Hydroquinone

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 303 A (Simulation Test - Aerobic Sewage Treatment. A: Activated Sludge Units)

Deviations:

yes

Remarks:

Coupled Unit Test, adaptation of the OECD Confirmatory Test (OECD, 1976)

GLP compliance:

no

Radiolabelling:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Initial conc.:

>= 12 mg/L

Based on:

DOC

Details on study design:

- initial sludge concentration: 2.5 g/l of dry matter;
- test conducted under steady-state conditions;
- organic base medium
Biodegradation is followed only by DOC analysis.

% Degr.:

89

St. dev.:

5

Sampling time:

14 d

Transformation products:

not specified

Validity criteria fulfilled:

yes

Conclusions:

In the Coupled Units Test, the DOC-removal was 89 ± 5% after a working-in time of 2 days.

Reference 2

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 303 A (Simulation Test - Aerobic Sewage Treatment. A: Activated Sludge Units)

Deviations:

yes

Remarks:

Deviations from OECD-Guideline 303A (22nd January 2001): - No control unit was run. - Hydraulic retention time was 12 h instead of 6 h required by the guideline. - The influent concentrations were higher than proposed by the guideline (10 - 20 mg DOC/L)

Principles of method if other than guideline:

In this publication, biodegradation of hydroquinone was investigated in a thorough manner (experiments E1 to E3; E1 and E2 are described in the section on biodegradation screening tests). Assessed were (E1) the extent of mineralization by radioisotopic labelling and determination of 14CO2; (E2) the biodegradation pathway of hydroquinone, identifying metabolites and investigating their possible accumulation; (E3 – summarized here) the extent of degradation in a laboratory activated sludge unit (equivalent to the set-up of OECD 303 A: Simulation Test – Aerobic Sewage Treatment) considering different synthetic sewages and analyzing for important metabolites.

Deviations from OECD-Guideline 303A (22nd January 2001):
- Hydraulic retention time was 12 h instead of 6 h required by the guideline. However, according to Simple Treat v. 4.0, the default hydraulic retention time for sewage treatment plants with primary clarifier and without primary clarifier is 11.5 hours and 18 hours, respectively. Thus, 12 h retention time is a very good approximate for real life STPs.
- The influent concentrations were higher than proposed by the guideline (10 - 20 mg DOC/L)

GLP compliance:

not specified

Radiolabelling:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, adapted

Details on inoculum:

The 6-liter laboratory activated sludge unit was seeded with photographic sludges.

Initial conc.:

55 - 400 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

other: analytical determination of the test item and several important metabolites

% Degr.:

>= 99.9

Parameter:

test mat. analysis

Remarks:

: based on hydroquinone; additionally, important metabolites were analyzed but could not be detected

Remarks on result:

other: 12 hours hydraulic retention time; measurements preformed after acclimation period (approximately 2 days)

Transformation products:

no

Remarks:

Benzoquinone, 2-hydroxy-1,4-benzoquinone, and β-ketoadipic acid were identified as metabolic intermediates, however at low concentrations (e.g. 0.11% of 1,4-benzoquinone after 2h with yeast cultures, decreasing thereafter).

When hydroquinone was first introduced into the various feeds at concentrations of 55 - 275 mg/L the hydroquinone concentration in the effluent rose initially to 2 - 7% of the influent value, then dropped after a period typically of 2 days to less than 0.5% of the influent value. After this acclimation period, the activated sludge unit consistently showed hydroquinone removals of greater than 99.5% and no adverse settling properites.

When hydroquinone was added to synthetic domestic waste feeds at levels of 400 and 1000 mg/l (results not shown here), the pH of the sludge unit dropped after several days of operation and the sludge developed poor settling properties. According to the authors, this result is either due to inhibitory effects at these hydroquinone concentrations or to inadequate buffering capacity of the feed.

TOC removal in laboratory activated sludge units with hydroquinone ranges from 70% to 92% depending on the synthetic domestic or photographic feeds and the applied hydroquinone concentrations. In the control unit without hydroquinon, 69% of TOC was removed on average. In all cases the average TOC removal was higher for hydroquinone-containing feeds than for the synthetic domestic waste. The lower TOC removal for synthetic domestic waste is attributed to the presence of peptone, which was incompletely degraded in the system and which contributed one-half of the TOC in the feed. TOC removal was not used to quantify HQ removal (substance specific analytics), but rather as an indicator for the overall performance of the biodegradation process.
 

Medium	HQ Influent conc. [mg/L]	Average TOC Removal [%]	Average HQ Removal [%]
Synthetic domestic waste	55	70	>99.9
	100	87	99.9
	400	89	93.1
Basal salts	100	84	>99.9
Synthetic photographic waste	275	92	>99.9
Mixture of synthetic domestic and photographic waste (ratio 80/20)	55	77	>99.9

 

1,4-Benzoquinone was not detected in the effluents nor in case of sulfite containing synthetic photographic waste. Neither detected was 2-hydroxy-1,4-benzoquinone.

Supporting experiment:

To assess whether there is significant buildup of other intermediates during biodegradation, filtrates from 750-950 mg/L hydroquinone with several pure cultures and sludges were assayed after various times for residual TOC and for “total hydroxylated aromatics”. The latter analysis responds to hydroxybenzoquinone, but was almost completely accounted for by hydroquinone. There was a good linear correlation (r = 0.9989) between TOC (y-axis) and total hydroxylated aromatics (abscissa), with a slope of 0.979 and an intercept of 2.1 % total organic carabon (i.e. 2.1% TOC left at 0% total hydroxylated aromatics). The linear relationship indicates that there was not substantial buildup of transient intermediates; otherwise, the points would have fallen above the line. The intercept corresponds to the TOC remaining after biodegradation and is attributed primarily to cell excretion products. This value is essentially the same as that observed in other experiments for the average residual TOC after 3-5 days for the degradation of 750 mg/L hydroquinone (2.8 +/- 0.2%, n=15) as well as the residual TOC for the easily metabolized substrates glucose, phenol, and acetate ion (2.4 +/- 0.29%, n=4).

Validity criteria fulfilled:

not applicable

Conclusions:

In a laboratory activated sludge unit (hydraulic retention time: 12 hours) hydroquinone was removed by >=99.9%, independently of the influent concentration at concentrations between 50 mg/L and to 275 mg/L. This high degradation extent was obtained after an acclimation period of typically 2 days. The extent of TOC removal was between 70% and 92% for hydroquinone containing experiments, while it was lower (69%) in the control experiment without hydroquinone and synthetic domestic sewage, only.

Executive summary:

In the work by Harbison and Belly (1982), biodegradation of hydroquinone was investigated in a thorough manner (experiments E1 to E3; E1 and E2 are described in more detail within the section on biodegradation screening tests). In experiment E1, the extent of mineralization by radioisotopic labelling and determination of ¹⁴CO₂ was studied; assay E2 investigated the biodegradation pathway of hydroquinone, identifying metabolites and investigating their possible accumulation; E3 was dedicated to investigate the extent of metabolization in a laboratory activated sludge unit (equivalent to the set-up of OECD 303 A: Simulation Test – Aerobic Sewage Treatment) considering different synthetic sewages and analyzing for important metabolites.

Radiorespirometric incubations of hydroquinone-2,3,5,6-¹⁴C in basal salt media with various sludges (E1) led to 74% (+/- 9%; n= 5) mineralization (as¹⁴CO₂) within 5 to 10 days, demonstrating the fast and thorough mineralization of hydroquinone.

Using cultures from isolated pure microorganism from soil (pseudomonad bacterium; yeasts) and sludges (yeasts, fungi) utilizing hydroquinone as the sole carbon source, metabolism experiments (yeasts and fungi) were performed using 750 mg/L hydroquinone (E2). These organisms resulted in an average TOC removal (as a measure of hydroquinone degradation) of 97.5% within 5 days. 1,4-Benzoquinone, 2-hydroxy-1,4-benzoquinone, and β-ketoadipic acid were identified as metabolic intermediates, however at low concentrations (e.g. 0.11% of 1,4-benzoquinone after 2h with yeast cultures, decreasing thereafter). In conclusion, no buildup of metabolic intermediates could be observed. This was further corroborated by analysis of filtrates from incubations of several pure cultures and sludges with 750-950 mg/L hydroquinone assayed after various incubation times for residual TOC and for “total hydroxylated aromatics”: there was a good linear correlation (r = 0.9989) between TOC (y-axis) and total hydroxylated aromatics (abscissa), with a slope of 0.979 and an intercept of 2.1 % total organic carbon (i.e. 2.1% TOC left at 0% total hydroxylated aromatics). The linear relationship indicates that there was no substantial buildup of transient intermediates, and residual TOC is found at similar levels with readily biodegradable compounds like glucose or acetate and was attributed to cell excretion products by the authors.

Finally (E3), the extent of degradation in a 6-liter laboratory activated sludge unit (equivalent to the set-up of OECD 303 A: Simulation Test – Aerobic Sewage Treatment) was assessed, considering different synthetic sewages and analyzing for important metabolites. The hydraulic retention time was 12 h instead of 6 h required by the guideline. However, according to Simple Treat v. 4.0 (Struijs, 2014), the default hydraulic retention time for sewage treatment plants with primary clarifier and without primary clarifier is 11.5 hours and 18 hours, respectively. Thus, 12 h retention time is a very good approximate for real life STPs. As a result, after an acclimation period of typically 2 days hydroquinone was removed by >=99.9%, independently of the influent concentration at concentrations between 50 mg/L and to 275 mg/L. This high value of degradation was observed independently from the synthetic sewage used, i.e. basal salts, only; synthetic domestic sewage; synthetic photographic sewage; or a 80:20 mixture of synthetic domestic and photographic sewage. The extent of TOC removal was between 70% and 92% for hydroquinone containing experiments, while it was lower (69%) in the control experiment without hydroquinone and synthetic domestic sewage, only. Thus, hydroquinone did rather stimulate than inhibit TOC removal in the STP simulation tests. TOC removal was assessed as an indicator for the overall performance of the biodegradation process; it was not used to monitor biodegradation of hydroquinone (test item specific). Further, effluents were also analyzed for important metabolites of hydroquinone. But neither 1,4-benzoquinone could be detected (independently from the presence of sulfite, contained in synthetic photographic waste), nor 2-hydroxy-1,4-benzoquinone. Together with the supporting experiments on hydroquinone mineralization and metabolism described above, it can be assumed with high certainty that the high extent of hydroquinone removal of ≥99.9 % observed in the simulation tests for aerobic sewage treatment plant can be attributed to mineralization and possibly microbial assimilation, and an accumulation of stable metabolites can be excluded.

 

Struijs, J. (2014)

SimpleTreat 4.0: a model to predict the fate and emission of chemicals in wastewater treatment plants.Background report describing the equations. RIVM Report 601353005/2014

RIVM, National Institute for Public Health and the Environment, Bilthoven, The Netherlands

Description of key information

In a test similar to OECD 303A (laboratory activated sludge unit) hydroquinone was removed by >=99.9%, independently of the influent concentration at concentrations between 50 mg/L and to 275 mg/L. Based on this extensive removal under relevant conditions (HRT 12 hours, independently of the kind of synthetic sewage used), a first order rate constant for the degradation in sewage treatment plants of 144/d is assumed for the chemical safety assessment.

Additional information

In the work by Harbison and Belly (1982), biodegradation of hydroquinone was investigated in a thorough manner (experiments E1 to E3). Assessed were (E1) the extent of mineralization by radioisotopic labelling and determination of ¹⁴CO₂ (74% within 5-10 days; n=5); (E2) the biodegradation pathway of hydroquinone, identifying metabolites and investigating their possible accumulation (low concentration only, no accumulation); (E3) the extent of metabolization in a laboratory activated sludge unit (equivalent to the set-up of OECD 303 A: Simulation Test – Aerobic Sewage Treatment) considering different synthetic sewages and analyzing for important metabolites.

With regard to E3, the extent of degradation in a 6-liter laboratory activated sludge unit (equivalent to the set-up of OECD 303 A: Simulation Test – Aerobic Sewage Treatment) was assessed, considering different synthetic sewages and analyzing for important metabolites. The hydraulic retention time was 12 h instead of 6 h required by the guideline. However, according to Simple Treat v. 4.0 (Struijs, 2014), the default hydraulic retention time for sewage treatment plants with primary clarifier and without primary clarifier is 11.5 hours and 18 hours, respectively. Thus, 12 h retention time is a very good approximate for real life STPs. As a result, after an acclimation period of typically 2 days hydroquinone was removed by >=99.9%, independently of the influent concentration at concentrations between 50 mg/L and to 275 mg/L. This high value of degradation was observed independently from the synthetic sewage used, i.e. basal salts, only; synthetic domestic sewage; synthetic photographic sewage; or a 80:20 mixture of synthetic domestic and photographic sewage. The extent of TOC removal was between 70% and 92% for hydroquinone containing experiments, while it was lower (69%) in the control experiment without hydroquinone and synthetic domestic sewage, only. Thus, hydroquinone did rather stimulate than inhibit TOC removal in the STP simulation tests. Further, effluents were also analyzed for important metabolites of hydroquinone. But neither 1,4-benzoquinone could be detected (independently from the presence of sulfite, contained in synthetic photographic waste), nor 2-hydroxy-1,4-benzoquinone. Together with the supporting experiments on hydroquinone mineralization and metabolism described above, it can be assumed with high certainty that the high extent of hydroquinone removal of≥99.9 % observed in the simulation tests for aerobic sewage treatment plant can be attributed to mineralization and possibly microbial assimilation, and an accumulation of stable metabolites can be excluded.

Based on this extensive removal under relevant conditions (HRT 12 hours, independently of the kind of synthetic sewage used), a first order rate constant for the degradation in sewage treatment plants of 144/d is assumed for the chemical safety assessment. This rate constant is based on the following considerations: Using SimpleTreat model v. 3.1 with a sludge loading rate of 0.1 kg BOD per kg dwt per day (updated default according to Strujis et al., 2014) a biodegradation of 98.3% is resulting (98.4% total elimination from waste water) using the rate constant of 144/d, which is associated with a hydraulic retention time of 10.4 hours in STPs with primary settler. Thus, biodegradation extent is still below the value of >=99.9 reported by Harbison and Belly (1982). Further, this work conclusively demonstrated that biodegradation is not limited to primary biodegradation but thorough, and metabolites do not accumulate (none detected).

Struijs, J. (2014)

SimpleTreat 4.0: a model to predict the fate and emission of chemicals in wastewater treatment plants.Background report describing the equations. RIVM Report 601353005/2014

RIVM, National Institute for Public Health and the Environment, Bilthoven, The Netherlands