Amines, C36-alkylenedi-

Adsorption / desorption

Description of key information

The amines in the test substance will to a large extent be protonated under ambient conditions and will therefore interact with the negative surface of mineral particles or with negative charges of humic substances. The ionic interactions play a more important role than hydrophobic partitioning with organic matter.  The log Koc is therefore considered as a poor predictor of the partitioning behaviour of cationic surfactants in the environment. The sorption test results are therefore not expressed in Koc but in their Kd values. The mean Kd value for the three soils of 43664 L/kg will be used as a realistic worst-case to derive the distribution constants for the C36-alkylenediamines. This Kd value of 43664 L/kg corresponds with a Koc of 873273 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 cationic surfactants the degree of sorption is not related to the organic carbon content, the value for soil will also be used for sediment and suspended particles. For sludge the removal by sorption in a waste water treatment plant will be close to what is observed in the waste water treatment simulation test i.e. 24.4% removal. 

Key value for chemical safety assessment

Koc at 20 °C:

873 273

Other adsorption coefficients

Type:

log Kp (solids-water in soil)

Value in L/kg:

4.64

at the temperature of:

20 °C

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

4.64

at the temperature of:

20 °C

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

4.941

at the temperature of:

20 °C

Additional information

The amines in the test substance will to a large extent be protonated under ambient conditions and will therefore interact with the negative surface of mineral particles or with negative charges of humic substances. The ionic interactions play a more important role than hydrophobic partitioning with organic matter. The log Koc is therefore considered as a poor predictor of the partitioning behaviour of cationic surfactants in the environment. Earlier results showed that using at least three soils with at least one loamy sand and a clay soil, can give as much information as using the full number of soils. These earlier tests also revealed that only rarely linear adsorption isotherms were obtained for cationic surfactants and that extrapolation to lower concentrations based on these non-linear isotherms leads to unrealistic results (e.g. EU RAR primary fatty amines Oct. 2008). According to the Danish EPA (2004) a more reliable method of extrapolation to lower concentrations, is to use the data originating from the lowest measured concentration and to assume that the coefficient remains constant at lower concentrations

The determination of a Koc from log Kow is not opportune, because the common equations for Koc derivation are not valid for both ionic and surface active substances and therefore an OECD 106 test was performed.

The adsorption behaviour of C36-alkylenediamines, on soil was measured according to a refined OECD Guideline no 106, Adsorption – Desorption using the Batch Equilibrium Method, adopted 21 January 2000 (Frid, 2012). Three soils (Speyer 2.2, loamy sand: 6.4% clay, 2.2% organic carbon; Eurosoil 4 silt: 20.3% clay, 1.3% organic carbon and Speyer S6, clay: 42.1% clay, 1.8% organic carbon) were used for testing, encompassing a range of % clay and organic carbon. The test substance adsorbed partially onto the container walls which was considered for the determination of the adsorption coefficients. Adsorption kinetics was determined by measurements at different sampling times. The preliminary test to determine the equilibrium time showed that equilibrium is reached within 24 hours for Speyer 2.2 soil. There are only minor changes between the 3 and 24 hours samples. The adsorption to Speyer 2.2 was around 92% after 24 hours. Equilibrium is faster for the Speyer 6S soil, with an initial adsorption at 98% and only small changes were observed for the aqueous concentrations. Based on these results, an equilibrium time of 24 hours was applied for the definitive test. Desorption occurred to a lesser extent than adsorption. The table below presents a summary of the most important soil properties and adsorption constants.

 

Soil	Clay (%)	Silt (%)	Sand (%)	CEC (meq/100g)	pH	Org C (%)	Caq (µg/L)	Kd (cm^3/g)
Speyer 2.2	6.4	12.2	81.4	10	5.4	2.16	33.7	2417
Eurosoil 4	20.3	75.7	4.1	17.3	6.8	1.31	5.2	20067
Speyer 6S	42.1	36.0	21.9	22	7.2	1.75	0.9	108507

 

 

From the data it can be observed that the sorption onto Speyer 6S is much higher than to Speyer 2.2 despite of the higher organic carbon content in Speyer 2.2 soil. This can be explained that ionic interactions play a more important role than hydrophobic partitioning with organic matter. Alkyl ammonium ions can interact with the surface of mineral particles or with negative charges of humic substances. The influence of the chain length on the sorption behaviour is therefore expected to be limited. As well, an influence of the double bond onto sorption is not expected.

The observed aquatic equilibrium concentrations in the experiment range from 0.9 to 33.7 µg/L.

For the prediction of the partitioning of the C36-alkylenediamines to soil, sediment and suspended matter not the equilibrium constant based on organic matter (Koc) should be used but the uncorrected Kdbecause there is no relation between the organic matter concentration and the sorption observed.

The mean Kd value for the three soils of 43664 L/kg will be used as a realistic worst-case to derive the distribution constants for the C36-alkylenediamines. Because there is no principal difference between soil and sediments considering the sorption properties and because for cationic surfactants the degree of sorption is not related to the organic carbon content, the value for soil will also be used for sediment and suspended particles. For sludge which consists mainly of organic matter the sorption may be estimated from sorption data as observed for soil via the Koc of 873273 L/kg. Better is it however to use the available measured sorption data from the waste water simulation test. The removal via sorption in a waste water treatment plant will be close to what is observed in the waste water treatment simulation test i.e. 24.4% removal.

 

In table the distribution constants used in this assessment are summarized:

             

           Table:Distribution constants for C36-alkylenediamines

Kpsoil	43664 L^.kg^-1	Ksoil-water	65496 m^3.m^-3
Kpsusp	87328 L^.kg^-1	Ksusp-water	21833 m^3.m^-3
Kpsed	43664 L^.kg^-1	Ksed-water	21833 m^3.m^-3

 

With a Kp_suspof 87328 L/kg and a concentration of 15 mg/L suspended matter in surface waters, the adsorbed fraction is calculated as 56.7%.

 

[LogKoc: 5.94]