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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The study was conducted according to a test protocol that is comparable to the appropriate test guideline. It was not compliant with GLP.
Principles of method if other than guideline:
Method: other (measured): Monsanto Environmental Sciences method ES-79-M-15
GLP compliance:
no
Type of method:
flask method
Partition coefficient type:
octanol-water
Analytical method:
other: Liquid scintillation counting
Key result
Type:
log Pow
Partition coefficient:
-4.7
Remarks on result:
other: No information on pH and temperature stated, 100 ppm concentration used
Type:
Pow
Partition coefficient:
0
Remarks on result:
other: No information on pH and temperature stated
Type:
Pow
Partition coefficient:
0
Remarks on result:
other: No information on pH and temperature stated
Key result
Type:
log Pow
Partition coefficient:
-4.1
Remarks on result:
other: No information on pH and temperature stated, 1000 ppm concentration used
Details on results:
The measured P values indicate that the Dequest phosphonates are very hydrophilic materials

Table 1: measured octanol/water partition coefficients

Dequest

Concentration in water (ppm)

Measured octanol/water partition coefficient

2051

100

2 x 10-5

100

2 x 10-5

100

2 x 10-5

1000

8.9 x 10-5

log Kow at 100 ppm = -4.7

log Kow at 1000 ppm = -4.1

Conclusions:
A measured Kow values of 2.0E-05 and 8.9E-5 were determined for HMDTMP-H at 100 ppm and 1000 ppm respectively in a reliable study conducted according to generally accepted scientific principles.

Description of key information

log Kow [HMDTMP (4-7Na)]: <-4.7

Key value for chemical safety assessment

Log Kow (Log Pow):
-4.7

Additional information

Log Kow values of -4.7 and -4.1 at 100 ppm and 1000 ppm respectively were reported for the parent acid, HMDTMP-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.

HMDTMP (4-7Na) is freely soluble in water and, therefore, the HMDTMP anion is fully dissociated from its potassium cations when in solution. The HMDTMP anion has eight P-OH groups that can be ionised. They lose a 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 HDMTMP 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 HMDTMP (4-7K), HMDTMP (4-7Na), HMDTMP-H or another salt of HMDTMP.

Therefore, the log Kow measured for HMDTMP-H is directly relevant for HMDTMP (4-7Na). The log Kow for an ionising substance will vary with pH as the ionised species will have a greater hydrophilicity and lower log Kow than the neutral species. The pH was not measured in the study with HMDTMP-H, however, a solution of HMDTMP-H in unbuffered water will have a very low pH. Therefore, the log Kow value relevant for the chemical safety assessment has been reported as <-4.7.

For further details of the speciation of HMDTMP see PFA 2020.

This value is supported by a predicted value of ≤-4 for HMDTMP-H using a relevant estimation method.

In a secondary source, a log Kow value of -4.4 was reported for HMDTMP-H in a summary of analytical data, full details are not available and the reliability is unassignable. The result is in agreement with the key study.

Reference

PFA 2020: HMDTMP speciation at pH relevant to Ecotoxicology and Toxicology, Reference: PFA.224.071.001, May 2020.