Chemicals exposure: scoring procedure and uncertainty propagation in scenario selection for risk analysis.

The present work aims to obtain a methodology to score dangerous chemical pollutants related to the exposure scenarios of human risk and to evaluate the uncertainty of the scoring procedure. For chronic human risk evaluation, the problem of characterizing the most dangerous situation is posed. In this paper a ranking procedure was assessed in order to score eight pollutants through a "scoring model" approach. The scoring system was organized in a matrix form in order to put in evidence the strong connection between properties of the substances and exposure scenarios. Two different modelling approaches were considered as cause-effect relationships for risk evaluation: Risk Based Corrective Action (RBCA) and a "mobility and degradation matrix". The first takes into account the exposure pathways (soil, water and air) and the exposure routes (inhalation, ingestion and dermal contact), while the second considers the capacity of the chemicals to move into the environment and the rate of degradation associated with chemical-biological processes as measure of persistence. A specific score for each chemical along its uncertainty were evaluated. The uncertainty of the scoring procedure was evaluated by using the law of propagation of uncertainty; it was used to estimate the global uncertainty related to each exposure pathway for the eight substances for both models. Results of scoring as well uncertainty put in evidence that the ordering of chemicals is strongly dependent on the model used and on the available data. The procedure is simple and easy to use and its implementation allows users to compare several and several compounds.