Bis(2-butoxyethyl) 2-Hydroxyethyl-d4 Phosphate Triester is a labeled form of Bis(2-butoxyethyl) 2-Hydroxyethyl Phosphate Triester (B415190), which is a metabolite of Tris(2-butyloxyethyl)phosphate (T875030), an organophosphate, that is used in the preparation of flame retardant, such as viscose fiber.