Antimony trioxide is very insoluble in water; therefore, the toxicity to fish and other aquatic organisms is very low. The acute and chronic toxicity to aquatic life is above the level of the dissolution potential under “worst case” environmental conditions. Antimony trioxide does not require labelling with R phrases that indicate toxicity to the aquatic environment. The IAOIA is currently sponsoring the collection of similar data in sediment-dwelling organisms and in terrestrial worms to fully determine the safety of antimony trioxide in these matrices as well.