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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Reference
Endpoint:
bioaccumulation: aquatic / sediment
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
Jan 2013
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Calculated BCF using the BCF base-line model v.02.05.
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Calculated BCF using the BCF base-line model v.02.05 (attached as appendix I) and CATALOGIC model for metabolism simulation (attached as appendix II).
GLP compliance:
no
Radiolabelling:
no
Type:
BCF
Value:
1.51 dimensionless
Basis:
other: QSAR estimation
Remarks on result:
other: Component A
Type:
BCF
Value:
0.87 dimensionless
Basis:
other: QSAR estimation
Remarks on result:
other: Component B
Type:
BCF
Value:
0.72 dimensionless
Basis:
other: QSAR estimation
Remarks on result:
other: Component C
Validity criteria fulfilled:
yes
Remarks:
Components A, B, C are in the structural and mechanistic domain of the model and estimations of log BCF are considered reliable.
Conclusions:
Component A - is characterized by high lipophilicity. Although its log Kow value (log Kow=5.74) would classify it as bioaccumulative, mitigating factors are taken into consideration which reduced its maximum bioaccumulation potential. The BCF base-line model estimates that size and metabolism as most significant mitigating factors reducing its bioaccumulation down to log BCF = 1.51 leading to ultimate classification as Not bioaccumulative.

Component B - the results are confirmed by observed data for structural analogues identified in the Toolbox (also in training set of the BCF base-line model).
Component B is characterized by extreme lipophilicity (calculated log Kow=14.3). Following the conceptual non-linearity of the BCF base-line model, a low bioaccumulation potential is estimated for component B due to its passive diffusion. As a result its log BCFmax is 0.97. Given the extremely low value of log BCFmax (0.97) the contribution of the significant mitigating factors - size and metabolism is formally very small (the ultimate log BCF is 0.87).
The Guidance on information requirements and chemical safety assessment - PBT assessment of ECHA recommends that a chemical may be considered as not bioaccumulative if: DiamMax average > 1.7 nm, molecular weight > 1100 g/mol, log Kow > 10. Component B meets the listed indicators. It has DiamMax in the range 19.0÷32.9 Å (1.9÷3.3 nm), MW=1256 and log Kow =14.3. Hence, based on direct analysis if its volumetric parameters, one could conclude that it is unlikely Component B to have BCF > 2000 (log BCF = 3.3).
Hence, component B should be classification definitely as Not bioaccumulative.

Component C - the estimated log BCFmax = 4.05 for component C is based on its high lipophilicity (calculated log Kow=5.5). The BCF base-line model estimates metabolism to be the most significant mitigating factor for component C. The significant contribution of metabolism in reducing the log BCFmax value for component C is due to the presence of hydroxyl groups in its structure. The presence of hydroxyl groups allows the direct application of high probability Phase II transformations (O-glucuronidation), skipping hydroxylating phase I reactions. It is estimated that metabolism reduces the bioaccumulation of component C down to log BCF = 0.72 leading to ultimate classification Not bioaccumulative.

Description of key information

Component A is the smallest component and has low but measurable water solubility value of 33.4ug/l thus, it is been considered as the worst case scenario.

Key value for chemical safety assessment

BCF (aquatic species):
1.51 dimensionless

Additional information

Component A - is characterized by high lipophilicity. Although its log Kow value (log Kow=5.74) would classify it as bioaccumulative, mitigating factors are taken into consideration which reduced its maximum bioaccumulation potential. The BCF base-line model estimates that size and metabolism as most significant mitigating factors reducing its bioaccumulation down to log BCF = 1.51 leading to ultimate classification as Not bioaccumulative.

Component B - the results are confirmed by observed data for structural analogues identified in the Toolbox (also in training set of the BCF base-line model). Component B is characterized by extreme lipophilicity (calculated log Kow=14.3). Following the conceptual non-linearity of the BCF base-line model, a low bioaccumulation potential is estimated for component B due to its passive diffusion. As a result its log BCFmax is 0.97. Given the extremely low value of log BCFmax (0.97) the contribution of the significant mitigating factors - size and metabolism is formally very small (the ultimate log BCF is 0.87). The Guidance on information requirements and chemical safety assessment - PBT assessment of ECHA recommends that a chemical may be considered as not bioaccumulative if: DiamMax average > 1.7 nm, molecular weight > 1100 g/mol, log Kow > 10. Component B meets the listed indicators. It has DiamMax in the range 19.0÷32.9 Å (1.9÷3.3 nm), MW=1256 and log Kow =14.3. Hence, based on direct analysis if its volumetric parameters, one could conclude that it is unlikely Component B to have BCF > 2000 (log BCF = 3.3). Hence, component B should be classification definitely as Not bioaccumulative.

Component C - the estimated log BCFmax = 4.05 for component C is based on its high lipophilicity (calculated log Kow=5.5). The BCF base-line model estimates metabolism to be the most significant mitigating factor for component C. The significant contribution of metabolism in reducing the log BCFmax value for component C is due to the presence of hydroxyl groups in its structure. The presence of hydroxyl groups allows the direct application of high probability Phase II transformations (O-glucuronidation), skipping hydroxylating phase I reactions. It is estimated that metabolism reduces the bioaccumulation of component C down to log BCF = 0.72 leading to ultimate classification Not bioaccumulative.