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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The bioaccumulation potential of benzyl salicylate has been assessed using read-across and QSAR. In applying the read-across two important aspects have been considered: the similar potential for metabolism of the two substances and the slight difference in lipophilicity (as modelled by log Kow). In accordance with ECHA guidance R.7.10.3.2, the BCF value for the analogue has been corrected by the same factor of difference as for Kow to give a reliable realistic estimate for benzyl salicylate of 120 to 180 L/kg. The BCFBAF v3.01 regression-based QSAR model gives a reliable estimated BCF value for benzyl salicylate of 202 L/Kg, which was adjusted to 311 L/kg after taking into consideration predicted and experimental values of the analogue read-across substance.

Key value for chemical safety assessment

BCF (aquatic species):
311 L/kg ww

Additional information

Reliable measured aquatic bioaccumulation data is not available for benzyl salicylate. 

According to REACH Annex IX, information on bioaccumulation in aquatic species, preferably fish, is required for substances manufactured or imported in quantities of 100 t/y or more unless the substance has a low potential for bioaccumulation (for instance a log Kow ≤ 3). However,REACH Annex XI encourages the use of alternative information before a new vertebrate test, including fish, is conducted.

Benzyl salicylate has a measured log Kow of > 3. Therefore a weight of evidence approach has been used to assess the bioaccumulation potential of benzyl salicylate using read-across from cyclohexyl salicylate, for which a valid BCF study is available and QSAR.

The read-across is based on the hypothesis that the target substance (benzyl salicylate) and source substance (cyclohexyl salicylate) have similar aquatic bioaccumulation potential as a result of structural similarity, expected similar metabolic potential in fish and limited differences in lipophilicity (as modelled by log Kow). The source and target substance are both mono-constituent substances with typical purities => 99.7%. They do not contain any impurities that are expected to affect their bioaccumulation properties.

The capability of fish to metabolise substances to more polar components, leads to lower BCF values. Therefore, when applying read-across it is important to examine the potential for metabolism for the substance to be evaluated and the analogue substance for which the BCF value is available. Indicators for similar potential for metabolism between the target (benzyl salicylate) and source substance (cyclohexyl salicylate) include:

1) The two substances are structurally closely related as both are alkyl 2-hydroxybenzoate esters. The only slight structural difference is the nature of the alkyl group (benzyl versus cyclohexyl).

2) The two substances share common “bioaccumulation metabolism alert substructures” as profiled in the BCFBAF v3.1 Whole Body Primary Biotransformation Rate constant model for fish (see table below). Both substances contain an “ester”, “aromatic alcohol” and "benzene" structural fragment, which are considered potential sites of metabolic attack as indicated by the negative coefficient values. Benzyl salicylate also contains an “unsubstituted phenyl group” which, according to the model, may further increase the capacity of benzyl salicylate for biotransformation. As such benzyl salicylate may have a higher potential for metabolism than cyclohexyl saliclyate, making the read-across a conservative one.

3) Both substances are readily biodegradable and thus are likely to be rapidly metabolised in organisms.  

Indicator of bioaccumulation potential

Benzyl Salicylate

Cyclohexyl Salicylate

Ready Biodegradability

readily

readily

Bioaccumulation – metabolism alerts (BCFBAF v3.01). 

 

 

Fragment description

Coefficient(1)

 

 

Ester [-C(=O)-O-C]

-0.7605

1

1

Unsubstituted phenyl group [C6H5]

-0.7605

1

0

Aromatic alcohol [OH]

-0.4727

1

1

Benzene

-0.4277

1

1

-CH- [cyclic]

0.0126

0

1

-CH2- [cyclic]

0.0963

0

5

Aromatic H

0.2664

4

4

Partition coefficient N-Octanol/water (Log Kow)(2)

4.0

4.7

BCFBAF v3.01 QSAR prediction

 

 

Regression-based BCF estimate, L/Kg

202

311(3)

586

Measured BCF, L/kg

 

600-900

1) Descriptors with positive signs reflect a general reduced capacity for biotransformation and negative values reflect a general increased capacity for biotransformation; 2) Determined according to OECD 107 guideline; 3) adjusted based on the predicted and experimental data for the analogue substance, cyclohexyl salicylate

A valid BCF value of 600-900 L/kg is available for cyclohexyl salicylate. This analogue is considered a suitable read-across substance based on its structural similarity to benzyl salicylate, expected similar metabolic potential in fish and limited differences in lipophilicity (as modelled by log Kow). The measured log Kow values for benzyl salicylate and cyclohexyl salicylate are 4.0 and 4.7 respectively. Since the BCF value of a substance is generally positively correlated with its lipophilicity (as modelled by log Kow), direct read-across from cyclohexyl salicylate would represent a worst-case and unrealistic estimate for benzyl salicylate. Thus in accordance with ECHA guidance R.7.10.3.2, the BCF value has been corrected by the same factor of difference as for Kow (i.e. 100.7= 5.0) to give a BCF estimate for benzyl salicylate of 120 -180 L/kg.

The BCFBAF v3.01 regression-based QSAR model gives estimated BCF values for benzyl salicylate and cyclohexyl salicylate of 202 and 586 L/kg respectively. The latter is in close agreement with the experimental value of 600-900 L/kg supporting the applicability of the QSAR to this group of chemicals and the reliability of the BCF prediction for benzyl salicylate. However, since the predicted value for cyclohexyl salicylate is slightly lower than the maximum experimental value, a conservative approach has been taken and a correction factor of 1.54 (900/586) has been applied to the predicted value of 202 L/Kg to give a reliable conservative BCF estimate for benzyl salicylate of 311 L/Kg for risk assessment purposes.

Based on the above information, it is concluded that there is no need for further investigation of aquatic bioaccumulation with fish.

For classification purposes, an experimentally derived high quality log Kow value is suitable when a measured BCF on an aquatic organism is not available. Benzyl salicylate has a measured log Kow of 4.0, which just meets the CLP Regulation EC 1272/2008 cut-off value of log Kow ≥ 4 to identify substances with a potential to bioconcentrate. However, an experimentally determined BCF provides a better measure and is used in preference for classification purposes. Benzyl salicylate has an estimated BCF value of 120 - 180 L/kg, based on measured data for a read-across analogue substance and corrected for slight differences in log Kow. It has an estimated value of 311 L/Kg, based on a QSAR prediction and adjusted to take into account slight differences in predicted and experimental data for the analogue substance. Both estimates are significantly less than the CLP threshold value of BCF ≥ 500 L/kg. Thus benzyl salicylate is considered not to have the potential to bioconcentrate for classification purposes.

For PBT/vPvB assessment purposes, predicted BCF estimates and log Kow may be used to provisionally assess bioaccumulation potential. Benzyl salicylate has a measured log Kow of 4.0, which is less than the B screening criteria of ≤ 4.5. Estimated BCF values for benzyl salicylate are in the range of 120 to 311 L/kg. This is well below the B definitive criterion of BCF > 2000 L/kg.

The estimated BCF value for benzyl salicyate based on read-across and QSAR is in the range of 120 to 311 L/kg. The highest value of 311 L/kg has been chosen as a relevant and reliable conservative estimate for risk assessment purposes.