7.4.1 Introduction
Mosses are suitable for analysing heavy metal deposition and retention since they depend solely upon atmospheric water supply. However, in order to use the heavy metal content of moss as an indicator of atmospheric deposition, a relationship between the two has to be established. This relationship will be dependent on the moss species, geographical location, and will differ between the investigated chemical elements. In order to define this relationship, also measurements of atmospheric deposition have to be undertaken. The relationship is fairly good for the elements Pb, As (not in coastal areas), V, and Cd, relatively good for Cu and Ni, and relatively poor for Zn, Cr, and Fe (Cr and Fe are generally originating from soil dust in background areas).
MC as a bioaccumulator of heavy metal deposition can be used to relate deposition to the biological subprogrammes EPand VG (trunk epiphytes and field and bottom layer vegetation). An other advantage of the MC method is the possibility for detailed regional surveys. In this respect mosses have proven to be a cheap and efficient tool.
7.4.2 Methods
Sample mosses in open areas of forests or young plantations. The sampling place should be located at least 5 m from the nearest tree in order not to be exposed to direct throughfall or stemflow water. If such sampling places can not be found, samples are taken from open heathland or peatland, where mosses often can be found (and should be sampled) in the neighbourhood of dwarf shrubs. Avoid a canopy of shrubs and large-leaved herbs. Do not sample on rocks.
Two moss species are preferred: Pleurozium schreberi and Hylocomium splendens. Where both are present priority is given to the former species. If these species do not exist other species can be used. A sample from an area should consist of only one of the two species - no mixture.
The sampling frequency for mosses is every 5 years.
Collect at least 3 composite moss samples. The most suitable collecting period is early summer, before the growing period of mosses. One composite sample should consist of five to ten subsamples spread around each sampling place. About 2 litres of moss material is needed (the final dry weight of the cleaned material will be about 20 g). Use clean plastic gloves and do not smoke during sampling.
Place the subsamples side by side in large (5 dm3) paper or plastic bags and carefully close the bags to prevent contamination during transport. Store the moss material in paper bags and dry at 40 °C as soon as possible. If stored in plastic bags (moist samples), the material should be moved to paper bags after air-drying or stored frozen until further treatment can take place.
Remove all dead material and attached litter from the samples so that only green (or brownish green) shoots from the three most recent years are included, i.e. three fully developed carpet segments of Pleurozium schreberi (or a corresponding portion of Hylocomium splendens), excluding the half-developed segment from the ongoing growing period if such exists. Broken individuals are discarded. Handle the mosses on clean laboratory paper, glass shields or clean polyethene and avoid contamination from smoke and laboratory tables.
Dry the samples at 40 °C to a constant weight, which is used as a reference in the calculations. Carefully close and store the dried material not used in the analyses in an environment specimen bank for later investigations.
Only wet ashes in closed systems are used during digestion of dried and homogenized mosses, since some metals (especially As) may escape when using dry ashing.
7.4.3 Chemical analyses
1 - 5 g of moss is boiled in conc. HNO3 or in a 4:1 mixture of conc. HNO3 and HClO4. The solutions are filtered and kept in polyethylene bottles before analysis (AAS in flame and graphite furnace or ICP or neutron activation).
7.4.4 Quality assurance/Quality control
See data quality management in Chapter 8.
7.4.5 Data reporting
Parameters:
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Parameters
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list
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unit
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AS
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DB
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arsenic
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mg/kg
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CD
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DB
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cadmium
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mg/kg
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CR
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DB
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chromium
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mg/kg
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|
CU
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DB
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copper
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mg/kg
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|
FE
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DB
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iron
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mg/kg
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|
HG
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DB
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mercury
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mg/kg
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|
NI
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DB
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nickel
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mg/kg
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|
PB
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DB
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lead
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mg/kg
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|
ZN
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DB
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zinc
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mg/kg
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Example files
MC example Excel file
MC example ASCII file
- File identifier SUBPROG states the subprogramme.
- Station number SCODE is given as 9999 to represent the whole IM site.
- MEDIUM refers to the analysed moss species, i.e. Pleurozium schreberi (PLEU SCH) or Hylocomium splendens (HYLO SPL), medium code list is M2 (from NCC species codelists, see Annex 6).
- Spatial pool SPOOL refers to the number of sampling places from which the composite samples are taken (5 in the example).
- Sampling year and month are given as YYYYMM, day field is left blank.
7.4.6 References
Atmospheric heavy metal Deposition in the Northern Europe 1990. Nord 1992:12.