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Use of Pollen in Plant Biomonitoring of Air Pollution
By: Jean-Pierre Garrec
Summary
There has been an ever-increasing interest in plant
bio-monitoring of air quality. This paper discusses the possibilities of
using pollen as biomonitor to evaluate air pollution. The advantages and
limitations of methods that use pollen as biomonitoring agent are also
described.
Introduction
Numerous studies have been devoted to the impact of air
pollutants on pollens but in contrast, only few works are available on the
use of pollen to evaluate atmospheric pollution (i.e. pollen as
bioindicator).
Pollen as other plant or animal bioindicators, does not
provide information on absolute concentrations of pollutants in the air,
however, it indicates, with accuracy, their relative levels. Bioindicators
can give relevant information on pollutants: their identities, their levels
and their geographical localisation, and may eventually help us drawing
pollution maps. Actually, the methods using plants for biomonitoring of air
quality may turn out to be successful, as they are simple, cheap and fast
and can supplement the classical physico-chemical methods.
This small paper discusses the possibilities of using pollen
for air pollution biomonitoring; the advantages and limitations of methods
using pollen as the biomonitor to evaluate air quality are also described in
this paper.
Pollen as Air Pollution Bioindicator
The information on the pollutants is derived from the study
of the biological response of pollen to air pollution. As a lot of primary
and secondary physiological processes are involved, the physiological
responses usable for bioindication could be numerous ranging from molecular
level to pollen functioning.
Pollen used as bioindicator gives, from its physiological
perturbations, time integrated information on doses of pollutants present in
the air. We can say that pollen does not indicate levels of pollutants, but
it measures their biological impact. Thereby pollen, as other bioindicators,
provides particularly original and interesting information on the potential
adverse effects of pollutants on living organisms. This direct assessment of
risk by bioindication methods is of greater importance compared to the
physicochemical methods.
If in the atmosphere the pollutants have a direct impact on
the physiology of pollen, they have also an indirect impact on its
ontogenesis via their effects on the producing plants. It may be pointed out
that this ontogenesis is also subordinated to the other environmental
factors (atmospheric and/or edaphic) acting on the producing plants.
When pollen is used as bioindicator and we want to eliminate
these indirect effects, we have to work with pollen coming from plants
cultivated in an unpolluted area (greenhouse) and then introduce “in situ”
at the beginning of the study (active bioindication), and not with pollen
coming from local endemic plants (passive bioindication) with unknown
environmental history.
Another easier solution is the “transplant method”. In this
case the pollen is first collected from flowers in an unpolluted area, and
then exposed in the polluted sites inside narrow-mesh bags.
These active bioindication methods have the advantage of
being easily standardized at the level of the producing plant and allow to
control the pollen characteristics, origin and quality. The “transplant
methods” inform with precision how long the pollen has been contaminated.
Pollen as Air Pollution Bioaccumulator
In this case, information on the pollutants is based on the
study of their accumulation on the pollen. The accumulated pollutants are
quantified after extraction from the pollinic matrix and from physico-chemical
analysis.
Due to the rugosity of the micro relief at the surface of
pollen (exine), and also due to its lipophilicity, the pollen is a very good
accumulator of all types of pollutants: gaseous or particulate on one hand
and organic or non-organic on the other hand. This accumulation is mainly
dependent on physico-chemical processes at the surface level, and for this
reason is not much influenced by the physiological condition of the pollen
or of the producing plant. Practically, all the pollutants (pesticides, HAP,
heavy metals, fluoride, etc…) can be accumulated on pollen for passive or
active bioindication.
Pollen used as bioaccumulator gives information directly
linked to pollutant concentrations. The accumulation of pollutants is
dependent on the fluctuating characteristics of the air as it is influenced
by the dynamic equilibrium between pollen and atmosphere. Indeed, numerous
factors tend to continuously eliminate, chemically or mechanically, the
pollutants accumulated on the pollen surface: rain, wind, dust, rubbing,
etc…
But this information is never instantaneous, as we have to
take into account an equilibrium time between atmosphere and pollen which is
not very well known.
To collect enough biological material, pollen is always
directly sampled from the flowers, but in polluted areas, by active or
passive bioindication, we never know precisely the contact time between
pollutants and pollen. To eliminate this problem, we have to use, as with
other bioindicators, the “transplant methods”.
Conclusions
Plant biomonitoring methods will be never a substitute to
physicochemical methods for air pollution studies, but they constitute
complementary methods, as they provide essential information on biological
impact of pollutants.
Among these methods of plant biomonitoring, the method using
pollen as bio-accumulators or as bioindicators could be a good one due to
the peculiar characteristics of the pollen surface. Unfortunately, some
constraints in relation to pollen physiology limit the wide application of
this method “in situ”. These constraints are as follows;
-
the contact time between pollutants and pollen
-
the influence of producing plant environment on pollen
physiology during its ontogenesis, and
-
the quality of the sampling sites including its homogeneity
and representativity.
-
Pollen production takes place over a limited period
during the year, and it is very often irregular.
-
Pollen life-time is always short (few days only) and it
could be a limiting factor for a good accumulation of pollutants or for
producing measurable physiological perturbations.
Dr. Jean-Pierre Garrec
is at the Laboratoire Pollution Atmospherique, INRA Centre de Recherche de
Nancy, 54280 Champenoux, France (E-mail address: [email protected]) |
