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Environmental fate & pathways

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Biodegradation

Several biodegradation tests were performed under various conditions as well as following or according to standard methods.

 

Water - screening tests

Aerobic degradation was investigated in waste water, freshwater, seawater and anaerobic degradation was investigated with inoculum created from activated sludge.

Following concentrations were applied:

waste water, activated sludge - MITI I test: 100 mg/L

fresh water - BOD test: 3 - 10 mg/L

salt water - BOD test: 3 - 10 mg/L

anaerobic degradation - 1 - 5 mM

In all aerobic tests degradation rates > 70 % was achieved within in short period (< 10 d). In the anaerobic test 100 % biodegradation was achieved up to a concentration of 4 mM.

Out of the available tests only two standardised tests for ready biodegradability are available. In these MITI-I-tests, levels of degradation amounting to between 60 and 70 % (after 4 days) and to 85 % (after 14 days) were determined (Urano & Kato, 1986; MITI, 1992). With these results phenol can be classified as readily biodegradable. The results from the other available tests also points toward ready biodegradability. However, on account of the ubiquitous occurrence of phenol, adaptation is to be assumed in the case of all of the inocula. Since this also applies to WWTPs, a degradation rate constant of k = 1 h-1can be used for them.

Due to the high degradation rates within a period of < 10 days phenol is ready biodegradable in waste water, freshwater, sea water, and at anaerobic conditions with inoculum created from activated sludge.

Degradation by adapted microorganisms

In various degradation studies employing adapted microbial inocula (e.g. activated sludge from industrial wwtp) removal rates in the range of 98.5-100 % were demonstrated (BUA, 1997).

  

Water - simulation tests

In estuarine water samples the half-lives for the mineralisation of phenol were 7 days (k = 0.095/d) in summer and 73 days (k = 0.01/d) in winter, in the presence of sunlight. The authors could show however, that biodegradation was the primary removal process for phenol in both winter and summer. Calculating the arithmetic mean of the rate constants of 0.095/dand 0.01/d result in an average rate constant of 0.05/d, equivalent to a DT50 of 14 days. This value is in good agreement with the default rate constant of 0.047/d (DT50 15 days) proposed in the TGD for readily biodegradable substances.

Sediment

Simulation testing on degradation in sediment need not be conducted since the substance is readily biodegradable and direct and indirect exposure of sediment is unlikely.

However, as in the EU RAR (2006) in Section 3.1.2.1.1. the calculation of kbio sediment according to TGD using an experimental value for kbio soil of 0.1/d (DT50 soil 7 d) result in a rate constant for sediment of 0.01/d, equivalent to a DT50 of 69 days.

Biodegradation of phenol in sediment under anaerobic conditions was shown by several authors (supporting study of Horowitz et al., 1982). However, a longer adaptation phase than under aerobic conditions and therefore a slower degradation of phenol was found.

Soil

A rate constant for biodegradation of phenol in soils of ksoil = 0.1/d can be derived. from the available investigation of Haider et al. (1981) which corresponds to a DT50 of 7 days.