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

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study without detailed documentation

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): New Bedford Wastewater Treatment Plant (New Bedford, MA, USA)
- Collected sludge was poured through a 2-mm sieve and settled for 30 min.
- Supernatant was decanted and discarded. Sieved sludge was centrifuged at 1,000 g for 30 min, and again supernatant was decanted and discarded.
- Sludge moisture content and solids concentrations were measured for the final prepared sludge.

Duration of test (contact time):

35 d

Initial conc.:

ca. 12 mg/L

Based on:

test mat.

Initial conc.:

10 mg/L

Based on:

DOC

Details on study design:

TEST SOLUTIONS:
- Solutions were prepared with reagent-grade water originating from dechlorinated Wareham (MA, USA) town water known through frequent testing to be free of any and all contaminants that could affect test results.

TEST CONDITIONS
- Test temperature: 22 °C
- Suspended solids concentration: 30mg/l


TEST SYSTEM
- Culturing apparatus: 3 L of reagent-grade water fortified with specified inorganic salts placed in 4-L glass bottles and inoculated with 3 ml of inoculum
- Number of culture flasks/concentration: duplicate
- Method used to create aerobic conditions: Carbon dioxide–free air was passed through the test solution
- Details of trap for CO2 and volatile organics if used: carbon dioxide released during bio-oxidation of test material was trapped by a solution of barium hydroxide


SAMPLING
- Sampling frequency: Carbon dioxide traps were removed from all vessels on days 1, 2, 4, 6, 9, 13, 22, 28, and 35 for analysis
- On days 15 and 35 (the approximate midpoint and the end date of the test), samples were collected from each vessel for analysis of NP

Reference substance:

benzoic acid, sodium salt

Remarks:

positive control

Parameter:

% degradation (CO2 evolution)

Value:

69.9

Sampling time:

35 d

Results with reference substance:

Sodium benzoate positive controls reached 60% mineralization in 6 d and 94.5% by day 35.

Results of HPLC and GC/MS analyses from samples collected on days 0, 15, and 35 (see Table 1):

- By day 15, OP was no longer detectable in the test systems.

- By day 35, OP was no longer extractable or identifiable as parent compound in the test media that included both dissolved material and any particulate-phase material.

Table 1: Analytical determination by high-performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS) of the composition of Octylphenol and degradation intermediates

Test substance	Days	OP * (µg/l)	NPE1 (µg/l)	NPE2 (µg/l)	NPE3-17 (µg/l)	NPEC1-4 (µg/l)	% Total removal
Octylphenol	0	12,283	0.0	0.0	0.0	0.0	0.0
	15	0.0	0.0	0.0	0.0	0.0	~ 100
	35	0.0	0.0	0.0	0.0	0.0	~ 100

 * Remark: changed from NP to OP, presumably error in original paper

Interpretation of results:

inherently biodegradable

Conclusions:

Based on the CO2 analysis results, only the reference substance sodium benzoate can be characterized as "readily biodegradable" under OECD definitions (60 % or greater CO2 produced within 28 days with this value being achieved within a 10-day window). Octylphenol was extensively mineralized (> 60 % CO2) during the 35-day study.

Executive summary:

The biodegradability of the test substance Octylphenol (CAS No. 140-66-9) was determined by the method laid down in the OECD Guideline 301B: „Ready Biodegradability: CO₂ Evolution Test”. Octylphenol was tested at a concentration of 12.3 mg/l (equivalent to 10 mg DOC/l). 

Control tests with sodium benzoate showed that the activity of the inoculum was sufficient.

Based on the CO2 analysis results, only the reference substance sodium benzoate can be characterized as "readily biodegradable" under OECD definitions (60 % or greater CO₂produced within 28 days with this value being achieved within a 10-day window). Octylphenol was extensively mineralized (> 60 % CO2) during the 35-day study (62 % after 28 days). Octylphenol can be regarded as readily biodegradable, but failing the 10-day window.

Results of HPLC and GC/MS analyses from samples collected on days 0, 15, and 35 indicate that by day 15, Octylphenol was no longer detectable. By day 35, OP was no longer extractable or identifiable as parent compound in the test media that included both dissolved material and any particulate-phase material.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1991-06-03 to 1991-07-09

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Test procedure in accordance with national standard methods with acceptable restrictions

Qualifier:

according to guideline

Guideline:

ISO Draft (BOD Test for Insoluble Substances)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of activated sludge: predominantly domestic sewage plant (sewage plant Marl-Ost, Germany)
- Preparation of inoculum for exposure: The sample was washed for several times with mineral medium (settled, supernatant discarded, re-suspended)
- Pretreatment: The test flasks were filled with 200 ml inoculated mineral medium (10 ml/l inoculum), aerated, closed with glass stoppers and incubated for one week on a shaking machine (second aeration after 2 days)
- Concentration of sludge: The dry weight of the concentrated sludge was 2.76 g/l
- Initial cell/biomass concentration: not mentioned
- Water filtered: not mentioned

Duration of test (contact time):

28 d

Initial conc.:

ca. 27.5 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium:
Stock solutions using analytical grade reagents:
(a) 8.50 g Potassium dihydrogen orthophosphate, KH2PO4
21.75 g Dipotassium hydrogen orthophosphate, K2HPO4
33.40 g Disodium hydrogen orthophosphate dihydrate, Na2HPO4x2H2O
0.50 g Ammonium chloride, NH4Cl
Dissolved in distillated water and made up to 1 litre. The pH of the solution was adjusted to 7.4.
(b) 20.9 g Magnesium sulphate heptahydrate, MgS04x6H20
Dissolved in distillated water and made up to 1 litre.
(c) 36.4 g Calcium chloride dihydrate, CaCl2x2H20
Dissolved in distillated water and made up to 1 litre.
(d) 0.25 g Iron (III) chloride hexahydrate, FeCl3x6H20
Dissolved in distillated water and made up to 1 litre.
10 ml of solution (a) was mixed with 800 ml water, then 1 ml of solutions (b), (c) and (d) each were added and made up to 1 l with distilled water.
- Additional substrate: none
- Solubilising agent: not used
- Test temperature: not mentioned
- pH: 7.6
- pH adjusted: no
- Aeration of dilution water: not mentioned
- Suspended solids concentration: not stated
- Continuous darkness: not stated

TEST SYSTEM
- Culturing apparatus: Narrow neck bottles with glass stoppers, 2/3 filled with mineral solution
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: aeration of each flask through a glass frit prior to the addition of test or control substance and after every O2 measurement
- Measuring equipment: O2-measuring device OXY 2000, WTW
- Test performed in closed vessels due to significant volatility of test substance: no

SAMPLING
- Sampling frequency: once a week (on days 7, 14, 21 and 28)
- Sampling method: O2 measurement after tempering the flasks at 20 ± 0.5 °C
- Sample storage before analysis: not stored
- Other: aeration (through a glass frit) of the flasks after each O2 measurement

CONTROL AND BLANK SYSTEM
- Inoculum blank: 4 test vessels with inoculum without test substance (1 of them for determination of the cell concentration, discarded afterwards)
- Abiotic sterile control: not performed
- Toxicity control: not performed
- Other: 3 test vessels with inoculum and reference substance

STATISTICAL METHODS:
No statistics performed

Reference substance:

diethylene glycol

Preliminary study:

not performed

Test performance:

Test substance and reference substance were weighed in reaction vessels (Eppendorf) and transferred into the test vessels. Concentration of test substance in each flask: and 5.5 ± 0.2 mg/flask; concentration of reference substance per control vessel: 14.0 ± 0.4 mg/flask.

Parameter:

% degradation (O2 consumption)

Value:

20

Sampling time:

28 d

Results with reference substance:

see below

Table: Degradation kinetics

Type of suspension	Vessel No.	% degradation at sampling time
		day 7	day 14	day 21	day 28
test substance	1	0	1	15	26
	2	0	1	0	18
	3	3	4	4	14
	mean	1	2	6	20
reference substance	1	4	27	49	88
	2	5	29	59	100
	3	5	31	51	91
	mean	5	29	53	93

Validity criteria fulfilled:

no

Remarks:

see below

Interpretation of results:

inherently biodegradable

Conclusions:

The reference substance did not reach a biodegradation level of 60% after 14 days, but the tested reference substance diethylene glycol is jugded to be less biodegradable than the recommended reference substances sodium acetate resp. sodium benzoate. Therefore with a degradation of 93% after 28 days the test is jugded as valid.

Executive summary:

The biodegradability of the test substance Octylphenol PT (CAS No. 27193-28-8) was determined according to the BODIS Test (BOD-Test for Insoluble Substances). Octylphenol was incubated for 28 days at a concentration of approx. 27.5 mg/l. 

The reference substance did not reach a biodegradation level of 60% after 14 days, but the tested reference substance diethylene glycol is jugded to be less biodegradable than the recommended reference substances sodium acetate resp. sodium benzoate. Therefore with a degradation of 93% after 28 days the test is judged as valid.

Based on the O₂consumption results, 20 % of the initial Octylphenol PT concentration was mineralized during the 28-day study. Therefore, Octylphenol PT can be regarded as inherently biodegradable.

Reference 3

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1998-05-14 to 1998-06-19

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, adapted

Details on inoculum:

- Source of inoculum/activated sludge: Wastewater Treatment Plant, New Bedford, Massachusetts, US
- Laboratory culture: no
- Storage conditions: not mentioned
- Storage length: not mentioned
- Preparation of inoculum for exposure: the sludge was poured through a 2 mm sieve and then allowed to settle for 30 min. After settling, the supernatant was decanted and discarded. The sieve sludge was once more centrifuged.
- Pretreatment: not mentioned
- Concentration of sludge: 30 mg/l suspended solids; dry weight of inoculum: not mentioned
- Water filtered: not mentioned

Duration of test (contact time):

35 d

Initial conc.:

ca. 12.3 mg/L

Based on:

test mat.

Initial conc.:

10 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: based on OECD document 301B (1992)
- Additional substrate: none
- Solubilising agent (type and concentration if used): not used
- Test temperature: day 10 = 27 °C, day 14 = 29 °C, day 20 until 36 = 19 °C
- pH: pH 7.4 - 7.5
- pH adjusted: no
- Aeration of dilution water: not specified
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes
- Other: none

TEST SYSTEM
- Culturing apparatus: 4 l vessels containing culture samples
- Number of culture flasks/concentration: 2 bottles, one concentration
- Method used to create aerobic conditions: All test systems were aerated continuously for 36 days under positive pressure using CO2-free air in order to provide oxygen for the microbes and to capture evolved carbon dioxide
- Method used to create anaerobic conditions: not applicable
- Measuring equipment: not mentioned
- Details of trap for CO2: collection of carbon dioxide as barium carbonate with barium hydroxide solution
- Other: none

SAMPLING
- Sampling frequency: on days 1, 2, 4, 6, 9, 13, 18, 22, 23, 28 and 36
- Sampling method: Ba(OH)2 carbon dioxide trap
- Sample storage before analysis: not mentioned
- Other: none

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes (2 vessels with inoculum without test substance)
- Abiotic sterile control: not performed
- Toxicity control: not performed
- Other: none

STATISTICAL METHODS: no statistics performed

Reference substance:

benzoic acid, sodium salt

Remarks:

51.4 mg/l final test medium (10 DOC mg/l)

Reference substance:

other: diisotridecyl adipate: 39.8 mg/l final test medium (10 DOC mg/l)

Preliminary study:

not performed

Test performance:

Deviations in temperature:
- Temperature was recorded daily during the study, generally ranged from 20 to 23 °C (meets OECD criteria of 22 +/- 2°C)
- Minimum temperature of 19 °C was recorded several times during the study while a maximum temperature of 29 °C was recorded once during the study.

Test duration:
- The test was extended from the normal 28-day period to 35 days since several test systems were continuing to evolve CO2.

Parameter:

% degradation (CO2 evolution)

Value:

ca. 62

Sampling time:

28 d

Details on results:

The mean net CO2 value from the aqueous medium fortified with Octylphenol was 69.9 % of the theoretical amount, based on titration measurements. Analyses of DOC concentration at test termination confirmed extensive removal (> 90 %) for all test and reference substances.

Results with reference substance:

The mean cumulative CO2 evolved from the sodium benzoate and diisotridecyl adipate procedural controls was 95.4 and 78.3 %, respectively, of the theoretical amount in 35 days. In addition, the reference substance, sodium benzoate, passed the OECD "10-Day window" criterion. This rapid degradation of the reference materials confirmed the presence of an acceptable microbial community and confirmed system integrity.

Table: Degradation kinetic

sampling time [days]	degradation [%]
	Octylphenol			sodiumbenzoate	diiostridecyl adipate
	vessel 1	vessel 2	mean	mean	mean
1	nd	nd	nd	9.7	nd
2	-1.8	- 2.1	- 2.0	20.2	0.6
4	-1.1	- 2.3	-1,7	46.0	8.9
6	3.6	-1.4	1.1	59.1	18.6
9	17.2	14.1	15.6	75.2	32.8
13	26.3	24.9	25.5	85.6	40.7
18	48.8	44.0	46.4	90.7	51.2
22	58.2	54.8	56.5	92.9	59.3
28	63.8	60.5	62.1	94.1	66.5
35 (after acidification)	69.0	70.8	69.9	95.4	78.3

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable, but failing 10-day window

Conclusions:

Based on the CO2 analysis results, only the reference substance sodium benzoate can be characterized as "readily biodegradable" under OECD definitions (60 % or greater CO2 produced within 28 days with this value being achieved within a 10-day window). Octylphenol and the diisotridecyl adipate control, however, were extensively mineralized (> 60 % CO2) during the 35-day study. DOC analyses of reference and test substance confirmed extensive removal, > 90 % DOC.

Executive summary:

The biodegradability of the test substance Octylphenol (CAS No. 140-66-9) was determined by the method laid down in the OECD Guideline 301B: „Ready Biodegradability: CO₂ Evolution Test”. Octylphenol was tested at a concentration of 12.3 mg/l (equivalent to 10 mg DOC/l). 

Control tests with sodium benzoate and diisotridecyl adipate showed that the activity of the inoculum was sufficient.

Based on the CO2 analysis results, only the reference substance sodium benzoate can be characterized as "readily biodegradable" under OECD definitions (60 % or greater CO₂produced within 28 days with this value being achieved within a 10-day window). Octylphenol and the diisotridecyl adipate control, however, were extensively mineralized (> 60 % CO2) during the 35-day study (62 % after 28 days). DOC analyses of reference and test substance confirmed extensive removal, > 90 % DOC. Octylphenol can be regarded as readily biodegradable, but failing the 10-day window.

Reference 4

Endpoint:

biodegradation in water: inherent biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

02/10/1991-30/10/1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study (OECD 302 C)

Qualifier:

according to guideline

Guideline:

OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))

Deviations:

no

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

other: a mixed population of activated sewage sludge microorganisms

Details on inoculum:

- Source of inoculum: Activated sewage was prepared by sampling 10 different sites around the UK in accordance with OECD Guideline No. 302C
- Preparation: the mixed sludge was fed daily with 0.1% synthetic sewage and maintained on a constant aeration at 25 ± 1°C
- Usage rate: equivalent to 100 mg dry weight/l

Duration of test (contact time):

28 d

Initial conc.:

30 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

- Test temperature: 25 ± 1°C
- Aeration of dilution water: constant
- Continuous darkness: yes
- Agitation: by magnetic stirrers
- Criteria: oxygen consumption measured by direct manometer reading
- Observations: manometer volumes were recorded daily

Reference substance:

aniline

Test performance:

TOC analysis of phenol, 4-1,1,3,3-tetramethylbutyl) was not possible due to the insoluble nature of test material.
A Modified Miti test was carried out due to the insoluble nature of test material.
A COD value of 2.85 mg O2/mg was obtained for the test material
For % degradation calculation a ThOD of 2.95 mg O2/mg was used based on the following approximate values for this test material:
Molecular formula: C14H22O
Molecular weight: 200

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

28 d

Parameter:

COD

Value:

2.85 other: mg O2/mg test . mat.

Results with reference substance:

Aniline attained 74% biodegradation after 14 days thereby confirming the suitability of the inoculum and culture conditions. Aniline attained 4% degradation within 7 days. However this is not considered to affect the overall integrity of the study given that aniline attained 74% degradation within 14 days. Total organic carbon analysis of the test media at day 0 and day 28 showed that aniline attained 87% degradation within 28 days.

Day	% Biodegradation
	Phenol, 4-1,1,3,3-tetramethylbutyl)	Aniline
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28	0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0	0 0 0 0 1 2 4 12 17 18 41 64 73 74 73 74 81 86 86 80 90 89 87 86 83 81 81 88

Validity criteria fulfilled:

yes

Interpretation of results:

not inherently biodegradable

Conclusions:

Phenol 4 -(1,1,3,3 -tetramethylbutyl) attained negligible degradation within 28 days calculated from oxygen uptake (% of COD and ThOD) and therefore, cannot be considered as inherently biodegradable under the strict terms and conditions of the OECD Guidelines.

Executive summary:

The inherent biodegradability of the test substance phenol, 4 -(1,1,3,3 -tetramethylbutyl) was evaluated. The method used followed that described in the OECD Guidelines for Testing of Chemicals / Section 2: Degradation and Accumulation, Test No. 302C "Inherent Biodegradability, Modified MITI Test (II)". A mixed population of activated sewage sludge microorganisms was used as inoculum and aniline as reference substance. Initial concentration of test substance was 30 mg/l and reference substance 100 mg/l. Phenol 4 -(1,1,3,3 -tetramethylbutyl) attained negligible degradation within 28 days calculated from oxygen uptake (% of COD and ThOD) and therefore, cannot be considered as inherently biodegradable under the strict terms and conditions of the OECD Guidelines. TOC analysis of phenol 4 -(1,1,3,3 -tetramethylbutyll) was not possible due to the insoluble nature of the test material. A modified Miti test was carried out due to this fact. A COD value of 2.85 mg O2/mg was obtained for the test material.

Reference 5

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

In accordance with Regulation (EC) 1907/2006 Annex XI (1.5) and the relevant ECHA guidance documents, the substances detailed in the table below are grouped for the purposes of read across to reduce the need for unnecessary repeat testing on the basis that the substances are similar on the basis of a common functional groups.

Reason / purpose for cross-reference:

read-across source

Preliminary study:

not performed

Test performance:

Test substance and reference substance were weighed in reaction vessels (Eppendorf) and transferred into the test vessels. Concentration of test substance in each flask: and 5.5 ± 0.2 mg/flask; concentration of reference substance per control vessel: 14.0 ± 0.4 mg/flask.

Parameter:

% degradation (O2 consumption)

Value:

20

Sampling time:

28 d

Results with reference substance:

see below

Table: Degradation kinetics

Type of suspension	Vessel No.	% degradation at sampling time
		day 7	day 14	day 21	day 28
test substance	1	0	1	15	26
	2	0	1	0	18
	3	3	4	4	14
	mean	1	2	6	20
reference substance	1	4	27	49	88
	2	5	29	59	100
	3	5	31	51	91
	mean	5	29	53	93

Validity criteria fulfilled:

no

Remarks:

see below

Interpretation of results:

inherently biodegradable

Conclusions:

The read across for 4-tert-octylphenol (CAS: 144-66-9); is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of biodegradation. Based on the information available for the read across substances, the substance is expected to be inherently biodegradable.

Description of key information

To determine the biodegradation characteristics of 4-tert-Octylphenol (CAS: 140-66-9; 4-(1,1,3,3-tetramethylbutyl)phenol) and Octylphenol (CAS: 27193-28-8; (1,1,3,3-tetramethylbutyl)phenol, tests according to following guidelines have been conducted:
4-tert-Octylphenol (CAS: 140-66-9):
-	OECD 302C: Inherent Biodegradability, Modified MITI Test (II) (Sewell, Safepharm Laboratories, 1991)
-	OECD 301B: Ready Biodegradability: CO2Evolution Test (Gledhill, Springborn Laboratories, 1998, and Staples, 2001)
Octylphenol (CAS: 27193-28-8):
-	BOD-Test for Insoluble Substances (Scholz, Hüls AG, 1991)

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

In the modified MITI Test (Sewell, Safepharm Laboratories,1991), which was not conducted according to GLP, 4-tert-Octylphenol (purity: 98.97 %) was tested at an initial concentration of 30 mg/l. In this test, 4-tert-Octylphenol attained negligible degradation within 28 days calculated from oxygen uptake (% of COD and ThOD). Therefore, 4-tert-Octylphenol cannot be considered as inherently biodegradable according to this result.

By contrast, in a 28 day BODIS Test with non-adapted microorganisms (BOD-Test for Insoluble Substances) on Octylphenol PT (CAS No. 27193-28-8; purity: 95.6 %) conducted by Scholz, Hüls AG, 1991, the test substance was classified as inherently biodegradable based on the O₂ consumption results (20 % of the initial Octylphenol PT concentration was mineralized during the 28-day study).

In a further test with Octylphenol (CAS No. 140-66-9; purity: 99.64 %) according to OECD Guideline 301B („Ready Biodegradability: CO2 Evolution Test”) conducted by Gledhill, Springborn Laboratories, 1998, and also reported by Staples, 2001, a domestic activated sludge from a WWTP where a high (>600 µg/L) concentration of NPE had been found was used. Octylphenol was extensively mineralized (> 60 % CO2) during the 35-day study (62 % after 28 days). DOC analyses of reference and test substance confirmed extensive removal, > 90 % DOC. Therefore, Octylphenol was classified as readily biodegradable, but failing the 10-day window. The results from this study suggest that microorganisms may need a period of adaptation before degradation of 4-tert-octylphenol can occur.

 

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 greater part of ready biodegradability tests conducted according to current guidelines (OECD, US EPA) use freshly collected inoculum from municipal wastewater treatment plants. In contrast, studies performed according to OECD 302C use a mixed inoculum that has been pre-conditioned for 30 days on a medium containing glucose/peptone as the sole carbon source, which results in substantial loss of microbial diversity originally present in the composite sample. Hence the environmental relevance of the preconditioned inoculum has been criticized. Due to the distinctive and unnatural inoculum used in OECD 302C tests, according to Melcer et al. (2007; Wastewater Treatment of Alkylphenols and their Ethoxylates – A State of the Science Review), the results should not be used for categorization of the persistence of 4-tert-Octylphenol.

In 2005, Scher (Scientific Committee on Health and Environmental Risks) published an “Opinion on Compatibility of the ISO standard 10708 (biodegradability test method) with the ultimate biodegradability requirements imposed through Annex III of Regulation 648/2004 of Parliament and of the Council”. Scher comes to the conclusion that the biodegradation results obtained with the ISO 10708 (BODIS Test) are consistent with those obtained with the OECD ready biodegradability methods (301B, 301C, 301 D and 301F).

The inconsistency between the result of the BODIS test and the result of the test conducted according to OECD 301B may be due to the higher content of impurities in the Octylphenol PT (CAS No. 27193 -28-8, 95.6 % pure) compared to the Octylphenol (CAS No. 140-66-9; 99.64 % pure). Moreover, micro-organisms from the sludge used in OECD 301B were probably adapted to Octylphenol because of the high concentration of NPE in the domestic activated sludge. Furthermore, biodegradation of the reference diethylene glycole in the BODIS test started after a lag phase of approx. 5 days. This indicates that the inoculum did not have the reqiured activity.

 

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.