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Biomonitoring
of Air Pollutants with Plants*
By:
Ludwig De Temmerman, J. Nigel, B. Bell, Jean Pierre Garrec,
Andreas
Klumpp, Georg H.M. Krause & Alfred E.G. Tonneijck
Since the Industrial Revolution
at the end of the 19th century it has been
recognized that air pollutants can cause dramatic effects
on plants. However, the first recognition in print of air pollution damage
to vegetation is in John Evelyn’s book “Fumifugium” published
in 1661.
Biomonitoring
consists of the use of responses of individual plants or plant associations at
several biological organization levels in order to detect or predict changes in
the environment and to follow their evolution as a function of time. Some plant
species are sensitive to single pollutants or to mixtures of pollutants. Those
species or cultivars are likely to be used in order to monitor the effects of
air pollutants as bioindicator plants. They have the great advantage to show
clearly the effects of
phytotoxic compounds present in ambient air. As such, they are ideal for
demonstration purposes. However, they can also be used to monitor temporal and
spatial distributions of pollution effects. Standardization of methods is
crucial in order to develop air quality standards based on effect monitoring.
Many
plants are useful as bioaccumulators
and the choice of species depends on the aims of biomonitoring. Mosses and
lichens accumulate heavy metals and other compounds very efficiently because
of their large specific surface and slow growth. As such they serve mostly as
passive biomonitors to provide an indication of the pollutant impact at the
ecosystem level. On the other hand,
field crops and vegetables can serve as an
immediate step to detect effects on
food and fodder quality and safety. Bioaccumulators are not only used to
measure deposits of heavy metals but also radionuclides,
polycyclic aromatic
hydrocarbons, dioxins and all kinds of aerosols which can also be accumulated
efficiently. As far as contaminants of food and fodder crops are concerned,
they are a crucial step to evaluate the potential transfer to consumers.
The
idea of biomonitoring goes back
to the 19th century when NYLANDER (1866) used the abundance of lichens as a
measure for air pollution effects. For the purpose of surveying ambient air
quality, biological indicators were used the first time in 1958 in the basin of
Los Angeles, US; however, the low cost of this method in comparison to the
chemical-analytical methods was the decisive factor by otherwise similar
objective targets (HECK 1966). HEGGESTAD & DARLEY (1969) reported work with
tobacco (Bel–W3) on
the detection of ambient oxidant effects in
California and VAN RAAY (1969) used indicator plants to study the effect
of
HF and SO2
in
the Netherlands. However, it was SCHONBECK
et
al. (1970) who pointed out for the first time,
that biological indicators gain
effects-related information which cannot be assessed by means of chemical
analytical methods of air pollution monitoring systems.
The
significance of biomonitoring air
pollution burden by plants offers some
important results from different abilities:
-
Plants show an integrated response to
the pollution climate, thus giving information even on the potency of complex
pollutant mixtures, occurring simultaneously or alternatively in a stochastic
pattern, reacting only to the
effective
part of a given pollution situation. This allows
largely
realistic estimates of the given risk potential with regard to the
objectives to be protected.
-
Plants react to an ambient air
pollution burden (often with a strongly fluctuating pattern) with an assessable
and verifiable reaction, while modeling of dose-effects renders information
with a much lesser degree of confidence due to e.g.
random distribution of pollutants in time and space.
-
Different levels of organization of the
plant can be used for biomonitoring, ranging from the single plant (leaf or
even plant cell) to the plant association and the ecosystem. The response that
is obtained at the community level (e.g. shift in species composition) is a
result of an integration of different factors over a relatively long period
experienced by competitive plant species and as such cannot be detected on the
basis of physical and chemical measurements.
-
Some air pollutants have very low
ambient concentrations and are difficult to measure
accurately with physical and chemical methods. Plants can accumulate those
pollutants to a level that is easier to analyze.
-
Effects
are expressed in
sensitive plant species as visible injury (leaf injury or changes in habit), and in less sensitive species (even pollution-tolerant species) in the
accumulation of pollutants; both providing an important tool in recognizing air
pollution
effects (making
the invisible visible) and/or the transfer of trace pollutants within the biological chain.
Many of these attributes render
biomonitoring as being particularly suitable for developing countries. In such
places there is generally only a very limited air monitoring network and
biomonitoring offers the opportunity to determine the large scale pattern of
pollutant distribution, as well as temporal changes. Continuous physico-chemical
monitoring requires the use of expensive equipment and skilled personnel, as
well as ready access to maintenance of the former and access to spare parts.
These are invariably in short supply in most developing countries and in many
cases effectively non-existent.
There are several possible goals
when carrying out biomonitoring of air pollutants.
-
Spatial distribution of air pollutants
in order to map pollution effects on regional or supra-regional scale. This can
be carried out for air pollution effects with bioindicators and for deposits of
particulate and gaseous pollutants with bioaccumulators.
-
Temporal distribution of air pollutants
(time series) can also be done to assess effects of particulate deposition as
well as gaseous pollutants.
-
Source monitoring is a lot easier than
large scale monitoring and is applicable to a broader range of pollutants when
they reach phytotoxic levels. The climatic differences between the different
measuring locations are almost negligible on a regional scale.
-
At the ecosystem
level, the plant
community is a very interesting tool to study the pressure of air pollution on
plant communities and ecosystems and to detect effects on biodiversity.
-
Bioindicator plants are also very
useful to draw public awareness to air pollution problems, since they can
demonstrate the visibility of otherwise invisible air pollutants, especially in
city environments and in developing countries where industrialisation and
urbanisation are increasing.
-
Plants could probably serve as health
indicators. Comparisons of biomonitoring work on trace elements and the
occurrence of epidemiological disturbances in human health can be helpful, but
are not yet convincing and need to be developed further. Bioaccumulator plants
are particularly valuable in order to study the transfer of airborne chemicals
to the food chain as crops can be used for this purpose.
-
Biomonitoring offers a support and
scientific background for the elaboration of effect-based limit values and
directives on air quality.
Ludwig De Temmerman,
Veterinary &
Agrochemical Research Centre,
Tervuren,
Belgium
Nigel
Bell, Imperial College, London, U.K.
Jean-Pierre
Garrec, INRA Nancy,
Champenoux,
France
Andreas
Klumpp, Institute for
Landscape & Plant Ecology,
University
of Hohenheim, Stuttgart,
Germany
Georg
H.M. Krause, Landesumweltamt Nordrhein-Westfalen,
Essen,
Germany
Alfred
E.G. Tonneijck,
Wageningen
University& Research Centre,
Wageningen,
The
Netherlands
(*Condenced from “Urban
Air Pollution, Bioindication & Environmental Awareness”
edited
by Andreas Klumpp, Wolfgang Ansel
& Gabriele Klumpp & published by
Cuvilier Verlag, Gottingen,
2004)
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