Modelling the fate of industrial organic chemicals in the aquatic environment - A review
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.