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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

In a ready biodegradation test according to OECD TG 310 >= 60% ultimate biodegradation based on CO2 evolution was determined, but the criterion of reaching the cut-off limit for ready biodegradability within 10 days was not met. But the degradation kinetics represented by CO2 evolution clearly supports ready biodegradability under environmental conditions.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

Biodegradation of (1-methylethyl)-1,1'-biphenyl was examined in three tests, only one of them is considered to be valid, suitable for assessment: Ready biodegradability was tested in a recent fully valid study according to OECD TG 310 OECD [CO2 in Sealed Vessels (Headspace Test)] (Fiebig/NOACK 2013) and in a non-verifiable modified MITI (I) test according to OECD TG 301 C (Handley/Safepharm 1994).

The third test was carried out not following a test guideline (Mendoza/DOW 1981), but the method used was similar to a closed bottle test, however using an initial test concentration of about 0.2 mg/L close to its maximum water solubility, however too low for this test method.

In the OECD 310 study of Fiebig/NOACK, 67% ultimate biodegradation (CO2 evolution) was determined during a 43 day test period. Within 28 days, about 60 % biodegradation was observed with a time window of 18-20 days. In this study, isopropylbiphenyl proved to degrade rapidly but the strict criteria for ready biodegradation were just missed, while primary degradation based on GC analysis was almost complete after 6 days (97 %).

In the study of Handley/Safepharm 1994, only 1% ultimate biodegradation (O2 consumption) was observed. Primary consumption of test material was determined to be 67% averaged over the three replicates. Due to its low water solubility (ca. 0.5 mg/L), the test substance was dissolved only to a slight extent (initial test substance concentration 100 mg/L). Test material was floating in globules on the surface of the test media until termination of the test.

In the study of Mendoza/Dow 1981, test substance concentrations were quite low (0.184 mg/L) falling within the range of water solubility of the substance. In this test, biodegradation of ca. 70% based on O2 consumption was apparently obtained within 10 days. But the sensitivity of the test has to be questioned.

Isopropylbiphenyl is considered to be a difficult to test substance in biodegradability tests due to its low water solubility. Depending on test conditions, more or less biodegradation will be observed. Test conditions of the modified MITI (I) test are unfavourable for isopropylbiphenyl biodegradation. This test will be disregarded. The results of the OECD 310 study are considered to be characteristic of the inherent properties of isopropylbiphenyl. On this basis, isopropylbiphenyl is graded as readily biodegradable but failing the 10-day window.