|Biological Monitoring: Signals from the Environment (GTZ, 1991)|
|Bioindicators for monitoring of atmospheric pollutants in Asian countries|
Active monitoring is clearly underrepresented in the surveyed countries. Only 22 - 26% of the publications from India and China deal with this approach to bioindication, and no studies at all on this aspect are available from Hong Kong, Thailand or South Korea. The problems involved are apparently associated with technical aspects of monitoring the established measurements stations and with the required standardization of procedures. In one study involving only 5 measurement sites, the authors (BORALKAR & MUKHERJEE, in press/lndia) pointed out the difficulties posed by management and supervision, and in particular the problems involved in providing a uniform water supply to the exposed plants. On the whole, insufficient information was supplied on fumigation conditions (FANG CAI-GIN & DUAN JIGUANG 1982/China, EIAS/1/1985-1986/lndia and CHAPHEKAR et al. 1985/India).
Equally little attention was paid to hydrocarbons and to photochemical oxidants. The latter class of pollutants comprises a special case in the sense that no component storage takes place. The extent of contamination can only be evaluated by using active monitoring to observe the incidence of typical symptoms.
A far larger number of publications deals with passive monitoring. This approach was used mainly to assess certain kinds of pollution within narrowly defined areas, serving to delimit and characterize the zone of influence of a contaminant source or to identify areas or urban zones with differing degrees of pollution. In some of the articles, information was given on the ability of individual plant species to filter out heavy metals, particulates or cement dust, and their potential significance for helping to prevent health hazards for humans discussed (FANG CAI-GIN & DUAN JI-GUANG, 1982/China; EIAS/1/1985-1986/lndia; BHATNAGAR et al. 1985/India; and VORA et al. 1986/lndia). The problem of bioconcentration of contaminants in the nutrient cycle was also dealt with (MEENAKSHY et al. 1981/lndia and SUCKCHAROEN 1980/Thailand).
The techniques and methods used correspond largely to those used in western industrialized nations. In a few cases, coauthors from western countries participated (YUNUS, AHMAD and GALE, 1979/lndia), the studies were conducted by foreign scientists in an Asian country (THROWER 1980/Hong Kong), or the inspiration for conducting the study in the first place was obtained by the author during a stay abroad (LEE et al. 1982/South Korea and SUCKCHAROEN 1980/Thailand). In some cases, the chemical analyses (SUCKCHAROEN 1980/Thailand) and electron-microscopic examinations (YUNUS et al. 1979/India) were carried out in Europe or North America.
The focus was on measurement of yields, assessment of macroscopically visible damage, morphological studies, light- or electron microscopic examinations, chemical analyses (of heavy metals, fluoride and sulfur content), and physiological measurements. In this context it should be noted that analysis of physiological parameters for assessment of the pollution situation can only be recommended if the stress factor "transport to the measuring station" can be eliminated. It is not apparent from the articles whether sufficient consideration was given to this aspect.
Only a few lichen, moss and liverwort mappings were carried out. However, THROWER (1980/Hong Kong) was able to show with his studies that the response of tropical lichen species to atmospheric pollution is similar to that of temperate varieties. Thus, lichen zones develop which reflect air pollution levels.
One attempt was made to utilize phytosociological mapping to obtain information on air pollution (WONG 1978/Hong Kong). It would be appropriate to continue this work by carrying out detailed research on plant successions, following the example of recent successful studies in western countries on continually observed study areas within the scope of endeavors to compile environmental impact inventories for certain pollutants.
The advantages of passive monitoring are that relatively little equipment is required and that the reactions of the bioindicators can be relatively dependably used to infer the condition of other organisms at the same site. A disadvantage of this method is that the sensitivity and ability to respond of a given plant individual is strongly dependent on its genetic disposition and on the conditions under which it has grown to maturity. For this reason, additional data is required on pollutant concentrations, the climate, soil parameters, etc., as well as information on the condition, chemical composition and reaction of the plants in order to permit interpretation of the results.
In many of the surveyed studies, an exceedingly one-dimensional approach was taken that failed to give adequate consideration to the complex functional processes of the organisms and their mutual interreactions. Two extreme examples of this are the studies by BORALKAR (1980/lndia) and CHAPHEKAR (1972/lndia). They merely assessed the leaf damage of all of the site vegetation along a transect and attributed the observed damage to pollutant emissions, without performing any chemical analyses on plant or soil samples. Climatic and soil parameters were ignored completely.
The importance of orographic and edaphic factors, climatic conditions and plant attributes - e.g. differing propensities of leaf surfaces to trap airborne particles- was only recognized and incorporated by WONG (1978/Hong Kong), HO & TAI (1979/Hong Kong) and MEENAKSHY et al. (1981/lndia).
The majority of the studies made only a first step towards fulfilling the conditions which must be met for successful analysis of air pollution over an entire area. In order to corroborate the results and facilitate their interpretation, it is essential for standardization of the test conditions to be optimized and for a comprehensive study to be made of meteorological and microclimatic factors.
Finally, on the basis of the results of numerous fumigation experiments and the Asian publications surveyed here, concrete proposals for phytomonitoring techniques can be made, in particular for active monitoring:
The reactions of Oryza sativa (rice) and Pharbitis nil (morning glory) to different pollution levels are sufficiently well known from a large number of fumigation and open-site experiments. In the studies by MATSUNAKA (1977/Japan), Pharbitis nil is utilized as a sensitive bioindicator in a passive monitoring approach. This species responds to high ozone burdens with chlorosis, necrosis and curling of its leaves. Extensive studies on the effect of O3 on its epidermis, chloroplasts, ribosomes and mitochondria (NOUCHI et al. 1977/Japan), and assessment of leaf damage following exposure to different ozone concentrations (NOUCHI & AOKI 1979/Japan), have provided additional data which permit evaluation of the potential of this plant species as a bioindicator.
A great deal is also known about the sensitivity and reactions of Oryza sativa to air pollution. FUJINUMA & AIGA (1980/Japan) established that the rice varieties Nihonbare and Kinmaze react sensitively to ozone and sulfur dioxide. Their sensitivity to NO2 is significantly lower. The effect of ozone on
Oryza sativa was also investigated by NAKAMURA & OTA (1975 and 1977/Japan). They described the macroscopic damage caused by fumigation. YAMAZOE & MAYUMI (1977/Japan) studied the effect of NO2, O3 and SO2 fumigation on rice leaves. Similar studies were performed by AGRAWAL et al. (1982/lndia). They studied chlorophyll and carotenoid contents, and assessed leaf damage after exposure to SO2.
On the basis of the results of the above-mentioned studies, it can be assumed that Pharbitis nil is suitable as a sensitive bioindicator for ozone and Oryza sativa for active monitoring of ozone and SO2. We recommend proceeding in accordance with VDI guideline 3792, sheet I (1978). This source contains both guidelines for fumigation and a description of a semiautomatic technique for supplying the plants with water.
In a large number of independently performed studies, Nerium
indicum ("kaner") has demonstrated a high filtering capacity and low sensitivity
to atmospheric contaminants (EIAS/1/1985- 1986/lndia; BORALKAR et al. in press;
and YIAN LI-YING et al. 1985/China). Under standardized fumigation conditions,
it could therefore be used as a cumulative indicator within the scope of an
active monitoring approach.