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Environmental fate & pathways

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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 Fishunprot.* fractionunprot. at pH  + BCF Fishprot.* fractionprot. 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.