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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Reference
Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
(Q)SAR
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Qualifier:
according to guideline
Guideline:
other: REACH Guidance on information requirements and chemical safety assessment: Chapter R.6
Principles of method if other than guideline:
1. Meylan, W.M., Howard, P.H, Aronson, D., Printup, H. and S. Gouchie.  1997.  "Improved Method for Estimating Bioconcentration Factor (BCF) from Octanol-Water Partition Coefficient", SRC TR-97-006 (2nd Update), July 22, 1997; prepared for: Robert S. Boethling, EPA-OPPT, Washington, DC; Contract No. 68-D5-0012; prepared by: ; Syracuse Research Corp., Environmental Science Center, 6225 Running Ridge Road, North Syracuse, NY 13212.
2. Meylan,WM, Howard,PH, Boethling,RS et al. 1999.  Improved Method for Estimating Bioconcentration / Bioaccumulation Factor from Octanol/Water Partition Coefficient. Environ. Toxicol. Chem. 18(4): 664-672 (1999).
Specific details on test material used for the study:
SMILES: CCCCCCCCC=CCCCCCCCCOP(=O)OCCCCCCCCC=CCCCCCCCC
Details on estimation of bioconcentration:
Dioctadec-9-en-1-yl phosphonate (non-stereospecific name of the substance) falls outwith the Log Kow domain of > -1.37 (non-ionic) and/or > -6.50 (ionic) and < 11.26 (general domain for the model) when the Log KOW value is predicted using KOWWIN v1.68. When using the value indicated in from the experimental testing (i.e. a Log KOW of (>)6.5; Walker, 2018), the Log KOW of the substance falls within the domain for the model.

The linear relationship between BCF and Log KOW is known to fail at higher Log KOW values. The relationship has been noted as parabolic or simply scattered at Log KOW > 6. In fact, it is true that bioaccumulation potential peaks at this log KOW (6) and then begins to decrease (ECHA, 2017). By using the experimental and in silico predicted Log KOW, we are able to reflect a worst-case with Log KOW being near 6.5 and BCF value. The non-linear relationship beyond a Log KOW of 6 is overcome in the current model by using the correction factors aforementioned. In this manner, the linear relationship holds true for higher log KOW values, but does of course eventually fail. In this instance, the relatively large molecules may cause an issue with such predictions, as well as low aqueous solubility and a difficulty in measuring the low concentrations accumulated and in the water column (ECHA, 2017). On solubility, it is also well established that bioaccumulation for normal chemistries can only occur for the soluble fraction of the chemical. Moreover, in its simplest form bioaccumulation is defined as “the [bio]accumulation of a substance dissolved in water by an aquatic organism.” As such the substance must be dissolved to lead to accumulation (ECHA, 2017). The substances present here with a high log KOW also have low water solubilities, another well-established relationship (ECHA, 2017). As such with the low water solubility (Walker, 2018) of the substance it is expected that there is low potential for bioaccumulation. This is reflected in the predictions. Nevertheless, the predictions for any constituent with a Log KOW > 14 should be used with caution, but are, accepted here due to their low potential to impact environmental biota.
Key result
Type:
BCF
Value:
3.162 L/kg
Remarks on result:
other: QSAR predicated value
Remarks:
using log Kow 6.5
Reported statistics:
When using the value indicated in the experimental testing (i.e. a log KOW of (>)6.5; Walker, 2018), the Log KOW of the substance falls within the domain for the model.

BCFBAF predicted that the substance has a BCF of 381.4 L/kg ww based on a log Kow of >6.5 (the experimentally derived log Kow).

BCFBAF predicted that the substance has a BCF of 3.162 L/kg ww based on a log Kow of 15.13 (the value predicted by KOWWIN v1.68). When using the value indicated in the experimental testing (i.e. a log KOW of (>)6.5; Walker, 2018), the log Kow of the substance falls within the domain for the model, but as a greater than value there is too much uncertainity in using this value. Hence, the BCF prediction based on the predicted log Kow value should be used.

Validity criteria fulfilled:
yes
Conclusions:
BCFBAF predicted that the substance has a BCF of 3.162 L/kg wwt.
Executive summary:

The bioconcentration factor in fish for the substance was predicted using the EPISuite (v4.11) BCFBAF (v3.01) programme. The SMILES notation was used as the input, along with the log Kow. Both the experimentally derived and predicted log Kow (KOWWIN v1.68) values were assessed.

BCFBAF predicted that the substance has a BCF of 381.4 L/kg ww based on a log Kow of 6.5 (the experimentally derived log Kow).

BCFBAF predicted that the substance has a BCF of 3.162 L/kg ww based on a log Kow of 15.13 (the value predicted by KOWWIN v1.68).

When using the value indicated in the experimental testing (i.e. a log KOW of (>)6.5; Walker, 2018), the log Kow of the substance falls within the domain for the model, but as a greater than value there is too much uncertainity in using this value. Hence, the BCF prediction based on the predicted log Kow value should be used.

Description of key information

BCF (QSAR) = 3.162 L/kg wwt.; Paul, K.B. (2019)

Key value for chemical safety assessment

BCF (aquatic species):
3.162 L/kg ww

Additional information

The bioconcentration factor in fish for the substance was predicted using the EPISuite (v4.11) BCFBAF (v3.01) programme. The SMILES notation was used as the input, along with the log Kow. Both the experimentally derived and predicted log Kow (KOWWIN v1.68) values were assessed.

BCFBAF predicted that the substance has a BCF of 381.4 L/kg ww based on a log Kow of 6.5 (the experimentally derived log Kow).

BCFBAF predicted that the substance has a BCF of 3.162 L/kg ww based on a log Kow of 15.13 (the value predicted by KOWWIN v1.68).

When using the value indicated in the experimental testing (i.e. a log KOW of (>)6.5; Walker, 2018), the log Kow of the substance falls within the domain for the model, but as a greater than value there is too much uncertainity in using this value. Hence, the BCF prediction based on the predicted log Kow value should be used.