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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

Key value for chemical safety assessment

Additional information

A bioaccumulation study (to method OECD 305) has been considered not to be feasible to conduct.

However, as the experiment log Kow of the substance was determined to be >6.5, indicating that the substance has potential for bioaccumulation, a further assessment of bioaccumulation has been made, which is detailed below.

 

A BCF of 43700 value has been calculated by EUSES (based on the physico-chemical properties of the substance entered, with log Pow stated as 6.5). This calculated BCF and molecular weight (681, based on the main component) indicate that the substance should have a high bioaccumulating potential. However, the length of the molecule (stated as ca. 50 Å) and the very high potential log Kow indicates that the substance may not be bioavailable (too long to pass the membranes), which is discussed further below.

 

Molecular size and weight:

Information on molecular size can be an indicator to strengthen the evidence for a limited bioaccumulation potential of a substance. One parameter for molecular size is the maximum molecular length of a substance. If this length exceeds 4.3 nm (43 Å), it is assumed that the substance disturbs the entire interior structure of the lipid bilayer of cell membranes and therefore does not accumulate to a significant amount, i.e. has a BCF value lower than 2000 L/kg.

The stated length of the molecule (based on the main component) is 50 Å indicating that the accumulation of the substance may not be significant.

However, it should be noted that folding of long linear structures may alter the length of the molecule of the substance, which renders it easier transferable across cell membranes. Therefore, the criterion for molecular length should only be used in a weight of evidence approach for bioaccumulation, along with other relevant data.

If the substance has a molecular weight higher than 700 g/Mol this is an indicator that the BCF is below 5000 L/kg. Two of the main substance components have molecular weights approaching 700 (664 and 681 respectively) and one has a molecular weight substantially over 700 at 962.

Log Kow:

The experimental log Kow of the substance was determined to be >6.5. Based on the screening criteria for bioaccumulation (log Kow >4.5 indicates potential for bioaccumulation) the substance has the potential for bioaccumulation. The assumption behind this is that the uptake of an organic substance is driven by its hydrophobicity. The substance is not known to bioaccumulate by a mechanism other than passive diffusion driven by hydrophobicity.

At log Kow values between 4 and 5, log BCF increases linearly with log Kow. However, at very high log Kow (>6), a decreasing relationship between the two parameters is observed. The aquatic BCF of a substance is probably lower than 2000 L/kg if the calculated log Kow is higher than 10 (i.e. a log Kow >10 is taken as an indicator for showing reduced bioconcentration).

Based on the high log Kow of the substance (>6.5), the log BCF may potentially not increase linearly depending on the value of log Kow. Therefore, bioaccumulation may not be significant for the substance based on log Kow.

Modelled (QSAR) for log Kow and BCF:

Based on the above information, the bioaccumulation potential of the substance is not certain. Therefore, estimations of log Kow and BCF were made for the three main substance components using computer programs.

log Kow Estimations:

An initial estimation of log Kow (Pow) was available as part of the experimental determination of the partition coefficient (refer to partition coefficient section of dossier) . Based on the structure of the main component in the substance, with the highest percentage present, (N,N'-1,6-hexanediylbis(12-hydroxyoctadecanamide)) calculation of the partition coefficient from the structural formula was performed using the Rekker calculation method (using a computer program, PrologP version 6.0).

The Pow was calculated to be log Pow 12.9 using the Rekker calculation method.

Further estimations of log Kow were made for the three main constituents using the following programs available in the EPI Suite program (v 3.20) (developed by the US EPA).

- Kowwin (v1.67): estimates octanol-water partition coefficient

- Bcfwin (v2.17) - estimates bioconcentration factor (BCF) and also log Kow as the program calculates BCF based on log Kow.

The estimates are summarised below and the raw data attached.

Table: Estimated log Kow values

Substance component

Log Kow: (Kowwin (v1.67)

 

Log kow: (Bcfwin (v2.17)

 

N,N'-1,6-hexanediylbis(12-hydroxyoctadecanamide) (CAS No: 55349-01-4)

13.28

13.28

Stearyl hydroxystearyl hexanediamine

 

14.41

14.41

bis(Hydroxystearyl) Hydroxystearyl hexanediamine

20.60

20.60

The predicted log Kow is greater than 10 for all three components for every estimation method. As stated above a calculated log Kow of 10 or above is taken as an indicator for showing reduced bioconcentration and the aquatic BCF of a substance is probably lower than 2000 L/kg.

Based on this information, the Bcfwin (v2.17) program was used to calculate BCF values for the three main components. Estimates were run using the estimated log Kow values, but also on intermediate log Kow values ranging from the experimental result to the predicted values (log Kow values of 6.5, 7, 8 and 10 were selected). This was done to try and predict a worst case BCF value and to see any effects on bioaccumulation with decreasing log Kow.

The results are summarised below and the raw data attached.

Table: Estimated BCF values

Substance component

Log Kow

 

BCF: (Bcfwin (v2.17)

 

N,N'-1,6-hexanediylbis(12-hydroxyoctadecanamide) (CAS No: 55349-01-4)

6.5

638.3

7

1549

8

87.1

10

3.162

13.28

3.162

Stearyl hydroxystearyl hexanediamine

 

6.5

638.3

7

1549

8

87.1

10

3.162

14.41

3.162

bis(Hydroxystearyl) Hydroxystearyl hexanediamine

6.5

638.3

7

1549

8

87.1

10

3.162

20.60

3.162

 

Based on the predictions for BCF using the Bcfwin program, for all three components the highest predicted BCF value was 1549, when the log Kow was given as 7.

Apart from the increase in BCF values from log Kow 6.5 to 7, these predicted BCF values follow the trends based on log Kow discussed above i.e. at high log Kow there is a decreasing relationship between log BCF increasing with log Kow and the aquatic BCF of the substance components are lower than 2000 L/kg using calculated log Kow of 10 and above, indicating reduced bioconcentration of the substance.

The predicted BCF values of 3.162, using the estimated log Kow values indicate bioaccumulation is not significant for the substance components.