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Biodegradation in water and sediment: simulation tests

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Description of key information

Surface waters
A weight of evidence approach has been used to assess biodegradation of nonylphenol; the justification for this approach is detailed in the discussion section.
In summary, laboratory and field studies demonstrate that nonylphenol will biodegrade, with half-lives normalised for environmental temperature ranging from 7 to 95 days, suggesting nonylphenol is not persistent in water under the majority of environmental conditions. A variety of factors, including mixing, adsorption, abiotic processes and the presence of particular algal and fungal species have been demonstrated to be important removal processes for nonylphenol in water bodies. For example, laboratory studies showed that half-lives decreased by a factor of about two to five as compared to static systems when test vessels (flasks) were shaken (Yuan et al, 2004). Adsorption of nonylphenol to sediments is a significant route of loss of nonylphenol from the water column (Toyama et al, 2011). Half-lives of 2.3 hours at 33°C (yielding a half-life of 1 day when normalised to 12°C) were calculated for nonylphenol in freshwater from a reservoir, due to photolysis. Abiotic processes are likely to significantly contribute to overall degradation in the aquatic environment and the half-life considering all degradation processes is likely to be lower than that for biodegradation alone.
Sediments
In summary a range of evidence is available to support the conclusion that nonylphenol is biodegradable in oxic sediments, both marine and freshwater and therefore would not be predicted to persist. As is commonly observed with many organic substances, nonylphenol may biodegrade more slowly under low temperature and anoxic conditions. Particular environmental conditions, such as pre-exposure to nonylphenol and nitrate reducing conditions, may enhance the degradation of nonylphenol under anoxic conditions.

Key value for chemical safety assessment

Additional information

A weight of evidence approach has been used to assess biodegradation of nonylphenol. This approach has been taken because many sources of information are available on the biodegradation of nonylphenol in water and sediment; when considered as individual information sources they would be insufficient to make this assessment due to the reliability and relevance, however when considered collectively they provide an adequate assessment of the potential for biodegradation. This weight of evidence approach has relied on Klimisch score studies 2, 3 and 4, read across from similar chemicals and testing which used nonstandard testing procedures. Additionally, the available literature indicates a range of degradation rates and half-lives for nonylphenol. A weight of evidence approach allows an overview of these and application of expert judgment to determine the most likely biodegradation scenario(s) for nonylphenol in water and sediment.

Where half-life data is provided in a study report, the half-life has been normalised to account for variations in the experimental temperature. Normalisation was carried by applying the Arrhenius equation in accordance with ECHA guidance R.7b. Half-life data was normalised to 12°C for freshwater environments (sediment and water) and 9°C for marine environments (sediment and water). The published half-life data and the normalised half-lives are presented below.

Biodegradation in Marine Waters

Two reliable studies consider biodegradation of nonylphenol in marine waters. Ying & Kookana (2003) determined a half-life for 4-n-nonylphenol in oxic marine waters of 5 days at 20°C ((half-life of 12 days when normalised to 9°C), using a methodology similar to EPA OPPTS 835.3180 (sediment/water microcosm biodegradation test). A study by Ekelund et al (1993), determined that after 58 days at 11 °C, approximately half of the nonylphenol remained. Where sediment was mixed with the marine water, the degradation rate was reduced, with only 44% degradation after 58 days. The reduced degradation rate was considered to be due to a lower oxygen content (the report noted ‘very low oxygen concentrations’, indicating conditions may not be fully oxygenated). Assuming an approximate half-life of 58 days at 11°C, a half-life of 68 days is estimated when the data is normalised to 9°C. However, Staples et al., (2001) carried out an alternative analysis of the degradation data, using the Larson equation, which is a procedure for calculating an optimised half-life for surfactants (Swisher, 1987). This method modifies the traditional method by incorporating an experimental lag phase and asymptotes to calculate an optimised rate constant and pseudo first order half-lives. Using this method, half-lives of 26.3 and 5.9 days at 11 °C with and without sediment were calculated (yielding half-lives of 31 and 7 days when normalised to 9°C). Optimisation of the half-life calculates the rate constant at the growth phase when the degradation rate is at its greatest. This may be realistic of environments which are continuously exposed to nonylphenol.  Liu et al (2010) demonstrated 21% biodegradation of technical mixture nonylphenol in marine waters byNavicula incertamarinediatom cultures after 96 hours indicating a potential removal mechanism. 

Based on these results, nonylphenol may be considered biodegradable in marine waters, the extent of biodegradation is dependent upon a number of factors, such as oxygen concentration. 

Biodegradation in Freshwaters

No simulation data are available on degradation of nonylphenol in freshwater. Data for 4-(1,1,3,3-tetramethylbutyl)-phenol (or p-tert-octylphenol, PTOP) was used in a read-across approach. The rationale for performing this read-across is detailed in the attached report ‘Background information on read across of Octylphenol biodegradation in freshwater’. In brief, nonylphenol and PTOP are considered similar in terms of their structure and physico-chemical properties. Biodegradation tests (including ready biodegradability and environmental simulation studies) demonstrate relatively similar results. For example both chemicals are classified as inherently biodegradable based on biodegradation tests and the reported half-lives for marine sediments, river bed sediments are within the same range. In summary, PTOP and nonylphenol are considered to show very similar degradation behaviour and thus, read-across between the two substances is appropriate for filling the existing data gap for nonylphenol biodegradation in freshwater.

A study by Johnson et al (2000), Klimisch rating 2, investigated potential octylphenol biodegradation in a range of English rivers. The study methodology was similar to the EPA Guideline OPPTS 835.5154 and OECD 309 guidelines. The recorded half-lives ranged from 13 to 50 days. The lowest biodegradation was apparent in samples taken from an upstream river (Cragg Brook), which is likely to experience the lowest levels of adaptation by native microorganisms. Normalisation of the half-lives to account for differences between experimental and environmental temperatures, results in half-lives ranging from 15 to 95 days.  See Table 1 for all results.

A variety of other factors, including mixing, adsorption, abiotic processes, and the presence of particular algal and fungal species have been demonstrated to be important determinants in nonylphenol biodegradation in water bodies. 

·       Adsorption of nonylphenol to sediments is a significant route of loss of nonylphenol from the water column (Toyama et al, 2011). 

·       A study by Martinez Zapata et al (2013) determined a photolysis half-life for nonylphenol of 0.1 days (2.3 hours) at 33°C (1 day when normalised a temperature of 12°C) in freshwater from a reservoir resulting from photolysis. An additional study on photolysis degradation of nonylphenol is available by Dulov et al (2013) which provides additional evidence to the potential role of photolysis in nonylphenol breakdown.

·       High degradation rates have also been demonstrated by a variety of species including the yeast Candida maltose (Corti, 1995) and the aquatic fungi Clavaripsis aquatic (Junghanns, 2005) Chlorella vulgaris and other Chlorella sp. (Gao et al., 2011). For example, NP biodegradation of greater than 70% occurred within 168 hours in the presence of Chlorella sp.

 

Available evidence indicates nonylphenol is likely to be degraded by biotic and abiotic processes in the freshwater environment and that the extent of degradation observed can vary considerably. Overall, using a weight of evidence approach, nonylyphenol is not expected to be Persistent or very Persistent in the majority of freshwater environments.

 

Table 1. Study details on nonylphenol degradation in waters and sediments, including classification as not Persistent, Persistent or very Persistent, according to REACH classification. Also included are the persistence classifications for study data normalised for environmental temperatures.

Compound

(CAS Number)

Purity [%]

Test Method

Result and REACH Persistence classification

Normalised half – life for temperature1and REACH Persistence classification

Medium

Experimental 

Conditions

Reference

Pre-2010 data

4-tert-octylphenol (CAS no not provided)

97

Similar to OECD 309 and EPA OPPTS 835.3180 (Sediment / Water Microcosm Biodegradation Test)

non-GLP

Half-lives of 8, 13, 13, 23(Not P)and 50 days(P, no vP)

Half-lives of 15, 25, 25 days(Not P),44 days(P)and 95 days(vP)

Freshwater

Temperature: 20 °C

Oxygen: oxic

Johnson et al (2000)

Nonylphenol

(CAS No. not reported)

98

Similar to EPA OPPTS 835.5154 (Anoxic Biodegradability in the Subsurface)

non-GLP

Half-life:

46.2 – 69.3 d

(Not P)

Half-life:

195 – 292 days

(P and vP)

Freshwater sediment

Temperature: 30 °C

Oxygen: anoxic

Chang (2004)

Nonylphenol

(CAS No. not reported)

98

Similar to EPA OPPTS 835.3180 (Sediment / Water Microcosm Biodegradation Test)

non-GLP

Half-life:

5.1 – 99.0 d(not P)

(acceleration of degradation caused by pre-adaptation of inocula)

Half-life:

22 – 418 d(ranged from not P and P to vP)

Freshwater sediment

Temperature: 20 - 50 °C

Oxygen: oxic

 

Yuan (2004)

Nonylphenol

(4-n-nonylphenol; linear isomer)

> 99

EPA OPPTS 835.3180 (Sediment / Water Microcosm Biodegradation Test)

non-GLP

Oxic conditions:

> 90 % in 32 d;

 Anoxic conditions:

No biodegradation within 154 d

In anoxic conditions would be classed as P

Freshwater sediment

Freshwater sediment

Bradley (2008)

Nonylphenol

(CAS No. not reported)

> 94

Microcosm experiments with nonylphenol polluted river sediments;

non-GLP

> 95 % degradation

in 8 d

 

Half-life:

1.1 - 1.9 d(Not P)

Half-life:

5 - 8 d(Not P)

Freshwater sediment

Temperature: 30 °C

Oxygen: oxic

De Weert (2009)

Nonylphenol

(mixture of different branched isomers)

No data

Similar to OECD 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test);

non-GLP

Seawater:

50 % degradation in 58 d

 

Seawater + sediment:

44 % degradation in 58 d (lack of oxygen)

 

Would be classed as either not P or P

Would be classed as P

Seawater and marine sediment

Temperature: 11 °C

Oxygen: oxic

Ekelund (1993)

4-n-Nonylphenol

No data

Similar to EPA OPPTS 835.3180 (Sediment / Water Microcosm Biodegradation Test),

and similar to OECD 309 (Oxic Mineralization in Surface Water - Simulation Biodegradation Test);

non-GLP

Seawater, oxic:

Half-life = 5 d

(Not P);

 

Marine sediment, oxic:

Half-life = 5.8 d;

> 98 % degradation within 1 week(Not P)

 

Marine sediment anoxic: No degradation recorded(P or vP)

Seawater, oxic

Half-life = 12 d;

(Not P)

 

Marine sediment, oxic:

Half-life = 14 d;

> 98 % degradation within 1 week(Not P)

Seawater and marine sediment

Temperature: 20 °C

Oxygen: oxic / anoxic

Ying (2003)

Post 2010 data

4n-nonylphenol

99%

Photolysis study. Results inform the persistence criteria by providing useful information on environmental degradation

Half-life = 2.3 d(Not P)

Half-life = 12 d

(Not P)

Freshwater

Temperature: 33 °C

Oxygen: oxic

Martinez Zapata et al (2013)

Linear 4-n- nonylphenol and branched technical nonylphenol (CAS numbers not detailed)

94 and 99%

Biodegradation in already nonylphenol polluted sediments was investigated. Biodegradation was studied under methanogenic, sulphate reducing and denitrifying conditions.

Linear 4-n- nonylphenol Half-life 0.43 d(Not P),104 d(not P)and not degraded(p and vP)

 

Branched technical nonylphenol not degraded(P and vP)

Linear 4-n-nonylphenol half-life 12 d(Not P),1146 d(P and vP)and not degraded(p and vP)

 

Branched technical nonylphenol not degraded(P and vP)

Freshwater sediment

Temperature: 30 °C

Oxygen: anoxic

De Weert et al (2011)

Linear 4-n- nonylphenol

99

Microcosm exposure of sediment to 4-n- nonylphenol for 9 days with and without sediment

Half-life not provided. Graph of degradation over time demonstrates between 60 and 10 % residual 4- nonylphenol at 6 and 9 days respectively.

A small amount of deg. in sterile controls(not P)

Not P

Freshwater sediment

Temperature: 25°C

Oxygen: oxic

Wang et al (2014)

Branched nonylphenol

94

Nonstandard flow through river sediment system, to assess desorption and aerobic degradation in a system mimicking changing resuspension conditions of a river system

The desorbed nonylphenol from the sediment was degraded in the first 20 days of the experiment

-

Freshwater sediment

Temperature: 30°C

Oxygen: oxic

De Weert et al (2010)

4-n- nonylphenol

99

Nonstandard test. Exposure of cultures of the filamentous fungus (Gliocephalotrichum simplex) to 4-n nonylphenol. Cannot use for persistence assessment, but can be used to demonstrates potential for degradation. High concentrations used

Elimination of between 88 and 50% after 24 hours. After 72 hours, 29% mineralization was shown demonstrating biodegradation

-

Freshwater

Temperature: 28°C

Oxygen: oxic

Rozalska et al (2010)

A range of branched nonylphenol isomers (approximately 16)

Range

Oxic and anoxicsediments incubated and exposed to different nonylphenol isomers for 84 days.

Half-life Oxic conditions = 0.9 to 13.2(Not P)

 

Estimated half-life anoxic conditions = 343 to 514(P and vP)

 

Half-life slightly anoxic conditions = 15.6 to 20.1(Not P)

 

Half-life oxic conditions = 2 to 27(Not P)

 

Estimated half-life anoxic conditions = 343 to 1056(P and vP)

 

Half-life slightly anoxic conditions = 32 to 41(Not P)

 

Freshwater sediment

Temperature: 21 °C

Oxygen: oxic, anoxic and slightly anoxic

Lu and Gan (2014). Additional half-life information detailed in Lu and Gan (2014b)

Branched t nonylphenol

 

Nonstandard test considering biodegradation with and withoutPhragmites australisplants

No half-life data provided. Maximum 52.7 % removed from the sediment after 42 days.(Not P)

Estimated at 151 days(Potentially P)

Freshwater sediment

Temperature: 28 °C

Oxygen: oxic,

Toyama et al, (2011)

Branched t nonylphenol

99

Nonstandard test. Exposure of cultures of the marine diatom(Navicula incerta) to 4-n nonylphenol. Cannot use for persistence assessment, but can be used to demonstrates potential for degradation.

Half-life not provided.

Biodegradation rate after 96 hours ranged from approx. 0% to 20% dependent upon the dose concentration. 20% at 1ug/L. 0% at 1000ug/L. Minimal information can be drawn from this due to duration.

-

Marine water

Temperature: 23 °C

Oxygen: Assumed oxic

Liu et al (2010)

n.a. = not applicable

1– Half-life normalised using the Arrhenius equation in accordance with ECHA guidance R.7b. Half-life data normalised to 12°C for freshwater environments (sediment and water) and 9°C for marine environments (sediment and water)

 

Biodegradation in Marine Sediments

Details on studies on biodegradation of nonylphenol in sediments are presented in Table 1. 

Ying & Kookana (2003) measured the biodegradation of nonylphenol in saltwater and marine sediments at 20 °C under oxic andanoxic(sediment only) conditions. It was demonstrated that under oxic conditions, degradation of nonylphenol occurred very quickly, with a calculated half-life of 5.8 days at 20°C(calculated as 14 days when normalised to 9°C) based on first-order reaction kinetics. No degradation could be observed in marine sediments under anoxic conditions. Based on this information, in oxic conditions nonylphenol would be classified as not Persistent, although is likely to persist in anoxic sediments.

Biodegradation in Freshwater Sediments

A large number of studies have been conducted investigating the degradation of nonylphenol in freshwater sediments, considering both oxic and anoxic conditions (e.g. Yuan et al, 2004; Lu and Gan, 2014; Wang et al 2014 and De Weert et al., 2009). Under oxic conditions, the majority of these studies demonstrated rapid degradation of nonylphenol with normalised half-lives well below the Persistent and Very Persistent criterion of 120 or 180 days (duration varies for marine and freshwater environments and P and vP classification) for PBT classification. 

Investigations by De Weert et al., (2009), Lu and Gan (2014) demonstrated half-lives of between 5 and 25 days after normalisation for the study temperature to 12°C in a range of different oxic samples. Other studies, did not provide half-life data (Bradley 2008; Wang et al 2014) but indicated rapid degradation rates of nonylphenol in oxic sediments. 

Yuan et al, (2004) who reported half-lives for nonylphenol ranging from 5.1 to 99 days at a range of test temperatures and other experimental conditions (yielding half-lives of between 22 to 418 days when normalised to 12°C) and Toyama et al (2011) who reported 52.7% degradation after 42 days at 28°C (yielding ahalf-lifeof151 days when normalised to 12°C). The degradation rate for nonylphenol was enhanced by a variety of factors, including shaking and increasing temperature and inhibited by the addition of Pb, Cd, Cu, Zn, phthalic acid esters (PAEs), and NaCl, as well as by reduced level of ammonium, phosphate, and sulfate. 

Under anoxic conditions, nonylphenol generally demonstrates poor degradability (Chang, 2004; Bradley 2008; De Weert et al, 2011; Lu and Gan 2014). Despite this, particular conditions in anoxic sediments demonstrate better biodegradability. For example, application of nonylphenol into only slightly reduced conditions still degraded nonylphenol (Lu and Gan, 2014) and pre-adaptation of the sediments to nonylphenol prior to testing increased degradation rates and decrease half-lives (Wang et al, 2014). Pre-adaptation of sediments is likely to occur in the environment where continual discharges of wastewater and industrial sources are emitted to the environment, which may aid with removal of nonylphenol in anoxic sediments. Different isomers of nonylphenol have also been demonstrated to undergo degradation at different rates, although in anoxic sediments, predicted half-lives for all tested isomers exceeded the 300 days (Lu and Gan, 2014b).

Transformation products 

With regard to biodegradation pathways of NP and the formation of transformation products, several references are available in the open literature:

Junghanns et al (2005) determined the degradation of technical nonylphenol by aquatic fungi and their laccases (enzymes). The results show that all of the t-NP constituents analytically resolved under the experimental conditions were degraded to individual extents. Degradation of t-NP was accompanied by the simultaneous formation of several metabolites (iso-alcohols, hydroxynonyl phenols, 4-hydroxybenzoic acid) and GC-MS analysis of these products implies that either subterminal or terminal hydroxylation had occurred at the respective nonyl moiety of individual t-NP isomers, due to the action of as yet unknown intracellular hydroxylating enzymes. Laccase-catalysed degradation of nonylphenol led to the formation of products with higher molecular masses than that of the parent compound, indicating oxidative coupling of primary oxidation metabolites. The results of this study support a possible role for fungi living in aquatic ecosystems in degradation of water contaminants, including nonylphenol. Furthermore, they emphasize two different mechanisms simultaneously employed by aquatic fungi to initiate nonylphenol degradation: intracellular hydroxylation of individual nonylphenol isomers at their branched nonyl chains and subsequent side chain degradation of certain isomers; and extracellular attack of nonylphenol by laccase, the latter leading to oxidative coupling of primary radical products to compounds with higher molecular masses.

Corti et al (1995) examined the biodegradation of linear NP by aCandida maltosaisolate (yeast) from a sludge sample collected from a sewage treatment plant. The results of this study indicate that a complete p-NP bioconversion occurred in cultures ofC. maltosa(disappearance of the nonylphenol peak signal after 7 days incubation). The concurrent significant growth of the yeast suggests that this compound is at least partially utilised as a carbon and energy source. Several different degradation products were formed among which 4-acetylphenol appears to be the major component.

The influence of nonylphenol on microbial growth was also evaluated by cultivatingCandida maltosaon yeast broth supplemented with glucose (10 g/l) in the presence of 50 and 200 mg/l nonylphenol. In these cultures, cell growth was monitored with time by optical density. The cell growth dynamics showed a longer lag phase in cultures containing 50 or 100 mg/l nonylphenol than in cultures containing glucose only. This lag phase suggested a possible toxic effect of nonylphenol onCandida maltosa(Corti et al, 1995).

Moreover, Gabriel et al (2005, 2008) reported the elimination of the alkyl side chain, possibly involving an ipso-hydroxylation mechanism. The differential degradation of different nonylphenol isomers by a strain ofSphingomonas bayramisolated from a sludge sample of a municipal wastewater treatment plant was measured.Sphingomonaswas able to utilise 4-(1-ethyl-1,4-dimethylpentyl)phenol (4- nonylphenol 112), one of the main isomers of technical nonylphenol, as the sole carbon and energy source. Growth experiments with different nonylphenol isomers showed that isomers with quaternary benzylic carbon atoms served as growth substrates with the subsequent formation of C9 alcohols, while the isomers with one or two hydrogen atoms in the benzylic position did not. In a novel pathway, bacteria were able to detach α-branched alkyl moieties of alkylphenols in order to utilise the aromatic portion of the molecule as a carbon and energy source. As a rule, isomers with less bulkiness at the α-carbon and those with an optimally sized main alkyl chain (4-6 carbon atoms) were degraded more efficiently. By mass spectrometric analysis, the two most recalcitrant main isomers of the technical mixture were identified as 4-(1,2-dimethyl-1-propylbutyl)phenols (4- nonylphenol 193a and 4- nonylphenol 193b), which are diastereomers with a bulky α-CH3, α-CH(CH3)C2H5 substitution.

 

Additional References cited in summary

Staples, C. A., Naylor, C. G., Williams, J. B., and Gledhill, W. E., 2001. Ultimate biodegradation of alklyphenol ethoxylate surfactants and their biodegradation intermediates. Environmental Toxicology and Chemistry, 20(11). p. 2450-2455

Swisher, R. D. 1987. Surfactant Biodegradation. 2nd Ed. Marcel Dekker, New York. USA