Trihexyl phosphate

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 - 13 Sep 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

adopted 22. Jan. 2001

Deviations:

no

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))

Version / remarks:

31 May 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Landesamt für Umwelt, Wasserwirtschaft und Gewerbeaufsicht, Rheinland-Pfalz, Germany

Type of method:

HPLC estimation method

Media:

soil/sewage sludge

Radiolabelling:

no

Test temperature:

25 ± 0.5 °C (column temperature)

Details on study design: HPLC method:

EQUIPMENT
- Apparatus: HPLC_MS Dionex Pump Dionex HGP-3400SD; Autosampler Dionex WPS-3000SL
- Type: HPLC Ultimate3000
- Type, material and dimension of analytical (guard) column: Reprosil PurCN 125 x 4.6 mm with pre column Phenomenex SecurityGuard CN, 4 x 3 mm; Column oven: Dionex TCC-3000SD with 6 fold motor switch valve
- Detection system: UV-Detector (Dionex VWD-3400RS), ELS-Detector (Agilent 380-LC)

MOBILE PHASES
- Type: Eluent: MeOH/H2O 55/45 (% v/v), ultrasonic and vacuum degassed; flow rate: 0.8 mL; injection vol: 20 µL; wave length 230 nm (reference item mix)
- Experiments with additives carried out on separate columns: yes; polar analytical columns packed with a cyanopropyl solid phase containing lipophilic and polar moieties
- pH: 6 – 7 (measured with pH paper)
- Solutes for dissolving test and reference substances: A mixture of 55% methanol/ and 45% water, isocratic, was used. The eluent was produced by mixing 275 mL methanol with 225 mL water.

DETERMINATION OF DEAD TIME
- Method: The dead time t0 was measured by using an unretained compound (sodium nitrate) which was included in the mix of the reference items.

REFERENCE SUBSTANCES
- Identity: DDT as reference item with the highest log KOC and a retention time of approx. 10.8 minutes

DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column: 1000 mg/L
- Quantity of reference substances: list of reference substance are summarized in table 1 in section "Any other information on material and methods incl tables"

REPETITIONS
- Number of determinations: 3

EVALUATION
- Calculation of capacity factors k': The capacity factors k’ were calculated from the retention times using k´= (tR-t0)/ t0 with “tR” = retention time and “t0”= dead time (retention time of sodium nitrate); The dead time t0 was measured by using an unretained compound (sodium nitrate) which was included in the mix of the reference items.
- Calculation of retention times: The retention time was checked in a pre-test and gave one peak at approx 9.8 min.
- Determination of the log Koc value: With the calculated capacity factors for the test item, each log KOC from the three determinations was calculated; One vial was filled with the reference item mix and one vial with the test item solution. The vials were analysed using HPLC. Three injections were measured from the reference item mix, test item solution and from the reference item mix.

Type:

log Koc

Remarks:

(mean)

Value:

5.41 dimensionless

Remarks on result:

other: 0.01 standard deviation

Details on results (HPLC method):

- Retention times of reference substances used for calibration: The RSD of the retention times of the reference items lay all below 0.7% except for DDT, which had a RSD of retention times of 1.1%; log k’ = 0.183 * logKOC – 0.0458, with a coefficient of determination r2 = 0.9984
- Details of fitted regression line (log k' vs. log Koc): log KOC = (log k’ + 0.0458)/0.183; r2 = 0.9984
- Graph of regression line attached: graph log k`versus log Koc linear regression r2 = 0.9984 and r = 0.9992
- Average retention data for test substance: 9.833 min

Table 1: Retention Times (RT) Reference Items

Compound	RT1	RT2	RT3	RT4	RT5	RT6
	min.	min.	min.	min.	min.	min.
Sodium nitrate	1.000	1.000	1.000	1.007	1.013	1.007
Phenol	2.600	2.600	2.600	2.600	2.593	2.593
Methylbenzoate	2.973	2.980	2.973	2.973	2.967	2.967
Naphthalene	3.893	3.893	3.893	3.893	3.867	3.873
1,2,3-Trichlorobenzene	4.347	4.347	4.347	4.347	4.313	4.313
Phenanthrene	5.913	5.913	5.913	5.913	5.840	5.840
4,4’-DDT	11.093	11.093	11.093	11.087	10.860	10.867

 

Table 2: Mean Retention Times (RT), Capacity Factors Reference Items

Compound	RT Mean	RT Standard Deviation	RT Relative Standard Deviation	k’
	min.	min.	%
Sodium nitrate	1.004	0.005	0.542	0.000
Phenol	2.598	0.003	0.133	1.5863
Methylbenzoate	2.972	0.005	0.169	1.9591
Naphthalene	3.886	0.012	0.315	2.8684
1,2,3-Trichlorobenzene	4.336	0.017	0.397	3.3164
Phenanthrene	5.889	0.038	0.643	4.8628
4,4’-DDT	11.016	0.118	1.071	9.9668

 

Table 3: Log k’ and log KOC of Reference Items

Compound	log k’	log KOC
Phenol	0.2004	1.32
Methylbenzoate	0.2921	1.80
Naphthalene	0.4576	2.75
1,2,3-Trichlorobenzene	0.5207	3.16
Phenanthrene	0.6869	4.09
4,4’-DDT	0.9986	5.63

  

Table 4: Retention Times (RT) Test Item

Peak 1 Test Item	RT
	min.
Measurement 1	9.795
Measurement 2	9.839
Measurement 3	9.865
Mean	9.833
Standard deviation	0.035

 

Table 5: Capacity Factor, log Capacity Factor, log KOC Test Item

Peak 1 Test Item	k’	log k’	log KOC
Measurement 1	8.7520	0.9421	5.40
Measurement 2	8.7951	0.9442	5.41
Measurement 3	8.8217	0.9456	5.42
Mean			5.41
Standard deviation			0.01

 

Validity criteria fulfilled:

yes

Description of key information

log Koc 5.41; OECD 121

Key value for chemical safety assessment

Koc at 20 °C:

257 040

Additional information

The adsorption coefficient (Koc) of the test item (CAS 2528-39-4) was determined in a study following OECD 121 (LAUS GmbH, 2017b). The adsorption of the substance on soil and sewage sludge was estimated by HPLC. The retention time of the test substance was compared to values obtained for the reference substance DDT. A log Koc of 5.41 was determined.