Didecyldimethylammonium chloride

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19 Mar, 2008 - 30 Aug, 2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This study result has been assigned a validity of 2, due to the very high concentrations of the test substance used (0.5 g test substance for 1 g soil) causing extrapolations to lower concentrations to be less accurate. (Adsorption is likely to be higher at lower concentrations than suggested by the outcome of this study).

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Test temperature:

20 °C

Analytical monitoring:

yes

Key result

Type:

Koc

Value:

ca. 280 547 L/kg

% Org. carbon:

>= 3.29

Remarks on result:

other: Soil 1

Key result

Type:

Koc

Value:

ca. 120 000 L/kg

% Org. carbon:

ca. 2.39

Remarks on result:

other: Soil 2

Key result

Type:

Koc

Value:

ca. 43 855 L/kg

% Org. carbon:

ca. 3.32

Remarks on result:

other: Soil 3

Key result

Type:

Koc

Value:

ca. 160 882 L/kg

% Org. carbon:

ca. 1.36

Remarks on result:

other: Soil 4

Key result

Type:

Koc

Value:

ca. 40 339 L/kg

% Org. carbon:

ca. 4.43

Remarks on result:

other: Soil 5

Key result

Type:

Kd

Value:

ca. 9 230 L/kg

Remarks on result:

other: Soil 1

Key result

Type:

Kd

Value:

ca. 2 868 L/kg

Remarks on result:

other: Soil 2

Key result

Type:

Kd

Value:

ca. 1 456 L/kg

Remarks on result:

other: Soil 3

Key result

Type:

Kd

Value:

ca. 2 188 L/kg

Remarks on result:

other: Soil 4

Key result

Type:

Kd

Value:

ca. 1 787 L/kg

Remarks on result:

other: Soil 5

Preliminary studies confirmed that there was no adsorption to the apparatus or filter material and stability of the test item in the pH range of selected soils. A preliminary mass balance showed recoveries of ca. 90 %. Therefore, both aqueous and soil phase were analysed in the definitive study.

Based on the results of preliminary tests 100, 500, 1000, 5000 and 10000 mg/L were selected as nominal test substance concentrations for adsorption/desorption isotherms for all tested soils. The concentrations of the test substance were determined in CaCl2 solution via spectrophotometry after formation of an ion pair with an azo dye and subsequent extraction. The concentration adsorbed to soil was then determined by calculation.

Under the test conditions didecyldimethylammonium chloride (DDAC) demonstrated a high tendency to adsorb to the five test soils. There was no correlation between the degree of adsorption and the organic carbon content of the soil. This suggest that other mechanisms were involved in the adsorption of DDAC (e.g. interactions with the inorganic matter of the
soil). 

Desorption was also very low (3 - 23 %). For ail soils and test concentrations, the mass balance was < 90 %.
This could be caused by non-extractable residues which means irreversible adsorption.

Therefore, on the basis of these results, DDAC can be considered immobile in soil.


Freundlich (Kads(F) isotherm for adsorption:
Euro   log     1/n     r^2
soil  Kads(F)
____________________________
1    3.9652  0.4447  0.9947
2    3.4576  0.5715  0.9855
3    3.1632  0.4739  0.9528 
4    3.3400  0.6248  0.9738 
5    3.2521  0.4582  0.9651 

Freundlich (Kdes(F) isotherm for desorption:
Euro   log    1/n      r^2
soil  Kdes(F)    
_____________________________
1    3.5703  0.8048  0.9920
2    3.6271  0.7288  0.9947
3    3.3257  0.6390  0.9753
4    3.4998  0.6386  0.9851
5    3.3779  0.5815  0.9848

Desorption coefficient Kdes and Freundlich desorption
coefficient Fdes(F):

            Soil 1 soil 2  soil 3  soil 4 soil 5
________________________________________________
%desorption    3      11      23      18     15
Kdes        1900     414     175     232    295
Fdes(F)     3718    4237    2117    3161   2387

Validity criteria fulfilled:

yes

Conclusions:

Under the study conditions, the average Koc of the test substance was determined to be 129125 L/kg, indicating high adsorption potential and low mobility.

Executive summary:

A study was conducted to determine the adsorption / desorption of the read across substance, DDAC (40.37% active) using the batch equilibrium, according to OECD Guideline 106, in compliance with GLP.

The amount adsorbed on soils was calculated from depletion of the test substance in the overlaying solution (indirect method). The soils used were EURO-soil standard numbers 1, 2, 3, 4 and 5. The soil/solution ratio was 1:50 (1.0 g soil and 50 mL solution). Based on the results of preliminary tests, 100, 500, 1000, 5000 and 10000 mg/L were selected as nominal concentrations. The concentration of test substance in solution was determined via spectrophotometry. The concentration adsorbed to the soil was then determined by calculation. Under the study conditions, the test substance can be considered as immobile in five soil types. The adsorption mobility (Kaoc) and desorption mobility (Kdoc) coefficients were in the range 40339 to 280547 L/kg and 53883 to 232426 L/kg respectively. Based on the Kd values and organic carbon percentage, the respective Koc values were determined as follows:

Soil type	% Organic carbon	CEC (mval/100g)	Adsorption			Desorption
			Ka	1/na	KaOC	Kd	1/nd	KdOC	Ka/Kd
Euro soil 1: clay	3.29	32.4	9230	0.4447	280547	3718	0.8048	113009	2.48
Euro soil 2: silt loam	28.9	28.9	2868	0.5715	120000	4237	0.7288	177280	0.68
Euro soil 3: loam	16.6	16.6	1456	0.4739	43855	2117	0.6390	63765	0.69
Euro soil 4: silt	17.3	17.3	2188	0.6248	160882	3161	0.6386	232426	0.69
5: loamy sand	24.1	24.1	1787	0.4582	40339	2387	0.5815	53883	0.75

Kaoc = Adsorption coefficient; Kaoc = Adsorption coefficient based on organic carbon content; Kd=Desorption coefficient; Kdoc = Desorption coefficient based on organic carbon content; Ka/Kd = Adsorption / Desorption distribution coefficient

The 1/n values indicate that a non-linear relationship exists between the concentrations in soil and the concentrations the water. DDAC adsorbs strongly onto soil and does not desorb very easily for all soil types (2-3%). Based on these results, it can be concluded that the substance is immobile in soil (Geffke, 2002). It is well known that, because of their positive charge, cationic surfactants adsorb strongly to the negatively charged surfaces of sludge, soil and sediments. The average Koc is 129125 L/kg.

Description of key information

Based on the study results, the test substance is expected to have little or no potential for mobility in soil. 

Key value for chemical safety assessment

Koc at 20 °C:

562 314

Additional information

A study was conducted to determine the adsorption / desorption of the test substance, DDAC (40.37% active) using the batch equilibrium, according to OECD Guideline 106, in compliance with GLP. 

The amount adsorbed on soils was calculated from depletion of the test substance in the overlaying solution (indirect method). The soils used were EURO-soil standard numbers 1, 2, 3, 4 and 5. The soil/solution ratio was 1:50 (1.0 g soil and 50 mL solution). Based on the results of preliminary tests, 100, 500, 1000, 5000 and 10000 mg/L were selected as nominal concentrations. The concentration of test substance in solution was determined via spectrophotometry. The concentration adsorbed to the soil was then determined by calculation. Under the study conditions, the test substance can be considered as immobile in five soil types. The adsorption mobility (Kaoc) and desorption mobility (Kdoc) coefficients were in the range 40339 to 280547 L/kg and 53883 to 232426 L/kg respectively. Based on the Kd values and organic carbon percentage, the respective Koc values were determined as follows:  

 

Soil type	% Organic carbon	CEC (mval/100g)	Adsorption			Desorption
			Ka	1/na	KaOC	Kd	1/nd	KdOC	Ka/Kd
Euro soil 1: clay	3.29	32.4	9230	0.4447	280547	3718	0.8048	113009	2.48
Euro soil 2: silt loam	28.9	28.9	2868	0.5715	120000	4237	0.7288	177280	0.68
Euro soil 3: loam	16.6	16.6	1456	0.4739	43855	2117	0.6390	63765	0.69
Euro soil 4: silt	17.3	17.3	2188	0.6248	160882	3161	0.6386	232426	0.69
5: loamy sand	24.1	24.1	1787	0.4582	40339	2387	0.5815	53883	0.75

Kaoc = Adsorption coefficient; Kaoc = Adsorption coefficient based on organic carbon content; Kd=Desorption coefficient; Kdoc = Desorption coefficient based on organic carbon content; Ka/Kd = Adsorption / Desorption distribution coefficient 

The 1/n values indicate that a non-linear relationship exists between the concentrations in soil and the concentrations the water. DDAC adsorbs strongly onto soil and does not desorb very easily for all soil types (2-3%). It is well known that, because of their positive charge, cationic surfactants adsorb strongly to the negatively charged surfaces of sludge, soil and sediments. Based on these results, it can be concluded that the substance is immobile in soil (Geffke, 2002). The average Koc was determined to be 129125 L/kg. 

Further, the DDAC biocides assessment report for Product Type 8 conducted under Directive 98/8/EC (evaluating Competent Authority: Italy, June 2015, attached in Section 13 of the IUCLID dataset), presented an additional study on DDAC, apart from the above EQC study (Geffke, 2002). In this study, DDAC was found to be immobile in in four soil/sediment types with the adsorption (Ka) and mobility (Kaoc) coefficients of Ka=1.095 and Kaoc=437805 for sand, Ka=8179 and Kaoc=908757 for sandy loam, Ka=32.791 and Kaoc=1599564 for silty clay loam, and Ka=30851 and Kaoc=1469081 for silt loam. The desorption (Kd) and mobility (Kdoc) coefficients are following reported: Kd=591 and Kdoc=236473 for sand, Kd=2074 and Kdoc=230498 for sandy loam, Kd=8309 and Kdoc=405328 for silty clay loam, and Kd=7714 and Kdoc=367334 for silt loam. The average Koc is 1103801 L/kg.   

The RMS further stated that:“Based on the conclusion of the Ad-hoc follow up on ATMAC/TMAC (PT 8) (opinion of the ENV WG on the Koc to be used for the risk assessment) the koc value to be used for risk assessment is the mean Koc from the both studies available. The Koc value is 562314 L/Kg.” 

 

In general, for quaternary ammonium compounds there is no relationship between the values of Kd and the OC-content of the soils. This confirms that organic carbon content alone is not a suitable normalization basis for charged organic substances (Droge & Goss 2013). When comparing the sorption data per soil, no consistent variation of the Kd–values with the different soils can be discerned. Nevertheless, in line with the biocides assessment report, the higher mean Koc value of 562314 L/kg, which was derived based on both the available studies on DDAC for all soil types, has been considered further for hazard/risk assessment as a worst case.