Glycollic acid

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance has a low octanol water partition coefficient and the adsorption potential of this substance is related to this parameter

the study does not need to be conducted because the substance and its relevant degradation products decompose rapidly

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to Column 2 of Annex VIII to REACH, the study does not need to be conducted because the substance is readily biodegradable (83.9% biodegradation after 28 days within the 10-day window, OECD TG 310, Hammersfahr 2021) and has a low potential for adsorption based on low octanol water partition coefficient (log Kow < -1.20, EU A.8., OECD TG 107, Foster 2021). However, the study may not be waived on the basis of low log Kow alone if the substance is surface active or ionisable at environmental pH (pH 4-9). Based on the chemical properties, the substance is not surface active (> 60 mN/m (exact value 73 mN/m), EU A.5., OECD TG 115, Foster 2021) but ionisable at environmental pH with a pKa at 3.77 (OECD TG 112, Foster 2021). The substance will mainly exist as the carboxylate anion (expected >99% ionised at pH >= pKa+2, so >= 5.77) but may exist under both base and acid forms at low pH and therefore, in the environmentally relevant range of 4 to 5.77. See details below:
- at pH <= 1.77 (pKa-2): > 99% unionised form (COOH);
- at pH <= 2.77 (pKa-1): > 90% unionised form (COOH);
- at pH > 2.77 but < 4.77: dissociation, mixture of forms (COOH/COO-);
- at pH >= 4.77 (pKa+1): > 90% ionised form (COO-);
- at pH >= 5.77 (pKa+2): > 99% ionised form (COO-).
However, the log Kow/logD of the substance was found to be < -1.20 at 20 °C and pH 2 (non-ionised form), 5, 7 and 9 (ionised form). pH differences and therefore ionisation of the substance have no effects on the octanol water partition coefficient. Therefore, the adsorption potential within the normal pH range and with the different forms of the substance are expected to be the same if only related to lipophilicity. With a log Kow <= 3 under both ionised and non-ionised forms, the substance has a low potential for adsorption at environmental pH based on lipophilicity related adsorption. This justification is supported by an adsorption study provided in the dossier (OECD TG 121, HLS 2002) with a Koc value measured < 25 at both pH 4 (mixture of forms) and pH 10 (dissociated/ionised form). In addition, considering particulate matter (e.g. clay and organic matter) are negatively-charged soil particles [1] and Dissolved Organic Matter (DOM) are largely negatively charged too under environmentally relevant pH based on the chemical properties of the substance, repulsion caused by anionic charges is expected (i.e. not adsorbed). In conclusion, a low potential for adsorption on soil and sewage sludge is expected for the substance based on the rapidly degradation, the pKa, the anionic nature of the substance and the log Kow/Koc results at varying pHs.

Reference:
[1] David D. Mengel, Fundamentals of Soil Cation Exchange Capacity (CEC). Cooperative Extension work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating: H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an equal opportunity/equal access institution.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

Version / remarks:

; equivalent to Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

no

GLP compliance:

yes

Type of method:

HPLC estimation method

Media:

soil

Test temperature:

25°C

Details on study design: HPLC method:

HPLC (HP 1050 LC), Column (Hypersil 5 µm, 25 cm L x 4.6 mm i.d., 25°C), mobile phase (acetonitrile/buffer solution 55/45 v/v, 1 mL/min), UV detection (wavelength 210 nm). The column deadtime was determined using sodium nitrate.
Injections (10 µL) were performed of the reference materials and the test solutions. A calibration graph of log KOC against capacity factor was determined for the reference materials.

Details on sampling:

Duplicate 12g/L solutions of Glycolic acid solution in HPLC mobile phase, containing internal deadtime standard (83 mg/l), were prepared and chromatographed. The samples of test substance were bracketed with samples of the reference mixture.

Details on test conditions:

Duplicate solutions of glycolic acid (ca 12 g/L) in mobile phase for pH 4, pH 10 were analysed using the HPLC system specified below. The test solutions also contained an internal deadtime standard (sodium nitrate) for determination of the column void time.

Type:

log Koc

Value:

< 1.4

Details on results (HPLC method):

Glycolic acid exhibited very little retention corresponding to a log KOC value of less than 1.4 at pH values of 4 and 10 mL/g (i.e. equivalent to a KOC value of less than 25 mL/g).

Validity criteria fulfilled:

yes

Conclusions:

Glycolic acid has a KOC value of less than 25 mL/g at pH values of 4 and 10.

Executive summary:

The adsorption properties of glycolic acid were investigated using the HPLC method (OECD 121). The GLP study was conducted in 2002.

Reference compounds were select with log KOC values in the range 1.4 to 5.4 mL/g (i.e. equivalent to KOC values of 25 to ca 250000 mL/g) to calibrate the HPLC set-up. Glycolic acid exhibited very little retention corresponding to a log KOC value of less than 1.4 at pH values of 4 and 10 (i.e. equivalent to a KOC value of less than 25 mL/g). With a KOC value of less than 25 mL/g, glycolic acid can be considered to have a low potential to adsorb to soil and is classified as very mobile to mobile according to the SSLRC (Soil Survey and Land Research Council,) classification index. 

 

Glycolic acid has a KOC value of less than 25 mL/g at pH values of 4 and 10.

Description of key information

Data waiving according to Column 2 of Annex VIII to REACH. A low potential for adsorption on soil and sewage sludge is expected for the substance based on the rapidly degradation, the pKa, the anionic nature of the substance and the log Kow/Koc results at varying pHs.

Additional information

The data waiving justification is supported by an adsorption study provided in the dossier (OECD TG 121, HLS 2002). Glycolic acid has an estimated log Koc value of less than 1.4 L/kg (i.e. equivalent to a Koc value of less than 25 L/kg). The EPIWIN model domain was evaluated for applicability to glycolic acid to further refine the Koc value. Glycolic acid is a polar compound with a MW of 76.05. The relevant regression equation within KOCWIN v2.0 is: log Koc = 0.5213 MCI + 0.60 + correction factors (where n = 447, r2 = 0.90). The preferred log Koc to use is that derived from the first order molecular connectivity index (MCI) model when an experimental log Kow is not available or reported as a less than value. The MCI of the glycolic acid lies within the range of values defined by the training set (MCI 1.0-16.58). A correction factor is applied to account for the test substance being an acid and therefore able to ionise. Since the test substance lies within the domain of the QSAR as defined by this parameter value and the mode of action, its prediction is considered valid for use. The predicted log Koc is -1.1596 L/kg which is adjusted to a lower limit log Koc of 0.00. Thus the predicted Koc is 1.0 L/kg. The low measured and calculated Koc values for the substance are consistent with its pKa of 3.77 and the fact that substance ionisation is not an important factor. The substance will mainly exist as the carboxylate anion at environmentally relevant pH.