Biphenyl-4,4'-diol

Endpoint summary

Description of key information

- No hydrolysable groups are within the structure of the test substance.

- An CO2 Evolution Test (OECD 301B) demonstrated the readily biodegradability of the test substance

Additional information

Biphenyl-4,4'-diol has no hydrolysable groups within its structure and is therefore considered not to be prone to hydrolysis.

Physico-chemical processes are expected to make a negligible contribution to the dissipation of biphenyl-4,4'-diol in the environment.

The ready biodegradability of biphenyl-4,4'-diol was determined with a non-adapted inoculum according to the CO2 Evolution Test (OECD 301B). The test item concentration was deliberately lowered below the range indicated in the guideline because the test item was considered capable of inhibiting the activity of the microbial inoculum and hence limiting the outcome of the test. The study was performed in two stages: an initial, non-GLP preliminary test was first used to establish the viability of the test conditions before conducting the main, fully GLP-compliant definitive test. Extensive biodegradation of biphenyl-4,4'-diol (with CO2 production >60% of the theoretical yield - the threshold that conventionally represents complete mineralisation) was observed in at least one replicate test vessel of the CO2 Evolution Test in both the preliminary and definitive stages.

In both the preliminary and definitive stages, the initial test based on measurement of CO2 production was followed by a further, confirmatory test that employed different methodology based on the measurement of cumulative oxygen uptake. For this purpose, adapted sludge was harvested at the end of the incubation from one or more of the replicate test vessels of the CO2 Evolution Test incubation where >60% theoretical CO2 production had occurred and was used to inoculate a confirmatory assessment performed according to the Manometric Respirometry Test (OECD 301F), with a higher concentration of the test item. In each case, complete biodegradation occurred in all replicates of the respirometric test based on oxygen uptake, confirming the outcome of the earlier phase that relied on CO2 yield measurements.

Biphenyl-4,4'-diol degraded erratically in the presence of unadapted microorganisms in the CO2 Evolution Tests of both the preliminary and definitive test stages. Degradation was sufficient in some replicates to indicate complete mineralisation and meet the 'pass' level for classification as readily biodegradable, but not in others. The length of the lag phase between test initiation and the onset of significant degradation was highly variable and in some replicates of the definitive test the rapid degradation phase was not observed at all despite extending the incubation to 60 days. In view of its erratic performance in relation to the pass criteria and the divergence permitted between replicates at test-end or plateau, biphenyl-4,4'-diol does not qualify for classification as readily biodegradable. Nevertheless, biphenyl-4,4'-diol has exhibited a potential to undergo rapid and ultimate biodegradation (i.e. complete mineralisation) and this finding in the CO2 Evolution Test was confirmed by further tests performed according to the Manometric Respirometry Test, using an inoculum pre-adapted in the earlier testing phase.

Based on these findings it may be concluded that biphenyl-4,4'-diol is non-persistent (not P).

As biphenyl-4,4'-diol does not qualify for classification as readily biodegradable, it is classified as "inherently biodegradable, not fulfilling specific criteria" (no specific inherent biodegradability tests have been performed) for the purposes of predicting concentrations of biphenyl-4,4'-diol that may enter the aquatic compartment via municipal STP.

The consistently high level of degradation achieved with an adapted inoculum is relevant to situations where waste-waters and process effluents containing biphenyl-4,4'-diol are likely to pass through dedicated industrial STPs before reaching the aquatic environment.

Biphenyl-4,4'-diol is classified as "rapidly biodegradable" for CLP purposes.