Contents
| AIR HYGIENE REPORT no. 10 | |
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Contents |
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The majority of published literature with regard to gaseous air pollution is concerned with SO2. However in response to a decline in SO2 levels since the 1970s focus has increased with regard to other pollutants such as NOx , NH3 and O3.
Lichens are the most widely recognised plant group in air pollution monitoring and will probably continue to be in the near future. Lichens are particularly useful in indicating pollution loads over long periods. Lichen surveying is routinely included as part of international and national monitoring programmes. Urban and industrial pollutant monitoring generally involves classification and mapping of pollutant zones and calculation of pollution indices. Responses of lichen species and communities has been related quantitative to air pollutant concentrations but often this would still require measurement of physio-chemical data. Recent developments show an increased emphasis on the use of biochemical and physiological responses of lichens as indicators of air pollution, probably due to technological advancement. A multivariate approach using a number of lichen parameters such as community changes, visible injury, physiological effects and element content would provide an integrated approach to air quality assessment.
Most bryophyte studies are associated with regional and urban sulphur dioxide (SO2) contamination. On a national and multi-national monitoring scale, bryophytes are used more as bioaccumulative indicators of aerial metal contamination than as bioindicators of gaseous air pollution.
The use of fungi in air pollution monitoring is generally limited in comparison to lichens and bryophytes but recent developments have proposed their use in the assessment of pollution impact on forests. Leafyeasts have also been proposed as bioindicators of SO2 pollution in urban and rural areas.
An increase in epiphytic algal growth usually coincides with a reduction or disappearance in epiphytic lichens since green algae respond positively to increased nitrogen. This group therefore have potential as bioindicators with regard to the recent increases in N deposition. Aerial green algae are currently used in international and national monitoring programmes in this respect.
In their comparisons of SO2 absorption capacities between vascular plants, mosses and lichens in a range of habitats, Winner et al. (1988) concluded that the cryptograms are much stronger SO2 sinks and therefore more sensitive to this pollutant than vascular plants. However for O3 the use of higher plants as bioindicators of crop and forest injury looks more promising. The use of higher plants in bioindication is relatively recent in comparison to lower plants. Generally the exposure time of higher plants to a pollutant is known because observation is normally restricted to the vegetation period. The detection of visible symptoms is the most widely recognised bioindication method using higher plants. However, symptomatic bioindication utilising higher plants may not always assist in the protection of vegetation. This is because air pollution may affect plant species at levels less than those resulting in visible injury. Furthermore visible injury is not specific to particular environmental stresses. Most studies using higher plants employ a bioassay approach whereby plants from standard genetical origin and state of development are utilised. This ensures that plant responses indicate pollution damage and does not reflect previous natural abiotic or biotic conditions of the plant.
Biochemical, physiological and structural bioindication methods are better developed for higher plants than lower plants. This is probably due to increased interest on the effects of air pollution on higher plants because of the economic implications for example in relation to crops and forests. For example, a special issue of the journal Environmental Pollution was dedicated to the response of crops to air pollutants. This was reported on an international conference on assessment of crop loss from air pollutants in October 1987. However, these responses are often not specific and careful assessment is required in identifying cause and effects relationships. One attempt to overcome this problem would be to use multivariate approach where several response parameters are combined into multivariate indices. References
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