Contents
| AIR HYGIENE REPORT no. 10 | |
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Contents |
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At present, mosses are probably the most widely used plant group in relation to the assessment of airborne organic compounds.
Thomas (1986) found that mosses were suitable in the monitoring of the chlorinated hydrocarbon, benzohexachloride (BHC) and polycyclic aromatic hydrocarbons (PAH) in Europe. Different moss samples from across Europe were analysed for their trace substance residue content by a variety of research groups in Germany, the Netherlands, Denmark, Norway and Iceland. Hypnum cupressiforme was analysed at most sites. The effective biomonitoring properties of this species in aerial heavy metal monitoring has previously been recognised (Chapter II, Section 1). Hylocomium splendens and Rhacomitrium lanuginosum were analysed at a few sites in the study. Both these species have also been utilised in the assessment of heavy metal contamination (Chapter II, Section 1).
Results showed a clear PAH concentration gradient in mosses, which was high in the industrial centres in middle Europe and low in northern Europe. The content of fluoranthene (1.0 ng g-1) and benzoperylene (0.6 ng g-1) in moss samples in Iceland were regarded as background levels. However, the ratio of fluoranthene to benzoperylene was lower at these sites than at industrial sites due to a high concentration of fluoranthene in the gaseous phase being transported longer distances to remote areas. The distribution of BHC content in moss samples does not show a clearly defined gradient due to the high mobility of this substance in air. Mosses in the remote sites accumulate comparable concentrations of BHC as industrial sites. References
An important component of Thomas's (1986) work was the derivation of multiple regression equations relating PAH concentrations in mosses with particulate air quality data. Such models are crucial since they allow quantifiable predictions in air quality monitoring to be made. However, no significant models were established for chlorinated hydrocarbons because mosses are more appropriate for measuring environmental chemicals deposited in particulate form.
In Finland, analysis of 26 Sphagnum moss samples collected from 12 locations over a period of ten years indicated substantially higher concentrations of PCBs in the industrial south compared to the non-industrialised northern part of the country (Himberg and Pakarinen, 1994).
Transplantation of plants to other areas for the purposes of pollution assessment is not restricted by the current distribution of a species at the sites of interest and allows the time of exposure to be defined.
Sphagnum moss bags were used to assess organic contamination (PCB and organochlorine pesticides) in three regions of Canada (Strachan and Glooschenko, 1988). Sheltered moss bags retained higher levels of compounds than bags exposed to wash off from rainwater. In conclusion, the authors did not recommend the use of such bags as monitors of atmospheric levels of persistent organic contaminants. Material in the commercially available polypropylene mesh bags was lost due to wind and the use of finer, air permeable mesh bags for surveying were suggested. However, the bags provided qualitative relative assessments and can act as early warning indicators for further action. References
Wegener et al. (1992) transferred sphagnum moss samples in nylon bags from a rural area in Ireland to a sampling location at one km distance from an aluminium production plant in Botlek, the Netherlands. Samples were also exposed to three rural areas of the country approximately 20 to 30 km away, to provide reference data. Exposure time was 30 days. Concentrations of PAHs in moss bags near the production plant were approximately 30 times higher than concentrations in bags in the rural areas. Concentrations in the rural areas were not significantly different. References
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