N-[3-(dimethylamino)propyl]stearamide

Endpoint summary

Additional information

READ-ACROSS JUSTIFICATION BIODEGRADATION

The registration substance is a cationic surfactant with the formula CH3(CH2)16CONH(CH2)3NH+(CH3)2 which is structurally closely related to the quat C20/22 ATQ (CAS No. 68607-24-9 already REACH registered) with the major constituent C22 ATQ CH3(CH2)18N+(CH3)3. The registration substance and the consituent C22 ATQ have the same number of carbons,

are both cationic surfactants and are strongly sorbing to solids due to ionic interactions and van der Waals forces. Both substances are also readily and ultimately biodegradable in an OECD 301B CO2 Evolution test. In addition the microbial metabolic pathway is the same for both substances as in the first step the alkyl chain is cleaved from the nitrogen forming the corresponding aldehyde and ammonium compound. The aldehyd is then oxidizied to the fatty acid which is subsequently degraded by beta oxidation (Kees van Ginkel, Handbook of Surfactants, Volume F, 1995). Based on these similarities it is justified to use the result of an OECD 303A STP Simulation test with C20/22 ATQ for read-across for the registration substances

BIODEGRADATION IN WATER: SCREENING TEST

The registration substance is readily biodegradable in an OECD 301B CO2 Evolution test fulfilling the 10d window. CO2 evolution was 88% after 28d and has reached the pass level of 60% CO2 formation after 16d already.

BIODEGRADATION IN SEDIMENT

According Annex IX, Section 9.2.1.4 column 2 of the REACH Regulation 1907/2006/EC a Sediment simulation test need not to be carried out if the substance is readily biodegradable. Based on EChA REACH Guidance R.16 Environmental Exposure Assessment, Section R.16.4.4.5 (May 2008) the C22 ATQ soil half-life of 45.5 d (12 deg C) may also be applied for aerobic sediment if no other data are available.

BIODEGRADATION IN SEWAGE TREATMENT PLANT – SIMULATION TEST
OECD 303A C20/22 ATQ Simulation Test Activated Sludge Unit -Aerobic Sewage Treatment
C20/22 ATQ was continuously dosed into the activated sludge unit resulting in an influent concentration of 300 µg/L (41 µg/L C20 isomer, 243 µg/L C22 isomer). Influent and effluent concentration of C20/22 ATQ were measured daily using LC MS MS (LOQ C20 influent = 4.1 µg/L, C22 24.3 µg/L; LOQ C20 effluent = 2.1 µg/L, C22 12.1 µg/L). Already one day after the start of the test the elimination of C20/22 ATQ was > 99% (C20 and C22 fraction). Biodegradation of C20/22 ATQ has started immediately and reached a maximum of 98% during the plateau phase. Biodegradation of the C20 fraction was 94-98% (median 96%) and of the C22 fraction 87-93% (median 91%). For exposure assessment a weighted average of 92.2% biodegradation was used.

BIODEGRADATION IN SOIL

OECD 307 Aerobic Transformation in Soil with 14C-C22 ATQ

According Annex IX, Section 9.2.1.3 column 2 of the REACH Regulation 1907/2006/EC a Soil simulation test need not to be carried out if the substance is readily biodegradable. Nevertheless available information is provided using read across.

In an Aerobic transformation study in soil with 14C-C22 ATQ rapid degradation was observed (details see IUCLID Chapter 5.2.3). The DT50 for the three soils tested were 23,2, 24 and 41.4 d at 20 deg C. The Median for the 3 soils at 12 deg C is 45.5d.

SUMMARY ON AEROBIC BIODEGRADATION

The registration substance is rapidly biodegraded in water, sediment and soil as demonstrated by the test results given before.

Hypothesis for the analogue approach

 

This read-across is based on the hypothesis that source and target substances have similar toxicological properties because

·        they are manufactured from similar or identical precursors under similar conditions

·        they share structuralsimilarities with common functional groups: quaternary amines, amides, and saturated fatty acid chains with comparable length

·        the metabolism pathway leads to comparable products (amine backbone and long chain fatty acids) and non-common products predicted to have no toxicological effects (long chain fatty acids).

 

Therefore, read-across from the existing ecotoxicity (sediment and soil) and environmental fate studies on the source substance is considered as an appropriate adaptation to the standard information requirements of the REACH Regulation for the target substance, in accordance with the provisions of Annex XI, 1.5 of the REACH Regulation.

The justification of the proposed read-across approach is elaborated in the next chapters.

 

1. Substance Identity

 

The target substance Stearic acid 3-(dimethylaminopropyl)amide is manufactured from octadecanoic acid and N, N-dimethylpropylenediamine.

 

The source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides is a quaternary ammonium chloride derived from fatty alcohol.

 

 

Table 1: Substance identities

	Target substance	Source substance
	Stearic acid 3-(dimethylaminopropyl) amide	Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides
	mono constituent substance	UVCB
IUPAC name	N-[3-(dimethylamino)propyl]octa-decanamide	n.a.
EC number	231-609-1	271-756-9
CAS number	7651-02-7	68607-24-9
Chain length distribution	< C16: < 1.6% C16: < 7% C18: > 88.9% > C18: < 2.5%	Mainly C20 and C22; <C20 in smaller amounts; C22 = main constituent

 

 

Figure 1: Molecular structures of the target substance Stearic acid 3-(dimethylaminopropyl) amide and the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides

 

 

2. Analogue approach justification

The read-across hypothesis is based on structural similarity of target and source substances. Based on available experimental data, including key physico-chemical properties and data from long-term aquatic ecotoxicity studies, the read-across strategy is supported by a similar ecotoxicological profile of the substances.

The respective reliable data (RL 1 or 2) are summarised in the table 2; robust study summaries are included in the Technical Dossier in the respective sections.

Ecotoxicological data are summarised in the data matrix.

 

2.1 Structural similarity

a. Structural similarity and functional groups (Table 1, Figure 1)

The target substance Stearic acid 3-(dimethylaminopropyl)amide is manufactured from octadecanoic acid and N,N-dimethylpropylenediamine. It is composed of mainly C18 amides (> 89.8%) of DMAPA and small amounts of the C16 amide (<7%).

 

The source substance Quaternary ammonium compounds, C20-22 -alkyltrimethyl, chlorides is a quaternary ammonium chloride derived from fatty alcohol. The general chemical structure is R-N(Me)3+ Cl-, whereas the alkyl chain R is variable for the main components C20 and C22 but also shorter and longer C-chains (in smaller amounts). The major constituent is the C22 derivative.

 

The target substance and the main constituent C22 ATQ of the source substance have a similar number of carbon atoms,are both cationic surfactants (see also 2.1.c) and are strongly sorbing to solids due to ionic interactions and van der Waals forces.

 

b. Common breakdown products

In principle, the amide-bond of the target substance can be cleaved abiotically but the half-life for the hydrolysis is >>100 years (US EPA Hydrowin Model).

The metabolism that is expected to occur is for the target substance Stearic acid 3-(dimethylaminopropyl)amide the hydrolysis of the amide-bond by amidases. Metabolism would result in free fatty acids and di- or trimethylaminopropylamine. The free fatty acids enter normal metabolic pathways (e.g. degradation by the mitochondrial beta-oxidation process) and are therefore indistinguishable from fatty acids from other sources.

The most likely metabolism of the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chloridesis oxidation of the alkyl chain.

Both substances were shown to be readily and ultimately biodegradable in an OECD 301B CO2 Evolution test. In addition the microbial metabolic pathway is the same for both substances as in the first step the alkyl chain is cleaved from the nitrogen forming the corresponding aldehyde and ammonium compound. The aldehyde is then oxidized to the fatty acid which is subsequently degraded by beta oxidation (Kees van Ginkel, Handbook of Surfactants, Volume F, 1995).

 

c. Differences

Chain length:

The target substance contains mainly C18 chains, whereas the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides consists of mainly C22 chains. However, the overall number of carbon atoms is similar resulting in a comparable molecular weight. Nevertheless, the target substance is slightly more soluble in water and has a slightly lower log Kow due to the more hydrophilic amide function. Long-term ecotoxicity data on both substances however, show comparable effect levels. Thus, it is assumed, that the impact of this difference on toxicity to sediment dwelling and soil organisms is negligible.

 

Methylation/quaternation:

The source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides is methylated during the manufacturing process resulting in the quaternised ammonium ion.

Stearic acid 3-(dimethylaminopropyl)amide) on the other hand is not methylated during the manufacturing process. However, based on physicochemical data (pKa) it is concluded that at physiological relevant pH, the substance is mostly protonated similarly resulting in a positively charged ammonium ion.

 

Amide:

In contrast to the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides, the target substance Stearic acid 3-(dimethylaminopropyl)amide) contains a polar amide function which may be susceptible to enzymatic hydrolysis.

 

 

3. Physicochemical properties

 

Table 2: Physicochemical properties

	Target substance	Source substance
Endpoints	Stearic acid 3-(dimethylaminopropyl)amide	Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides
Molecular weight	368.64 g/mol	375.5 - 432.209 g/mol
Physical state at 20°C / 1013 hPa	Solid (paste)	Solid
Melting point	OECD TG 102   67.4°C	OECD TG 102   > 220 - < 240 °C
Boiling point	OECD TG 103   412.3°C	n.a.
Surface tension	ISO 4311, plate method   37.86 mN/m at 25°C and 0.22 g/L	OECD TG 115, plate method   47mN/m at 25°C and0.01g/L (pure C22)
Water solubility	ISO 4311, plate method   CMC = 220 mg/L at 25°C	ISO 4311, plate method   CMC = 10 mg/L at 25°C and pHca. 5.4 (C22)
Log Kow	EU method A.8, calculation based on solubility in n-Octanol and water   log Kow: 2.01 at 20°C, pH7	EU method A.8, calculation based on solubility in n-Octanol and water   Log Kow: 3.29 at 20°C, pH ca. 5.4
Vapour pressure	OECD TG 104    3.4E-08 Pa at 20°C	OECD TG 104 7.0E-05

 

The physical state of both substances is solid. The surface tension, water solubility and log Kow are in a comparable range. The vapour pressure of both substances is very low.

The similar physic-chemical properties – especially surface activity, similar water solubility and partition coefficients – of the target and source substance support the read-across approach.

 

4. Comparison of data from environmental fate endpoints

 

Table 3: Data matrix: environmental fate

	Target substance	Source substance
Endpoints	Stearic acid 3-(dimethylaminopropyl)amide	Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides
Biodegradation: screening test	OECD TG 301 B   readily biodegradable (88% after 28 d, >60% within the 10 d window)	OECD TG 301 B   readily biodegradable (ca. 70% after 28 d, ca. 48% within the 10 d window)
Biodegradation in soil: simulation testing	No data, read-across	OECD TG 307   DT50 of 23 to 41 days at 20°C in different soils
Adsorption / desorption	No data, read-across	OECD TG 106   Koc> 950 - < 516 000 L/kg Log Koc> 3 - < 5.7

 

The target substance is readily biodegradable in an OECD 301B CO2 Evolution test fulfilling the 10d window. CO2 evolution was 88% after 28d and has reached the pass level of 60% after 16d.

 

The source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides was readily biodegradable in a screening test, but failed the 10 d window criterion.

 

In an Aerobic transformation study in soil with 14C-C22 ATQ rapid degradation was observed. The DT50 for the three soils tested were 23.2, 24 and 41.4 d at 20°C. The Median for the 3 soils at 12 deg C is 45.5 d.

 

Sorption behaviour of the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides was measured in three different soils, one sediment and one secondary sludge. The Freundlich isotherms for the different matrices are non-linear (1/n < 1).

 

C22-Trimethylammonium Chloride adsorption isotherms could be described by the Freundlich equation. KFoc(ads) values were 19.8E03 L/kg (Cranfield 164 soil), 516E03 L/kg (Cranfield 277 soil), 52.8E03 L/kg (Cranfield 299 soil), 17.4E03 L/kg (SW sediment) and 0.95E03 L/kg (Tilburg sludge).

 

Overall, based on structural similarity, and comparable physico-chemical properties, the results of the environmental fate studies conducted with the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides can be used in a read-across approach forthe target substance Stearic acid 3-(dimethylaminopropyl)amide.

 

5. Comparison of data from ecotoxicological endpoints

 

Table 4: Data matrix: ecotoxicity studies

	Target substance	Source substance
Endpoints	Stearic acid 3-(dimethylaminopropyl)amide	Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides
Short-term toxicity to fish	OECD TG 203 Oncorhynchus mykiss; tapwater   96 h LC50 > 0.1 and <1 mg/L	Not used in this read-across
Long-term toxicity to fish	OECD TG 212 Danio rerio; natural river water    9 d NOEC =0.1mg/L (abnormal behaviour)	OECD TG 212 Danio rerio; natural river water   9 d NOEC =0.243mg/L (Hatch, Growth & Fry survival)
Short-term toxicity to aquatic invertebrates	OECD TG 202 Daphnia magna; natural river water   48 h EC50 =381µg/L (95% c.i.62.5 - 345 µg/L)	Not used in this read-across
Long-term toxicity to aquatic invertebrates	OECD TG 211 Daphnia magna; natural river water   21 d NOEC =200µg/L (mortality)	OECD TG 211 Daphnia magna; natural river water   21 d NOEC =128µg/L (reproduction)
Toxicity to algae	OECD TG 201 Desmodesmus subspicatus; natural river water   72 h EC50 =140 µg/L (95% c.i.130 – 154µg/L) 72h EC10 = 70.8 µg/L (95% c.i.62.7 – 78.7 µg/L)	OECD TG 201 Desmodesmus subspicatus; natural river water   72 h EC50 =3.48mg/L (95% c.i.3.28 - 3.70 mg/L) 72 h EC10 =0.927mg/L (95% c.i.0.798-1.07 mg/L)
sediment toxicity: long-term	No data, read-across	OECD TG 225 Lumbriculus variegates 28 d EC50 =169mg/kg sediment dw (reproduction) 28 d NOEC =62.5mg/kg sediment dw (reproduction)
		Draft ISO/DIS 10872 Caenorhabditis elegans   96 h NOEC =250mg/kg sediment dw (mortaliy, fertility, reproduction, growth)
toxicity to soil macroorganisms except arthropods: short-term	No data, read-across	OECD TG 207 Eisenia fetida   14 d NOEC =1 000 mg/kg soil dw (mortality, biomass, development)
toxicity to soil macroorganisms except arthropods: long-term	No data, read-across	OECD TG 222 Eisenia fetida   54 d NOEC =250mg/kg soil dw (eproduction, mortality and body weight)
toxicity to terrestrial arthropods: long-term	No data, read-across	ISO 11267 Folsomia candida   28 d NOEC =500mg/kg soil dw (mortality, reproduction)
toxicity to soil microorganisms	No data, read-across	OECD TG 216 Soil microorganisms   28 d EC50 =76mg/kg soil dw (95% c.i.66.0 - 84.3mg/kg soil dw) (nitrate formation rate) 28 d EC10 =15mg/kg soil dw (95% c.i.12-38mg/kg soil dw) (nitrate formation rate) 28 d NOEC = 10 mg/kg soil dw (nitrate formation rate)

 

The effect levels in the long-term studies with fish and daphnia were similar for the target substance Stearic acid 3-(dimethylaminopropyl)amide and the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides, differing by a factor of 2.4 and 1.5, respectively. These ratios are well within the boundaries on variability / uncertainty accepted e. g. for reference substances.

The ratio for ErC10 (72h) for the target substance Stearic acid 3-(dimethylaminopropyl)amide and the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides is 12.9 and higher than expected. Nevertheless, variability within approx. one order of magnitude is not uncommon between different laboratories. Overall, based on structural similarity, comparable physico-chemical properties, and similar results in the long-term aquatic toxicity studies, the results of the ecotoxicity studies on sediment and soil organisms conducted with the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides are also valid for the target substance Stearic acid 3-(dimethylaminopropyl)amide.The remaining uncertainty is addressed by applying the appropriate assessment factors.

 

6. Classification and labelling

Table 3: Classification and labelling for target and source substances

 

Classification Endpoints	Target substance Stearic acid 3-(dimethylaminopropyl) amide	Source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides
Physical hazards	No classification required	No classification required
Hazards to the aquatic environment: acute	Aquatic Acute 1, M factor: 1	Aquatic Acute 1,M factor: 1
Hazards to the aquatic environment: chronic	Aquatic Chronic 2	Aquatic Chronic 2

 

No classification is required for physical hazards for both, the target and the source substance.

The target substance as well as the source substance are classified as Aquatic Acute 1 with an M factor of 1 and as Aquatic Chronic 2. Neither substance is regarded as PBT or vPvB.

Classification with regard to human health effects is not relevant for this read-across approach, as only ecotoxicity and environmental fate endpoints are assessed.

 

7. Conclusion

The physico-chemical and structural similarities between of the source and the target substances as presented above support the read-across hypothesis. Adequate and reliable scientific information (similar results were obtained in the long-term aquatic toxicity studies, which are available for both, the target and the source substance) indicates that the source and target substances have similar ecotoxicity profiles.

Based on the available data it can be concluded that:

 

-         the results of the environmental fate studies conducted with the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides can be used in a read-across approach forthe target substance Stearic acid 3-(dimethylaminopropyl)amide

 -         the ecotoxicity data for the sediment and soil compartment available for the source substance Quaternary ammonium compounds, C20-22-alkyltrimethyl, chlorides can be used in read-across to the target substance Stearic acid 3-(dimethylaminopropyl)amide. This approach is supported when comparing the PNEC sediment and PNEC soil with the respective PNECs derived with the Equilibrium partitioning method.