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Environmental fate & pathways

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Melcer et al. (2007) conducted a literature review with regard to physical-chemical properties and environmental fate characteristics of alkylphenols and alkylphenol ethoxylates. The authors found that Nonylphenol released to the atmosphere is likely to be degraded by photo-oxidation with a half-life of approximately 5 hours. This result was calculated by using EPISuite v3.12 (U.S. Environmental Protection Agency (US EPA). (2000a) EPISuite. Estimation Program Interface (EPI) Suite Version 3.12. Washington, DC).

Ahel et al. (1994) found that the photochemical transformation of Nonylphenol in surface waters is also a significant route of abiotic degradation. From the experiments, which were conducted according to general accepted scientific standards, 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.

Additional laboratory experiments by using a merry-go-round reactor (MGRR) have shown that the photochemical degradation of nonylphenol was due mainly to sensitized photolysis whilst direct photolysis was comparatively slow. Although sunlight photolysis rates of nonylphenol were found to be much slower than reported for some other alkylphenols (Faust and Hoigné, 1987, cited in Ahel et al., 1994), the results suggest that a significant portion (30 %) of these compounds could be photochemically degraded in the surface layer of natural waters within one day. Studies by Martinez-Zapata et al (2013) and Dulov et al (2013) considering indirect photochemical transformation of 4-n-nonylphenol, demonstrated a range of sensitizers that increased the photodegradation rate, including humic acids, Fe (III) and H2O2. pH was also demonstrated to affect phototransformation of nonylphenol. A first order reaction kinetics was adjusted to describe the photodegradation of 4n- nonylphenol with a half-life of 2.3 hours. 

Hydrolysis is not assumed to be a dominant route of abiotic degradation for Nonylphenol, because of the chemical structure and particularly the lack of susceptible functional groups. This assumption is also supported by the EU Risk Assessment Report 2002 (p.54) which states that hydrolysis is a negligible removal processes for nonylphenol in the aquatic environment. This assumption is based upon the stability of nonylphenol during storage and several biodegradation studies reviewed by the UK rapporteur on behalf of the European Union where no degradation was observed in the control experiments. The authors of these studies concluded that abiotic degradation was likely to be negligible (Corti et al., 1995; Trocmé et al., 1988; both cited in the EU Risk Assessment Report 2002).

These findings indicate that photo-oxidation and photochemical transformation, in contrary to hydrolysis, can be important removal processes for nonylphenol released to water and air, whereas hydrolysis is not.