Registration Dossier
Registration Dossier
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EC number: 443-870-0 | CAS number: 163520-33-0
Biodegradation in water: screening tests
Administrative data
Link to relevant study record(s)
- Endpoint:
- biodegradation in water: ready biodegradability
- Data waiving:
- study scientifically not necessary / other information available
- Justification for data waiving:
- other:
Reference
Description of key information
A screening study on biodegradation is not considered to be necessary since higher-tier simulation studies in water/sediment systems as well as in soil are available.
Key value for chemical safety assessment
Additional information
According to the structure and the low solubility in water, the substance is not expected to fulfill the stringent criteria of a ready biodegradation test. However, abiotic degradation via hydrolysis is a relevant pathway for the degradation of the target compound isoxadifen-ethyl (DT50: 2.3 d at 25 °C, pH 7) (OECD 111, EPA Guideline Subdivision N 161-1). Studies have been conducted investigating the transformation of the target compound in different sediment/water systems under aerobic and anaerobic conditions. Under environmental conditions the target substance will degrade with half-lives less than 4 days (DT50 values in sediment/water systems: 0.4 days, and 3.2 days at 12 °C) (US EPA Subdivision N Pesticide Guideline 162-3 and 162-4). Under anaerobic conditions the degradation of the target compound was also fast with a DT50 value of 1.3 days at 12 °C. Three metabolites of the target compound were identified and the degradation of these metabolites was investigated as well. Overall, the metabolites also showed a degradation under aerobic conditions and the formation of CO2 was considerable, thus the metabolites were mineralized. Under anaerobic conditions the mineralization for the metabolites was negligible. But when converting the metabolites to aerobic conditions after 120 days a mineralization to CO2 was determined. There are studies available that demonstrate the same pattern of the target compound and its metabolites for the degradation in soil (US EPA Pesticide Assessment Guidelines, Subdivision N, 162-1, and Society of Environmental Toxicology and Chemistry (SETAC - Europe) Procedures for addressing the environmental fate and ecotoxicology of pesticides; Annex II, Point 7.1.1.1). DT50 values in different soils (4 EU soils and 1 US soil) for the target compound were 0.8 – 2.4 days at 12 °C under aerobic conditions, and 0.042 days under anaerobic conditions. Based on these results, a persistence of the target compound in the aquatic and terrestrial environment is not expected. Hence, an additional readily biodegradation test according to OECD 301 is not reasonable.
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