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.