N-[3-(dimethylamino)propyl]stearamide

Endpoint summary

Additional information

SPECIATION OF TERTIARY ALKYL AMINE GROUP IN THE REGISTRATION SUBSTANCE SAPDMA

In aqueous medium the unprotonated and the protonated amine are in equilibrium. The percentage of the unprotonated and the protonated amine is determined by the acid constant pKa and the given pH. In the table the percentages are given as function of pH and the pKa of 9.45 (ACD Software) for Primary alkyl amines.

pH	Percentage Protonated amine (N+)	Percentage Unprotonated amine (N)
9	73.8%	26.2%
7	99.6%	0.4%
4	>99.999%	<0.001%

CONCLUSION:

Under environmental conditions it is not relevant if the unprotonated or the protonated amine will be introduced in an aquatic medium. The composition of the protonated and unprotonated amine is solely determined by the pKa and the given pH (see table above). Therefore aquatic test results from the unprotonated and protonated amine are equivalent.

CATIONIC SURFACTANT PROPERTIES

Cationic surfactants like the registration substance SAPDMA sorb strongly to negatively charged surfaces like glass or biota. In order to avoid sorption to the glass of the test vessel and on the test organism well characterized river was used as aquatic medium to allow reliable test results. In the following the acute and chronic ecotoxicity values in river water are given.

SUMMARY OF ACUTE AND CHRONIC ECOTOXICITY RESULTS OF THE REGISTRATION SUBSTANCE SAPDMA

Table 6.1 Acute and chronic ecotoxicity values for the registration substance SAPDMA

Test type	Guideline	Species	Endpoint	Value	Remark
Acute Fish	OECD 203	Danio rerio	LC50 (96h)	>0.1 -<1 mg/L	Tap water testLC0 0.1 mg/L
Acute Daphnia	OECD 202	Daphnia magna	EC50 (48h)	0.38 mg/L	River water test
Algae	OECD 201	Desmodesmus sups.	ErC50 (72h)	0.14 mg/L	River water test
Sludge respir, inhib.	OECD 209	Non-adapted sludge	NOEC (3h)	100 mg/L	EC50 (3h) >100 -<1000 mg/L
Chronic Fish	OECD 211	Danio rerio	NOEC repro (9d)	0.1 mg/L	River water test
Chronic Daphnia	OECD 202	Daphnia magna	NOEC repro (21d)	0.2 mg/L	River water test
Algae	OECD 201	Desmodesmus sups.	ErC10 (72h)	0.07 mg/L	River water test

Algae is the most sensitive species. The PNEC freshwater and marine is derived from the ErC10 (72h) algae of 0.07 mg/L.

CHRONIC ECOTOXICTY PROFILE OF SAPDMA AND THE READ ACROSS SUBSTANCE C20/22 ATQ

Background

The registration substance SAPDMA 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 e.g. the constituent C20 ATQ CH3(CH2)18N+(CH3)3. The registration substance and the constituent C20 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 aldehyde is then oxidizied to the fatty acid which is subsequently degraded by beta oxidation (Kees van Ginkel, Handbook of Surfactants, Volume F, 1995).

Chronic ecotoxicity of the registration substance SAPDMA and the read-across substance C20/22 ATQ

In the following table the river water test results for SAPDMA and C20/22 ATQ are given.

		SAPDMA	C20/22 ATQ	Ratio highest:lowest value
Chronic fish OECD 212 River water test	NOEC repro (9d)	0.1 mg/L	0.24 mg/L	2.4
Chronic daphnia OECD 211River water test	NOEC repro (21d)	0.2 mg/L	0.13 mg/L	1.5
Algae OECD 201River water	ErC10 (72h)	0.07 mg/L	0.93 mg/L	13.2
Algae OECD 201Reconstituted water	ErC10 (72h)	0.2 mg/L	0.93 mg/L(RW)	4.7

The ecotoxicity ratios for Chronic fish and Chronic daphnia is 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 SAPDMA and C20/22 ATQ is 12.9 and much higher than expected. But from the tertiary alkyl dimethylamines (see above) it is known that the algae ecotoxicity in river water is sometimes higher than in reconstituted water. When comparing the SAPDMA algae ErC10 (72h) in reconstituted water with the algae value for C20/22 ATQ river water the ratio for the endpoint drops from 12.9 to 4.5. The value 4.5 is well within the range for variability / uncertainty acceptable for algae test (3 standard deviations). The PNEC freshwater and marine for SAPDMA is derived from the ErC10 (72h) river water algae test of 0.07 mg/L whereas the PNEC freshwater and marine for C20/22 ATQ is derived from the NOEC repro (21d) daphnia of 0.13 mg/L. The ratio between these two NOEC is 0.13/0.07=1.9 and well acceptable with respect to uncertainty / variability of test results.

Conclusion:

Based on the chronic ecotoxicity profile for SAPDMA and C20/22 ATQ it is justified to conclude that the ecotoxicity data for the sediment and soil compartment available for C20/22 ATQ can be used in read-across to SAPDMA. This approach is supported when comparing the PNEC sediment and PNEC soil with the respective PNECs derived with the Equilibrium partitioning method (see IUCLID Chapter 6.2 & 6.3).