Évaluation d’indices de comparaison pour la substitution des solvants en milieu de travail

Substitution is a primary preventive method which allows the elimination of hazards to workers at the source. One of the steps in substitution analysis is the comparison between options in order to choose the best alternative. Various comparison indices based on physicochemical, health and environmental parameters of substances may facilitate the choice. However, no evaluation of theses indices has been done in the case of solvent substitution. Development research was undertaken in order to propose an improved methodology for solvent substitution.  A systematic procedure of solvent substitution was applied to a real workplace case and the comparison between options was made using the Vapour Hazard Ratio (VHR). Three Overexposure Potential Indices (OPIs) (VHR, « Måleteknisk Arbejdshygiejnisk Luftbehov » (MAL) and SUBstitution FACtor (SUBFAC)) and three comprehensive hazard screening indices (air index (ψiair), Indiana Relative Chemical Hazard Score (IRCHS) and Final Hazard Score (FHS)) were evaluated and compared using a list of 56 and 67 solvents respectively. In the case of mixtures, the effect of nonideality on OPIs was also investigated by comparing 50 solvent mixtures. Quantitative property-property relationship (QPPR) models were developed for estimating Occupational Exposure Limits (OELs) for solvents without OELs. QPPR models were made from octanol:air, blood:air and metabolic constants using a list of 88 solvents.  The case study showed that the use of the VHR made comparison of replacement options easier, although it was limited by the absence of an OEL for a solvent. VHR and SUBFAC were shown to be close with excellent correlation between the two indices (R=0.99) but a worse correlation was calculated between MAL and VHR (R=0.75). This was attributed to the discrete nature of the volatility parameter in MAL. The impact of nonideality, evaluated by the calculation of activity coefficients on 50 solvent mixtures, resulted in ratios between corrected and non corrected VHRs varying between 0.57 and 2.7, suggesting that a safety factor of five could be used when comparing solvent mixtures. Correlation and sensitivity analysis showed that hazard screening indices differed in the way they integrate key substitution factors such as volatility, OEL, skin exposure, flammability, carcinogenicity and various environmental parameters. No index was found to be suitable for performing solvent substitution. Two QPPR modeling approaches were developed for computing OELs and VHRs; and 61 % and 87 % of the predicted VHRs were within a factor of two and five, respectively, of the calculated VHRs.  Our results lead us to propose an improved comparison procedure using a two-tier approach. In the first tier, a selection would eliminate solvent candidates having crucial health, safety and environmental impacts. In the second tier, the comparison would emphasize the VHR but also consider other parameters which are relevant to the specific context. Comparison would also take into account nonideality for mixtures and predicted OELs for solvents without such values.

Keyphrases: Substitution, VHR, QPPR, Solvents, Comparison indices, Mixtures, Occupational hgiene