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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. The assessment is mainly focused on the two substance constituents typically present at the highest concentration, which are:

N,N'-[1,3-phenylenebis(methylene)]bis(12-hydroxyoctadecanamide) (CAS No. 128554-52-9) and

12-hydroxy-N-{3-[(stearoylamino)methyl]benzyl}octadecanamide (CAS No. 1262779-46-3)

 

The octanal/water partition coefficient (log Kow >6.5) indicates that the substance should have a high bioaccumulating potential. However, the molecular weight and the very high potential log Kow indicate that the substance may not be bioavailable, which is discussed further below.

 

Molecular weight:

If the substance has a molecular weight higher than 700 g/Mol this is an indicator that the BCF is below 5000 L/kg.

The two substance constituents typically present at the highest concentration (CAS No. 128554-52-9 and 1262779-46-3) have molecular weights of 701.13 and 685.13 repectively. This indicates that for these constituents BCF may be predicted to be marginally under 5000 L/kg or marginally over 5000 L/kg respectively.

Overall, the substance constituents molecular weight ranges from 300 - 982, with the majority of bisamides being in an approximate range of 650 - 750. The constituents with the higher molecular weight (>900) are the estolides.

The molecular weight should only be considered along with other information to form a weight of evidence argument. However, based on molecular weight alone, the substance constituents would be anticipated to show some variation in BCF.

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 twp substance constituents typically present at the highest concentration (CAS No. 128554-52-9 and 1262779-46-3).

log Kow Estimations:

Estimations of log Kow were made for the constituents were made 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 constituents

Log Kow: (Kowwin (v1.67)

 

Log kow: (Bcfwin (v2.17)

 

N,N'-[1,3-phenylenebis(methylene)]bis(12-hydroxyoctadecanamide)

(CAS No. 128554-52-9)

13.08

13.08

 

12-hydroxy-N-{3-[(stearoylamino)methyl]benzyl}octadecanamide (CAS No. 1262779-46-3)

 

14.21

14.21

The predicted log Kow is greater than 10 for both constituents for the estimation methods. 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 two constituents. 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, 9 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 constituent

Log Kow

BCF: (Bcfwin (v2.17)

 

N,N'-[1,3-phenylenebis(methylene)]bis(12-hydroxyoctadecanamide)

(CAS No. 128554-52-9)

6.5

 142.9

7

 346.7

8

 19.5

9

 3.162

10

 3.162

13.08

 3.162

12-hydroxy-N-{3-[(stearoylamino)methyl]benzyl}octadecanamide

(CAS No. 1262779-46-3)

6.5

 142.9

7

 346.7

8

 19.5

9

 3.162

10

 3.162

14.21

 3.162

 

Based on the predictions for BCF using the Bcfwin program, for both constituents the highest predicted BCF value was 346.7, 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 two substance components which are typically present at the highest concentration.

Based on the structurally similarity between these two constituents and the other bisamides and estolides constituents, it is expected that these other constituents will show similar log Kow and BCF properties. Therefore, bioaccumulation is not anticipated to be significant for the substance.