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

Endpoint summary

Additional information

Validity of the read-across

The aquatic toxicity of potassium (R)-2-(4-hydroxyphenoxy)propionate (CAS 1184648-08-5) was determined by read-across from aquatic toxicity studies conducted with the free acid, namely (R)-2-(4-hydroxyphenoxy)propanoic acid (CAS 94050-90-5).

This read-across is valid as all tests were performed in aqueous solutions where the potassium salt of the acid normally dissociates into potassium cations and the free acid anion.

Regarding the pK_a of (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 it can be assumed that also the potassium salt should not cause greater changes in test medium pH.

The additional potassium ions dissociating from the salt should have no further impact on toxicity. Compared to the highest test item concentrations of 100 mg/L (0.45 mmol/L for the potassium salt) the potassium levels in the OECD recommended test media for fish and daphniae are more than 6 times higher (3 mmol/L).

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 estimation of toxicity from the acid to the potassium salt is quite conservative.

 Aquatic toxicity of (R)-2-(4-hydroxyphenoxy)propanoic acid

The aquatic toxicity tests of (R)-2-(4-hydroxyphenoxy)propanoic acid were assessed on the organisms fish, daphniae, algae and bacteria.

In an acute fish-toxicity study, the NOEC was found to be 100 mg/L (Rufli 1995). Immobilisation of daphnids was visible only at 100 mg/L, with 58 mg/L being the NOEC (Neumann 1996). Algal growth was also reduced not until 100 mg/L with a NOEC of 46 mg/L (Memmert 1996). Inhibition of bacterial respiration was in all concentrations ≤ 15% with no visible dose response (Grade 1996). The respective LC50/EC50 values were all > 100 mg/L.

Based on the aforementioned results and applying the classification criteria according to the Regulation (EC) No 1272/2008, Annex I, Part 4, 4.1.2.6, the test item (R)-2-(4-hydroxyphenoxy)propanoic acid is not classified as hazardous to the aquatic environment.

 

Aquatic toxicity 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. It can therefore be assumed that the aquatic toxicity of the potassium salt is equal to the aquatic toxicity of the acid. It is therefore highly likely that potassium (R)-2-(4-hydroxyphenoxy)propionate can also be considered to be not hazardous to the aquatic environment.