Once the accident is finished, the responsible authorities and involved parties have to:

Ö         learn from the event with the aim to improve the prevention of accidents and the training of the emergency teams;

Ö         follow up the evolution of the damage to the environment;

Ö         restore the damage done.

The follow-up and restoration phase is a process that can last many years after the event.

It’s necessary to determine accurately the zones that have been affected and where restoration actions are needed using all available information about the accident. For example, the deposition of suspended gaseous/particulate toxic materials can take place over an important area exceeding the immediate vicinity of the site. In the case of a spill of a liquid pollutant, the leakage in the soil can take place over long time intervals depending on the soil structure.

In this context, the use of dispersion models can be very relevant in combination with in-situ measurements to obtain a good overview of the extent of the pollution in the wider area. Satellite images can in a few situations add complementary information. Remote sensing cannot detect directly the minor presence of deposited material on the ground or the leakage of liquids in the soil, but it can observe the effects of the pollution on the environment, and in particular the vegetation that is exposed to stress through soil/water and air pollution.

Analysis

The images demonstrate the methodological aspects of the implementation in case of an accident involving a liquid spill having an impact on the river and neighboring soil areas.

Ecotoxity

In eco-toxicology, the potential toxicological effects of natural or synthetic pollutants upon ecosystems are measured. Only effects that are relevant for the survival of the population are assessed: acute (mortality) and chronic (effects on reproduction and mortality) effects.

Different threshold values are defined for the concentration-effect relationship:

• NOEC (No Observed Effect Concentration): the highest test concentration of a pollutant that does not cause statistically a significant health effect.

• LOEC  (Lowest Observed Effect Concentration): the lowest test concentration of a pollutant that does cause statistically a significant health effect.

• LC50 (Lethal Concentration, 50%): the concentration of a pollutant that causes 50% effect when compared to the controls

• LC100 (Lethal Concentration, 100%): the concentration of a pollutant that causes 100 % effect.

(LC50/LC100 are expressed in mg/L when the receptor compartment is water, and mg/kg when the receptor compartment is soil.)