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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Five relevant and reliable (with restrictions) studies were allocated to this endpoint: three sediment/water simulation tests and two simulation tests in surface water only.  Based on the studies of Bailey et al. (1980, 1983), the half-life of biphenyl in water can be set to 3 days at 20°C. Based on the sediment/water simulation tests of Saeger et al. (1988a,b), the half-life of biphenyl in sediment can be set to 10 days at 22°C. These half-lives were the longest half-lives observed in the respective studies, and represent a reasonable worst-case approach. According to the study of Saeger et al. (1988c), anaerobic biodegradation can be considered of limited importance for the elimination of biphenyl from aquatic systems.
A single study, Pruell & Quinn (1985) reported a half-life for biphenyl of 333 days is a mesocosm study of highly contaminated sediment and is considered to be unreliable (Klimisch 3) for the determination of the biphenyl half-life. The study failed to provide appropriate controls, standard experimental measurments, and failed to provide adequately scientific evidence for speculative results.

Key value for chemical safety assessment

Half-life in freshwater:
3 d
at the temperature of:
20 °C
Half-life in freshwater sediment:
10 d
at the temperature of:
22 °C

Additional information

The studies of Bailey et al. (1980, 1983) report the results of a river die-away study conducted according to the same principles as described in OECD guideline 309. In these tests, performed in a closed system and using microorganisms present in natural river water, biphenyl was observed to be eliminated with half-lives of around 2 days depending on the initial concentration (1, 10 or 100 µg/L). Based on measurements of trapped 14CO2, it can be concluded that biphenyl is rapidly biodegradable, i.e., > 70% biphenyl is ultimately biodegraded in 28 days. The highest half-life reported in these studies (i.e., 3 days at 20°C) can be used as key value for biodegradation in water in the chemical safety assessment.

In the study by Saeger et al. (1988a), biodegradation of biphenyl was examined during 10 days in a natural river water/sediment system with naturally present microorganisms. Analysis of trapped 14CO2 indicates ultimate biodegradation of 38.5% in the high dose treatment (1 mg/L) and 42.4% in the low dose treatment (0.077 mg/L). Although the exposure duration is relatively short, the results are in agreement with the results of longer simulation tests which indicate rapid biodegradability of biphenyl (Bailey et al., 1980, 1983). Moreover, the half-life for biphenyl was determined to be 2-3 days, which also agrees with results for primary degradation of biphenyl in other simulation tests (Bailey et al., 1980, 1983). In the second study (Saeger et al., 1988b) biodegradation of biphenyl was examined during 10 days in a natural lake water/sediment system with naturally present microorganisms. Analysis of trapped 14CO2 indicates ultimate biodegradation of 17.7% in the high dose treatment (1 mg/L, high variability) and 37.8% in the low dose treatment (0.077 mg/L). The results obtained in the low dose treatments are quite similar to those obtained with low dose ecocores from the Illinois River (42.4% in 10 days, Saeger et al., 1988a). The half-life of biphenyl was estimated to be 6-10 days in the lake water/sediment system, which is longer than the estimated half-life of 2-3 days observed for ecocores from the Illinois River (Saeger et al., 1988b). This may be due to the fact that the lake was more pristine and that the microorganisms in the lake are most likely less frequently exposed to low concentrations of a variety of chemicals. The exposure duration of this study was only 10 days, which is relatively short compared to typical durations of at least 28 days. However, the results are in good agreement with those from longer simulation tests which indicate rapid biodegradability of biphenyl (Bailey et al., 1980, 1983). The results of these tests can be used in a weight of evidence approach. For refinement of exposure calculations, one may consider using the highest half-life reported in these studies (i.e., 10 days at 22°C) as key value for biodegradation in sediment.

In the third study (Saeger et al., 1988c) anaerobic biodegradation of biphenyl was examined during 12 weeks in a water/sediment system obtained from a sewage lagoon. Analysis of trapped 14CO2 and 14CH4 indicated no significant biodegradation of biphenyl via methanogenic or denitrifying processes. Positive controls dosed with glucose however indicated the presence of an active microbial community. The absence of anaerobic biodegradation of biphenyl may have been partly due to the presence of other organic substrates in the highly organic sediment (17.3% OC). However, taking into account its good aerobic biodegradability, anaerobic biodegradation is not expected to play an important role in the elimination of biphenyl from natural sediment/water systems.

Pruell & Quinn (1985) reported a half-life for biphenyl of 333 days is a mesocosm study of highly contaminated sediment and is considered to be unreliable (Klimisch 3) for the determination of the biphenyl half-life. The study experimental design lacked basic controls, water quality measurements including dissolved oxygen and temperature, did not determine if microbial inhibtion was occurring from the presence of other more prevelant substances in the highly contaminated sediment, and did not account for additional imputs of contaminants from sea water renewals or contaminant movement within the sediments.