p-(1,1-dimethylpropyl)phenol

Biodegradation in water: screening tests

Description of key information

 A reliable study by Haener (1999) showed that p-tert.-amylphenol degraded 73% at 28 days, although did not pass the 10-day window.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

Reliable measured biodegradation studies for p-tert-amylphenol are available and included in the dossier. A supporting measured biodegradation study for the analogue, p-tert-butylphenol, is also available.

A reliable study (Klimisch 1) by Haener (1999), following OECD 301B guidelines, showed that p-tert.-amylphenol is not deemed readily biodegradable in water, as the study did not pass the 10-day window. The biodegradability of p-tert.-amylphenol exposed to microorganisms derived from the activated sludge of a municipal sewage treatment plant was investigated under aerobic static exposure conditions. The biodegradability, based on CO2 evolution, of p-tert.-amylphenol was calculated to be 73% of the theoretical value after an incubation time of 28 days. Biodegradation had reached 52% at the end of the 10-day window and, although the pass level of 60% was not reached within the 10-day window, significant biodegradation occurred by the end of the test. As per REACH Guidance Ch R.7.b, ready biodegradability tests can be used to prove inherent biodegradability when the pass level criterion is almost fulfilled (i.e., slightly below 60% degradation). Therefore the substance is not considered readily biodegradable, but can be considered inherently biodegradable.

Mathews and Schaefer (2013) conducted a reliable (Klimisch 1) GLP compliant study following OECD 301B Guidelines. The biodegradability of the analogue, p-tert.-butylphenol, exposed to microorganisms derived from the activated sludge of a municipal sewage treatment plant was investigated under aerobic static exposure conditions. The study was conducted at two concentrations; 5 and 10 mg/L test substance. The biodegradability, based on CO2 evolution, of p-tert.-butylphenol was calculated to be 59% for the 5 mg/L concentration and 64% for the 10 mg/L concentration after an incubation time of 28 days. Although biodegradation was measured, neither concentration reached the pass level of 60% degradation within the 10-day window. Therefore, the study concludes that the test substance is not readily biodegradable as it failed the 10-day window. As per REACH Guidance Ch R.7.b, ready biodegradability tests can be used to prove inherent biodegradability when the pass level criterion is almost fulfilled (i.e., slightly below 60% degradation). Since degradation of 59% and 64% occurred during the study, the test substance can be deemed inherently biodegradable.

Safepharm (1992a) conducted an (Klimisch 2) inherent biodegradation study with p-tert-amylphenol following OECD 302C (MITI) methods. Activated sludge microorganisms were exposed to the test substance under aerobic conditions. The oxygen consumption (% chemical oxygen demand and ThOD) was monitored in a test system inoculated with 100 mg/L of mixed population of activated sludge and 30 mg/L of p-tert-amylphenol for 28 days. Aniline was used as a reference substance at an initial concentration of 100 mg/L. No biodegradation was observed with p-tert-amylphenol within 28 days, likely due to an inhibitory concentration of p-tert-amylphenol (30 mg/L) combined with a long lag-phase. Additionally, p-tert-amylphenol can be used as an anti-microbial agent further complicating interpretation of test results. Aniline attained 87% degradation within 28 days, confirming the viability of the inoculum used. The results of this study suggest that p-tert-amylphenol cannot be considered as inherently biodegradable, under the strict terms and conditions of the OECD Guidelines.

Reliable measured biodegradation studies for p-tert-amylphenol and the analogue, p-tert-butylphenol are available and included in the dossier. A reliable study by Haener (1999) showed that p-tert-amylphenol degraded 73% at the end of the 28 day test, although did not pass the 10-day window. A reliable study by Mathews and Schaefer (2013) showed that p-tert.-butylphenol degraded 59% and 64%, in two different test condentrations, at 28 days, although did not pass the 10-day window.As per REACH Guidance Ch R.7.b, ready biodegradability tests can be used to prove inherent biodegradability when the pass level criterion is almost fulfilled (i.e., slightly below 60% degradation). Since degradation of 73% (Haener 1999) and 59% and 64% (Mathews and Schaefer 2013) occurred during the study, the test substance can be deemed inherently biodegradable. The key and supporting study results indicate that the test substance biodegrades rapidly once microbes have had a chance to acclimate. All effluents related to the use of p-tert-amylphenol will be through industrial WWTP as the substance is used as an intermediate. Any release to wastewater treatment plant or soil from residual p-tert-amylphenol in resin is negligible.