Petroleum substances are a prototypical example of UVCBs (Unknown or Variable composition, Complex reaction products and Biological materials), which present challenges for science-informed toxicity regulatory decision making. Although UVCBs are identified on global chemical inventories with unique Chemical Abstract Services (CAS) numbers and names, evaluating their toxicity remains challenging due to the chemical complexity and multi-constituent nature with largely unknown and variable composition. Therefore, regulators and industry have a common interest to define a process for (petroleum) UVCBs to ensure that there is no underestimation of hazards while minimizing or eliminating the use of animals in toxicology testing.

All petroleum products were registered in the European Union for the 2010 submission deadline under REACH (≥1000 tons registration band), comprising more than 8000 individual registrations. A number of these submissions were accompanied by testing proposals to fill data gaps in specific toxicity endpoints. To minimize the need for testing in vertebrate animals, the majority of data gaps were addressed using read-across to similar substances for which the required data were available.

Read-across of petroleum substances within the REACH framework is typically done by grouping the individual substances into product categories with similar manufacturing processes and phys/chem- properties (including refining history and boiling point/carbon number ranges/hydrocarbon class). However, category read-across approaches for (petroleum) UVCBs that are based solely on such broad similarity parameters are not always be considered sufficient.

The Cat-App project initiated and funded by Concawe tackles this specific challenge by investigating practical strategies for grouping and read-across approaches for UVCBs with the aim of providing a cost-effective integrative approach to solving the similarity challenges of UVCBs using biological activity instead of a phys./chem. approach. The project will integrate innovations in (i) in vitro testing, (ii) high-throughput genomics and (iii) integrative data analyses and visualisation into a workflow for biologically based read-across assessment of UVCBs in regulatory programmes.