Glycollic acid

Endpoint summary

Description of key information

Glycolic acid is a naturally occurring low molecular weight organic acid. It is a ubiquitous part of the organic matter in surface water and is known to be an excretion product of algae. It is also found in the fruit, leaf, stem and root portions of all plants. Commonly consumed fruits and vegetables are reported to contain from 4.5 to 74 mg glycolic acid/kg. Tea, coffee, fruit juice and other beverages derived from plant sources may contain 50 to 70 mg glycolic acid/L. Foods of animal origin are generally low in glycolic acid, with milk and beef reported to contain 0.6 to 1.2 mg glycolic acid/kg (NICNAS, 2000).

 

Degradability of glycolic acid:

Glycolic acid is concluded to be hydrolytically stable based on results from the key hydrolysis study (conducted according to OECD Guideline 111), which showed < 10% hydrolysis in the preliminary study conducted in pH 4, 7 and 9 buffered solutions at 50°C after 5 days, corresponding to a half-life of > 1 year at 25°C (Berti, 2002a).  

 

The UV/Vis absorption spectra of glycolic acid demonstrates no absorption in the visible region (i.e. wavelengths ³290 nm). Consequently, photolysis of glycolic acid is not considered to be a significant pathway and studies to investigate phototransformation in aqueous solution are scientifically irrelevant. This conclusion is supported by the peer reviewed publication by Klementova and Wagnerova (1990), which showed that glycolic acid was not significantly photolysed under artificial sunlight without the aid of a catalyst or sensitisers. Therefore, a worst-case half-life of 1E+6 days is assumed for environmental risk assessment purposes.

 

Although a half-life life of 41.247 hours in air (based on a 12-hour day OH concentration of 1.5E+6 OH radicals/cm³) was estimated for glycolic acid via the AOPWIN (v1.90) QSAR model, it is noted that the substance was not within the applicability domain of the model, thus this predicted atmospheric degradation half-life cannot be considered valid (Curl, 2007). Due to the chemical lifetime of glycolic acid in the air, it is to be expected that the active substance cannot be transported in the gaseous phase over large distances and cannot accumulate in the air. Thus, no difference in the behaviour between glycolic acid and other organic substances emitted into the air from natural sources (e.g. plants, soil) is indicated.

 

Glycolic acid is concluded to be ready biodegradability based on data from the key ready biodegradability study, which resulted in 83.9% degradation (based on CO₂ evolution) after 28 days, meeting the 10-day window (Hammesfahr, 2021a).

 

An aerobic and anaerobic soil degradation study according to OECD Guideline 307 is currently ongoing for glycolic acid, the dossier will be updated accordingly when available.

 

Based on the abovementioned data, glycolic acid is concluded to be rapidly degradable.

 

Mobility of glycolic acid:

Glycolic acid will exist as an anion under all environmental conditions (pKa = 3.1) and is likely to be mobile in soil. Adsorption/desorption data are available for glycolic acid according to the HPLC method (OECD Guideline 212) which resulted in a Koc value of < 25 L/kg (log Koc = < 1.4 L/kg) at pH values of 4 and 10 (Comb, 2002). Glycolic acid is therefore considered low adsorption potential and therefore to be very mobile in soil.

Additional information

NICNAS (2000). Commonwealth of Australia. Glycolic Acid, Priority Existing Chemical Assessment. Report no.: 12. Report date: 2000-03-30.