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Toxicity to terrestrial plants

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Reference
Endpoint:
toxicity to terrestrial plants: long-term
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 acute toxicity test in plants 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 acute toxicity test in plants is unjustified on the basis of no exposure.

Description of key information

Key value for chemical safety assessment

Additional information

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 acute toxicity test in plants is unjustified on the basis of no exposure.


One supporting study (Carillo, 1996) with terrestrial plants is available.The aim of this study was to reveal whether water treated with Halox E-100 (buffered preparation of chlorine dioxide) has any adverse effects on plant growth. This was conducted by evaluating the effect of irrigating a plant species susceptible to chlorine toxicity (radish) with diluted Halox E-100.Chlorine dioxide only slightly decreased plant dry weight. At the end of the experiments, the plants appeared unaffected by the treatments. Other common plant parameters were unaffected or even enhanced. Halox did not reduce the total level of soil bacteria, even after four consecutive applications at any dilution rate. In nonsterile soil, high Halox dilution (1:1000) significantly decreased plant dry weight and the other concentrations (1:10000, 1:50000 and 1:100000) had no apparent effect on the size of the plants. In sterile soil, high concentrations of Halox (1:1000 and 1:10000) significantly decreased plant growth, but higher dilutions produced no significant reduction in plant weight. For radish plants growing in organic matter-free sand only, dilution of 1:10000 reduced plant growth. High levels of Halox (1:1000) were toxic to radish seedlings growing in sand and resulted in chlorosis and significant depression of plant growth. Further dilutions of Halox (equivalent to the level used in water disinfection) significantly decreased toxicity for the radish. Low concentrations of Halox (1:50000) had no apparent effect on the appearance of the plant. This study suggests that chlorine dioxide-treated drinking water can be considered safe for growing plants.

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