Salinization is an ongoing global threat, which is exacerbated by population growth and climate change. Rising temperatures that increase evaporation rates and road salt use (due to milder winters), as well as increasing urbanization and associated wastewaters, agricultural practices, and resource extraction activities (e.g., mountaintop mining, fracking, oil sands and shale gas extraction) are all contributing to salinization in freshwaters, marine systems and soils. Osmotic stress due to increases in ion concentrations, or changes to ion balance, can be a significant source of toxicity and can have adverse impacts on the toxicity of other chemicals within contaminant mixtures. With the considerable advancement of major ion toxicity research in the last decade, it is becoming more evident that this topic is important to the broader SETAC community, not only due to the direct risk to aquatic organism health, but also the potential for irreversible impairment on the structure and function of marine, freshwater and soil ecosystems.