methods + Precision, accuracy and well established techniques of background evaluation + Wide selection of different statistical tests, graphical methods, which can be applied in calculating geochemical background + The possibility of using the easy available computer programs for data processing

41 Disadvantages of indirect methods Neglecting the significance of natural processes that influence distribution of elements or chemical compounds in environmental materials Not considering uncertainty of sample treatment stages, including sampling, sample preparation and chemical analysis Background concentrations are understood as nonanomalous (traditional approach in exploratory geochemistry)

42 Integrated method It combines both the prerequisite to collect samples in relatively pristine areas, and subjecting the results obtained to statistical calculations In the first use of integrated method for geochemical background evaluation in the Holy Cross Mts, the samples were collected in forest ecosystems within protected areas and iterative 2-σ technique was applied

43 Pros and cons of integrated method + Samples represent natural geochemical variability and due to low anthropogenic influence, the distributions of results are usually normal, which allows to restrict the data processing Subjectivity of selection of the study area High costs and heavy laboratory workload The neccessity of expert knowledge

44 Tasks for the future Terminology relating to geochemical background in environmental and exploration geochemistry should be systematized Reliable and plausible methodology of establishing geochemical background concentrations should be worked out Geochemical background should be taken into account when considering environmental quality criteria

45 Austria Czech Republic Finland Italy Lithuania Netherlands Poland Slovakia UK Denmark Soil screening values for unacceptable risk in selected European countries mg/kg As Cd Cr Cu Hg Pb Ni Sn Zn Derivation methods of soil screening values in Europe. A review and evaluation of national procedures towards harmonization

46 Wishing you great backgrounds!

47 1 hour break for LUNCH