2-tert-butylphenol

Biodegradation in water: screening tests

Description of key information

It was determined the test substance is inherently biodegradable under test conditions.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

Reliable studies on the biodegradation of o-tert-butylphenol are available and included in this dossier. In addition, reliable studies on the biodegradation of the structural analogue, o-sec-butylphenol are available and included in this dossier.

The biodegradation of o-tert-butylphenol was assessed in a "DOC die-away test" according to OECD guideline 301A conducted by Schoberl (1994). However the study had the following methodological shortcomings:

- No adsorption control was conducted

- No toxicity control was included

- Frequency of sampling was insufficient for proper identification of the 10-d-window

- pH was not measured, thus could not be corrected if necessary

A measured volume of mineral medium, containing a known concentration of the test substance was inoculated with effluent from a sewage treatment plant receiving predominantly domestic sewage. The carbon content in the inoculum is negligible. The test duration was 28 days. The removal of organic carbon was measured by DOC analysis (IR). Removal of test substance (mean values) was determined to be 16, 64, 99, 100, and 98 % after 7, 14, 21, 27, and 28 days, which indicates that o-tert-butylphenol may be readily biodegradable. However, in view of the observed deficiencies and inability to determine if 10 -day window criterion was met, it would be conservative to deem the substance as inherently biodegradable.

A reliable (Klimisch 2) biodegradation study was performed by Safepharm (1990) for o-tert-butyphenol following OECD 302C methods using activated sludge. The test substance attained negligible degradation within 28 days as determined by oxygen consumption. Although following the guidance, the substance is considered not inherently biodegradable, it is postulated that the high test concentration (30 mg/L) may have inhibited adequate degradation.

Desmares-Koopmans (2009) conducted a reliable (Klimisch 1) GLP compliant study where the biodegradation of o-sec-butylphenol was assessed in a biodegradation test performed according to OECD guideline 301D, closed bottle test. Degradation was assessed at two test concentrations; 1.5 mg/L and 3 mg/L and test duration was 28 days. Biodegradation measured, based on oxygen measurements showed an average of 63% degradation for both concentrations at the end of 28 days. Degradation exceeded 60% within the 10 day window. The toxicity control showed that o-sec-butylphenol did not inhibit microbal activity. Study results indicate the test substance is readily biodegradable, passing the 10 day window.

CITI (1998) conducted a reliable (Klimisch 2) GLP compliant study according to OECD 301C (Modified MITI Test) methods.

The biodegradation test duration for o-sec-butylphenol, the structural analogue, was 28 days. No degradation, by measurement of BOD, of test substance occurred under test conditions in 28 days. Although following the guidance, the substance is considered not inherently biodegradable, it is postulated that the high test concentration (100 mg/L) inhibited adequate degradation.

Following OECD guideline 301B, two more biodegradation studies are available. The GLP study performed by Flach (2013) showed no significant biodegradation based on ThCO2D after 28 days. In the other 301B GLP-study (Desmares-Koopmans,2013), these findings were reproduced for two different concentrations of o-tert.-butylphenol (5 mg TOC/L and 10 mg TOC/L). Both studies are considered valid, although in the latter, less than 25 % biodegradation occured in the toxicity control at 5 mg TOC/L.

A further inherent biodegradation study according to OECD guideline 302B was performed in 2014 (Ute Hammesfahr, IBACON). Under the test conditions the mean percentage biodegradation reached by o.-tert.-butylphenol was 100 % after 28 days of incubation based on DOC elimination. As the final biodegradation is above 70% in this test and all validity criteria were met, o.-tert.-butylphenol can be considered to be potentially biodegradable. But there remains uncertainty whether the final DOC-elimination was partly due to adsorption, although no significant DOC decline was observed during the first 3 hours.

These observations are supported by another OECD 302 B study with a combined test setup, measuring DOC removal as well as CO2 evolution. This study was conducted in 2014 (Felicitas Flach, Hydrotox) and showed a biodegradation of 96.0% based on DOC removal after 28 days. Whereas the CO2 measurement revealed 8.9% biodegradation of o-tert.-butylphenol after 28 days indicating the adsorption of the test substance to the inoculum. Furthermore, the test item had a slight inhibitory effect on the inoculum.

 

Reliable studies on the biodegradation of o-tert-butylphenol are available and included in this dossier. Additionally, reliable studies on the biodegradation of the analogue, o-sec-butylphenol are available and included in the dossier. Although the studies included in the dossier appear to have contradictory results, the lack of degradation seen in the inherent biodegradable test may have been due to the high test concentrations. It is evident from the available studies that both the test substance and the analogue biodegrade. Therefore, it is conservative and consistent with other alkylphenol results, that the test substance, o-tert-butylphenol, be considered inherently biodegradable.