Propanoic acid, 2-(4-hydroxyphenoxy)-, potassium salt (1:1), (2R)-

Biodegradation in water: screening tests

Description of key information

Ready biodegradability of (R)-2-(4-hydroxyphenoxy)propanoic acid was assessed using a CO2evolution test with activated sludge from a domestic sewage treatment plant according to OECD 301/B. 
Biodegradation of the test substance was 87 % in 29 days. The pass level (60 %) was achieved on day 12. Within the time window of 10 days after start of degradation at day 6, 76% degradation occurred.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Validity of the read-across

Biodegradation of potassium (R)-2-(4-hydroxyphenoxy)propionate, (CAS 1184648-08-5) was determined by read-across from a biodegradation study conducted with the free acid, namely (R)-2-(4-hydroxyphenoxy)propanoic acid (CAS 94050-90 -5).

This read-across is valid as the test was performed in aqueous medium where the potassium salt of the acid normally dissociates into potassium cations and the free acid anion.

Regarding the pK_aof (R)-2-(4-hydroxyphenoxy)propanoic acid of 3.32 it can be assumed that the acid, when dissolved in water under environmental relevant concentrations (pH > 4), will instantly be deprotonated and become the same acid anion as after dissociation of the potassium salt. As in the experiments (R)-2-(4-hydroxyphenoxy)propanoic acid showed no alteration of the test medium pH of 7.8 it can be assumed that also the potassium salt should not cause greater changes in pH.

The additional potassium ions dissociating from the salt should have no further impact on biodegradation as the concentration of potassium ions in the test medium according to OECD 301 is already 6 times higher. Furthermore, potassium ion concentration needs not to be assessed for biodegradation as these tests focus only on degradation of organic compounds.

At the highest tested concentration of (R)-2-(4-hydroxyphenoxy)propanoic acid (100 mg/L), the molar concentration of the acid is 0.55 mmol/L. Due to the different molar weight of the potassium salt, the limit concentration of 100 mg/L corresponds to a lower molar concentration of only 0.45 mmol/L for the potassium salt. It can therefore be concluded that biodegradation of potassium (R)-2-(4-hydroxyphenoxy)propionate is at least equal or even higher compared to the acid.

Biodegradation of (R)-2-(4-hydroxyphenoxy)propanoic acid

Ready biodegradability of (R)-2-(4-hydroxyphenoxy)propanoic acid was assessed using a CO₂evolution test with activated sludge from a domestic sewage treatment plant according to OECD 301/B.

Biodegradation of the test substance was 87 % in 29 days. The pass level (60 %) was achieved on day 12. Within the time window of 10 days after start of degradation at day 6, 76% degradation occurred.

Based on the criteria according to the Regulation (EC) No 1272/2008, Annex I, Part 4, 4.1.2.9 the test item was demonstrated to be rapidly (or readily) biodegradable.

 Biodegradation of potassium (R)-2-(4-hydroxyphenoxy)propionate

As stated above, potassium (R)-2-(4-hydroxyphenoxy)propionate, when dissolved in water becomes equal to the test item (R)-2-(4-hydroxyphenoxy)propanoic acid and ready biodegradability of the potassium salt is therefore equal to the biodegradability measured for the acid. It can therefore be concluded without reasonable doubt that potassium (R)-2-(4-hydroxyphenoxy)propionate is also rapidly (or readily) biodegradable.