Toxicity of iodine, iodide, and iodate to Daphnia magna and rainbow trout (Oncorhynchus mykiss)

Abstract

The acute toxicity (96-h LC₅₀) of aqueous stable iodine species (I⁻, IO ⁻₃ , I₂) to rainbow trout and Daphnia magna were measured at three individual concentrations of hardness, total organic carbon, and chloride. Rainbow trout were most sensitive to I₂ (LC₅₀⩾0.53 mg/L), and much less sensitive to IO ⁻₃ (LC₅₀⩾220 mg/L) or I⁻ (LC₅₀⩾860 mg/L). Daphnia magna were equally sensitive to I₂ (LC₅₀⩾0.16 mg/L) and I⁻ (LC₅₀⩾0.17 mg/L), but were less sensitive to IO ⁻₃ (LC₅₀⩾10.3 mg/L). The external and internal radiological dose imparted by equivalent molar quantities of radioactive ¹²⁵I, ¹²⁹I, and ¹³¹I were calculated for both the Daphnia and trout using the LC₅₀ values obtained from a standard water treatment. As expected, the dose from ¹²⁵I and ¹³¹I would exceed the expected lethal dose rate long before a chemically toxic level is reached. In contrast, a molar concentration of ¹²⁹I likely to cause death by chemical toxicity would impart a radiological dose less than that expected to be lethal. Thus, for short-lived aquatic organisms, risks due to chemical toxicity of ¹²⁹I may exceed risks due to its radioactive emissions.