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Biodegradation in water: screening tests

Results on biodegradation of DIPN are ambiguous. In the study rated as key study, no ultimate biodegradation was demonstrated in a test for ready biodegradability (OECD TG 310) (LAUS 2011a). Approximately 20 - 25% primary biodegradation was observed in this test by analysing DIPN concentrations in test medium (LAUS 2011b). An inherent test (OECD 302D with adaptation) resulted in biodegradation of 37 % within 56 d.

In a MITI II test using a concentration of 30 mg/L (far above water solubility of DIPN), no biodegradation was observed (CERI 1977/CITI1992). In contrast, in an OECD 301 B ready biodegradability test, using concentrations between 0.4 mg/L and 10 mg/L, biodegradation decreased from ca. 84% for a concentration of 0.4 mg/L (result readily biodegradable) to ca. 20% for the 10 mg/L concentration (Yoshida and Kojima 1978). As this study cannot be reliably assessed and methodological deficiencies cannot be excluded, the study is not considered being reliable (RL3). DIPN is considered as not biodegradable.

 

Biodegradation in surface water, sediment and soil: simulation tests

Tests on aerobic mineralisation in surface water according to OECD 309 were performed for the isomers 1,3-DIPN and 1,4-DIPN (Eurofins, 2020), which were shown on screening test level to be less degradable. Since only a negligible amount of CO2 (0 – 0.1% AR) was formed and no metabolites occurred both isomers can be considered as stable under the OECD 309 test condition. However, based on volatility the dissipation time from water phase was very short. The determined DisT50 values were below 2 days indicating a rapid evaporation from the water phase, which means that the results of the OECD 309 studies are not sufficient for a final persistence assessment. Therefore, QSAR estimates for the degradation in the compartments sediment and soil considered additionally in a weight of evidence approach. For degradation in sediment the QSAR prediction is persistent (P) and/or very persistent (vP). For the soil compartment the QSAR prediction leads to a “borderline result” with a DT50 close to the P threshold of 120 days. Both QSARs can be considered as reliable. Based on study results and QSAR estimates, it can be assumed that bis(isopropyl)naphthalene (CAS 38640-62-9) contains persistent and/or very persistent isomers. Therefore, the isomer mixture bis(isopropyl)naphthalene (CAS 38640-62-9) needs to be assessed as potentially persistent (P) and/or very persistent (vP). No substantial new findings can be expected from further simulation tests with DIPN isomers. Therefore, further testing is not intended.

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