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Environmental fate & pathways

Adsorption / desorption

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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 or Kfads values. The mean KFads value for the four soils of 520 L/kg will be used as a realistic worst-case to derive the distribution constants for the alkyl-1,3-diaminopropanes. This Kd value of 520 L/kg corresponds with a Koc of 10400 L/kg. This latter Koc may be used to derive other Kd values for risk assessment purposes.

Because ionic interactions play a more important role than hydrophobic partitioning with organic matter, the influence of the chain length on the sorption behaviour is expected to be low, and the experimental results obtained in the test with octadecyl-1,3-diaminopropanes can be taken as representative for the other alkyl-1,3-diaminopropane products as well. Furthermore is an influence of the double bond (in octadecenyl-1,3-diaminopropane) onto sorption is not expected.

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 which consists mainly of organic matter the sorption data as observed for soil are not considered to be representative. This is however not a serious problem because 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. 4.1% removal.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
2.318
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
2.716
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
3.017
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 1-14C-labelled n-octadecyl-1,3-diaminopropane was studied in a batch equilibrium experiment according OECD 106 (Corral and Brands, 2009). Three soils collected in Germany (Speyer 2.2, loamy sand: 6.4% clay, 3.7% organic matter; Speyer 2.3, sandy loam: 9.4% clay, 1.7% organic matter and Speyer S6, clay: 42.1% clay, 3.0% organic matter) and one in UK (Cranfield 164, silty clay loam: 28% clay, 6.4% organic matter) were used, encompassing a range of % clay and organic matter. 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 (up to 48 h), an equilibrium was reached after 6 hours. Desorption occurred to a lesser extent than adsorption. Table 12 presents a summary of the most important soil properties and observed Freundlich constants.

 

Table 12:Soil properties and related Freundlich adsorption coefficients fortest material (CAS number): 68603-64-5

Test system

Texture

% OC

pH

% Clay

Kfads

(cm3/g)

KFAdsoc

(103cm3/g)

Speyer2.2

Loamy sand

2.16

5.4

6.4

530

22.3

Speyer2.3

Sandyloam

0.98

6.4

9.4

250

24.7

Cranfield164

Silty clay loam

3.7

6.0

28

450

12.1

Speyer6S

Clay

1.75

7.2

42.1

850

45.2

 

From the data it can be observed that the sorption onto Speyer 6S is much higher than to Cranfield 164 despite of the higher organic matter content in Cranfield 164 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 and the experimental results obtained in the test with octadecyl-1,3-diaminopropane can be taken as representative for other alkyl-1,3-diaminopropane products. As well, an influence of the double bond (in octadecenyl-1,3-diaminopropane) onto sorption is not expected.

The concentration used for the determination of the adsorption isotherms range from 0.01 to 1 mg/L. The isotherms observed are not linear but considered to be acceptable for extrapolation to lower concentrations (r2≥ 0.9). The observed aquatic equilibrium concentrations in the experiment range from 0.3 to 2.6 µg/L.

For the prediction of the partitioning of the Diamines C16-18 in soil, sediment and suspended matter not the KFads based on organic matter will used but the uncorrected KFads because there is no relation between the organic matter concentration and the sorption observed.

The mean KFads value for the four soils of 520 L/kg will be used as a realistic worst-case to derive the distribution constants for the alkyl-1,3-diaminopropanes. 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 data as observed for soil are not considered to be representative. This is however not a serious problem because 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. 4.1% removal.

In table 12 a, the distribution constants used in this assessment are summarized:

                       Table 12a:Distribution constants for alkyl-1,3-diaminopropanes

Kpsoil

520 L.kg-1

Ksoil-water

780 m3.m-3

Kpsusp

1040 L.kg-1

Ksusp-water

261 m3.m-3

Kpsed

520 L.kg-1

Ksed-water

261 m3.m-3

 

With a Kpsusp of 1040 L/kg and a concentration of 15 mg/L suspended matter in surface waters, the adsorbed fraction is calculated as 1.5%.