Registration Dossier

Diss Factsheets

Ecotoxicological information

Long-term toxicity to fish

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Chlorine dioxide is highly toxic for acute toxicity to fish , its extremely short half-life in the environment following use  and the fact that there is no direct release of the active substance to aquatic systems, means that there is no concern for the aquatic compartment. Chlorine dioxide in aqueous solution reacts rapidly, abiotically with organic matter and oxidisable metals, generating chlorite, chlorate and ultimately chloride as dominant species. Under the conditions of use, no chlorine dioxide is expected to be found in the environment (see justification for non-submission), however the principal decomposition products, chlorite, chlorate and chloride will be. Therefore, key studies concerning these substances (except chloride) have  been included in this section where appropriate, such that their toxicity and ultimately risk can be characterised in the CSR.  

Based on the data available, the LC50 of chlorite for fish is more than 10 times higher than that of daphnia or algae. Therefore, according to the decision table, a long term fish study on chlorite is not required as part of the long term dataset in order to obtain an assessment factor of 10 for chronic data. A long term study on fish for chlorate found no effects at 500 mg/L (as sodium chlorate).  

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
500 mg/L

Additional information

While chlorine dioxide presence is not relevant in aquatic compartment (see JNS), presence of transformation products (chlorite and/or chlorate) needs to be assessed.

For chlorite, due to LC50 values far greater than 10 times higher for fish compared to other aquatic organisms, and in order to reduce studies on vertebrate animals, no long term study on fish has been carried out.

One long-term toxicity study on chlorate was found for fresh water fish (Thomas et al. 2004). The purpose of this study was to assess the toxicity of the test substance dissolved in fresh water, on the early life stages of Danio rerio, in a GLP 36-day flow-through test complying with the OECD Guideline No. 210,17 July 1992. The test criterion of toxicity used was the effects on hatching, larvae mortality, morphological abnormalities and growth of Danio rerio exposed to the test substance over the test period.

However, as all embryos hatched at the highest concentration tested of 500 mg/l as well as in the control and post-hatch mortality was less than that of the control, a statistical test was not used for this parameter and the NOEC was considered to be at or greater than the highest concentration tested. No teratogenic malformations were noted for any larvae at any concentration.

Based on results from weight and length, the Lowest Observed Effect Concentration (LOEC) cannot be calculated and the No Observed Effect Concentration (NOEC) was determined as greater than or equal to the highest concentration tested, 500 mg/L.