Fatty acids, C18-24, zinc salts

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This read-across is based on the hypothesis that key source substance and target substance have similar biodegradability because they are biodegraded through a common mechanism.

Source(s) and target are all fatty acid(s) zinc salts. They have a very close structural similarity only varying in their fatty acids chain length distribution and consequential minor variations in their relative zinc content. They are produced by the oleochemistry sector, starting from natural fatty materials and consist of natural fatty acids and zinc. Once emitted into the environment, fatty acids zinc salts will partly dissociate into the zinc cation and the fatty acids anions, especially in an acidic environment (c.f. EU RAR Zinc distearate (CAS-No.: 557-05-1 & 91051-01-3 EINECS-No.: 209-151-9 & 293-049-4) Part 1 - Environment (Final report R074_0805_env, May 2008, http://echa.europa.eu/documents/10162/08799aec-42c5-44e0-9969-baa022c66db1). Fatty acids biodegrade readily according to the β-oxidation pathway including three major steps (activation in the cytosol, transport into mitochondria, β-oxidation until the entire chain is cleaved into acetyl CoA units)(c.f. common Handbooks on biochemistry). Thus, stable degradation products are not being formed in the environment. However, only the fatty acid moiety is biodegradable in the proper sense. The concept of “biodegradability” has been developed for organic substances and is not applicable to inorganic substances, including zinc, which is the cation in both the source and the target. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” has been developed to assess whether or not a respective metal ion would remain present in the water column upon addition (and thus be able to exert a chronic effect) or would be rapidly removed from the water column. In this concept, “rapid removal” (defined as > 70% removal within 28 days) can be considered equivalent to “rapid degradation”. For zinc in water, information is available on the removal of zinc from the water column. The removal from the water column was modelled referring to the EUSES model parameters and different conditions of pH. Zinc is removed by > 70% under the reference conditions for the EU regional waters (EUSES). Consequently, zinc is considered as equivalent to being ‘rapidly degradable in the context of classification for chronic aquatic effects.
Therefore, read-across from the existing ready biodegradability study on the key source substance is considered as an appropriate adaptation to the standard information requirements of Annex VII, 9.2.11 of the REACH Regulation for the target substance, in accordance with the provisions of Annex XI, 1.5 of the REACH Regulation.

2. SOURCE AND TARGET CHEMICALS COMPOSITION
Source(s) and target have a very close structural similarity only varying in their chain lengths distribution.

2.1. Composition of key source substance Fatty Acids, C16-18, zinc salts / 91051-01-3 / 293-049-4:
- Fatty Acids, - zinc dipalmitate / zinc dihexadecanoate / 4991-47-3 / 225-652-5: >=20.0 - <=65.0% (w/w)
- zinc distearate / zinc dioctadecanoate / 557-05-1 / 209-151-9: >=35.0 - <=80.0% (w/w)
- Fatty Acids, >C18, zinc salts: <= 6.0% (w/w)
- Fatty acids, C16-18 / Fatty acids, C16-18 / 67701-03-5 / 266-928-5: <= 3.0% (w/w)
- water / dihydrogen oxide / 7732-18-5 / 231-791-2: <= 2.0% (w/w)
Only components which do not affect the classification may be present in the source substance.

2.2. Composition of supporting source substances

2.2.1. Composition of supporting source substance zinc bis[12-hydroxyoctadecanoate] / 35674-68-1 / 252-669-5:
- zinc bis[12-hydroxyoctadecanoate] / 35674-68-1 / 252-669-5: >=80.0 - <=100.0% (w/w)
- zinc distearate / zinc dioctadecanoate / 557-05-1 / 209-151-9: <=15.0% (w/w)
- zinc dipalmitate / zinc dihexadecanoate / 4991-47-3 / 225-652-5: <=4.0% (w/w)
- zinc dioleate / zinc dioctadec-9-enoate / 557-07-3 / 209-154-5: <=3.0% (w/w)
- zinc diricinoleate / zinc bis(12-hydroxyoctadec-9-enoate) / 13040-19-2 / 235-911-4: <=3.0% (w/w)
- zinc didocosanoate / zinc didocosanoate / 16529-65-0 / 240-597-7: <=1.0% (w/w)
- 12-hydroxystearic acid / 12-hydroxyoctadecanoic acid / 106-14-9 / 203-366-1: <=4.0% (w/w)
- stearic acid / stearic acid / 57-11-4 / 200-313-4: <=1.0% (w/w)
- water / dihydrogen oxide / 7732-18-5 / 231-791-2: <=1.0% (w/w)

2.2.2. Composition of supporting source substance Octanoic acid, zinc salt, basic / 90480-58-3 /291-793-4:
- Octanoic acid, zinc salt, basic / 90480-58-3 /291-793-4: >=80.0 - <=100.0% (w/w)
Only components which do not affect the classification may be present in the target substance.

2.3. Composition of target substance Fatty acids, C18-24, zinc salts / 84776-57-8 / 283-985-1:
- zinc distearate / zinc dioctadecanoate / 557-05-1 / 209-151-9: >=30.0 - <=45.0% (w/w)
- zinc diicosanoate / zinc diicosanoate / 7278-04-8 / 230-693-7: >=5.0 - <=15.0% (w/w)
- zinc didocosanoate / zinc didocosanoate / 16529-65-0 / 240-597-7: >=40.0 - <=55.0% (w/w)
- Zinc salts of fatty acids C24: <= 10.0% (w/w)
- Fatty acids, C18-24 / 98106-57-1 / 308-578-9: <= 5.0% (w/w)
- water / dihydrogen oxide / 7732-18-5 / 231-791-2: <= 2.0% (w/w)
Only components which do not affect the classification may be present in the target substance.

3. ANALOGUE APPROACH JUSTIFICATION
Source and target have a very close structural similarity only varying in their chain length distribution and consequential minor variations in their relative zinc content. They are produced by the oleochemistry sector, starting from natural fatty materials and consist of natural fatty acids and zinc. Once emitted into the environment, fatty acids zinc salts will partly dissociate into the zinc cation and the fatty acids anions, especially in an acidic environment. Fatty acids biodegrade readily according to the β-oxidation pathway including three major steps (activation in the cytosol, transport into mitochondria, β-oxidation until the entire chain is cleaved into acetyl CoA units) (c.f. common Handbooks on biochemistry). In the Closed Bottle test according to OECD 301 D, 93% of the key source substance Fatty acids, C16-18, zinc salts biodegraded after 28 days. Similar biodegradation rates are observed in different supporting tests with Zinc bis[12-hydroxyoctadecanoate], i.e. a zinc salt of a C18 fatty acid with an additional hydroxyl group, as well as octanoic acid, zinc salt, basic, i.e. a zinc salt of a shorter-chained (C8) fatty acid. Ready biodegradability predictions for the individual fatty acids using an appropriate QSAR-method (BIOWIN) confirm the biodegradability of the fatty acid moiety of Fatty acids, C18-24, zinc salts and indicate on a prolonged biodegradation time with increasing chain length, which can be explained by the decreasing solubility by increasing chain length. It is concluded that Fatty acids, C18-24, zinc salts is readily biodegradable.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across: supporting information

Key result

Parameter:

other: % degradation based on read-across data on structural analogue substance Fatty acids, C16-18, zinc salts

Value:

> 93 - <= 100

Sampling time:

28 d

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Executive summary:

Read-across from existing ready biodegradability study on the source substances as an appropriate adaptation to the standard information requirements of Annex VII, 9.2.11 of the REACH Regulation for the target substance, in accordance with the provisions of Annex XI, 1.5 of the REACH Regulation.

Source(s) and target have a very close structural similarity only varying in their chain lengths distribution. They are produced by the oleochemistry sector, starting from natural fatty materials and consist of natural fatty acids and zinc. Once emitted into the environment, fatty acids zinc salts will partly dissociate into the zinc cation and the fatty acids anions, especially in an acidic environment. Fatty acids biodegrade readily according to the β-oxidation pathway including three major steps (activation in the cytosol, transport into mitochondria, β-oxidation until the entire chain is cleaved into acetyl CoA units) (c.f. common Handbooks on biochemistry). In the Closed Bottle test according to OECD 301 D, 93% of the key source substance Fatty acids, C16-18, zinc salts biodegraded after 28 days. Similar biodegradation rates are observed in different supporting tests with Zinc bis[12-hydroxyoctadecanoate], i.e. a zinc salt of a C18 fatty acid with an additional hydroxy group, as well as octanoic acid, zinc salt, basic, i.e. a zinc salt of a shorter-chained (C8) fatty acid. Ready biodegradability predictions for the individual fatty acids using an appropriate QSAR-method (BIOWIN) confirm the biodegradability of the fatty acid moiety of Fatty acids, C18-24, zinc salts and indicate on a prolonged biodegradation time with increasing chain length, which can be explained by the decreasing solubility by increasing chain length.

It is concluded thatFatty acids, C18-24, zinc salts is readily biodegradable.

Description of key information

By read-across to structural analogues, substance Fatty acids, C18-24, zinc salts is considered biodegradable. Source and target have a very close structural similarity only varying in their chain lengths distribution. They are produced by the oleochemistry sector, starting from natural fatty materials and consist of natural fatty acids and zinc. Once emitted into the environment, fatty acids zinc salts will partly dissociate into the zinc cation and the fatty acids anions, especially in an acidic environment. Fatty acids biodegrade readily according to the β-oxidation pathway including three major steps (activation in the cytosol, transport into mitochondria, β-oxidation until the entire chain is cleaved into acetyl CoA units) (c.f. common Handbooks on biochemistry). In the Closed Bottle test according to OECD 301 D, 93% of the key source substance Fatty acids, C16-18, zinc salts biodegraded after 28 days. Similar biodegradation rates are observed in different supporting tests with Zinc bis[12-hydroxyoctadecanoate], i.e. a zinc salt of a C18 fatty acid with an additional hydroxyl group, as well as octanoic acid, zinc salt, basic, i.e. a zinc salt of a shorter-chained (C8) fatty acid. Ready biodegradability predictions for the individual fatty acids using an appropriate QSAR-method (BIOWIN) confirm the biodegradability of the fatty acid moiety of Fatty acids, C18-24, zinc salts and indicate on a prolonged biodegradation time with increasing chain length, which can be explained by the decreasing solubility by increasing chain length. It is concluded that Fatty acids, C18-24, zinc salts is readily biodegradable