94
Water In Ecosystems: A Non Renewable Resource
1
INTRODUCTION
The ecological catastrophes of these past years (Bopal, pollution of the Rhine at
Basel, ... ) combined with the spectacular effects of acute toxicity resulting in a high
mortality rate for fish, clearly point to the need for better knowledge of the results
and effects produced by chemical compounds in the environment.
Ecotoxicology, at the cross-roads of biological and chemical knowledge, is in full
development because compulsory requirements and increased growth of new
products go hand in hand with a concern for the protection of ecosystems. Recent
debates, centered on acid rain or on the origin of eutrophication of aquatic
ecosystems, have only served to bring out the limits of our capacity to make
medium or long range forecast for xenobiotics introduced, voluntarily or not, into
nature ([I]).
It is clearly still very difficult to cross the boundary between the results obtained
from biological tests (bioassays) and scientific data from the field ([2]), and
coherent scientific methods must be applied before we can attempt to generalize
behavior, set up rejection thresholds and, a fortiori, establish estimated
ecotoxicological risks, based essentially on risk analysis (cf. EPA, 1992 and Fig.
1) .
The main difficulty is the need to predict medium and long term effects. The
procedure for estimating ecological risk must, above all, make use of recent
advances in methods for detecting and quantifying ecotoxicological effects of
xenobiotics and complex sewages.
Recent methodological progress and new measures applicable to various steps
from the laboratory to the field, permit better knowledge of toxic action sites and
better selection of endpoints and perturbation bio-indicators. Research objectives
focus on correlating these ecotoxicity results obtained at different structural and
functional levels of natural environments in order to propose coherent regulation
procedures.
Bio-tests and bio-indicators must not be considered separately but should be
integrated in a single procedure; bio-tests study the effects and action mechanisms
of contaminants in laboratory controlled conditions, while bio-indicators reveal the
effects in ecosystems and in mesocosms (these latter are comprehensive units
placed in outdoor conditions so as to recreate the "natural" functioning of a pond
or a lake, for example) ([3], [4]).
In the case of chemical stress, work published over a period of many years reveals
the increasing rarity of the most sensitive species. Functionally, perturbations are
closely linked to the trophic dynamics of the system. The disappearance of such
groups from an ecosystem means that the balance of production and decomposition of organic matter is perturbed for a very long time, and sometimes permanently, thereby affecting the evolution of all species present in the ecosystem.
Such problems encouraged recent measures for parallel follow-up of the
perturbations in the composition and functioning of the disturbed ecosystem.
Water In Ecosystems: A Non Renewable Resource
1
INTRODUCTION
The ecological catastrophes of these past years (Bopal, pollution of the Rhine at
Basel, ... ) combined with the spectacular effects of acute toxicity resulting in a high
mortality rate for fish, clearly point to the need for better knowledge of the results
and effects produced by chemical compounds in the environment.
Ecotoxicology, at the cross-roads of biological and chemical knowledge, is in full
development because compulsory requirements and increased growth of new
products go hand in hand with a concern for the protection of ecosystems. Recent
debates, centered on acid rain or on the origin of eutrophication of aquatic
ecosystems, have only served to bring out the limits of our capacity to make
medium or long range forecast for xenobiotics introduced, voluntarily or not, into
nature ([I]).
It is clearly still very difficult to cross the boundary between the results obtained
from biological tests (bioassays) and scientific data from the field ([2]), and
coherent scientific methods must be applied before we can attempt to generalize
behavior, set up rejection thresholds and, a fortiori, establish estimated
ecotoxicological risks, based essentially on risk analysis (cf. EPA, 1992 and Fig.
1) .
The main difficulty is the need to predict medium and long term effects. The
procedure for estimating ecological risk must, above all, make use of recent
advances in methods for detecting and quantifying ecotoxicological effects of
xenobiotics and complex sewages.
Recent methodological progress and new measures applicable to various steps
from the laboratory to the field, permit better knowledge of toxic action sites and
better selection of endpoints and perturbation bio-indicators. Research objectives
focus on correlating these ecotoxicity results obtained at different structural and
functional levels of natural environments in order to propose coherent regulation
procedures.
Bio-tests and bio-indicators must not be considered separately but should be
integrated in a single procedure; bio-tests study the effects and action mechanisms
of contaminants in laboratory controlled conditions, while bio-indicators reveal the
effects in ecosystems and in mesocosms (these latter are comprehensive units
placed in outdoor conditions so as to recreate the "natural" functioning of a pond
or a lake, for example) ([3], [4]).
In the case of chemical stress, work published over a period of many years reveals
the increasing rarity of the most sensitive species. Functionally, perturbations are
closely linked to the trophic dynamics of the system. The disappearance of such
groups from an ecosystem means that the balance of production and decomposition of organic matter is perturbed for a very long time, and sometimes permanently, thereby affecting the evolution of all species present in the ecosystem.
Such problems encouraged recent measures for parallel follow-up of the
perturbations in the composition and functioning of the disturbed ecosystem.