(1-hydroxyethylidene)bisphosphonic acid, potassium salt

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

comparable method to OECD guideline, but with some information not present.

Principles of method if other than guideline:

Monsanto Environmental Sciences method ES-79-M-15: Log Kow of the substance was measured by equilibrating aqueous solutions of radiolabelled compounds with n-octanol. The concentrations of the substance in each phase were determined by Liquid Scintillation Counting (LSC).

GLP compliance:

no

Type of method:

other: equilibrating aqueous solutions of radiolabelled compounds with n-octanol

Partition coefficient type:

octanol-water

Key result

Type:

log Pow

Partition coefficient:

-3.5

Remarks on result:

other: No other information is given.

Concentration in water (ppm)	Measured octanol/water partition coefficient
100	2.79 x10^-4
1000	3.29 x10^-4
1000	3.14 x10^-4
1000	3.39 x10 ^-4

average partition coefficient value = 3.15E-4 ( low Pow = -3.50)

Conclusions:

A log Pow value of -3.5 is was obtained for HEDP-H. The result is considered to be reliable.

Description of key information

log K_ow [HEDP-xK]: <-3.5

Key value for chemical safety assessment

Log Kow (Log Pow):

-3.5

Additional information

A log K_ow value of -3.5 was reported for the parent acid, HEDP-H in a reliable study conducted according to generally accepted scientific principles comparable to an appropriate test guideline. The method has been adequately described in the report. The result is considered to be reliable and has been assigned as key study.

HEDP-xK is freely soluble in water and, therefore, the HEDP anion is fully dissociated from its potassium cations when in solution. The HEDP anion has four P-OH groups that can be ionised. They lose hydrogen to form a negatively charged group (P-O^-). As the pH increases, the number of ionised groups increases. Under any given conditions, the degree of ionisation of the HEDP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was HEDP acid or salt.

Therefore, the log K_ow measured for HEDP-H is directly relevant for HEDP-xK. The log K_ow for an ionising substance will vary with pH as the ionised species will have a greater hydrophilicity and lower log K_ow than the neutral species. The pH was not measured in the study with HEDP-H, however, a solution of HEDP-H in unbuffered water will have a very low pH. Therefore, the log K_ow for HEDP-xK is reported as <-3.5.

For further details of the speciation of HEDP see PFA 2022 attached in Section 13 of the IUCLID dataset (Assessment reports: Speciation of HEDP).

Reference

PFA 2022: HEDP speciation at pH relevant to Ecotoxicology and Toxicology, Reference: PFA.224.612.001, March 2022.