Dibutyl hydrogen phosphate

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

HPLC estimation method

Media:

soil/sewage sludge

Radiolabelling:

no

Test temperature:

The adsorption coefficient (Koc) of dibutyl hydrogen phosphate was determined according to the HPLC method at 40 °C. In order to comply with the guideline OECD 121 and considering environmental relevance, pH 6 was chosen as pH value for the buffer. The reference Koc-values in the OECD-guideline presumably refer to 25 °C. Even though the column temperature was 40 °C, this temperature is without influence on the result of the determination. The calibration was done referring to Koc-values of reference substances determined at 25 °C.

Details on study design: HPLC method:

Chromatograph: High Performance Liquid Chromatograph, HP 1100 MSD:
Chromatographic conditions:
- Column type: length: 250 mm, inner diameter: 4 mm
- Stationary Phase: LiChrospher 100 CN, particle diameter: 5 μm
- Supplier: Fa. Merck
- Mobile Phase:
- A: 1000 ml demineralized water (Millipore) + 0.8 g ammonium acetate*
- B: 1000 ml acetonitrile + 0.8 g ammonium acetate*
*(Merck, Art. No. 1.01116)

- Flow rate: 0.75 ml / minute
- Column Temperature: 40 °C
- Injection volume: 3 μl
- Detection: UV, 210 nm MS, ESI negative Sim, m/z 209, 210
- Gas temperature: 350 °C
- Drying gas: 13 l / minute
- Capillary voltage: 2500 V

Computational methods:

The log Koc value was calculated with the software PCKOCWIN v1.66 assuming the nonionic form. PCKOCWIN is owned by the U.S. Environmental Protection Agency.
For dibutyl hydrogen phosphate, the calculated adsorption coefficient is: log Koc = 2.2.

Key result

Type:

log Koc

Value:

0.5

Temp.:

25 °C

Determination of the Adsorption Coefficient (Koc). Mean of 3 single values.

Calibration item	Retention time [tr] = (min)	Standard deviation of the retention time [tr] (min)	Relative standard deviation%	Capacity factor k'	Log k'	log Koc
Sodium nitrate(dead time (t0))	2.529	-	-	-	-	-
2 -Nitrobenzamide	4.673	0.001	0.012	0.848	-0.072	1.45
3 -Nitrobenzamide	5.310	0.001	0.011	1.100	0.041	1.95
3,5 -Dinitrobenzamide	6.337	0.001	0.018	1.505	0.178	2.31
Triazoxide	11.694	0.004	0.031	3.624	0.559	2.44
Naphthalene	17.932	0.006	0.032	6.091	0.785	2.75
1,2,3 -Trichlorobenzene	22.427	0.011	0.050	7.868	0.896	3.16
Test item	2.964	0.0	0.0	0.172	-0.764	0.25

Remark:

Contrary to the calibration substances, the substance could only be detected with MSD instead of DAD. Because of the small difference in the retention times between the two detectors, no significant influence on the outcome of the study was assumed.

Validity criteria fulfilled:

yes

Remarks:

Although the determined value does not exactly meet the range of application of the test guideline (1.45 – 3.16), we consider the value as valid (measurement uncertainty +/- 0.5 log units).

Conclusions:

The adsorption coefficient of dibutyl hydrogen phosphate determined by HPLC was log Koc = 0.5 at 25°C.

Executive summary:

Based upon its pKa, dibutyl hydrogen phosphate exits predominantly in its dissociated form under relevant environmental pH 5-9. The non-dissociated form of dibutyl hydrogen phosphate exists at pH values < 0.5. The determination of the adsorption coefficient of the non-dissociated form of dibutyl hydrogen phosphate could not be performed at pH < 0.5 because the material of the HPLC column is not stable at pH values <2. For this reason the determination of the adsorption coefficient of dibutyl hydrogen phosphate was carried out at pH 6 with the dissociated form.

The adsorption coefficient (Koc) ofdibutyl hydrogen phosphatewas determined according to the HPLC method mentioned in EU-method C.19 and OECD TG 121 at 40 °C. In order to comply with the guideline OECD 121 and considering environmental relevance, pH 6 was chosen as pH value for the buffer. The reference Koc-values in the OECD-guideline presumably refer to 25 °C. Even though the column temperature was 40 °C, this temperature is without influence on the result of the determination. The calibration was done referring to Koc- values of reference substances determined at 25 °C. For adsorption coefficient of the dissociated form ofdibutyl hydrogen phosphatedetermined by HPLC was log Koc = 0.5.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Study period:

2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification

Justification for type of information:

QSAR prediction

Guideline:

other: REACH guidance QSARs R6, May 2008

Principles of method if other than guideline:

Estimation Program Interface EPI-Suite version 4.11: KOCWIN (v2.00) for the estimation of the organic carbon-normalized sorption coefficient for soil and sediment (Koc). The Estimation Program Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics, and Syracuse Research Corporation (SRC). © 2000 - 2012 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in November 2012).

GLP compliance:

no

Type of method:

other: Estimation

Media:

soil

Specific details on test material used for the study:

In order to estimate the organic carbon partition coefficient (log Koc) for the dissociated form of dibutyl hydrogen phosphate, the corresponding sodium salt of dibutyl hydrogen phosphate (CAS No. 16298-74-1) was chosen as a surrogate for calculation.
(values relate to the pure substance)
SMILES: CCCCOP(O([Na]))(=O)OCCCC; (dissociated form)
Molecular weight: 232.19 g/mol (dissociated form)
An estimated log Kow of -0.90 was used for calculation of the dissociated form (log Kow method).

Radiolabelling:

no

Key result

Type:

log Koc

Value:

0.53

Temp.:

25 °C

Remarks on result:

other: log Kow method calculation (dissociated form)

Key result

Phase system:

other: Koc

Type:

other: Koc

Value:

3.39 L/kg

Remarks on result:

other: log Kow method calculation (dissociated form)

In order to estimate the organic carbon partition coefficient (log Koc) for the dissociated form of dibutyl hydrogen phosphate, the corresponding sodium salt of dibutyl hydrogen phosphate (CAS No. 16298 -74 -1) was chosen as surrogate for calculation, as generally estimation by the program apply to compounds that are predominantly in a non-ionized/non-dissociated form.

Validity of the model:

1. Defined Endpoint: Organic carbon partition coefficient, given as logarithmic Koc and Koc

2. Unambigous algorithm: The molecule is first classified as a polar substance. Based on structure of the molecule, the following fragment was applied: Organo Phosphorus [P=O], aliphatic. The number of times of the fragment that occurs in the structure of the substance applied by the program is verified. For estimation of logKoc according to the logKow method the estimated logKow of -0.90 for the dissociated form of the substance, as calculated by the program, was used. Estimation of the dissociated form of a substance via MCI-method is not considered by the program.

3. Applicable domain: With a molecular weight of 232.19 g/mole (dissociated form) the substance is within the range of the training set (32 - 665 g/mole) as well as in the validation set (27 - 991 g/mole). Regarding the structure of dibutyl hydrogen phosphate, the fragment descriptor found by the program is complete.

4a. Statistical characteristics (MCI method): N training set without corrections = 69; N training set with correction = 447; N validation set = 158; Correction coefficient of the total training set without corrections r² = 0.967; Correlation coefficient of the total training set with corrections r² = 0.900; Correlation coefficient of the total validation set r² = 0.850.

4b. Statistical characteristics (Kow method): N training set without corrections = 68; N training set with correction = 447; N validation set = 150; Correction coefficient of the total training set without corrections r² = 0.877; Correlation coefficient of the total training set with corrections r² = 0.855; Correlation coefficient of the total validation set r² = 0.778.

5. Mechanistic interpretation: Log Koc is estimated based on the likeliness of a substance for sorption to surfaces of soil/sediment particles. The log Koc is a physical inherent property used extensively to describe a chemical's likeliness to adsob to organic carbon. Adequacy of prediction:

The result for the dissociated form of dibutyl hydrogen phosphate falls within the applicability domain described above and the applied estimation rules appear appropriate.

Validity criteria fulfilled:

not applicable

Conclusions:

The QSAR determination of the logarithmic carbon partition coefficient using the model KOCWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed a value of 0.53 for the dissociated form of dibutyl hydrogen phosphate (log Kow method).

Executive summary:

The organic carbon partition coefficient (log Koc) for the dissociated form of dibutyl hydrogen phosphate was estimated using the Estimation Program Interface (EPI) Suite version 4.11.

For dibutyl hydrogen phosphate KOCWIN estimated the log Koc using two separate estimation methodologies. The estimations are based on the first-order Molecular Connectivity Index (MCI) and the log Kow (internally calculated by KOCWIN), respectively. In order to estimate the organic carbon partition coefficient (log Koc) for the dissociated form of dibutyl hydrogen phosphate, the corresponding sodium salt of dibutyl hydrogen phosphate (CAS No. 16298-74-1) was chosen as a surrogate for calculation, as generally estimation by the program apply to compounds that are predominantly in a non-ionized/non-dissociated form.

Estimation of the dissociated form of a substance via MCI method is not considered by the program.

The log Koc for the dissociated form of dibutyl hydrogen phosphate was estimated to be 0.53.

The result for the dissociated form of dibutyl hydrogen phosphate falls within the applicability domain described above and the applied estimation rules appear appropriate.

The predicted value can be considered reliable yielding a useful result for further assessment.

Reference 3

Endpoint:

adsorption / desorption: screening

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Study period:

2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification

Justification for type of information:

QSAR prediction

Guideline:

other: REACH guidance QSARs R6, May 2008

Principles of method if other than guideline:

Estimation Program Interface EPI-Suite version 4.11: KOCWIN (v2.00) for the estimation of the organic carbon-normalized sorption coefficient for soil and sediment (Koc). The Estimation Program Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics, and Syracuse Research Corporation (SRC). © 2000 - 2012 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in November 2012).

GLP compliance:

no

Type of method:

other: Estimation

Media:

soil

Specific details on test material used for the study:

(values relate to the pure substance)
SMILES: O=P(OCCCC)(OCCCC)O; (non-dissociated form)
molecular weight: 210.21 g/mol (non-dissociated form)
An estimated log Kow of 2.29 was used for calculation of the non-dissociated form (logKow method).

Radiolabelling:

no

Key result

Type:

log Koc

Value:

2.295

Temp.:

25 °C

Remarks on result:

other: log Kow method calculation (non-dissociated form)

Key result

Type:

log Koc

Value:

2.297

Temp.:

25 °C

Remarks on result:

other: MCI method calculation (non-dissociated form)

Phase system:

other: Koc

Type:

other: Koc

Value:

197.3 L/kg

Remarks on result:

other: log Kow method calculation (non-dissociated form)

Phase system:

other: Koc

Type:

other: Koc

Value:

198.1 L/kg

Remarks on result:

other: MCI method calculation (non-dissociated form)

Validity of the model:

1. Defined Endpoint: Organic carbon partition coefficient, given as logarithmic Koc and Koc

2. Unambigous algorithm: The molecule is first classified as a polar substance. Based on structure of the molecule, the following fragment was applied: Organo Phosphorus [P=O], aliphatic. The number of times of the fragment that occurs in the structure of the substance applied by the program is verified. For estimation of log Koc according to the log Kow method the estimated log Kow of 2.29 for the non-dissociated form of the substance, as calculated by the program, were used.

3. Applicable domain: With a molecular weight of 210.21 g/mole (non-dissociated form) dibutyl hydrogen phosphate is within the range of the training set (32 - 665 g/mole) as well as in the validation set (27 - 991 g/mole). Regarding the structure of dibutyl hydrogen phosphate, the fragment descriptor found by the program is complete.

4a. Statistical characteristics (MCI method): N training set without corrections = 69; N training set with correction = 447; N validation set = 158; Correction coefficient of the total training set without corrections r² = 0.967; Correlation coefficient of the total training set with corrections r² = 0.900; Correlation coefficient of the total validation set r² = 0.850.

4b. Statistical characteristics (Kow method): N training set without corrections = 68; N training set with correction = 447; N validation set = 150; Correction coefficient of the total training set without corrections r² = 0.877; Correlation coefficient of the total training set with corrections r² = 0.855; Correlation coefficient of the total validation set r² = 0.778.

5. Mechanistic interpretation: Log Koc is estimated based on the likeliness of a substance for sorption to surfaces of soil/sediment particles. The log Koc is a physical inherent property used extensively to describe a chemical's likeliness to adsob to organic carbon. Adequacy of prediction:

The result for the non-dissociated form of dibutyl hydrogen phosphate falls within the applicability domain described above and the applied estimation rules appear appropriate.

Validity criteria fulfilled:

not applicable

Conclusions:

The QSAR determination of the logarithmic carbon partition coefficient using the model KOCWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed values of 2.30 for the non-dissociated form of dibutyl hydrogen phosphate (log Kow method and MCI method).

Executive summary:

The logarithmic organic carbon partition coefficient (logKoc) for the non-dissociated form of dibutyl hydrogen phosphate was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v4.11. The log Koc was estimated to be 2.30 for the non-dissociated form of dibutyl hydrogen phosphate (log Kow method and MCI method). The result for the non-dissociated form of dibutyl hydrogen phosphate falls within the applicability domain described above and the applied estimation rules appear appropriate yielding a useful result for further assessment.

Description of key information

The adsorption coefficient of dibutyl hydrogen phosphate determined by HPLC was log Koc = 0.5 at 25°C, indicating a low potential for adsorption. 

Key value for chemical safety assessment

Koc at 20 °C:

3.16

Additional information

Based upon its pKa, dibutyl hydrogen phosphate exists predominantly in its dissociated form under relevant environmental pH 5-9. The non-dissociated form of dibutyl hydrogen phosphate exists at pH values <0.5.

The determination of the adsorption coefficient of the non-dissociated form of dibutyl hydrogen phosphate could not be performed at pH <0.5 because the material of the HPLC column is not stable at pH values <2. For this reason the determination of the adsorption coefficient of dibutyl hydrogen phosphate was carried out at pH 6 with the dissociated form.

The adsorption coefficient (Koc) of the substance was determined according to the HPLC method mentioned in EU-method C.19 and OECD TG 121 at 40 °C. In order to comply with the guideline OECD 121 and considering environmental relevance, pH 6 was chosen as pH value for the buffer. The reference Koc-values in the OECD-guideline presumably refer to 25 °C. Even though the column temperature was 40 °C, this temperature is without influence on the result of the determination. The calibration was done referring to Koc-values of reference substances determined at 25 °C. For adsorption coefficient of the dissociated form of dibutyl hydrogen phosphate determined by HPLC was log Koc = 0.5.

In addition, the organic carbon partition coefficients (Koc) for the dissociated and non-dissociated form of dibutyl hydrogen phosphate were predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v4.11. For dibutyl hydrogen phosphate KOCWIN estimated the log Koc using two separate estimation methodologies. The estimations are based on the first-order Molecular Connectivity Index (MCI) and the log Kow (internally calculated by KOCWIN), respectively.

The log Koc was estimated to be 2.30 for the non-dissociated form of dibutyl hydrogen phosphate (log Kow method) and also 2.30 (MCI method). In order to estimate the organic carbon partition coefficient (log Koc) for the dissociated form of dibutyl hydrogen phosphate, the corresponding sodium salt of dibutyl hydrogen phosphate (CAS No. 16298 -74 -1) was chosen as surrogate for calculation, as generally estimation by the program apply to compounds that are predominantly in a non-ionized/non-dissociated form. Thus, estimation of the dissociated form of a substance via MCI method is not considered by the program. The log Koc for the dissociated form of dibutyl hydrogen phosphate was estimated to be 0.53 at 25°C. The results for the non-dissociated form and dissociated form of dibutyl hydrogen phosphate fall within the applicability domain described above, the applied estimation rules appear appropriate and the predicted value can be considered reliable.

It is shown, that the estimated log Koc value for the dissociated form is in very good correlation with the experimental determined value. As dibutyl hydrogen phosphate is mainly present in the dissociated form at environmental relevant pH, the Koc value for the dissociated form is taken into account for assessment.

 

[LogKoc: 0.5]