Chlorine dioxide

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

adult fish: sub(lethal) effects

Data waiving:

exposure considerations

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING:
According to the TNsG on Data Requirements for Active Substances and Biocidal Products, and REACH Guidance, a study on the reproduction and growth rate of fish may be required. Although chlorine dioxide is very acutely toxic to fish, its 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 degrades rapidly to chlorite and chlorate ions. CHLORITE As chlorite may be expected to be discharged from cooling towers and slimicide uses, a chronic fish test on chlorite may be considered important to determine the long term effects on these animals. However, acute tests on fish, invertebrates and algae, have shown that fish are the least sensitive species to chlorite with LC50s more than a factor of 10 higher than the EC50s for algae or daphnids. According to the TGD, if invertebrates and algae are considerably more sensitive than fish in acute studies, taking into account the principals of animal welfare, chronic studies on fish are not considered necessary. CHLORATE A long-term study on fish already exists for this substance.

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).  

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.