Many substances fall under the category of “difficult to test substances” either due to their physicochemical properties (e.g. surfactant, low water solubility, because they are ionised across the environmentally relevant pH range) and/or because they are multi-constituent or UVCB (substances of unknown, variable or complex composition, or of biological origin). There is increasing requirement for testing of difficult substances either because waivers from testing under REACH have not been accepted or existing tests have not adequately accounted for a substance’s properties. Although there is guidance for testing of difficult substances (OECD GD 23), all substances are unique and approaches that work for one type of chemical may not work for another.

At wca, we specialise in testing of “difficult to test substances” and interpretation of study outcomes. Our REACH experience includes registering UVCB substances which pose particular challenges especially regarding endocrine disruption (ED), in vitro, ecotoxicity and PBT testing, because it can be unclear whether the effects of all relevant constituents are accounted for. Strategies for evaluating the effects UVCBs may incorporate both whole substance and individual constituent approaches. We also have specialists in testing of metals and ionisable pharmaceuticals including interpretation of effects based on bioavailability.

We recognise the importance of ensuring that available tests meet regulatory standards (e.g. maximising the amount of chemical in solution, minimising solvent use) and therefore we work with a network of testing laboratory partners and can provide recommendations for the best solution for testing of your substance. We also provide technical support and study monitoring for the testing.

Example projects:

• Reviewing best approaches for testing of surfactants
• Testing of pharmaceuticals at an environmentally relevant stable pH maximising the amount of substance in its neutral (most bioavailable) form
• Developing an approach for ED assessment of UVCB substances
• Developing a testing strategy for deriving environmental quality standards for a radioactive metal