Naphthenic acids

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption

Remarks:

adsorption

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Qualifier:

no guideline followed

Principles of method if other than guideline:

Calculation based on equation Di Toro et al (2985)

Type of method:

other: calculated

Media:

soil

Type:

log Koc

Value:

4.65 dimensionless

Remarks on result:

other: calculated for representative structures

The equation of Di Toro to calculate log Koc: log Koc = logKow*0.983 + 0.00028 for semivolatile nonionising organic substances ( Di Toro DM, A particle interaction model of reversible organic chemical sorption. Chemosphere, Volume 14, Issue 10, 1985, Pages 1503-1538)

The log Kow values are calculated with KowWin v1.68

Note: only compounds with log Kow <7 i.e. <C17 (only these are relevant for ecotox); Koc is used for PNEC calculations (see IUCLID section 6)

Results: log Koc range 2.02 -6.59; median 4.70; mean 4.64

					Di Toro	Di Toro
C-number	Ring	Branch	SMILES	log Kow	log Koc	Koc
C6	-	-	C(=O)(O)CCCCC	2,05	2,02	103,62
C7	-	-	C(=O)(O)CCCCCC	2,54	2,50	314,12
C8	-	-	C(=O)(O)CCCCCCC	3,03	2,98	952,29
C8	1 pentane	-	C(=O)(O)CCC1CCCC1	2,85	2,80	633,62
C9	-	methyl	C(=O)(O)CCCC(C)CCC	3,45	3,39	2463,94
C10	-	ethyl	C(=O)(O)CCCC(CCC)CC	3,94	3,87	7469,65
C10	1 pentane	-	C(=O)(O)CCC1C(CC)CCC1	3,76	3,70	4970,04
C11	1 pentane	-	C(=O)(O)CCC1C(CCC)CCC1	4,25	4,18	15067,11
C12	1 hexane	-	C(=O)(O)CCC1C(CCC)CCCC1	4,74	4,66	45677,26
C12	1 pentane	-	C(=O)(O)CCC1C(CCCC)CCC1	4,74	4,66	45677,26
C12	2 pentanes fused	-	C(=O)(O)CCC1C2C(C)CCC2CC1	3,79	3,73	5319,25
C13	2 pentanes	-	C(=O)(O)CCC1C(C2CCCC2)CCC1	5,04	4,95	90074,11
C13	pentane hexane fused		O=C(O)CCC2CCCC1CCC(C)C12	4,2859	4,21	16342,55
C14	1 hexane	-	O=C(O)C1C(CCCCCCCC)CCC1	5,72	5,62	419797,65
C14	2 pentanes	-	C(=O)(O)CCC1CC(C2C(C)CCC2)CC1	5,46	5,37	233055,85
C14	2 pentanes fused	-	C(=O)(O)CCCC1C2C(CC)CCC2CC1	4,78	4,70	50005,76
C15	-	propyl	C(=O)(O)CCCCC(CCCCCC)CCC	6,4	6,29	1956500,67
C15	1 pentane	ethyl	C(=O)(O)CCC1C(CC(CCC)CC)CCC1	6,1	6,00	992156,08
C15	2 pentanes	-	C(=O)(O)CCC1C(CC2CC(C)CC2)CCC1	5,95	5,85	706529,01
C15	2 hexanes fused		O=C(O)CCC1CCC2CCCC(CC)C2C1	5,2681	5,18	150946,24
C15	3 pentanes fused	-	C(=O)(O)CCCC1C2C3C(CC2CC1)CCC3C	4,78	4,70	50005,76
C16	1 pentane	-	C(=O)(O)CCC1C(CCCCCCCC)CCC1	6,7	6,59	3858157,92
C16	2 pentanes	-	C(=O)(O)CCC1CC(C2C(CCC)CCC2)CC1	6,44	6,33	2141903,99
C16	2 hexane	-	C(=O)(O)C1C(CCC2C(C)CCCC2)CCCC1	6,44	6,33	2141903,99
C16	3 pentanes of which 2 fused	-	C(=O)(O)CC1C2C(CC3CCCC3)CCC2CC1	5,57	5,48	298944,11

Conclusions:

Based on the analysis results (IUCLID section 1.4) of a number of representative naphthenic acids samples, a list of potential chemical components was compiled. The log Koc of these structures was estimated with the equation of Di Toro et al. (1985). The log Koc range is 2.02-6.59.

Executive summary:

The Koc of these structures was estimated with the equation of Di Toro et al. (1985). The log Koc range is 2.02-6.59. The median is 4.70; the mean 4.64.

Reference 2

Endpoint:

adsorption / desorption

Remarks:

adsorption

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

GLP compliance:

not specified

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

The initial trial was conducted using the 200 mg/L solution at room temperature (23 ± 1°C), and the second trial was conducted with the 5 concentrations at 4 ± 1°C.

Analytical monitoring:

yes

Details on sampling:

After each sampling the vials were removed from the shaker and centrifuged (~15, 000 g ) for 15 minutes until the supernatant was sufficiently clear of particulate matter. An appropriate aliquot of the background solution was then removed and placed in autosampler vials.

Type:

Kd

Value:

1.9 L/kg

Temp.:

4 °C

% Org. carbon:

2.7

Remarks on result:

other: low ionic strength

Type:

Kd

Value:

17.8 L/kg

Temp.:

4 °C

% Org. carbon:

2.7

Remarks on result:

other: high ionic strength

Type:

Kd

Value:

1.3 L/kg

Temp.:

4 °C

% Org. carbon:

1.6

Remarks on result:

other: low ionic strength

Type:

Kd

Value:

3.7 L/kg

Temp.:

4 °C

% Org. carbon:

1.6

Remarks on result:

other: high ionic strength

The results also indicate that compounds in the Z= 0 to Z=-12 families in the carbon number range of 13 to 17 appear to sorb preferentially. This could have implications to the toxicity and transport in water since different naphthenic acids are known to have varying degrees of toxicity.

Validity criteria fulfilled:

yes

Conclusions:

Naphthenic acids obtained from OSTPW as a concentrate were observed to undergo rapid sorption to the soils tested. The values of Kd ranged
from 1.3 mL/g in Milli-Q water to 17.8 mL/g in synthetic groundwater. Selective sorption of naphthenic acids was observed, with components in the carbon number range of approximately 13 to 17 sorbing more readily than others. Soils with higher organic content appear to cause higher levels of sorption. Strong and selective sorption of oil sand tailings waters derived naphthenic acids to soils is therefore expected to be a significant attenuating process in groundwater transport. In general, low partitioning to the water column is expected for oil sands naphthenic acids in aquatic environments. Furthermore, preferential sorption of the individual naphthenic acids is expected to have high importance from a toxicity stand point since different naphthenic acid species have varying degrees of toxicity.

Executive summary:

Soils used as sorbents in this study were obtained from Fort McMurray, AB, Canada. Soil 1 was a mixture of peat and mineral soil that was produced during soil salvage operations. Soil 2 was a reclamation soil that was mixed with a small amount of peat material during the soil salvage operations. It was primarily a sandy clay to clay loam mineral material. Naphthenic acids obtained from OSTPW as a concentrate were observed to undergo rapid sorption to the soils tested. The values of Kd ranged from 1.3 mL/g in Milli-Q water to 17.8 mL/g in synthetic groundwater. The results also indicate that compounds in the Z= 0 to Z=-12 families in the carbon number range of 13 to 17 appear to sorb preferentially. This could have implications to the toxicity and transport in water since different naphthenic acids are known to have varying degrees of toxicity. Analyses of the naphthenic acid of this dossier show that the most predominant group of compounds has a Z number from zero to 3 and is situated in the C-range C10 to C19.

Description of key information

Modelled values indicate a minor to strong adsorption of naphthenic acids to soil.  Experimental values seem to indicate a low degree of adsorption.

Key value for chemical safety assessment

Koc at 20 °C:

50 005

Additional information

Based on the analysis results (IUCLID section 1.4) of a number of representative naphthenic acids samples, a list of potential chemical components was compiled. The criteria for choosing these specific structures were the occurrence of C-numbers, the number of rings and their relative share in the analysed samples. The log Koc of these structures was estimated with the equation of Di Toro et al. (1985). The log Koc range is 2.02-6.59.

Janfada et al. (2006) reported values for the Kd of naphthenic acids from oil sands, between 1.3 and 17.8L/kg at 4°C, which corresponds to calculated values of Log Koc of 1.85 to 2.82, corresponding in turn to the lower end of the estimated values (2.02-6.59).

 

[LogKoc: 4.69]