Phosphorodithioic acid, O,O-di-dodecyl-esters, zinc salts, neutral and basic

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Study period:

10 Dec - 18 Dec 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)

Version / remarks:

adopted in 2004

Qualifier:

according to guideline

Guideline:

EU Method A.8 (Partition Coefficient - HPLC Method)

Version / remarks:

adopted in 2008

GLP compliance:

yes (incl. QA statement)

Remarks:

Ministerium für Arbeit, Integration und Soziales des Landes Nordrhein-Westfalen, Düsseldorf, Germany

Type of method:

HPLC method

Partition coefficient type:

octanol-water

Specific details on test material used for the study:

Storage conditions: at room temperature; tightly closed; dry

Analytical method:

high-performance liquid chromatography

Type:

log Pow

Partition coefficient:

>= 3.4 - <= 5.6

Temp.:

25 °C

pH:

6.95

Results
Table 1 – Summary of HPLC test item results

Sample	tR1[min]	tR2 [min]	k’	log k’	log POW
Test item	3.00		1.564	0.194	3.289*
	11.83		9.111	0.960	5.601*
Test item		3.38	1.89	0.276	3.536*
		11.82	9.103	0.959	5.598*
Mean value					3.4
					5.6

*interpolated from the linearized function of the calibration data

The test item was determined by double determination in 2 independent measurements. The test item resulted in an unresolved band, therefore upper and lower limits of log P_OWwere determined.

Discussion
The deviation of the log P_OWvalues of the test item (upper limit) from the mean value fall within a range of ≤0.1 units as given by the guideline. In case of the lower limit, the deviation is slightly larger (0.12) but it resulted from a small difference of retention time of 0.38 min. It was thus regarded as not relevant for the test evaluation.

The reference item ‘Spindelöl R2’ (given by the study sponsor, used as solvent for zinc dialkyl dithiophosphate) was investigated in comparison to the test item. The components of this item eluted in the form of a broad distribution below the components of the test item. The compounds mounted onto this broad distribution were evaluated; in the range around 3 min ‘Spindelöl R2’ caused an unusual high fluctuation of the left limit of the Zn compound.

Conclusion
The partition coefficient of the test item at 25 °C was determined to be log P_OW= 3.4 – 5.6.

Description of key information

log P_OW = 3.4 – 5.6 at 25 °C and pH 6.95 (OECD 117, HPLC Method)

Key value for chemical safety assessment

Log Kow (Log Pow):

3.4

at the temperature of:

25 °C

Additional information

In the study of determination of partition coefficient, two peaks show in the HPLC chromatogram during the measurement of log Pow, which implies the complex structures of ZDDP: The monomeric or dimeric neutral forms together with the basic form are present in the substance. The basic form might be less water soluble than the neutral forms, therefore it might have a higher log Pow than the neutral forms. Based on this assumption it can be concluded that the log Pow value of 5.6 determined by HPLC belongs to the basic form of ZDDP, whereas the log Pow value of 3.4 is obtained because of neutral forms.

Because the basic form is a big size molecule (m.w. ca. 3072), it has low bioaccessibility and bioavailability. Although its log Pow is higher than 4.5, it is considered not relevant for the bioaccumulation. This is supported by the profilers in QSAR tool box: the basic form has a very slow bioaccumulation metabolism half-live.

Therefore the log Pow from neutral forms (3.4) is used as key value for the chemical safety assessment.