Résumés
Résumé
La nécessité de connaître aussi bien que possible l'impact des produits rejetés dans l'environnement a conduit à la mise au point de modèles mathématiques permettant de mieux comprendre le devenir des produits et de prédire l'exposition à laquelle pourra étre soumis l'environnement.
Le présent article fait le point des différents modèles publiés pour ce qui concerne le milieu aquatique et suggère différents critères permettant de classer les modèles suivant une complexité croissante.
Reprenant la terminologie de MACKAY (1979), 4 types de modèles sont décrits :
- modèles homogènes, équilibrés, conservatifs et stationnaires,
- modèles homogènes, non-équilibrés, non-conservatifs et stationnaires,
- modèles homogènes, non-équilibrés, non-conservatifs et non-stationnaires,
- modèles de dispersion.
Mots-clés:
- Environnement aquatique,
- modélisation,
- devenir des produits,
- revue bibliographique
Abstract
Assessing the hazard of a chemical to aquatic life is based on comparing the exposure concentration and the « no effects » concentration. The Greater the ratio between these two concentrations, called the margin of safety, the smaller the hazard to aquatic life.
For chemicals already in the environment, monitoring programs can lead to an estimate of the exposure concentrations, but for new chemicals, predictive methods are necessary. This leads to the development of mathematical models which give an estimate of the environmental concentrations front the characteristics of the environment, of the chemical and of the quantity released in the environment.
This article gives an overview of the different models which have been already published and suggests a classification based on the following criteria :
- number of compartments,
- closed or open system,
- the degradation of the chemical is or is not taken into account,
- an equilibrium has or has not been achieved between the compartments,
- the situation is or is not at steady-state.
Based on these criteria and quoting MACKAY (1979), four types of models are described :
- Homogeneous, equilibrium, conservative and steady-state models,
- Homogeneous, non-equilibrium, non-conservative and steady-state models,
- Homogeneous, non-equilibrium, non-conservative and unsteady-state models,
- Dispersion models.
A review of these models applied to artificial or natural ecosystems la presented showing the extent to which these models have beau validated.
These models are used not only to predict the exposure concentrations but they also help towards understanding the different phenomena which can affect the fate of a chemical. They allow to identify the mort important phenomena and those which have to be extensively studied. They are also useful for organizing experiments.
However and though they are more and more used, these models have still to be improved since several fundamental phenomena, such as the sediment/water exchanges, are still badly understood.
Keywords:
- Aquatic environment,
- modelling,
- fate of chemicals,
- review