Glycollic acid

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:

guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

not specified

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Reference substance:

acetic acid, sodium salt

Preliminary study:

The Theoretical Oxygen Demand (TOD) of glycolic acid was calculated as 0.5 mg O2 per mg of test substance.

Value:

89.6

Sampling time:

7 d

Details on results:

No further information.

Results with reference substance:

Biodegradation of the control chemical, sodium acetate, exceeded 60% within 14 days

Glycolic acid reached 89.6% biodegradability after 7 days and the test was stopped. 

So, biodegradability was > 60% within 28 days and that this level of biodegradability was achieved within 14 days of exceeding the 10% level of biodegradability.

Validity criteria fulfilled:

yes

Remarks:

The biodegradation of the control chemical, sodium acetate, exceeded 60% within 14 days, therefore the test is considered valid.

Interpretation of results:

readily biodegradable

Executive summary:

The biodegradability of glycolic acid was investigated using the OECD 301D guideline (Closed bottle test).Glycolic acid is classified as readily biodegradable. After 7 days, 89.6% of the test material was biodegraded. A minimum 60% biodegradability is required to pass this test. In addition, the "pass level" of 60% must be reached within a 14-day window after exceeding the 10% level.

Reference 2

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:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

; Modified Sturm test

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

Activated sludge collected from the City of Wilmington POTW was used as the inoculum

Duration of test (contact time):

28 d

Initial conc.:

71.7 other: µL/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

The study meets the recommended guideline (EC methods C.4 A to F or the corresponding OECD 301 A to F guidelines).

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

78

Sampling time:

11 d

Results with reference substance:

In the presence of glycolic acid and the reference substance, sodium benzoate, greater than 25% biodegradation was observed within 14 days.

Validity criteria fulfilled:

yes

Remarks:

Sodium benzoate (the positive control chemical) was >=60% biodegraded within 4 days, therefore the test is considered valid.

Interpretation of results:

readily biodegradable

Conclusions:

The test material (glycolic acid) reached a peak of 78% biodegradability at day 11. Glycolic acid is classified as readily biodegradable since biodegradability was > 60% within a 10-day window after exceeding the 10% level of biodegradability.

Executive summary:

The biodegradability of glycolic acid was investigated using the OECD 301B guideline (Modified Sturm test).

Biodegradability was > 60% within the 10 day window after exceeding the 10% level of biodegradability. In the presence of glycolic acid and the reference substance, sodium benzoate, greater than 25% biodegradation was observed within 14 days. Therefore glycolic acid is not considered as inhibitory to microorganisms in the inoculum.

 

Glycolic acid is classified as readily biodegradable (and passing the 10-day window).

Reference 3

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

5 January to 21 April, 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)

Version / remarks:

26 September, 2014

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Origin:
Activated sludge, microorganisms from a domestic wastewater treatment plant were supplied by a municipal sewage treatment plant (Rossdorf, Germany).

Conditioning:
The activated sludge was used as collected, but coarse particles were removed by settling for a short period (15 minutes) and the supernatant liquid phase was decanted. The solid material was re-suspended in test water and again centrifuged. This procedure was repeated three times. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined. Based on this ratio, calculated aliquots of washed sludge suspension were mixed with test water, corresponding to 4 g dry material per litre.

Duration of test (contact time):

28 d

Initial conc.:

31.7 mg/L

Based on:

TOC

Remarks:

10.0 mg carbon per litre, based on an organic carbon content of 0.316 mg carbon/mg test item

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

Test units and conditions:
Tests were conducted in glass bottles with screw-caps and Teflon-coated septa (125 mL nominal, 128 mL total volume) in a controlled environment room (20 - 21°C) in the dark. The pH value of the test water was 7.6. The activated sludge was aerated with CO2-free air prior to test start. Test conditions were recorded with suitable instruments and documented in the raw data.

Test solutions preparation:
Test Item: 79.29 mg test item was weighed into a total volume of test water (2500 mL) and activated sludge (2.5 mL of a stock solution of 4 g/L suspended solids) was added to achieve a concentration of 4 mg/L suspended solids in test water. The mixture was stirred intensively, and appropriate amounts were dispensed into the test vessels and sealed with gas-tight septum caps.
Inoculum Control: Activated sludge (2.5 mL of a stock solution of 4 g/L suspended solids) were added to the test water (2500 mL) to achieve a concentration of 4 mg/L suspended solids in test water. The mixture was stirred intensively, and appropriate amounts were weighed into the test vessels and sealed with gas-tight septum caps.
Procedure Control: 25.74 mg reference item sodium benzoate was weighed into a total volume of test water (1500 mL) and activated sludge (1.5 mL of a stock solution of 4 g/L suspended solids) was added to achieve a concentration of 4 mg/L suspended solids in test water. The mixture was stirred intensively, and appropriate amounts were weighed into the test vessels and sealed with gas-tight septum caps.
Toxicity Control: The toxicity control contained both the test item and the reference item. 47.64 mg test item and 25.86 mg reference item were weighed into a total volume of test water (1500 mL) and activated sludge (1.5 mL of a stock solution of 4 g/L suspended solids) was added to achieve a concentration of 4 mg/L suspended solids in test water. The mixture was stirred intensively, and appropriate amounts were weighed into the test vessels, containing the evaporated test item and sealed with gas-tight septum caps.
Sodium Hydroxide Solution 7M: To avoid an additional background carbon entry via the Sodium hydroxide solution, two additional flasks with Sodium hydroxide solution were prepared at each sampling date. The measured inorganic carbon content of the test flasks were corrected by this blank value.

Headspace to Liquid Ratio: 1:2
Test Item Loading Rate: 31.7 mg test item/L (10.0 mg carbon per litre, based on an organic carbon content of 0.316 mg carbon/mg test item).
Reference Item Loading Rate: 17.2 mg/L (10.0 mg carbon per litre, based on an organic carbon content of 0.583 mg carbon/mg reference item).
Test Item and Reference Item Loading Rate for Toxicity Control: 31.8 mg test item/L (10.0 mg carbon per litre) and 17.2 mg reference item /L (10.0 mg carbon per litre).

Course of the test:
Three replicates per treatment and per sampling were prepared. For the day 28 sampling totally 5 replicates per treatment were prepared. For the test item and inoculum control test solutions, samples were taken on days 0, 3, 6, 10, 13, 17, 20, 28 and on days 0, 6, 13, 28 for the procedure control and toxicity control solutions. Test vessels were shaken during the incubation time until sampling.

Sampling Procedure:
The produced CO2 was converted into carbonate using 7M NaOH solution (0.8 mL to 85 mL test medium) injected into the test vessels at each sampling. The alkalised medium was shaken for 1 hour and subjected to TIC (total inorganic carbon) analysis. The analysis was done immediately after sampling or the alkalised samples were stored in the refrigerator (4±4°C) for a maximum of 7 days. The same sodium hydroxide solution used for alkalisation was used within the experiment. The TIC (total inorganic carbon) of that solution was between 0.71 and 3.27 mg TIC/L (mean).

Determination of evolved CO2 (TIC) by TOC-analyser:
The total inorganic carbon content (TIC) consists of the carbon contained in carbonates and in carbon dioxide dissolved in water. By acidifying the sample with a small amount of hydrophosphoric acid to obtain a pH less than 3, all carbonates were converted to carbon dioxide. Carbon dioxide and dissolved carbon dioxide in the sample were volatilized by bubbling CO2-free air through the sample and flushed by the carrier air into the detector of the TOC analyser. The TIC-content was analysed automatically using the sealed test vessels as sampling vials.

Reference substance:

benzoic acid, sodium salt

Preliminary study:

Not applicable

Test performance:

The mean amounts of TIC present in the inoculum controls at the end of the test was 0.34 mg C/L, therefore fulfilling this validity criteria (i.e. < 3 mg C/L (after correction with NaOH-solution)).
The toxicity control showed 86.9% biodegradation within 13 days and 81.7% biodegradation after 28 days of incubation, therefore concluding that the test item is non-inhibitory.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

83.9

Sampling time:

28 d

Parameter:

% degradation (CO2 evolution)

Value:

63.4

Sampling time:

3 d

Details on results:

The mean degradation of Glypure™ 99 was 63.4% at the first post-initiation measurement made on day 3 and simultaneously exceeded both the 10% degradation threshold and the 60% trigger for classification as readily biodegradable. In this situation, and as the first measurement was made after fewer than 10 days, the 10- day window further consideration of the 10-day window is not necessary. Subsequently, the degradation of Glypure™ 99 reached plateau phase by day 6 and remained constantly high for the remainder of the test. Degradation was 83.9% at test end at day 28.

Results with reference substance:

The reference item (sodium benzoate) was sufficiently degraded to 78.9% after 13 days and to 85.9% after 28 days of incubation, thereby confirming the suitability of the used aerobic activated sludge inoculum and fulfilling this validity criteria (i.e. >60% biodegradation by day 14).

Inorganic Carbon produced in Test Flasks during the Test Period of 28 Days

Treatment	C-content [mg/L]	Replicate	Day
			0	3	6	10	13	17	20	28
			TIC [mg/L]
Control	---	1	0.00	0.00	1.40	0.00	0.36	0.70	0.51	0.43
		2	0.00	0.00	1.36	0.00	2.07	0.46	0.28	0.35
		3	0.00	0.00	1.37	0.00	0.79	0.54	0.39	*
		4	--	--	--	--	--	--	--	0.27
		5	--	--	--	--	--	--	--	0.32
		Mean	0.00	0.00	1.38	0.00	1.07	0.56	0.39	0.34
Na-benzoate	10.000	1	0.34	--	9.48	--	10.76	--	--	8.71
		2	0.55	--	7.92	--	10.47	--	--	9.31
		3	0.61	--	7.87	--	6.28	--	--	10.16
		4	--	--	--	--	--	--	--	8.04
		5	--	--	--	--	--	--	--	9.45
		Mean	0.50		8.43		9.17			9.13
Glypure glycolic acid 99	10.024	1	0.00	5.34	10.69	7.25	9.78	8.77	8.32	8.34
		2	0.00	9.09	9.43	6.64	10.01	8.09	8.37	8.83
		3	1.60	4.63	10.28	7.28	9.08	8.53	8.52	9.25
		4	--	--	--	--	--	--	--	8.51
		5	--	--	--	--	--	--	--	8.80
		Mean	0.53	6.35	10.14	7.06	9.62	8.46	8.40	8.75
Toxicity control	20.082	1	1.15	--	15.41	--	19.29	--	--	15.62
		2	0.47	--	15.47	--	18.99	--	--	18.07
		3	0.78	--	15.35	--	17.27	--	--	15.99
		4	--	--	--	--	--	--	--	17.00
		5	--	--	--	--	--	--	--	17.01
		Mean	0.80		15.41		18.52			16.74
NaOH-solution		1	1.71	1.62	1.39	3.96	1.49	0.77	0.81	1.65
		2	1.10	4.92	1.51	1.49	1.70	0.66	0.72	1.45
		Mean	1.41	3.27	1.45	2.72	1.59	0.71	0.77	1.55

1: corrected by blank value of the NaOH-solution --: not applicable; *: flask could not be measured due to technical reasons

 

Biodegradation of Test Item, Reference Item and Toxicity Control during the Test Period of 28 Days

Treatment	C-content [mg/L]	Replicate	Day
			0	3	6	10	13	17	20	28
			% biodegradation [net measured TIC / initial C x 100] [mg/L]
Na-benzoate	10.000	1	3.3	--	79.2	--	94.4	--	--	81.8
		2	5.3	--	63.9	--	91.6	--	--	87.6
		3	6.0	--	63.4	--	50.7	--	--	95.9
		4	--	--	--	--	--	--	--	75.3
		5	--	--	--	--	--	--	--	89.0
		Mean	4.9		68.8		78.9			85.9
Glypure glycolic acid 99	10.024	1	0.0	53.2	92.9	72.4	86.9	81.9	79.1	79.8
		2	0.0	90.7	80.3	66.2	89.2	75.2	79.6	84.7
		3	16.0	46.2	88.8	72.6	79.9	79.5	81.1	88.9
		4	--	--	--	--	--	--	--	81.5
		5	--	--	--	--	--	--	--	84.4
		Mean	5.3	63.4	87.3	70.4	85.3	78.9	79.9	83.9
Toxicity control	20.082	1	5.7	--	69.9	--	90.7	--	--	76.1
		2	2.3	--	70.2	--	89.2	--	--	88.3
		3	3.9	--	69.6	--	80.7	--	--	77.9
		4	--	--	--	--	--	--	--	83.0
		5	--	--	--	--	--	--	--	83.0
		Mean	4.0		69.9		86.9			81.7

1: corrected by the inoculum control; --: not applicable

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The mean degradation of Glypure™ 99 was 63.4% at day 3, thereby simultaneously exceeding both the 10% degradation threshold and the 60% trigger for classification as readily biodegradable. The mean biodegradation of Glypure™ 99 was 83.9% at day 28.

Executive summary:

The ready biodegradability of Glypure™ 99 was investigated in a CO₂ headspace test over a period of 28-days, according to OECD Guideline 310.

Biodegradation was determined by following the CO₂ evolution of the test item in the incubation flasks during exposure. As a reference item, sodium benzoate was tested simultaneously under the same conditions as the test item, functioning as a procedure control. In addition, an inoculum control and a toxicity control were also tested simultaneously under the same test conditions. The degradation rate of the test item is calculated by the CO₂ evolution of the aerobic activated sludge microorganisms by measuring the inorganic carbon in the test flasks corrected by control vessels.

 

Sodium benzoate was sufficiently degraded to 78.9% after 13 days and to 85.9% after 28 days of incubation, thereby confirming the suitability of the used aerobic activated sludge inoculum and fulfilling this validity criteria (i.e. >60% biodegradation by day 14). The mean amounts of TIC present in the inoculum controls at the end of the test was 0.34 mg C/L, therefore fulfilling this validity criteria (i.e. < 3 mg C/L (after correction with NaOH-solution)). The toxicity control showed 86.9% biodegradation within 13 days and 81.7% biodegradation after 28 days of incubation, therefore concluding that the test item is non-inhibitory.

 

The mean degradation of Glypure™ 99 was 63.4% at day 3, thereby simultaneously exceeding both the 10% degradation threshold and the 60% trigger for classification as readily biodegradable. The mean biodegradation of Glypure™ 99 was 83.9% at day 28.

Description of key information

Studies assessing the ready biodegradability of glycolic acid are available, with the key (most reliable) study resulted in 83.9% degradation (based on CO₂ evolution) after 28 days, meeting the 10-day window (Hammesfahr, 2021a). Glycolic acid is therefore concluded to be ready biodegradability. This key study was GLP compliant and met all validity criteria of the study guidelines followed (OECD Guideline 310 and ISO 14593).

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

Glycolic acid is classified as readily biodegradable.