Sodium acrylate

Biodegradation in water: screening tests

Description of key information

Based on results of the structural analogue acrylic acid, sodium acrylate is readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

 

Based on the structural similarity and dissociation behavior of sodium acrylate in aqueous environment (see attached WoE justification in chapter 13.2), data from two highly reliable (Klimisch score 1) experimental studies with acrylic acid were mainly used to access the biodegradation potential of sodium acrylate. Due to the pH dependency of the reaction shift toward acrylic acid (at low pH values), the data for acrylic acid picture the worst-case scenario. Reliable QSAR calculations with sodium acrylate were used to support these findings (Klimisch score 2).

The biodegradability in water of the structural analogue acrylic acid was assessed in an experimental study according to GLP regulations and guideline EU Method C.4-A (Determination of the “Ready” Biodegradability -Dissolved Organic Carbon (DOC) Die-Away Test) (HuelsAG, 1995). Domestic activated sludge from a German municipal waste water treatment plant with a sludge concentration of 3.8 g/L was exposed to an initial test substance concentration of 15.08 mg/L DOC for 9 d. The DOC removal was measured via an infrared analyzer and compared to the reference substance benzoic acid, sodium salt and a blank control. After 9 d more than 90 % were degraded. According to OECD criteria acrylic acid is readily biodegradable. Based on the structural similarity and the dissociation process to acrylic acid, this can also be assumed for sodium acrylate.

The results from another reliable experimental study according to OECD guideline 301 D (Ready Biodegradability: Closed Bottle Test) confirm this finding (BAMM, 1991; REACH Dossier). The study was conducted according to GLP regulations, but only the draft report is available. Since study followed an OECD guideline and generally the GPL regulations, the results are considered trustworthy and no relevant deviations from the final report are expected.  A comparable inoculum was used and exposed to 3 mg/L test substance over 28 d. The same reference was used to assure the quality of the test system. The degradation was measured by the oxygen consumption over time. After 28 d more than 80 % were degraded and the OECD 10-day window criterion for readily biodegradability was fulfilled.

Sodium acrylate  is dissociating fast in aqueous medium (see Henderson-Hasselbach calculation). Therefore, no experimental studies can be conducted with sodium accrylate in water. To support the information from the studies with the structural analogue acrylic acid, QSAR calculations have been carried out with OASIS CATALOGIC v.5.14.1 and the model CATALOGIC Kinetic 301B v.02.10. Since sodium acrylate is a salt, it was not falling in the structural domain of the model and was therefore not completely within the applicability domain. Apart from that, NaA fulfils the general chemical properties requirements and is in the metabolic domain of the model. In order to this, the calculation can be considered reliable in combination with the experimental data from acrylic acid. Sodium acrylate and its possible metabolites were predicted to be ready biodegradable according to OECD criteria.

The entire data consisting of experimental studies for acrylic acid and a QSAR calculation with sodium acrylate indicate a fast biodegradation process for sodium acrylate and give no indication for persistence.