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Stability of 4-tert-Octylphenol in the environment:

Octylphenol (OP) released to the atmosphere is likely to be degraded by photo-oxidation, with a half-life of approximately 6 hours, based on calculations using EPISuite v3.12 (U.S. Environmental Protection Agency (US EPA)).

Photochemical transformation of OP in surface waters is also a significant route of abiotic degradation. From experiments (Ahel et al., 1994), a half-life of 10-15 hours could be deduced for continuous clear sky, noon, summer sunlight conditions in the surface layer of natural waters. The photolysis rate in the deeper layers is strongly attenuated, being approximately 1.5 times slower at depths of 20-25 cm than at the surface.

These findings indicate that photo-oxidation and photochemical transformation can be important removal processes for OP released to water and air.

Hydrolysis is unlikely to be a dominant route of abiotic degradation for OP, because of the chemical structure and particularly the lack of susceptible functional groups.


Biodegradation of 4-tert-Octylphenol:

Available reliable experimental data for tests on ready biodegradability of 4-tert-Octylphenol (CAS: 140-66-9; 4-(1,1,3,3-tetramethylbutyl)phenol; PTOP) conducted by Sewell (1991), Gledhill (1998), and Staples (2001), as well as on Octylphenol (CAS: 27193-28-8; (1,1,3,3-tetramethylbutyl)phenol; OP) conducted by Scholz (1991), showed contradictory results. Taking into account methodological differences with regard to microbial inoculums and test substance purity, it can be concluded that Octylphenol can be regarded as inherently biodegradable. With regard to the stringent conditions employed in screening tests, Octylphenol cannot be considered persistent.

Reliable simulation tests for 4-tert-Octylphenol (PTOP) are available for river water and sediments (Johnson et al., 2000), as well as for marine water and sediments (Ying & Kookana, 2003). From these studies it can be concluded that PTOP 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 PTOP is likely to be persistent and may accumulate in anoxic sediments.

As no PTOP data for biodegradation in soil is available, read-across from Nonylphenol (NP) data was used, based on the structural similarity, similar physio-chemical data and similar biodegradation of both substances in screening tests for ready biodegradability and simulation tests in water and sediments. The available data indicate that NP undergoes biodegradation in soil systems. NP degradation in soils is dependent on soil temperature and soil moisture conditions (Topp et al., 2000) as well as on oxygen conditions. The overall conclusion from the data is that NP is biodegradable in soils and would be rapidly dissipated in well-aerated soils following application of sewage sludge. For Octylphenol it can be concluded that this substance is likely to be biodegradable in soils with rapid degradation in well-aerated soils.

Available data shows that biodegradation is an important process for removal of 4-tert-Octylphenol from environmental compartments under oxic conditions. PTOP is not expected to be persistent in the environment.


Bioaccumulation of 4-tert-Octylphenol:

A reliable bioconcentration study for octylphenol (OP presented a BCF value of 261, based on whole body wet weight, for Oryzias latipes (Tsuda et al., 2001).

Bioconcentration for nonylphenol was also considered for octylphenol using read-across to support this finding.

The BCF value for nonylphenol (Brooke, 1993b) recommended for use in risk assessment is 740. A BCF of 740 for fish would also be a conservative value for OP bioconcentration in the risk assessment, with reference to the relatively higher Kow and experimentally derived BCF for nonylphenol compared to octylphenol.

No experimental data for the bioaccumulation of OP in terrestrial species is available; the BCF for earthworms is calculated using measured LogKow data.The calculated BCF of 758, therefore, is recommended for OP bioconcentration in this risk assessment.

With reference to experimental data for octylphenol, read-across from the available reliable experimental data for nonylphenol and the calculated BCF for earthworms, it is concluded that OP can bioaccumulate in aquatic species and has a low tendency to accumulate in terrestrial organisms. 

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)), a substance does not fulfil the criteria “bioaccumulative (B)” or “very bioaccumulative (vB)” if the bioconcentration factor (BCF) is below 2000 or 5000, respectively, or the log Kow is below 4.5.

With reference to experimental data for octylphenol, read-across from the available reliable experimental data for nonylphenol and the calculated BCF for earthworms, it is concluded that OP is not bioaccumulative within the PBT criteria.


Transport and distribution of 4-tert-Octylphenol:

Koc values of between 3500 and 18000 l/kg determined in laboratory experiments show that octylphenol (OP) tends to adsorb strongly to organic matter. Therefore, adsorption is likely to play an important role as a sequestration process in soil, sediment, and sewage sludge. Adsorption to solids such as sediments and sewage sludge is likely an important removal process for OP.

The available data suggest that volatilization of OP is likely to be a removal process from water which is of low to medium importance (HLC of 0.52 Pa m³/mol at 298 K).


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