A key environmental concern in relation to wildfires is that they constitute a diffuse source of contamination to aquatic ecosystems. In burnt forest areas, the increase in surface runoff and associated soil losses induced by fire, promotes the mobilization of hazardous substances, such as metals and polycyclic aromatic hydrocarbons (PAHs), which are well known for their toxicity, environmental persistence and tendency to bioaccumulate. Whilst the effects of wildfires on hydrological and erosion processes have received considerable research attention, the effects of fire-related contaminants on the aquatic environment and biota, have been poorly investigated. As highly hydrophobic substances, metals and PAHs, preferentially adsorb to sediment particles, so adverse effects are more likely to occur on benthic than on pelagic species. Sediment quality assessment is, therefore, as equally important as water quality assessment when evaluating the ecological status of a fire-affected water body. However, water boards typically follow the Water Framework Directive that focuses primarily on chemicals in water. Post-fire runoff is typically a cocktail of metals and PAHs so the toxicity of complex chemical mixtures rather than of single chemical or binary mixtures, as it is common in most ecotoxicological studies, should be addressed for a realistic assessment of the risks posed by wildfires. As it is impossible to, experimentally, assess the adverse effects of all possible mixtures for all benthic species and exposure conditions, tools that can make extrapolations to untested conditions, such as models, are needed to deal with the high number of combinations of these chemicals in fire-affected water bodies. The overarching goal of the FIREMIX project is to develop an ecotoxicological model for predicting the toxicity of complex metal-PAH mixtures on benthic aquatic species, to aid water authorities in ecological risk assessment.