Hydrocarbons, C18-C24, iso-alkanes <2% aromatics

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

1. Hypothesis for the analogue approach:
The hypothesis for the analogue approach is that the test substance, GTL Gasoil (C8-C26) (C8-C26 branched and linear hydrocarbons – Distillates / 848301-67-7 / 481-740-5) is the starting material from which the registration substance is produced by fractional distillation. The source substance contains constituents of the target substance, Hydrocarbons, C18-C24, iso-alkanes, <2% aromatics, although it covers a wider carbon number distribution. The substances therefore have qualitatively similar properties (RAAF Scenario 2 applies).
2. Source and target chemical(s)
The source substance GTL Gasoil (C8-C26) (C8-C26 branched and linear hydrocarbons – Distillates) is composed of linear, branched and cyclic hydrocarbons of chain length C8-C26.
The target substance, Hydrocarbons, C18-C24, iso-alkanes, <2% aromatics, is composed of linear, branched and cyclic hydrocarbons of chain length C18-24.
3. Analogue approach justification
The constituents of the source and target substances are all hydrocarbons. Identical constituents have identical potential for adsorption.

Reason / purpose for cross-reference:

read-across source

Type:

Koc

Value:

> 427 000 dimensionless

Type:

log Koc

Value:

> 5.63 dimensionless

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April 2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Study conducted to GLP and in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. Read-across is considered to be reliability 2.

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:

yes

Remarks:

, see "Principles of method if other than guideline"

Principles of method if other than guideline:

As the test material had a high affinity for the HPLC column stationary phase, it was necessary to increase the methanol content of the mobile phase to 100% to elute the test material. This was performed at a time greater than the retention time of DDT (26.5 minutes) such that all constituents eluted by the amended mobile phase shared a common adsorption coefficient value, that of greater than the highest calibration standard. To allow detection of the test material, fractions of eluent were collected from the HPLC instrument for analysis by gas chromatography (GC).
Furthermore the method guideline states that the measurement of absorption coefficient be performed on the ionised and unionised form of the test material. However in the absence of any dissociating groups, the test material being a mixture of alkanes, the determination was performed at an approximately neutral pH only, on the test material in an unionised form.

GLP compliance:

yes (incl. QA statement)

Type of method:

HPLC estimation method

Media:

other: HPLC column: Phenospere Next 5µ CN

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
PHYSICO-CHEMICAL PROPERTIES
- Water solubility: Information not available
- Solubility in organic solvents: Information not available
- Dissociation constant: Information not available
- log Pow: Information not available

Radiolabelling:

no

Test temperature:

40°C

Details on study design: HPLC method:

EQUIPMENT
- Apparatus: Agilent Technologies 1050, incorporating autosampler and workstation
- Type: HPLC system
- Type, material and dimension of analytical (guard) column: Phenosphere Next 5µ CN (250 x 4.6 mm id)
- Detection system: UV detector (dead time and reference standards: 210 nm; sample: 205 nm)


MOBILE PHASES
- Type: methanol: water (55:45 v/v)
- Experiments with additives carried out on separate columns: no
- pH: 7.0, obtained using 0.1 M sodium hydroxide
- Solutes for dissolving test and reference substances: methanol


DETERMINATION OF DEAD TIME
- Method: measuring the retention time of formamide (purity≥99.5%, 509 mg/L solution in methanol)


REFERENCE SUBSTANCES
- Identity:

Standard Purity (%) Concentration (mg/L)
--------------------------------------------------------------------
Acetanilide ~ 99 163
Atrazine 99.2 112
Triadimenol 98.5 104
Linuron ≥99 105
Naphthalene 99.9 112
Endosulfan-diol 99.7 103
Fenthion 99.7 256
α-Endosulfan 99.8 101
Phenanthrene ≥97.0 104
Diclofop-methyl 99 104
DDT 98 105



DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column: 100 µL
- Quantity of reference substances: 10 µL
- Intervals of calibration: information not available


REPETITIONS
- Number of determinations: 2


EVALUATION (for fraction analysis by GC)
- Calculation of capacity factors k': k = (tr-t0)/t0
where:
k = capacity factor
tr= retention time (min)
t0= dead time (min)
- Calculation of retention times: unknown
- Determination of the log Koc value: the log Koc value was determined with reference to the calibration curve

Type:

Koc

Value:

> 427 000 dimensionless

Type:

log Koc

Value:

> 5.63 dimensionless

Details on results (HPLC method):

- Details of fitted regression line (log k' vs. log Koc): A=-1.354; B=0.385; r=0.992
- Graph of regression line attached:
- Average retention data for test substance: >26.5 min

1) Calibration (GC)

The retention times of formamide and the retention times, capacity factors (k) and log10 Koc values for the reference standards are shown in the two following tables:

Dead Time	Retention Time (min)		Mean Retention Time (min)
	Injection 1	Injection 2
Formamide	3.297	3.282	3.821

Standard	Retention Time (min)		Mean Retention Time (min)	Capacity factor (k)	Log10k	Log10Koc
	Injection 1	Injection 2
Acetanilide	3.718	3.717	3.718	0.133	-0.875	1.25
Atrazine	3.990	3.990	3.990	0.216	-0.665	1.81
Linuron	4.707	4.714	4.711	0.436	-0.361	2.59
Naphthalene	5.124	5.136	5.130	0.564	-0.249	2.75
Endosulfan-diol	5.240	5.246	5.243	0.598	-0.223	3.02
Fenthion	6.420	6.443	6.432	0.961	-1.75 x 10e-2	3.31
α-Endosulfan	9.513	9.541	9.527	1.904	0.280	4.09
Phenanthrene	7.121	7.125	7.123	1.171	6.87 x 10e-2	4.09
Diclofop-methyl	9.705	9.723	9.714	1.961	0.293	4.20
DDT	25.702	25.700	25.701	6.834	0.835	5.63

2) Remarks

The test material was known to primarily be a complex mixture of alkanes and therefore a majority of the components were not anticipated to absorb in the ultraviolet region. The use of a refractive index (R1) detector was therefore the first choice for monitoring the test material.

However the requirement to use a gradient method, increasing the solvent content of the mobile phase to 100% methanol after the retention time of the highest calibration standard to successfully elute the test material, invalidated the use of such a detector. This is since the detector baseline is adversely affected by the continuing shift in the refractive index of the mobile phase caused by the gradient. Therefore the sample was monitored in the far UV region and the elution of the test material confirmed by fraction collection and subsequent GC analysis. The retention time limit value used for the calculation of the sample adsorption coefficient result represents the start of the amended 100% methanol mobile phase. All components of the test material were demonstrated to elute after this time and shared a common adsorption coefficient value, that of greater than the highest calibration standard.

3) Results

The retention times, capacity factors and  Log₁₀K_oc values determined for the sample are shown in the following table:

Injection	Retention Time (min)	Capacity factor (k)	Log10k	Log10Koc
1	>26.5	>7.078	>0.850	>5.63
2	>26.5	>7.078	>0.850	>5.63

mean  Log₁₀K_oc: >5.63

Adsorption coefficient: >4.27 x 10⁵

Validity criteria fulfilled:

yes

Conclusions:

The adsorption coefficient (Koc) of the test material has been determined to be greater than 4.27 x 10e5, log 10 Koc>5.63 [the limit value of 5.63 is
based on the retention time of the reference substance DDT].

Executive summary:

The determination of the adsorption coefficient was carried out using the HPLC screening method, EU Method C.19. To allow detection of the test material, which had a high affinity for the HPLC column stationary phase, fractions of eluent were collected from the HPLC instrument for analysis by gas chromatography (GC).

The adsorption coefficient (K_oc) of the test material has been determined to be greater than 4.27 x 10⁵ (log K_oc>5.63). The limit value of 5.63 is based on the retention time of the reference substance DDT.

Description of key information

adsorption coefficient (Koc) of the test material: >4.27 x 10E5, log10 Koc >5.63

Key value for chemical safety assessment

Koc at 20 °C:

5.63

Additional information

A study was performed according to EU test method C19 (HPLC method) in which the adsorption coefficient for Distillates (Fischer-Tropsch), C8-26, branched and linear was reported to be greater than 4.27E+05 (log K_oc>5.63) (O’Connor and Mullee, 2006). This result is also relevant to Hydrocarbons, C18-C24, isoalkanes, <2% aromatics.

Adsorption coefficients for individual constituents is described in Section 4.2.1 of the Chemical Safety Report attached in Section 13.