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Partition coefficient


According to Reach-regulation, Annex VII, a value for logKow has to be presented: “…If the test cannot be performed…a calculated value for log P…shall be provided.”


 


1stStep: Experimental Studies


Two experimental studies in accordance with Reach guidance were attempted: A), using the slow stirring method with 14C-MDIPA-Esterquat C16-18 and C18 unsatd. according to guideline OECD 123 and B), the measurements of individual MDIPA-Esterquat C16-18 and C18 unsatd. solubilities in octanol and water.


The results of both studies cannot be used for log Kow derivation. Reasons for the shortcomings of the experimental results are detailed in the “Applicant’s summary” of the corresponding endpoint study records. In summary these studies are valid in view of experimental design and execution of the experiments in the lab, but the usability of the results for logKow derivation is not given due to substance inherent properties. The following observations were made:


- aggregation of individually solubilised MDIPA-Esterquat C16-18 and C18 unsatd. molecules with temperature decrease forming vesicles in water as well as in octanol (forming of precipitates in octanol),


- self solubilisation of vesicles,


- strongly kinetically hindered solution / dissolution equilibrium at room temperature (no steady state in the slow-stir test),


- high adsorbency on surfaces.


As a consequence and conclusion, the direct experimental determination of log Kow, as made for the registration substance, was recognised as not being conclusive and the experimental results of the log Kow tests with MDIPA-Esterquat C16-18 and C18 unsatd. are not considered for the log Kow endpoint.


It is questioned in general whether for substances with properties like MDIPA-Esterquat C16-18 and C18 unsatd., the available guideline studies are appropriate.


 


2ndStep: QSAR


As it turned out that experimental studies cannot be used for the derivation of log Kow, standard increment based QSAR calculations (Epiwin (KOWWIN v1.68), ACD) were considered and evaluated in a second step. These QSAR models have two restrictions: handling of ion pairs and applicability domain. As a consequence, theses QSAR approaches are of limited value for MDIPA-Esterquat C16-18 and C18 unsatd. log Kow derivation.


 


3rdStep: Read-Across


To fill the data gap for this endpoint, a read-across approach to a similar substance was undertaken. Based on OECD QSAR Toolbox Dimethyldioctadecylammonium chloride (DODMAC) was the only substance sufficiently similar to MDIPA-Esterquat C16-18 and C18 unsatd. For this substance the EU RAR (2002) states a log Kow of 3.80 whereas one Reach-registration (CAS: 61789-80-8, DHTDMAC, still containing some oleic acid) states a log Kow of 3.99 (individual solubilities). Another Reach-registration (CAS: 92129-33-4, Quaternary ammonium compounds, di-C16-18-alkyldimethyl, chlorides) with a log Kow of 8.4 (slow-stirring method).


It is questionable to which extent these substances, not having the same composition and containing some different molecular structures can be used as one read-across substance. These substances show inconsistent, strongly diverging log Kow results. The cause for this cannot be judged looking at the present information. It is a strong affirmation for the questioning of experimentally derived log Pow for substances like MDIPA-Esterquat C16-18 and C18 unsatd. as conclusion at “1st Step: Experimental Studies”.


Summarised, all three approaches for an evaluation of a log Kow value for MDIPA-Esterquat C16-18 and C18 unsatd. (experimental, QSAR (increment based), read-across to DODMAC) lead to inconclusive results.


 


4thStep: log Kow – log Koc linear relationship


Finally, instead of the approaches described in the steps 1 to 3, the partitioning coefficient log Kow will be deduced based on other valid, experimentally determined partitioning data for MDIPA-Esterquat C16-18 and C18 unsatd. itself. Instead of the partitioning between water and octanol, the partitioning of MDIPA-Esterquat C16-18 and C18 unsatd. between water and organic carbon (log Koc) is used for log Kow derivation. Reach guidance R7a (2012), detailed in R7a (2008) and EU TGD guidance (2003) report linear correlations between log Kow and log Koc for different classes of substances. These correlations are proposed by the guidances for the deduction of log Koc from log Kow. The registrant however proposes to use this correlation in reverse to deduce log Kow from log Koc.


As the most appropriate correlation, corresponding to the substance class, “pred. hydrophobics” an equation published by Sabljic and Güsten (1995) was recognised. For a detailed rationale for selection of this equation see annex “Rationale for selection of the appropriate log Kow – log Koc linear relationship”.


The experimental Koc used for log Kow calculation is measured for 14C-MDIPA-Esterquat C16-18 and C18 unsatd. in a GLP batch equilibrium study according to OECD guideline 106. For two sludges (high organic carbon content, mean 34%) and three soils (low organic carbon content, mean 1.4%) the partitioning constant is measured and the geometric mean calculated to be log Koc = 3.69.


With the “predominantly hydrophobic” log Koc – log Kow relationship the log Kow is calculated as 4.43.


 


Surface Tension


The OECD harmonized ring method was applied for the determination of the surface tension of MDIPA-Esterquat C16-18 and C18 unsatd. The surface tension of a test solution at a concentration of 0.9 mg/L at 20°C was in the same order as water. Based on the results of this OECD harmonized ring method, the test substance would not be considered as being surface active. However, this result is not in line with the expected surface tension behaviour of the test substance. Cationic surfactants carrying two C16/C18 alkyl chains, such MDIPA-Esterquat C16-18 and C18 unsatd., are designed to possess surface active properties and typically exhibit surface tension values as low as 27 mN/m (depending on the area per molecule) when studied on a Langmuir film balance. Therefore due to the intrinsic properties (crystallisation) of this double-chain cationic amphiphiles at temperatures below the melting point no reliable results were obtained using the ring method. At temperatures of 20 °C, the inner-molecular mobility of the fatty acid C-chains is hindered. Corresponding to this hinderance, on the one hand, the time to reach solubilisation equilibrium is long and on the other hand, there is a tendency to form vesicles. This can be seen i.e. at the test on hydrolysis with low correlation rates for pseudo-first order curve determination for 20°C but high correlation rates at 50 and 60°C.


 


Auto flammability


For this endpoint a read-across approach was made to the closely related substances MDIPA Esterquat C18 unsatd. and MDEA-Esterquat C16-18 and C18 unsatd. A justification for read-across is attached to Iuclid section 13.


 


The auto-ignition temperature of the source substance MDIPA Esterquat C18 unsatd. was determined according to EU Method A.15 (30 May 2008) and DIN 51794 (2003). The auto-ignition temperature was determined to be 340°C at 1012 hPa.


 


MDEA-Esterquat C16-18 and C18 unsatd.  proved to be not self-ignitable between 20°C and the melting temperature (54°C) in a study conducted according to EU Method A.16 (Relative Self-Ignition Temperature for Solids; 2008).


 


Flammability


For this endpoint a read-across approach was made to the closely related substance MDEA-Esterquat C16-18 and C18 unsatd. A justification for read-across is attached to Iuclid section 13.


 


In a preliminary screening test according to EC no. 440/2008, A.10., the flammability of the source substance MDEA-Esterquat C16 -18 and C18 unsatd. was investigated. After removal of the ignition source, no propagation of combustion of the test substance was observed. With this result the outcome of the screening test is negative and according to CLP (2012) classification criteria the substance is not classified.