Hexadecyldimethylamine

Endpoint summary

Additional information

For the determination of the BCF fish of cationic surfactants classical test methods like OECD 305 are not suitable as the test substance sorbs to negatively charged surfaces like glass and fish leading to incorrect results. Therefore modeling is currently the most reliable approach to estimate the bioaccumulation potential.

The Arnot & Gobas Model (2003) for the estimation of the BCF fish takes into adsorption, distribution, metabolism and excretion (ADME) of a substance in fish. This model is included in the US EPA Estimation program BCF BAF Version 3.01. The octanol-water partitioning coefficient log Kow is an important input parameter for this model. The log Kow for the unprotonated Dimethylalkylamines (DMAs) is calculated with the US EPA KOWWIN Version 1.68 program. For the protonated DMAs the log Kow for the unprotonated DMAs were calculated by subtraction the empirical factor 3.5 (Fu et al, 2009). This empirical factor is a reasonable one as can be seen when comparing the difference between the measured Log Kow for the protonated and unprotonated DMAs (see IUCLID Chapter 4 Endpoint summary Physical and chemical properties).

Table             Log Kow for unprotonated and protonated DMAs

Log Kow		C18	C16	C14	C12	C10
US EPA KOWWIN V 1.68	unprotonated amin R-NH2	8.4	7.4	6.4	5.4	4.8
	protonated amine R-NH3+	4.9	3.9	2.9	1.9	1.3

With the Log Kow given in the table above the BCF Fish for the unprotonated and protonated DMAs were estimated with US EPA BCF BAF Version 3.01 program.

Table            BCF Fish using the US EPA BCF BAF V. 3.01 Program

BCF Fish Arnot & Gobas		C18	C16	C14	C12	C10
US EPA BCF BAF V. 3.01	unprotonated amin R-NH2	58	247	534	411	206
	protonated amine R-NH3+	242	105	28	4.6	1.9

For all DMAs the estimated pKa (see IUCLID Chapter 4.21) is 9.78 which means that in the aquatic environment most of the DMA is protonated.

Table            Speciation of DMAs depending on pH

Speciation of DMAs pKa=9.78	unprotonated amin R-NH2	protonated amin R-NH3+
pH 9	14.2%	85.8%
pH 7	0.2%	99.8%
pH 4	0.00017%	99.99983%

As the chemical acitivity of a substance in a mixture is additive (Schwarzenbach et al, Environmental Chemistry, Wiley Interscience, 2003) the BCF fish for a chain homologue can be at a given pH can be calculated as follows

 

BCF Fish (pH) = BCF Fish_unprot.* fraction_{unprot. at pH}  + BCF Fish_prot.* fraction_{prot. at pH}  

 

In order to calculated the overall BCF Fish for a DMA substance the BCF Fish (pH) of all homologues in the substance will be summed up according their relative fraction in the mixture.

 

Table             BCF fish for DMA substances for pH 9, 7 and 4

ARNOT & GOBAS MODEL US EPA BCF BAF	C Chain length	C fraction	BCF contribution per component		BCF in solution (Species and Chain weighted)
			RNH2	RNH3+	BCF at pH 9	BCF at pH 7	BCF pH 4
C10 DMA	C10	0.95	196	2
	SUM	0.95	196	2	29	2	2
C12-14 DMA	C12	0.71	292	3
	C14	0.25	134	7
	C16	0.03	7	3
	SUM	0.99	433	13	73	14	13
C12-18 DMA	C12	0.50	206	2
	C14	0.23	123	6
	C16	0.14	35	15
	C18	0.11	6	27
	SUM	0.98	369	50	95	51	50
C12-16 DMA	C12	0.40	164	2
	C14	0.50	267	14
	C16	0.08	20	8
		0.98	451	24	85	25	24
C16 DMA	C12	0.01	4	0
	C16	0.98	242	103
	SUM	0.99	246	103	123	103	103
C14-18 DMA	C14	0.03	16	1
	C16	0.35	86	37
	C18	0.62	36	150
	SUM	1.00	138	188	181	188	188
C16-18 DMA	C12	0.01	4	0
	C16	0.33	82	35
	C18	0.64	37	155
	SUM	0.98	123	190	180	189	190
C18 DMA	C18	0.92	53	223
	SUM	0.92	53	223	199	222	223

Conclusion

As can be seen from the table above the overall BCF of the DMAs are low and well below 2000.

As DMAs are readily biodegraded by microorganisms it can be assumed that metabolism in fish is reasonable fast as well and can explain why the BCF Fish for DMAs are low.

The highest estimated value of 223 can be used for the exposure assessment for secondary poisoning.