Phenol, 4-nonyl-, branched

Endpoint summary

Additional information

Stability of Nonylphenol in the environment

Nonylphenol released to the atmosphere is likely to be degraded by photo-oxidation with a half-life of approximately 5 hours (EPISuite v3.12 (U.S. Environmental Protection Agency (US EPA); see Melcer (2007)).

In laboratory experiments (Ahel (1994)) it could be demonstrated that the photochemical transformation of nonylphenol in surface waters is also a significant route of abiotic degradation. 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 are further validated by studies by Martinez-Zapata (2013) and Dulov (2013) which indicate significant potential for indirect photodegradation of nonylphenol in surface waters.

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

Hydrolysis is not likely to be a dominant route of abiotic degradation for nonylphenol, because of the chemical structure and particularly the lack of susceptible functional groups.

Biodegradation of Nonylphenol

From tests on ready biodegradability that were conducted according to the OECD 301B (Gledhill (1999), Staples (2001)) and OECD 301F (Staples (1999), Stasinakis (2008)), nonylphenol was found to be inherently biodegradable and in some cases met the threshold for ready biodegradability but did not meet the 10-day window. Together these data indicate that nonylphenol, at least, is inherently biodegradable. In view of the stringent conditions employed in screening tests on ready biodegradability, nonylphenol cannot be considered persistent. Biodegradation is an important removal process of nonylphenol in surface water and treatment plants.

Based on reliable experimental data (Ekelund (1993), Chang (2004), Ying (2003), Yuan (2004), Bradley, De Weert (2009), Johnson (2000)), Lu et al (2014), Toyama (2011), Wang et al (2014), in river bed sediments, marine sediments, and surface waters, nonylphenol is biodegradable under most oxic conditions but is likely to be persistent under anoxic conditions and will accumulate in anoxic sediments. Some evidence suggests a potential for nonylphenol to be persistent in oxic conditions, particularly when data is normalised for temperature.

Furthermore, experimental data (Junghanns (2005), Corti (1995), Gabriel (2005, 2008)) confirm nonylphenol also undergoes biodegradation in soil systems and would be rapidly dissipated in well-aerated soils following application of sewage sludge.

To conclude nonylphenol is not expected to be persistent in the environment as a whole, however it is likely to biodegrade more slowly under lower temperature and anoxic conditions, such as may be found in some buried sediments.

Bioaccumulation of Nonylphenol

A weight of evidence (WoE) approach has been taken to the determination of the potential for nonylphenol to bioaccumulate in aquatic organisms and is described in a separate technical report in Section 13 of the CSA.

For the purposes of the risk assessment, the BCF from the Ekelund et al (1990) study with the fish Gasterosteus aculeatus is used. Based on whole body tissue wet weight the BCF is 1200 for Test 1 and 1300 for Test 2. The results have been lipid normalised based on the lipid values provided in the report, with calculated BCFs of 833 to 896. The highest value of 896 and most conservative value is used in the risk assessment. Results of this study show the BCF of valid fish bioconcentration studies are lower than the REACH bioaccumulation criterion of < 2,000.

No experimental data for the bioaccumulation in terrestrial organisms are available. A BCF value for the earthworm was calculated using measured Log K_OWdata, resulting in an estimated BCF of 3015.

Transport and distribution of Nonylphenol

Nonylphenol has a low water solubility (6 mg/l at 20 °C) and available data (EU RAR (2002) and Staples (2008), including a Henry Law Constant: 11.02 Pa m³/mol) indicate that volatilization of nonylphenol is likely to be a low to medium removal process from water.

The Key study for the adsorption endpoint is the highly reliable study by Milinovic et al (2015) using five field-collected soils reported the Kd (Log Kd) for nonylphenol ranged from 24 to 1,059 ml g^-1(1.4 to 3.0) and a Koc value of 11,060, with a strong relationship indicated between the soil organic carbon and adsorption. Desorption experiments showed nonylphenol was irreversibly sorbed onto the soils, demonstrating the significant potential for adsorption of nonylphenol to soils. An array of different approaches have been considered to determine the predicted adsorption of nonylphenol to sludge within WWTP. This has included experimentally derived Koc and Kd values, modelled Koc and Kd values, and the application of those values into two different modelling approaches - SimpleTreat and based on equations detailed in the OECD 106 guidelines. All results indicate that nonylphenol will be strongly adsorbed to sewage and sewage treatment plant solids similarly to the absorption onto soil and sediment in the environment.  

Nonylphenol tends to adsorb strongly onto organic matter. 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 nonylphenol. Adsorption to sewage sludge enables removal of nonylphenol prior to entering aquatic environments.