Today, it is estimated that there is more than 100' 000 chemicals which are used regularly in industry and which are potential contaminants and pollutants of the total ecosystem (Maugh, 1978). The toxic chemical substances are rejected into the environment in two manners:
-directly, when they are used directly by humans. It is the case of pesticides, fertilizers and various solvents.
-but these substances can also be rejected indirectly in the form of industrial waste, coming from various activities like mining extraction, industrial production, incineration, consumption of fuels or accidental rejections
With particularly regard to pesticides, it is in the Forties that the first syntheses of these substances appeared on the market, with very positive results on the increase in the agricultural outputs. Twenty years later, appeared the first charges of attack to human health and the environment (Carson, 1962).All chemical substances are thus more or less toxic. The dangers that a given chemical presents for health depends on the toxicity and the exposure.
Definition: The term "ecotoxicology" was introduced by Truhaut in 1969 and was derived from the words "ecology" and "toxicology". Up to that point, the environmental studies of toxicology related mainly to the harmful effects of the poisons on man. Ecotoxicology thus takes into account the effects of chemicals in the context of ecology.
Definition: ecotoxic: substances and preparations which present or can present an immediate or differed risks for one or more components in the environment
How can we evaluate toxocity and ecological risks?
The current strategies of evaluation of the risks are as follows:
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Evaluation of the potential toxicity of chemical, while based on its physicochemical properties and its similarities with known poisons
- Studies of the follow-up of the pollutant: the concentrations of the pollutant in water, the substrate, and of the selected biotopes are given, in order to evaluate wide contamination and exposure. This type of studies is relatively delicate, long and expensive.
These two strategies present the following disadvantages: they do not give any indication on the toxicity and the biodisponibility of the pollutant on organisms. Other approaches were thus developed:
- Ecological evaluation of the effect: this strategy consists of using various ecological parameters (for example diversity of species, the presence or absence of indicator organisms) to evaluate the impact of the pollutant on varied ecosystems.
- Evaluation of the real toxicity under controlled conditions in laboratory, with a limit in the number and the variety of the organisms, by tests of toxicity.
These last two points concern ecotoxicology.
