4-(1,1,3,3-tetramethylbutyl)phenol

Endpoint summary

Additional information

Available data shows that biodegradation is the main process influencing the environmental fate of 4-tert-octylphenol (CAS: 140-66-9; 4-(1,1,3,3-tetramethylbutyl)phenol; PTOP) and Octylphenol (CAS: 27193-28-8; (1,1,3,3-tetramethylbutyl)phenol; OP).

 

Tests on ready biodegradability conducted according to OECD 302C (Modified MITI Test (II)) and BOD-Test for Insoluble Substances with PTOP, and a test conducted according to OECD 301B (CO₂Evolution Test) with OP showed contradicting results:

- In the Modified MITI Test (II) no biodegradation was observed within 28 days for PTOP.

- The BODIS Test results show inherent biodegradability of PTOP

- In the experiment according to OECD 301B Octylphenol was classified as readily biodegradable, but failing the 10-day window.

The results of the Modified MITI Test (II) are not used for categorization of the persistence of 4-tert-Octylphenol due to the distinctive and unnatural inoculum used in OECD 302C tests.

For the overall evaluation of these test results it is important to note that discrepancies are often noted between results of OECD 301C or 302C (typically used by MITI) and other ready biodegradability tests like OECD 301B. These inconsistencies are due to differences in the microbial inoculum used in these studies.

The inconsistency between the result of the BODIS test and the result of the test conducted according to OECD 301B may be due differences in the purity of both test substances, microbial inoculum and initial test substance concentration in the BODIS Test and the OECD 301B study with 27.5 mg/l and 12.6 mg/l, respectively.

In summary, the data show that Octylphenol can be regarded as inherently biodegradable, and in one case meets the criteria for ready biodegradability except for the 10-day window. With regard to the stringent conditions employed in screening tests, Octylphenol cannot be considered persistent.

In a laboratory experiment conducted by Tanghe et al. (2000), the aerobic biodegradation of branched octylphenol and the formation of degradation products formed by a Sphingomomas sp. strain isolated from activated sludge with and without the addition of an easily assimilable carbon source (sodium acetate) were determined. Octylphenol was degraded to 94.5 % and 99 % with and without the addition of sodium acetate, respectively. In both cases the formation of the metabolite 2,4,4-trimethyl-2-pentanol, representing the intact alkyl chain as a tertiary alcohol, was observed.The formation of 2,2,4-trimethyl-2-pentanol as the most prominent intermediate detected in the Sphingomonas sp. culture in all test series implies that the alkyl side chain may remain intact as a tertiary alcohol after fission of the aromatic ring of the parent compound (octylphenol).

 

 

Simulation test for 4-tert-Octylphenol (PTOP) are available for river water and sediments, as well as for marine water and sediments. The results indicate that PTOP is biodegradable in water and sediments under aerobic conditions. Half-lives were 8 to 50 days and 60 days for freshwater and saltwater, respectively. In river bed sediments and marine sediments, no biodegradation was observed under anaerobic conditions. Under aerobic conditions in marine sediment, the half-life was determined to be > 20 days.

From these two studies it can be concluded that 4-tert-Octylphenol can be aerobically degraded in freshwater, marine water, and marine sediments. No degradation was observed in freshwater bed sediments and marine sediments under anaerobic conditions. Therefore, it can be concluded that 4-tert-Octylphenol is likely to be persistent and may accumulate in anoxic sediments.

 

 

No PTOP data for biodegradation in soil are available. Therefore, read-across from Nonylphenol was used, based on the structural similarity, similar physo-chemical data and similar biodegradation of both substances in screening tests for ready biodegradability and simulation tests in water and sediments.

The available Nonylphenol data indicate that nonylphenol undergoes biodegradation in soil systems. NP degradation in soils is dependent on soil temperature and soil moisture conditions as well as on oxygen conditions. The mineralization of NP is not dependent on the initial concentration except for very high concentrations (e.g. 1000 mg/kg, Trocmé et al., 1988) which inhibit biodegradation of NP because of toxicity to micro-organisms. The overall conclusion from the nonylphenol data is that nonylphenol is biodegradable in soils and would be rapidly dissipated in well-aerated soils following application of sewage sludge. Reported half-lives for NP degradation in soil were between 4.5 and 51 d.

For Octylphenol it can be concluded that this substance is likely to be biodegradable in soils with rapid degradation in well-aerated soils.

 

It can be deduced that biodegradation is an important process for removal of 4-tert-Octylphenol from environmental compartments.

 

In the persistence assessment according to Annex XIII of Regulation (EC) No 1907/2006 and to the Guidance on information requirements and chemical safety assessment Chapter R.11 (PBT Assessment, ECHA (2008)), octylphenol is considered not persistent with reference to available screening data show that octylphenolcan be regarded as inherently biodegradable and data supporting the fact that octylphenoldoes not fulfill persistence criteria for freshwater, marine sediments, freshwater sediments as well as soil, and only very marginally meets the persistence criteria for marine waters.