Environmental hazard and risk characterisation of petroleum substances: a guided "walking tour" of petroleum hydrocarbons.

Petroleum substances are used in large quantities, primarily as fuels. They are complex mixtures whose major constituents are hydrocarbons derived from crude oil by distillation and fractionation. Determining the complete molecular composition of petroleum and its refined products is not feasible with current analytical techniques because of the huge number of molecular components. This complex nature of petroleum products, with their varied number of constituents, all of them exhibiting different fate and effect characteristics, merits a dedicated hazard and risk assessment approach. From a regulatory perspective they pose a great challenge in a number of REACH processes, in particular in the context of dossier and substance evaluation but also for priority setting activities. In order to facilitate the performance of hazard and risk assessment for petroleum substances the European oil company association, CONCAWE, has developed the PETROTOX and PETRORISK spreadsheet models. Since the exact composition of many petroleum products is not known, an underlying assumption of the PETROTOX and PETRORISK tools is that the behaviour and fate of a total petroleum substance can be simulated based on the physical-chemical properties of representative structures mapped to hydrocarbon blocks (HBs) and on the relative share of each HB in the total mass of the product. To assess how differing chemical compositions affect the simulated chemical fate and toxicity of hydrocarbon mixtures, a series of model simulations were run using an artificial petroleum substance, containing 386 (PETROTOX) or 160 (PETRORISK) HBs belonging to different chemical classes and molecular weight ranges, but with equal mass assigned to each of them. To this artificial petroleum substance a guided series of subsequent modifications in mass allocation to a delineated number of HBs belonging to different chemical classes and carbon ranges was performed, in what we perceived as a guided "walking tour" through the chemical space of petroleum substances. We show that the PETROTOX and PETRORISK predictions reflect changes in mass distribution introduced to selected HBs by affecting hazard and risk estimates in correspondence with what is expected based on physical-chemical properties of individual constituents in the corresponding HBs.