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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Justification for type of information:
JUSTIFICATION FOR READING ACROSS INFORMATION FOR PARTITION COEFFICIENT
A study does not need to be conducted for this substance, as it is considered to be neither scientifically necessary nor technically possible.
The octanol/water partition coefficient, Pow, is defined as the ratio of the equilibrium concentrations of a dissolved substance in each of the phases in a two-phase system consisting of octanol and water. It is a key parameter in studies of the environmental fate of organic substances, indicating the potential for bioaccumulation and soil absorption. Whereas this may also be applicable for organometallic substances, it does not pertain to the substance in question here because of its inorganic nature. For inorganic substances, the determination of a partition coefficient is not considered to be required (ECHA Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance, section R.7.1.8.4; July 2017); since the substance is an inorganic substance in accordance with the definitions of the International Union of Pure and Applied Chemistry (IUPAC) because of its ionic structure, waiving in accordance with Annex VII, section 7.8, Column 2 of regulation (EC) 1907/2006) is also justified. In conclusion, the conduct of further experimental verification is considered to be neither technically nor scientifically feasible, and for the reasons stated above derogation from testing is hereby applied for.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The environmental fate and distribution of the dissociation products of this substance in water are better assessed according to the dissociation products in water as follows:
(i) the mechanisms for partitioning of Zn2+ in environmental media, including the adsorption and/or absorption by organic matter and living cells, are understood to be different from those traditionally attributed to carbon-based substances (see IUCLID section 5.4 for information on the partitioning of zinc in the environment). Thus, octanol/water partitioning has little relevance to ionic zinc. In order to measure an octanol/water partition coefficient, it is necessary to determine the concentration in each phase (as in OECD method 107), or to conduct an HPLC assay (as in OECD method 117). However, zinc is a metallic element that exists only in an ionic form in solution. The solubility of divalent zinc cations in water is low and can safely also be expected to be low in organic solvents such as octanol. Because of the unlikely partitioning of zinc cations into the octanol phase, it is not appropriate to determine the partition coefficient by direct quantification of zinc in both phases. Similarly, any aqueous HPLC mobile phase will cause dissociation of inorganic zinc compounds, and thus not allow the determination of an Pow by this method.
(ii) regarding the partitioning behaviour of fatty acid constituents, handbook data (Sangster 1993, 1994) for tetradecanoic acid (CAS# 544-63-8), hexadecanoic acid (CAS# 57-10-3), cis-9-hexadecenoic acid (CAS# 373-49-9), octadecanoic acid (CAS# 57-11-14), 9-octadecenoic acid (CAS# 112-80-1), 9,12-octadecadienoic acid (CAS# 60-33-3), 9,12,15-octadecatrienoic acid (CAS# 463-40-1) report log Pows of 6.11, 7.17, 6.58, 8.23, 7.64, 7.05 and 6.46, respectively.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source: tetradecanoic acid, hexadecanoic acid, cis-9-hexadecenoic acid, octadecanoic acid, 9-octadecenoic acid, 9,12-octadecadienoic acid and 9,12,15-octadecatrienoic acid (see source study records; purity is not of relevance for this endpoint)
Target: Fatty acid, C14-18 and C16-18-unsatd., zinc salts (purity is not of relevance for this endpoint)

3. ANALOGUE APPROACH JUSTIFICATION
see justification given above

4. DATA MATRIX
not required
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
read-across: supporting information
GLP compliance:
not specified
Type of method:
other: not specified
Analytical method:
not specified
Remarks on result:
other: please refer to the field `Justification for type of information´
Conclusions:
A study does not need to be conducted for this substance, as it is considered to be neither scientifically necessary nor technically possible.

The octanol/water partition coefficient, Pow, is defined as the ratio of the equilibrium concentrations of a dissolved substance in each of the phases in a two-phase system consisting of octanol and water. It is a key parameter in studies of the environmental fate of organic substances, indicating the potential for bioaccumulation and soil absorption. Whereas this may also be applicable for organometallic substances, it does not pertain to the substance in question here because of its inorganic nature.
For inorganic substances, the determination of a partition coefficient is not considered to be required (ECHA Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance, section R.7.1.8.4; July 2017); since the substance is an inorganic substance in accordance with the definitions of the International Union of Pure and Applied Chemistry (IUPAC) because of its ionic structure, waiving in accordance with Annex VII, section 7.8, Column 2 of regulation (EC) 1907/2006) is also justified.

Instead of the determination of a Pow value, the environmental fate and distribution of the dissociation products of this substance in water are better assessed according to the dissociation products in water as follows:

(i) the mechanisms for partitioning of Zn2+ in environmental media, including the adsorption and/or absorption by organic matter and living cells, are understood to be different from those traditionally attributed to carbon-based substances (see IUCLID section 5.4 for information on the partitioning of zinc in the environment). Thus, octanol/water partitioning has little relevance to ionic zinc. In order to measure an octanol/water partition coefficient, it is necessary to determine the concentration in each phase (as in OECD method 107), or to conduct an HPLC assay (as in OECD method 117). However, zinc is a metallic element that exists only in an ionic form in solution. The solubility of divalent zinc cations in water is low and can safely also be expected to be low in organic solvents such as octanol. Because of the unlikely partitioning of zinc cations into the octanol phase, it is not appropriate to determine the partition coefficient by direct quantification of zinc in both phases. Similarly, any aqueous HPLC mobile phase will cause dissociation of inorganic zinc compounds, and thus not allow the determination of an Pow by this method.

(ii) regarding the partitioning behaviour of fatty acid constituents, handbook data (Sangster 1993, 1994) for tetradecanoic acid (CAS# 544-63-8), hexadecanoic acid (CAS# 57-10-3), cis-9-hexadecenoic acid (CAS# 373-49-9), octadecanoic acid (CAS# 57-11-14), 9-octadecenoic acid (CAS# 112-80-1), 9,12-octadecadienoic acid (CAS# 60-33-3), 9,12,15-octadecatrienoic acid (CAS# 463-40-1) report log Pows of 6.11, 7.17, 6.58, 8.23, 7.64, 7.05 and 6.46, respectively.

In conclusion, the conduct of further experimental verification is considered to be neither technically nor scientifically feasible, and for the reasons stated above derogation from testing is hereby applied for.

Description of key information

The partition coefficient of the substance Fatty acids, C14-18 and C16-18-unsatd., zinc salts is not considered to be relevant.

Key value for chemical safety assessment

Additional information

A study does not need to be conducted for this substance, as it is considered to be neither scientifically necessary nor technically possible.

The octanol/water partition coefficient, Pow, is defined as the ratio of the equilibrium concentrations of a dissolved substance in each of the phases in a two-phase system consisting of octanol and water. It is a key parameter in studies of the environmental fate of organic substances, indicating the potential for bioaccumulation and soil absorption. Whereas this may also be applicable for organometallic substances, it does not pertain to the substance in question here because of its inorganic nature.

For inorganic substances, the determination of a partition coefficient is not considered to be required (ECHA Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance, section R.7.1.8.4; July 2017); since the substance is an inorganic substance in accordance with the definitions of the International Union of Pure and Applied Chemistry (IUPAC) because of its ionic structure, waiving in accordance with Annex VII, section 7.8, Column 2 of regulation (EC) 1907/2006) is also justified.

Instead of the determination of a Pow value, the environmental fate and distribution of the dissociation products of this substance in water are better assessed according to the dissociation products in water as follows:

(i) the mechanisms for partitioning of Zn2+ in environmental media, including the adsorption and/or absorption by organic matter and living cells, are understood to be different from those traditionally attributed to carbon-based substances (see IUCLID section 5.4 for information on the partitioning of zinc in the environment). Thus, octanol/water partitioning has little relevance to ionic zinc. In order to measure an octanol/water partition coefficient, it is necessary to determine the concentration in each phase (as in OECD method 107), or to conduct an HPLC assay (as in OECD method 117). However, zinc is a metallic element that exists only in an ionic form in solution. The solubility of divalent zinc cations in water is low and can safely also be expected to be low in organic solvents such as octanol. Because of the unlikely partitioning of zinc cations into the octanol phase, it is not appropriate to determine the partition coefficient by direct quantification of zinc in both phases. Similarly, any aqueous HPLC mobile phase will cause dissociation of inorganic zinc compounds, and thus not allow the determination of an Pow by this method.

(ii) regarding the partitioning behaviour of fatty acid constituents, handbook data (Sangster 1993, 1994) for tetradecanoic acid (CAS# 544-63-8), hexadecanoic acid (CAS# 57-10-3), cis-9-hexadecenoic acid (CAS# 373-49-9), octadecanoic acid (CAS# 57-11-14), 9-octadecenoic acid (CAS# 112-80-1), 9,12-octadecadienoic acid (CAS# 60-33-3), 9,12,15-octadecatrienoic acid (CAS# 463-40-1) report log Pows of 6.11, 7.17, 6.58, 8.23, 7.64, 7.05 and 6.46, respectively.

In conclusion, the conduct of further experimental verification is considered to be neither technically nor scientifically feasible, and for the reasons stated above derogation from testing is hereby applied for.

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