Exposure assessment is a critical component of the study. We define the study population as people living up to 3.5 km far from the plants. This choice is based on previous studies [8,10] and information by model simulations on the profile of the distribution of pollutant emitted by plants. In fact, this choice provided a good contrast of exposure conditions and a better comparability of the contrasted population groups. We geo-coded all the residential addresses and exposure was assessed using the results of a model of dispersion of pollutants into the atmosphere. A French study has validated Gaussian dispersion model for dioxins from an incinerator with a campaign of measurements on the ground in 75 sampling points [33]. The results confirmed the validity of the model in defining the different gradients of exposure, and identified inconsistencies between measured levels and those estimated by the model only in the presence of complex topographical situations (e.g. hills), a condition that does not apply to the Po Valley. A recent British study compared the use of distance as a proxy of exposure from a source of pollution by means of estimates derived from dispersion models and concluded that the use of the models significantly reduces the risk of misclassification embedded in the use of the distance from a point source