Chlorine dioxide

Toxicity to other above-ground organisms

Description of key information

Chlorine dioxide reacts rapidly in aqueous solution degrading to chlorite and chlorate as dominant species under environmental conditions. In the absence of oxidisable substances, and in the presence of pH > 9, chlorine dioxide dissolves in water and decomposes with the slow  formation of chlorite and chlorate ions.

Additional information

According to the TNsG on Data Requirements for Active Substances and Biocidal Products, and REACH Guidance, further tests may be required if there is still a concern for the terrestrial compartment.

The direct exposure of the terrestrial compartment to chlorine dioxide is highly unlikely.

Three routes or release to the soil compartment are possible: via deposition of manure, via deposition of aerosols from cooling towers, or via deposition of sewage sludge.

As described in the data waiver for anaerobic degradation, the active substance, chlorine dioxide is highly reactive and it will readily react with organic matter and microorganisms present in manure, in aerosols and sewage sludge, and will be reduced to chloride via the transient intermediate chlorite.

The ESD for disinfection of animal houses assumes that up to six disinfection treatments are performed during a year, with the manure itself being stored for a total of one year prior to use. On this basis there will be sufficient contact time between the chlorine dioxide and the manure to ensure that complete degradation to chloride ion occurs. Hence there will be no release to soil via manure.

With regards to exposure via sewage sludge, the vast quantity of organic matter and metal ions dissolved in the aqueous phase in the STP would ensure the complete conversion of chlorine dioxide to chloride via the transient intermediate chlorite. Hence there will be no release to soil via sewage sludge. Chlorite in aerosols deposited in soil would also be expected to degrade to chloride on contact with soil. Further studies on terrestrial non target organisms are therefore scientifically unjustified.

Besides, according to the TNsG on Data Requirements for Active Substances and Biocidal Products, and REACH Guidance, for some product types, direct and/or indirect exposure for mammals is possible and some tests with mammals may be required in rare cases on the basis of concern for severe risk for the terrestrial environment. There will be no direct or indirect exposure to mammals. Therefore, an acute oral toxicity test in mammals is not required.

Chlorine dioxide react easily and rapidly generating chlorite and chlorate as dominant species. In the absence of oxidisable substances, and in the presence of pH > 9, chlorine dioxide dissolves in water and decomposes with the slow formation of chlorite and chlorate ions.

No key study was found in Chlorite for above-ground organisms. However, five key studies valid were found in Sodium chlorate for Typhlodromus pyri Scheuten (Kelly 2004, according to IOBC method), worker honey bees Apis mellifera L. (Wilkins 2003, according to EPPO Bulletin, OECD Guideline 213 and 214), Aleochara bilineata Gyllenhal (Kelly 2005, according to IOBC method), Chrysoperia carnea and Aphidius rhopalosiphi De Stefani-Perez (Kelly 2003, according to IOBC method).

Sodium chlorate studies demonstrated a LR50 based on mortality at 84.4 kg/ha, greater than 250.95 kg/ha and greater than 250.60 kg/ha of sodium chlorate (the three studies of Kelly for Typhlodromus pyri Scheuten, Chrysoperia carnea and Aphidius rhopalosiphi De Stefani-Perez, respectively). Besides, the study of Wilkins (2003) revealed a NOEC (48h) and a LD50 (48h) >= 116 µg/bee of sodium chlorate for the acute contact toxicity test and >= 75 µg/bee of sodium chlorate for the acute oral toxicity test. Finally, the study of Kelly (2005) shows a NOEC based on mortality at 250 kg/ha for sodium chlorate.