Glycollic acid

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

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 potential for bioaccumulation based on log Kow <=3

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to Column 2 of Annex IX to REACH, the study does not need to be conducted because the substance has a low potential for bioaccumulation 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-).
The non-dissociated form (unionised form) is considered to be the most bioaccumulative form [1]. In other words, ionisation lowers the tendency of a chemical for bioaccumulation, compared to non-ionised chemicals, due to the lipophobicity of ionic molecule moieties. Indeed, due to the relationship between logD and pH [2], logD of ionised forms are generally lower than non-ionised forms. For acid compound, when pH increase, logD decrease, meaning that the more COO- form we have, the less hydrophobic and bioaccumulative the substance is. In addition, fast depuration, due to rapid metabolism of charged compounds, seems to be a major reason for the observed low bioaccumulation of ionic compounds, in particular anions [3] (Mueller et al., 2020). Then, due to the low membrane permeability of organic ions, increased ionisation is expected to reduce gill absorption rates [4] (Armitage et al., 2016). 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. A negative value of log Kow in the physiologically relevant pH range lead to the conclusion that this compound would be more susceptible to higher aqueous solubility and of lower lipophilicity in the body/organism [2]. In conclusion, a low potential for bioaccumulation is expected for the substance based on the pKa, the anionic nature of the substance and the log Kow results at varying pHs.

References:
[1] OECD guidance document No. 23, February 2019
[2] https://www.scribd.com/presentation/98530535/pKa-log-P-log-D-and-absorption
[3] Carolin Mueller, Stefan Trapp, Fabio Polesel, Sebastian Kuehr and Christian Schlechtriem, 2020. Biomagnification of ionizable organic compounds in rainbow trout Oncorhynchus mykiss. Environmental Sciences Europe (2020) 32:159.
[4] James M. Armitage, Russell J. Erickson, Till Luckenbach, Carla A. Ng, Ryan S. Prosser, Jon A. Arnot, Kristin Schirmer and John W. Nichols, 2016. Assessing the bioaccumulation potential of ionizable organic compounds: current knowledge and research priorities. Environmental Toxicology and Chemistry, Vol. 36, No. 4, pp. 882-897, 2017.

Description of key information

Data waiving according to Column 2 of Annex IX to REACH. A low potential for bioaccumulation is expected based on the pKa, the anionic nature of the substance and the log Kow results at varying pHs.