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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

A weight of evidence is presented to demonstrate the lack of bioaccumulation potential for this substance. A BCF of 2.2 is assigned for risk assessment purposes and, while this value was obtained using an alternative method compared to, e.g., a standard OECD 305 fish bioconcentration study, this value is reasonable according to a weight of evidence approach. 

Key value for chemical safety assessment

BCF (aquatic species):
2.2 dimensionless

Additional information

A weight of evidence is presented to demonstrate the lack of bioaccumulation potential for this substance. A BCF of 2.2 is assigned for risk assessment purposes and, while this value was obtained using an alternative method compared to, e.g., a standard OECD 305 fish bioconcentration study, this value is reasonable according to a weight of evidence approach.

 

Key study:

 

The key study (Rausina et al., 1996) is considered to have a reliability of 2 according to the criteria of Klimisch, 1997 as the study was well-conducted but a non-guideline and non-GLP study.

 

This test system utilizes Semipermeable Membrane Devices (SPMDs), first developed by the United States Fish and Wildlife Service for field sampling studies assessing environmental contamination. SPMDs are low-density polyethylene tubing, with a pore-size similar to the cell membranes in fish. SPMDs are filled with the lipid triolein, the predominant lipid in fishes, and function as "model fish or mollusks" with selective membranes and lipid reservoirs that concentrate organic compounds from water. The BCF of EC 272-234-3 was determined to be 2.2 in this study.

 

Supporting study 1:

 

BCF was modelled using LMC OASIS Catalogic (v.5.11.17) BCF base-line (v.02.09) modeling software. This substance is a highly complex mixture comprising a number of molecules of varying structure with a distribution of carbon chain lengths with varying numbers of alkyl-phenol rings and sulphur bridging between those alkyl-phenol rings. To better assess the UVCB substance being registered, UVCB G Graph 1.0 was used to create a Generic SMILES to incorporate all variations possible in the UVCB nature of the registered substance. Over 1500 isomers were predicted and a filter was used to reduce the number to a manageable but representative amount of structures to be predicted by catalogic. The filter option selected was Molecular Weight with 3 intervals in order to separate the isomers based on the amount of sulfur bridging (1-3). Five members were randomly selected from each distribution group for a total of 15 constituents for final modeling.

 

Note that the modelled substance was based on EC 272-486-4, which is a similar alkaryl phenate sulfide as EC 272-234-3 (see appendix for read across justification). Alkyl phenate sulfides made from the alkylphenol TPP have the same basic structure (i.e., the difference among alkyl phenate sulfides made from TPP is the amount of calcium carbonate overbasing). The modelled structure did not include calcium carbonate overbasing as salt species are not appropriate for modeling; instead the basic calcium alkyl phenate structure was modeled, which is equivalent to what would be modelled for EC 272-234-3. Therefore, the BCF modeling assessment and QPRF for EC 272-486-4 is used for EC 272-234-3.

 

BCF can accurately be predicted using physical/chemical and molecular properties, including:

 

- Kow

- Metabolism

- Water solubility

- Molecular size

- Molecular charge

The BCF-base line model incorporates all of these factors after starting with a BCF based on Kow (see figure 1). Based on a Kow of approximately 10, the predicted BCF without further modification of EC 272-486-4 was 251. The BCF is then modified based on the factors previously described, reducing the BCF prediction to a final value of 7.41. Specifically, the BCF for the molecules evaluated was further decreased due to low water solubility, large molecular size (exclusion from uptake), and metabolism. The BCF prediction was similar for each of the 15 modeled constituents and exactly the same (7.41) for the final prediction where all modifiers are applied. A full description of the model, inputs, and results is found in a report of this QSAR Prediction (QPRF format) attached to the IUCLID endpoint study record.

 

Supporting study 2:

 

A Klimisch code 1 guideline and GLP study was conducted with TPP (EC 310-154-3), which is present in the registered substance as a residual impurity/constituent. The BCF value assigned is 823.

Steady-state TPP concentrations were achieved in the tissues of rainbow trout (Oncorhynchus mykiss) after 3 days for both the 1.1 and 11 μg/L treatment groups. Steady-state BCF values based on total radioactivity TPP concentrations were 289, 1601 and 823 in edible, nonedible and whole fish tissue, respectively, for the 1.1 μg/L treatment group, and 289, 1428 and 749 in edible, nonedible and whole fish tissue, respectively, for the 11 μg/L treatment group. Steady-state BCF values based on TPP chain lengths for the 1.1 μg/L treatment group were 209 and 544 for the C5 – C10 edible and nonedible fraction, 362 and 786 for the C11 – C12 edible and nonedible fraction, and 426 and 987 for the C13 and greater edible and nonedible fraction, respectively. Steady-state BCF values were 217 and 603 for the C5 – C10 edible and nonedible fraction, 388 and 845 for the C11 – C12 edible and nonedible fraction, and 423 and 936 for the C13 and greater edible and nonedible fraction, respectively for the 11 μg/L treatment group. During depuration, TPP was eliminated quickly with mean tissue concentrations 10% or less than the mean measured steady-state test concentrations by Day 11.

TPP is relevant for this assessment as it is present as a residual raw material in the manufacture of EC 272-234-3. In addition, based on a comparison of the physical and chemical properties (see table below), alkyl phenate sulfides are expected to have a much lower BCF, which is consistent with the results obtained with the SPMD study and the modeling in Catalogic:

 

Property

TPP

Registered alkyl phenate sulfide

Molecular weight

262.4

667.1-731.2

Water solubility

1.54 mg/L @ 20C

0.082 mg/L @55C

Log Kow

7.14

9.5

 

The following information is taken into account for any hazard / risk / bioaccumulation assessment:

 

Alkyl phenate sulfides do not demonstrate a potential to bioconcentrate. The BCF value used is 2.2.

Value used for CSA:BCF: 2.2 dimensionless (L/kg ww or dimensionless)