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Toxicity to soil microorganisms

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Reference
Endpoint:
toxicity to soil microorganisms
Data waiving:
exposure considerations
Justification for data waiving:
the study does not need to be conducted because direct and indirect exposure of the soil compartment is unlikely
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, an inhibition to microbial activity study might be required. Two routes of entry to the soil compartment are possible: via deposition of manure 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 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 exposure 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 exposure to soil via sewage sludge. Therefore, an inhibition to microbial activity study is unjustified on the basis of no exposure.

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.

Key value for chemical safety assessment

Additional information

According to the TNsG on Data Requirements for Active Substances and Biocidal Products, and REACH Guidance, an inhibition to microbial activity study might be required. Three routes of entry to the soil compartment are possible: via deposition of manure, via deposition from aerosols emitted 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 will readily react with organic matter and microorganisms present in manure, in sewage sludge or in soil, 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 exposure 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 exposure to soil via sewage sludge. Chlorite in aerosols deposited in soil would also be expected to degrade to chloride on contact with soil. Therefore, an inhibition to microbial activity study is unjustified on the basis of no exposure.

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 valid was found in chlorite for soil microorganisms but one key study valid was found in Sodium chlorate for evaluated toxicity to soil microorganisms (Servajean 2004, according to OECD Guideline 216 and 217), however no endpoints were specified.

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