Zinc bis[12-hydroxyoctadecanoate]

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

20.6 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

6.1 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

52 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

117.8 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

56.5 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

35.6 mg/kg soil dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Zinc bis[12-hydroxyoctadecanoate]

Zinc bis[12-hydroxyoctadecanoate] consists of fatty acid anions and zinc cations. Based on similar structural analogy, water solubility and zinc content of zinc bis[12-hydroxyoctadecanoate] (CAS 35674-68-1) and Fatty acids, C16-18, zinc salts (CAS 91051-01-3), a 1:1 read-across of ecotoxicological and transformation/dissolution data of Fatty acids, C16-18, zinc salts is applied to zinc bis[12-hydroxyoctadecanoate]. 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)). Zinc compounds, however, may have an impact to the environment. For PNEC derivation and the decision on C&L requirements, read-across of data for Fatty acids, C16-18, zinc salts as well as data for more soluble zinc compounds is applied. Read across within this group of substances is justified as ionic zinc (Zn²⁺) is the common toxophore.

Zinc bis[12-hydroxyoctadecanoate] and the structural analogue Fatty acids, C16-18, zinc salts are poorly soluble in water, and thus the respective bioavailability in environmental compartments is very low. The ecotoxicity data available for the structural analogue Fatty acids, C16-18 zinc salts, although limited, show that the acute aquatic toxicity of Fatty acids, C16-18, zinc salts to algae, daphnia and fish is orders of magnitude above the water solubility limit of this compound:

- The acute toxicity of Fatty acids, C16-18 zinc salts toDaphnia magnawas determined according to OECD 202 in M7 medium at pH 6 and 8 (Bouwman et al., 2003). The EC₅₀was not reached up to a loading rate of 100 mg Fatty acids, C16-18, zinc salts /L. At this loading, the zinc concentration at the beginning of the test was 1170 μg Zn/L at pH 8 and 800 μg Zn/L at pH 6. The test report concludes: “No daphnids became immobilised during the test period...Although all daphnids exposed to the undiluted water fraction had test substance on their bodies at the end of the test, this did not hinder them”.

- Information on fish toxicity is available from a study performed according to EU Method C.1 (Acute Toxicity for Fish) in the former version of 1992 (Henkel KGaA, 1995), from a study performed according to OECD Guideline 203 (Fish, Acute Toxicity Test) but reported only in a short study report (TÜV Bayern Sachsen E.V., 1992) and from an older publication (Dowden and Bennett, 1965). In the most reliable study (Henkel KGaA, 1995), fish (Danio rerio) were exposed for 96 hours to nominal concentrations of 0 (control), 1000, 3000 and 10000 mg/L under semi-static conditions. The nominal concentrations far exceed the water solubility of Fatty acids, C16-18, zinc salts by 3 to 4 orders of magnitude. Measures to disperse the test substance in the test water were used. At all tested concentrations, including the highest nominal test concentration, neither behavioural abnormalities nor mortality occurred. In addition, no effects were observed at nominal Fatty acids, C16-18, zinc salts concentrations up to the water solubility limit in two further studies. In accordance with the evaluation given in the EU Risk assessment on zinc distearate (Final report R074_0805_env, May 2008), from the results of these tests it is concluded, that the toxicity of the substance Fatty acids, C16 -18, zinc salts to fish is (far) above the water solubility limit of around 1 mg/L.

 

These daphnia and fish toxicity data have already been assessed within the EU risk assessment on zinc stearate. In the meantime since finalisation of the EU risk assessment additional data on the algal toxicity of Fatty acids, C16-18, zinc salts were generated:

- The toxic effects of Water Accommodated Fractions (WAF) of Fatty acids, C16-18, zinc salts on the growth rate of algae (Pseudokirchneriella subcapitata) were studied in three tests according to OECD Guideline 201 (Wenzel, 2010a, b and 2013). While in the first test, the WAF of a loading of 100 mg/L in a non-standard test medium was dilutedin series to allow the calculation of toxicity parameters (EL10, EL50) (Wenzel, 2010a), the WAFs of several loadings (1, 10, and 100mg/L) in non-standard medium were applied in the second test according to OECD Series No. 23 (Wenzel, 2010b). In the third test by Wenzel (2013), lower concentrations were applied (i.e. 0.01, 0.1, 1.0, 10.0 and 100.0 mg/L) in the standard test medium to enable the classification for a potential aquatic hazard based on WAFs. The EL10 and EL50 values for the 72-h inhibition of growth rate of P. subcapitata in the standard test medium are 3.31 mg/L and > 100 mg/L, respectively. Thus, algae appear to be the most sensitive trophic level with regard to acute toxicity of Fatty acids, C16-18, zinc salts.

- The data indicate that Fatty acids, C16 -18, zinc salts and by read-across zincbis[12-hydroxyoctadecanoate] has a significant lower aquatic toxicity than soluble zinc salts, including zinc chloride or zinc sulphate. It is therefore assumed that a high portion of zinc from Fatty acids, C16 -18, zinc salts is not bioavailable, likely because the substance only partly dissociates into zinc cations and fatty acid anions, and this is also likely for zinc bis [12-hydroxyoctadecanoate] as it is a structural analogue to Fatty acids, C16-18, zinc salts with a similar zinc content and also poor water solubility.

Based on the stoichiometrical content of zinc (10 % by weight) in a saturated solution of Fatty acids, C16-18, zinc salts and the reference values for Zn²⁺ion toxicity, derived from tests on soluble zinc compounds (see hazard assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006 in Appendix 1), the substance Fatty acids, C16-18, zinc salts and subsequently by read-across zinc bis[12-hydroxyoctadecanoate] may be classified for the aquatic environment (Category Chronic 3) according to measured zinc concentrations in a highly reliable transformation/ dissolution protocol study and reference values for the Zn²⁺-ion as derived in the hazard assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006:

Loading 1 mg/L OECD medium:          -after 7 days:     19 µg Zn/L

                                                                    -after 28 days:   29 µg Zn/L

Loading 10 mg/L OECD medium:       -after 7 days:     90 µg Zn/L

Loading 100 mg/L OECD medium:     -after 7 days:     369 µg Zn/L

 

Based on the hazard assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006, reference values for the Zn2+- ion are:

Acute

For low pH:                 0.413 mg Zn/L (based on single lowest value for Ceriodaphnia dubia),

for neutral/high pH:      0.136 mg Zn/L (based on single lowest value for Pseudokirchneriella subcapitata,

Chronic

-for low pH:                 0.082 mg Zn/L (Daphnia magna)

-for neutral/high pH:     0.019 mg Zn/L (Pseudokirchneriella subcapitata).

Thus, algae appear to be the most sensitive trophic level with regard to acute toxicity of zinc.

 

The solubility of Fatty acids, C16-18, zinc salts in the OECD medium may not correspond to the actual bioavailability and subsequent ecotoxicity of zinc, possibly due to the formation of micelles in the medium rendering dissolved zinc unavailable. Indeed, the lack of toxicity in acute aquatic toxicity tests to daphnia and fish indicate that the actual toxicity as observed during testing is substantially lower than the predicted toxicity by use of the transformation/ dissolution data and the aquatic data on Zn²⁺toxicity.

Based on toxicity scores of the most sensitive trophic level, i.e. EL10 value (3.31 mg/L) and EL50 value (> 100 mg/L) derived for growth rate of the alga P. subcapitatain a standard test medium, Fatty acids, C16-18, zinc salts does not require classification for acute and chronic aquatic hazard, and by read-across neither does zinc bis[12-hydroxyoctadecanoate]. In addition, zinc bis[12-hydroxyoctadecanoate] is readily biodegradable (71.4% after 28 days in the OECD 301B test) and is not expected to bioaccumulate, knowing that fatty acids degrade by the ß-oxidation pathway. The classification and labelling decision for zinc bis[12-hydroxyoctadecanoate] is based on studies performed with the structural analogue Fatty acids, C16-18, zinc salts, which showed neither a toxicity to aquatic organisms below relevant criteria values for classification nor a potential for bioaccumulation. It is therefore concluded that zinc bis[12-hydroxyoctadecanoate] does not need to be classified for the environment according to Regulation (EC) No 1272/2008 and Directive 67/548/EEC. This conclusion on non classification is consist with the conclusion drawn in the EU risk assessment for the structural analogue zinc distearate carried out within the framework of EU Existing Chemicals Regulation (EEC) No 793/93 (Final report R074_0805_env, May 2008):

“Based on the stoichiometrical content of zinc (10% by weight) in a saturated solution of zinc distearate and the lowest acute EC₅₀value for soluble zinc, being 70μg Zn/L for crustacean Daphnia magna (based on accepted tests with soluble zinc, see the environmental classification and labelling section in the RAR Zinc metal), zinc distearate should be classified for the aquatic environment with R50-R53, according to the transformation / dissolution protocol. However, since there were doubts whether the stoichiometrical calculation corresponds to the true content in Zn²⁺free cations concentration, different approaches have been used to measure the water solubility of zinc from zinc distearate. The measurements were carried out in different media, a/o ISO 6341 medium and Elendt M7, using different detection methods, a/o photometric detection and Differential Pulse Anodic Stripping Voltammetry (DPASV). At a loading rate of 100 mg zinc distearate/L, the detection techniques reveal different zinc concentrations: ranging from 30-60μg Zn/L using photometric detection and 250-500μg Zn/L using DPASV. No explanation can be given to clarify this difference (Mayer et al., 2001; Bowmer, 2002).

In order to come to a final conclusion, the acute toxicity of zinc distearate to Daphnia magna was determined according to OECD 202 in M7 medium at pH 6 and 8 (Bouwman et al., 2003) Up to a loading rate of 100 mg zinc distearate/L the EC₅₀was not reached. The zinc concentration (detected using ICP-MS) at the beginning of the test was 1170μg Zn/L at pH 8 and 800μg Zn/L at pH 6, at a loading rate of 100 mg zinc distearate/L. In ISO medium at pH 6 the same concentration was measured, whereas at pH 8 the concentration was much lower: 550μg Zn/L. The absence of toxicity can not be explained by the presence of EDTA in the Elendt medium, since the EDTA concentration present could bind at maximum 11% of the zinc being analysed (based on one to one ratio). It is therefore assumed that a high portion of zinc in solution is not bioavailable, likely because zinc distearate is only partly dissociated into the zinc cation and the fatty acid anions. It is assumed that this low bioavailability not only applies for daphnids, but for algae en fish as well. For fish this is confirmed by the limited information available on acute toxicity in three tests: no effects on the fish were observed in these tests at concentrations at or far above the maximum water solubility limit of zinc distearate (see section 3.3).

According to the transformation/dissolution protocol, a chronic toxicity test had to be performed with a solution stirred for 28 days at a loading rate of 1000μg zinc stearate/L. Since in the above-mentioned acute toxicity test with D. magna no effect were found at a concentration of approximately 900μg Zn/L, measured by ICP-MS (Bouwman et al., 2003), it can be argued that the free Zn²⁺ion concentration has to be lower than the lowest acute EC₅₀of 70μg Zn/L for soluble zinc (from a test with D. magna, see earlier in this section). Assuming that 1000μg zinc distearate/L will be completely dissolved, giving a total Zn concentration of 100μg Zn/L, the equilibrium between stearate and Zn ions has to shift strongly to the right in order to reach the lowest reported NOEC (34μg Zn/L) included in the RAR Zinc metal². This is considered unlikely and therefore R53 is not applicable. Although distearate can not be considered as ready biodegradable (based on an OECD 301D study), distearate is not expected to bioaccumulate, knowing that fatty acids will degrade by theβoxidation pathway.

(²In the final version of the RAR Zinc metal, which was finalised after the decision on the classification of zinc distearate (see below), the lowest chronic NOEC is 17μg Zn/L, being the ‘species mean’ value for alga Pseudokirchneriella subcapitata. For Daphnia magna, the aquatic species with the lowest acute L(E)C₅₀(70μg Zn/L), the ‘species mean’ chronic NOEC is 88 μg Zn/L).

Conclusion: “Zinc distearate is not classifiedfor the environment.”

In the meantime since finalisation of the EU RAR Zinc stearate, a further transformation/dissolution test and algal toxicity tests (see above and sections 4.8 and 6.1.5) have been performed. The measured zinc concentrations in the now available transformation/dissolution test, which was performed in accordance with ECHA guidance following the method described in OECD Series on Testing and Assessment. Draft Guidance Document on Transformation/Dissolution Metals and Metal Compounds in Aqueous Media. Number 29 (2001) were below the values measured in the tests evaluated in the EU Risk Assessment (see above). The result of the algal toxicity test confirms the low toxicity of the structural analogue (Fatty acids, C16-18, zinc salts) to aquatic organisms, as already consistently seen in tests performed with this substance on fish, aquatic invertebrates and micro-organisms, which were considered in the EU Risk Assessment. Thus, the now additional available transformation/dissolution and toxicity data support the conclusion made in the EU Risk assessment, that Fatty acids, C16-18, zinc salts and by read-across zinc bis[12-hydroxyoctadecanoate] do not pose a hazard to the environment und therefore, there is no reason to classify this substance for environmental hazards.

Nevertheless, as only limited environmental toxicity data are available for zinc bis[12-hydroxyoctadecanoate] and only limited environmental toxicity data are available for the structural analogue Fatty acids, C16-18, zinc salts, a read-across to insoluble/ slightly soluble zinc substances is made, and the PNECs as derived in the Chemical Safety Assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006 are read-across to zinc bis[12-hydroxyoctadecanoate] .

ZINC:

A basic assumption made in this hazard assessment and throughout this CSR, (in accordance to the same assumption made in the EU RA process) is that the ecotoxicity of zinc and zinc compounds is due to the Zn⁺⁺ion. As a consequence, all aquatic, sediment and terrestrial toxicity data in this report are expressed as “zinc”, not as the test compound as such, because ionic zinc is considered to be the causative factor for toxicity. A further consequence of this is that all ecotoxicity data obtained on different zinc compounds, are mutually relevant for each other. For that reason, the available ecotoxicity databases related to zinc and the different zinc compounds are combined before calculating the PNECs. The only way zinc compounds can differ in this respect is in their capacity to release zinc ions into (environmental) solution. That effect is checked eventually in the transformation/dissolution tests and may result in different classifications.

Conclusion on classification

Based on reliable, adequate and relevant studies, zinc bis[12-hydroxyoctadecanoate] does not require classification according to Directive 67/548/EEC and to Regulation (EC) No 1272/2008. This conclusion is consistent with the conclusions from the EU risk assessment for the structural analogue zinc distearate carried out within the framework of EU Existing Chemicals Regulation (EEC) No 793/93 (Final report R074_0805_env, May 2008): "Zinc distearate is not classified for the environment."