# Numerical estimates

The term analysis and estimate of risk indicates different methodologies which are applied in an ample variety of disciplines of human activity, such as the estimate of the risk of accidents which could potentially occur in the course of an industrial  manufacturing activity or the forecast of natural disastrous phenomena. The element these different risk calculating methodologies have in common is that they are based on mathematical models to which we ask to forecast the future: for instance if and when the polluting leachate formed at the bottom of a landfill will reach the drinking water wells, 200 m downstream in two years.

But given that anticipating the future is not possible, the numerical values of the risk obtained by these modelling exercises are always accompanied by a high incertitude. But we must underline also an element of reality, even though all estimates are affected by uncertainty, the order of magnitude of the numerical value of the risk gives a consistent and clear expression, verifiable as time goes by, of the fact that a specific damaging event could or not take place within a given time. These information can thus be used to design the solutions to the problems that it is anticipated will be associated with a specific risk.

Thus, the numerical value of a specific risk is the results of a process of modelling and calculating; it is based on what is known of the toxicity of each substance and on the direct measurement of its concentration in the different environmental media. The analysis of the risk of exposure of human(residents, workers …), and ecological receptors, to hazardous chemicals present in the environment is thus a formal process by which the potential occurrence and consequences of a hazard are evaluated in a quantitative fashion.

To quantify if a given contamination source will release a substance that will reach selected targets, it is necessary to begin by defining and quantifying three elements:

SOURCE –> MIGRATION PATHS –> TARGETS

After having located sources, pathways and targets, the formulation of a CONCEPTUAL MODEL is the tool by which the amounts of a substance migrating from the source to the targets are expressed.

The methodology is scientific and it produces a result – the value of the DOSE OF EXPOSURE and the resulting HEALTH RISK – reproducible and verifiable on the basis of the hypothesis formulated in the description of the problem. This numerical value can be ‘falsified’ (that is being found correct or wrong) by the monitoring in time of what happens.

This methodology can be used to quantify the risk posed by an existing contamination, or to estimate the risks posed by plants that are planned but not built yet or by the production and commercialisation of hazardous substances (as required by the REACH Directive).

Essential documentation describing the complete procedure for the assessment of exposure to hazardous chemicals is available at: