Fatty acids, C18-24, zinc salts

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

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 and supporting source substance(s) and target substance have similar acute toxicity based on their structural similarity.

2. SOURCE AND TARGET CHEMICALS COMPOSITION
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.

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 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(s) and target 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. In the aquatic environment and the body, fatty acids zinc salts will partly dissociate into the zinc cation and the fatty acids anions. As zinc is an essential trace element and fatty acids are major nutrients, both moieties are effectively processed and regulated in the body. A minor variation in the fatty acid composition and the zinc amount of source(s) and target is not expected to substantially impact the systemic activity. The NOEC of 1560 mg/L for the toxicity of the analogue substance Fatty acids,C16-18, zinc salts to microorganisms is above the respective OECD test limit. Thus, a zinc salt of similar-chained fatty acids appears to have a low potential for toxicity microorganisms. A similar low potential is assumed for substance Fatty acids, C18-24, zinc salts, a zinc salt of similar- and longer-chained fatty acids (C18-24) with a lower zinc content and solubility.
Read-across of data available for a zinc salts of similar chained (C16 -18) fatty acids based on structural similarity, water solubility and zinc content in a conservative, worst-case approach is assumed to adequately describe the toxicological potential of Fatty acids, C18-24, zinc salts.
Therefore, read-across from the existing toxicity studies to microorganisms on the source substance(s) is considered as an appropriate adaptation to the standard information requirements of Annex VII, 8.5.1 of the REACH Regulation for the target substance, in accordance with the provisions of Annex XI, 1.5 of the REACH Regulation.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Key result

Duration:

30 min

Dose descriptor:

EC50

Effect conc.:

> 6 250 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: luminescence

Remarks on result:

other:

Remarks:

read-across data on structural analogue substance Fatty acid, C16-18, zinc salts

Key result

Duration:

30 min

Dose descriptor:

NOEC

Effect conc.:

1 560 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: luminescence

Remarks on result:

other:

Remarks:

read-across data on structural analogue substance Fatty acid, C16-18, zinc salts

Conclusions:

The NOEC of 1560 mg/L for the toxicity of the analogue substance Fatty acids,C16-18, zinc salts to microorganisms is above the respective OECD test limit. Thus, a zinc salt of similar-chained fatty acids appears to have a low potential for toxicity microorganisms. A similar low potential is assumed for substance Fatty acids, C18-24, zinc salts, a zinc salt of similar- and longer-chained fatty acids (C18-24) with a lower zinc content and solubility.

Description of key information

Aquatic toxicity studies with substance Fatty acids, C18-24, zinc salts are not available. In the assessment of substance Fatty acids, C18-24, zinc salts, read-across to analogue substances and/or the assessment entities soluble zinc substances and fatty acids, C18-24 is conservatively applied since the ions of substance Fatty acids, C18-24, zinc salts determine its fate and toxicity in the environment.

The NOEC of 1560 mg/L for the toxicity of the analogue substance Fatty acids, C16-18, zinc salts to microorganisms is above the respective OECD test limit. Thus, a zinc salt of similar-chained fatty acids appears to have a low potential for toxicity microorganisms. A similar low potential is assumed for substance Fatty acids, C18-24, zinc salts, a zinc salt of similar- and longer-chained fatty acids (C18-24) with a lower zinc content and solubility.

This is in agreement with the conclusion on toxicity to microorganisms of the EU risk assessment on the structural analogue zinc distearate (Fatty acids, C16-18, zinc salts, CAS-No.: 557-05-1 & 91051-01-3 EINECS-No.: 209-151-9 & 293-049-4)carried out within the framework of EU Existing Chemicals Regulation (EEC) No 793/93 (Final report R074_0805_env, May 2008) in which it is concluded, "The two available tests with bacteria resulted in NOEC values of 1000 mg zinc distearate/L (Berger, 1995b: Pseudomonas putida) and 1560 mg zinc distearate/L (TÜV, 1992: Microtoxtest according to DIN 38412, part 34). In the latter study an EC20of 6250 mg zinc distearate /L was calculated, with the remark that an EC50could not be derived because of the low effect response. These nominal concentrations are at least 3 orders of magnitude higher than the water solubility limit for zinc distearate (around 1 mg/L)."

Considering the dissolved moieties upon dissolution, reliable data indicate that the moiety of ecotoxicological concern are zinc cations. The acute toxicity data further indicate that zinc salts of shorter- and similar-chained (C12-C18) fatty acids have a significantly lower aquatic toxicity than soluble zinc salts. It is therefore assumed that a high fraction of zinc from zinc salts of medium- and longer chained (>C12) fatty acids is not bioavailable. The ecotoxic potential of the fatty acid chain, i.e. fatty acids, C18-24, is assumed to be negligible.

Fatty acids are generally not considered to represent a risk to the environment, which is reflected in their exclusion from REACH registration requirements (c.f. REACH Annex V (Regulation (EC) No 987/2008)).

The aquatic hazard assessment is based on the most toxic moiety, i.e. the zinc cation.

Key data (lowest EC50value) for zinc is:

The EC50 of 5.2 mg zinc/L reported from the study by Dutka et al (1983)

Dutka BJ, Nyholm N and Petersen J. (1983). Comparison of several microbiological toxicity screening tests.Water research volume 17, nr10, 1363-1368]

Please refer to the section for the respective assessment entity.

Additional information

ANALOGUE SUBSTANCE FATTY ACIDS, C16-18, ZINC SALTS:

The toxicity of Fatty acids, C16-18, zinc salts to micro-organisms is far above the water solubility limit of around 1 mg/L.

Conclusions from 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): "The two available tests with bacteria resulted in NOEC values of 1000 mg zinc distearate/L (Berger, 1995b: Pseudomonas putida) and 1560 mg zinc distearate/L (TÜV, 1992: Microtoxtest according to DIN 38412, part 34). In the latter study an EC₂₀of 6250 mg zinc distearate /L was calculated, with the remark that an EC₅₀could not be derived because of the low effect response. These nominal concentrations are at least 3 orders of magnitude higher than the water solubility limit for zinc distearate (around 1 mg/L)."

Please refer to the section for the respective assessment entity for data on the moieties. In brief:

ZINC:

Several data were available for this endpoint. Formerly (ECB 2008), and in the REACH-registrations of a number of zinc substances of November 2010, a PNEC of 52 µg/L for STP was derived, based on the lowest EC50 of 5.2 mg Zn/L observed in a sludge respiration inhibition test (Dutka et al. 1983). According to the guidance (ECHA 7.8.17.1) preference should be given to nitrification inhibition because respiration inhibition is a less sensitive endpoint. A study conducted by Juliastuti et al. (2003) reported a NOEC of 0.1 mg Zn/L in an ISO 9509 nitrification inhibition test.

FATTY ACIDS, C18-24:

The ecotoxic potential of the fatty acid chain, i.e. fatty acids, C18-24, is assumed to be negligible. Fatty acids are generally not considered to represent a risk to the environment, which is reflected in their exclusion from REACH