Potassium iodide

Endpoint summary

Additional information

The 96 hours acute toxicity test to Rainbow Trout (Laverock, M.J., M. Stephenson, and C.R. MacDonald, 1995) was conducted according to Protocol to determine the acute lethality of liquid effluents to fish, which was established by Ontario Ministry of the Environment. The results showed that the 96 hour LC50 is over 860 mg/l.

The acute toxicity to daphnia of potassium iodide was determined (Laboratoire d'Ecotoxicologie Parc technologique ALATA, 1996) according to method of “French standard”, which was similar to OECD test guideline 202. After 48 hours exposure period, the EC50 of immobilization was measured. The result of 48 hrs- EC50 was 7.5 mg/l.

The acute toxicity to daphnia of sodium iodide was determined (INERIS Parc Technologique ALATA, 2012) according to OECD test guideline 202 following GLP procedure to give a result of 48hrs-EC50 as 1.27 mg/L (95%CL, 1.19 -1.38 mg/L), which supports the result of KI but seems more toxic than NaI.

As the first study (Laboratoire d'Ecotoxicologie Parc technologique ALATA, 1996) is a standard test for potassium iodide, and fulfilled validation criteria. The 48 hrs- EC50 of 7.5 mg/l is taken as the key value.

One study of acute toxicity of iodide to algae was published in well known journal “water research” (Bringmann, G., and R. Kuhn, 1980). However, it was not a standard test and without declaration of GLP compliance, and in the test the 7 days cell multiplication inhibition test was applied to the model organism, Scenedesmus quadricauda(green algae) for iodide, which fulfilled basically scientific principles. The results showed the toxicity threshold (≥3% inhibition of the biomass of green algae) of iodide to green algae is 2370 mg/l.

One of long term toxicity test to fish (Eales, J.G., D.G. Cyr, and R.F. Cook, 1986) was performed to investigate the effects of iodide to thyroid (T3 and T4 concentration level). Because the test only focused on the effects to thyroid, but other tissues and organs were ignored, the test result is recognized as reliable with restrictions. In the test, it concluded that no Wolff-Chaikoff effect, characteristic of mammals, was observed but plasma L- thyroxine (T4) levels increased after a single iodide injection (1 mol/l).

There is no long-term toxicity test on aquatic toxicity, but testing for this endpoint is not considered to be necessary as the CSR does not indicate a risk to aquatic organisms when considering the environmental partitioning that would result from point source exposure.  Iodine is a natural ubiquitously present essential trace element. It is highly mobile and cycles through all environmental compartments via a range of mechanisms including disproportionation to different oxidation states by abiotic and biotic mechanisms coupled with binding to organic matrices and biological organisms. These act to significantly mediate the aquatic toxicity when compared to laboratory conditions, which are not indicative of actual exposure should the substance be released.

This opinion is further confirmed by the use of theECOSAR™ v.1.00 programme operated by theU.S.  Environmental Protection Agency. Potassium iodide is listed within the definitive database of this system, and is utilised to provide an indication of potential toxicity in the wider environment. The results of this assessment are as follows:

Organism	Duration	End Point	Result (mg/l)
Fish	96-hr	LC50	6736.780
Fish	14-d	LC50	6600.207
Daphnid	48-hr	LC50	2844.798
Green Algae	96-hr	EC50	577.397
Fish	30-day	CHV	615.632
Daphnid	-	CHV	241.908
Green Algae	-	CHV	159.232
Fish (SW)	-	CHV	10867.097
Mysid Shrimp	96-hr	LC50	27123.457
Fish (SW)	-	CHV	318.739
Mysid Shrimp (SW)	-	CHV	4186.333
Earthworm	14-day	LC50	460.463

It is acknowledged that the ECOSAR™ v.1.00 programme does not provide optimal results for inorganic substances; however as the substance is listed within the database, it is considered appropriate to utilise the results of the assessment in support of the statement that the substance is not toxic to environmental organisms. The results of the assessment clearly demonstrate no toxicity. As stated above, significant environmental partitioning upon any release to the environment results in potential exposure to the component ions only, which exist naturally within the environment. As such, toxicity is not predicted within the environmental compartments due to dilution and partitioning effects; such effects are not mimicked in laboratory experiments, leading to results that are not indicative of actual toxicity.

Based on above information the most sensitive species can be determined to be daphnia, and the 48 hrs - EC50: 7.5 mg/l is taken as key vale in the hazard classification and chemical safety assessment.