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EC number: 202-163-5
CAS number: 92-52-4
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.
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
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.
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