Synopsis Since time immemorial man has been subjecting the earth to an increasing variety of pollutants in the form of chemical substances and others. The emission of pollutants into the environment is a complex phenomenon which can't be limited to the fixed image of waste pipe spilling out its effluents into a lake or river. Almost all discharged substances are going to be carried a long way from their sources. Atmospheric and hydrologic circulation system disperses them progressively throughout the bio-sphere. Pollutants affect living system in many ways. Acute and/or long term actions are the obvious eco-toxicological impacts of a given pollutant. Its demo ecological effects at population levels are displayed through immediate or premature death, reduced productive success, reduced growth and/or increased loss at the Juvenile stage. These are ultimately reflected in the lower abundance and perturbed distribution of the exposed populations of sensitive species. The effect of the sub-lethal concentrations of some pollutants is by far the most frequent eco-toxicological problem and it can be far more noxious in the long run for the exposed species resulting in chronic deterioration of the ecosystem.