Amines, N-(C16-18 and C18-unsatd. alkyl)trimethylenedi-, dioleates

Adsorption / desorption

Description of key information

The amines in the test substance have formed ionpairs with oleic acid and due to that no ionic interaction is expected to occur. When considering the results there is no relationship between the observed Kd values and soil properties like Koc, CEC, pH  and clay content. In general the log Koc is considered to be a poor predictor of the partitioning behaviour of cationic surfactants in the environment but this substance is an ion-pair (salt). The sorption test results are therefore not expressed in Koc but in their Kd  values. The mean Kd value for three soils of 30068 L/kg will be used as a realistic worst-case to derive the distribution constants for N-C16-C18-alkyl-(evennumbered, C18 unsaturated) propane-1,3-diaminium di[(9Z)-octadec-9-enoate]. This Kd value of 30068 L/kg corresponds with a Koc of 601360 L/kg. This latter Koc may be used to derive other Kd values for risk assessment purposes.
Because there is no principal difference between soil and sediments considering the sorption properties (EU RAR primary alkyl amines, 2008) and because for this substance the degree of sorption is not related to the organic carbon content, the value for soil will also be used for sediment, suspended particles and STP sludge.  
In the table below the distribution constants used in this assessment are summarized: 
Kpsoil = 30068 L/kg;       Ksoil-water = 45102 m3/m3
Kpsusp = 60136 L/kg;  Ksusp-water = 15035 m3/m3
Kpsed = 30068 L/kg;       Ksed-water = 15035 m3/m3
With a Kpsusp of 60136 L/kg and a concentration of 15 mg/L suspended matter in surface waters, the adsorbed fraction is calculated as 47.5%.

Key value for chemical safety assessment

Koc at 20 °C:

601 360

Other adsorption coefficients

Type:

log Kp (solids-water in soil)

Value in L/kg:

4.478

at the temperature of:

20 °C

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

4.478

at the temperature of:

20 °C

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

4.779

at the temperature of:

20 °C

Additional information

The available study reports adsorption and desorption parameters for N-[(9Z)-octadec-9-en-1-yl]propane-1,3-diaminum di[(9Z)-octadec-9-enoate] (CAS No. 34140 -91 -5), on soil measured according to a refined OECD Guideline no 106; Adsorption – Desorption using the Batch Equilibrium Method, adopted 21 January 2000.

The results have been read-across to N-C16-C18-alkyl-(evennumbered, C18 unsaturated) propane-1,3-diaminium di[(9Z)-octadec-9-enoate] (CAS No. 1307863-78-0, old CAS no 61791-53-5). Both substances are structurally similar with the only difference being slight variations in the composition of C16 – C18 alkyl chains. This is not expected to have an influence on the sorption behavior. 

K_d, K_ocand K_desvalues have been calculated. The preliminary test to determine the equilibrium time showed that equilibrium is reached within 24 hours for both the Speyer 2.2 soil and the Speyer 6S soil. There are only minor changes between the 3 and 24 hours samples. Based on these results, an equilibrium time of 24 hours was applied for the definitive test. The measured equilibrium concentrations in the water phase had an average of 6.8 and 1.6 µg/L respectively in the preliminary test and it was decided to increase the starting concentration to about 7 mg/L in the final test.

The final sorption test was performed for 24 hours followed by a 48 hours desorption test. The observed K_dvalues in the preliminary and final sorption test agree well. K_d for Speyer 2.2 is 1.5*10⁴in the preliminary test and 3.3*10⁴in the final sorption test, a difference of a factor of approximately 2.3. The K_d for Speyer 6S is 6.5*10⁴and 2.0*10⁴for the preliminary and final sorption test, respectively.

The recovery for the control sample in the final sorption test was 84%. The recovery of the individual components varies between 81% to 87%.

The results are calculated as a sum for all three components (C16’, C18’’ and C18’) individual contribution to the total amount test substance adsorbed and desorbed. When these results

achieved with different soils are compared (Table 7), it can be noticed that the K_descorrelates with CEC, pH and clay content, while the organic carbon content of the soils not seems to have a major impact on the desorption of the substance to the soils. Adsorption measured as Kd do not seem to correlate to any individual parameter, this might indicate that it is the hydrofobicity that is the main driver for adsorption to different soil particles and to glassware.

Table 1. Comparison between the results and soils

Soil	Clay (%)	Silt (%)	Sand (%)	CEC (meq/100g)	pH	Org C (%)	Caq (µg/l)	Kd (10^4cm^3/g)	Kdes (10^4cm^3/g)
Speyer 2.2	6.4	12.2	81.4	10	5.4	2.16	24.1	3.3	4.2
Eurosoil 4	20.3	75.7	4.1	17.3	6.8	1.31	38.9	3.8	5.9
Speyer 6S	42.1	36.0	21.9	22	7.2	1.75	21.0	2.0	10