Phenol

Endpoint summary

Additional information

Phototransformation in air:

Phenol is relative quickly photodegraded in air by reaction with OH radicals. Half-lives of 14 h based on the experimentally determined reaction rate constant and 11 h based on the calculated reaction rate constant were calculated.

Hydrolysis:

According to Annex VIII of Regulation (EC) No 1907/2006 a hydrolysis study is not required, when a substance is readily biodegradable. In addition, hydrolysis of phenol in water is not expected due to the chemical structure of the substance.

Therefore, further studies are not required.

Phototransformation in water:

According to the EU- RAR (2006) on phenol biodegradation is the dominant elimination process of phenol in the hydrosphere. The reaction with hydroxyl radicals plays a subordinate role in the hydrosphere.

Photodegradation in soil:

No information about photodegradation in soil is given in the EU-RAR (2006). As for the water compartment biodegradation is regarded as the dominant elimination process of phenol in soil. The reaction with hydroxyl radicals plays a subordinate role in the hydrosphere and soil.

Biodegradation

Several biodegradation tests were performed under the varied 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. In all aerobic tests degradation rates > 70 % were 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/dresult 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. thecalculation of k_{bio sediment}according to TGD using an experimental value for k_{bio 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.

Bioaccumulation

Ten reports on bioaccumulation of phenol in 6 fish species are available. Nine studies are based on measured values, however, only 5 studies are regarded reliable. One study calculated the BCF using an equation derived from studies with 30 chemicals and Pimephales promelas (Veith et al. 1979). This equation is also given in the Technical Guidance Document. Only the study of Butte et al. (1985) was conducted according to OECD guideline 305E under flow-through conditions using Danio rerio. The BCF was calculated from kinetic parameters (accumulation-/clearance phase). The BCF for total fish was calculated to be 17.5. The depuration half-life (DT50) was calculated to be 0.83 hours and the DT90 was 2.75 hours.

As a conclusion from the available test results it can be stated that phenol has only a low bioaccumulation potential. This is also supported by the log Kow of 1.47. According to the equation of Veith et al. (1979) given in the TGD a BCFfish of 3.5 can be calculated from this value. For the further assessment the BCF of 17.5 found by Butte et al. (1985) is used.

 Two reliable studies on bioaccumulation of phenol in green algae are also available with BCF values between 1.08 and 6.55 (max. BCF based on dry weight) confirming the low bioaccumulation potential of phenol.

 

Regarding bioaccumulation in terrestrial environment, no reliable studies are available. Due to the low log Pow and the insignificant bioaacumulation potential in aquatic species, an experimental study does not seem justified.

Transport and distribution

Adsorption/desorption

The soil sorption coefficient (Koc values) for phenol was measured in four different soils. The soils cover a big variability with respect to sand (4% to 73%), silt (22% to 76%), clay (7% to 23%), organic carbon (1.6% to 3.7%), and pH (5.2 to 7.5). The soil sorption coefficients (Koc values) for phenol which are described in this study are located within the range 14.0 L/kg to 26 L/kg. In addition to the batch equilibrium studies the Koc was determined using the HPLC-method resulting in Koc values between 38 L/kg and 73 L/kg. On the basis of the log Pow value (measured log Pow value for phenol: 1.47), in accordance with the TGD, the Koc value is calculated as 82.8 l/kg. The calculated Koc value is located within the range of the experimentally determined values and is taken into account in the further considerations.

Henry's Law constant

The Henry's law constant of phenol was calculated to be 0.022 Pa m3/mol at 20°C.

Distribution modelling

The theoretical distribution of phenol in the environment was calculated using the Mackay Level I. According the simulation the hydrosphere is the main target compartment for phenol in the environment (98.8 % in water) and only a very minor amount is distributed into the air (0.8 %).