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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Six studies have been allocated to this endpoint. Two studies were conducted under the OECD 301 testing guideline for ready biodegradability. The key study (Dow, 2016; Klimisch 1) was conducted using the 301F manometric respirometry method, and demonstrated that biphenyl can be classified as readily biodegradable. The results from a supporting study by the 301C modified MITI test method, taken from the Japanese biodegradation database (Japan Chemical Industry Ecology-Toxicology and Information Center, 1992; Klimisch 2), also indicate that biphenyl is readily biodegradable. The studies of Trehy et al. (1994; Klimisch 2; 5-d BOD test), Saeger (1983; Klimisch 2; modified SCAS test and Sturm test), and Mieure et al. (1976; Klimisch 4; modified SCAS test) were not conclusive on ready biodegradability but supported the results of the key study.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

In a fully valid GLP-compliant study of the biodegradability of biphenyl by the OECD 301F manometric respirometry test method (Dow, 2016; Klimisch 1), 68% consumption of theoretical oxygen demand (ThOD) was observed over 28 days, with the 60% threshold achieved within 10 days of the onset of biodegradation, showing that biphenyl is readily biodegradable.  Additionally, the results of a OECD 301C modified MITI test are documented in the Japanese biodegradation database (Japan Chemical Industry Ecology-Toxicology and Information Center, 1992; Klimisch 2). In this supporting study, 66% BOD was observed after a 14-d incubation period, indicating that biphenyl is readily biodegradable. Primary biodegradation was observed to be 84% and 91% using GC and UV-VIS spectroscopy, respectively. The results of the aforementioned studies were supported by other screening tests, which for several reasons, were not conclusive on ready biodegradability. The first additional supporting study was the 5-day BOD test of Trehy et al. (1994, Klimisch 2), reporting a 5-d BOD of 67.0% of the theoretical oxygen demand. Although the results of a 5-d BOD test cannot be considered conclusive, the results reported by Trehy et al. support the findings of the studies based on the OECD 301 test guideline, that biphenyl is readily biodegraded by non-acclimated microorganisms. The study of Saeger (1983, Klimisch 2) reported the results of a CO2 evolution test (Sturm test) in which pre-adapted activated sludge microorganisms were exposed to 20 mg/L biphenyl for 43 days. Ultimate degradation by 88% after 43 days, and around 69% after 28 days, was observed. Although the use of adapted inoculum precludes use of this study in determining ready biodegradability, these results also support the findings of the 301F and 301C tests. Finally, the results of the SCAS tests reported by Saeger (1983, Klimisch 2) and Mieure et al. (1976, Klimisch 4), indicated good primary biodegradability. The SCAS test conducted by Mieure et al. (1976) yielded 94 and 81% primary degradation after 35 days of exposure at initial concentrations of 3 and 13 mg/L, respectively. In the SCAS test conducted by Saeger (1983), activated sludge microorganisms were exposed to a step-wise increase of biphenyl concentrations from 1 mg/L up to 50 mg/L over 20 weeks. The results of the test indicate > 95% primary biodegradation within 24 h up to initial concentrations of 50 mg/L. The 5-d study of Freitag et al. (1982), indicating 8.5% 14CO2 evolution using non-acclimated activated sludge from a municipal waste water treatment plant, was considered not reliable and did not add further add valuable information to that obtained in the studies described above.