Zinc dilaurate

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 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 DILAURATE:

Zinc dilaurate consists of fatty acids anions and zinc cations. The ecotoxic potential of the fatty acid chain, i.e. laurate, 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)). Zinc compounds, however, may have an impact to the environment. For PNEC derivation and the decision on C&L requirements, data for zinc dilaurate as well as data for more soluble zinc compounds are taken into consideration. Read across within this group of substances is justified as ionic zinc (Zn²⁺) is the common toxophore (see discussion below).

Zinc dilaurate is slightly soluble in water, and thus its bioavailability in environmental compartments is low. The available ecotoxicity data, although limited, show that the acute aquatic toxicity of zinc dilaurate to daphnia and fish is above the water solubility limit of this compound:

- The acute toxicity of zinc dilaurate to Daphnia magna was determined according to OECD Guideline 202 in synthetic environmental medium (EN ISO 6341) at 7.8 (Muckle et al., 2009). Daphnids did not become immobilised during the test period of 48 h at any of the tested concentrations (0, 0.1, 1, 10 mg/L). Thus, the EC50 was not reached up to a concentration of 10 mg zinc dilaurate/L.It is concluded, that the acute toxicity of the zinc dilaurate to invertebrates is above the measured water solubility limit ranging from 5.2 to 6.4 mg/L.

- Information on acute fish toxicity is available from a study performed according to OECD Guideline 203. Fish (Danio rerio) were exposed for 96 hours to nominal concentrations of 0 (control), 0.1, 1, 10 mg/L under static conditions. At all tested concentrations, including the highest nominal test concentration, neither behavioural abnormalities nor mortality occurred. It is concluded, that the acute toxicity of the zinc dilaurate to fish is above the measured water solubility limit ranging from 5.2 to 6.4 mg/L.

- The toxic effects of Water Accommodated Fractions (WAF) of zinc dilaurate on the growth rate of algae (Pseudokirchneriella subcapitata) were studied in two tests according to OECD Guideline 201 (Wenzel, 2011 and 2013b). The WAFs were prepared according to OECD Series No. 23. In the first test, the WAFs of the loadings 1, 10, and 100mg/L were tested in a non-standard test medium (Wenzel, 2011), while in the second state-of-the-art test by Wenzel (2013a) lower concentration were applied (i.e. 0.01, 0.1, 1.0, and 10.0 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 3.73 mg/L and 12.87 mg/L, respectively. Thus, algae appear to be the most sensitive trophic level with regard to acute toxicity of zinc dilaurate.

The data indicate that zinc dilaurate 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 zinc dilaurate is not bioavailable, likely because the substance is only partly dissociated into the zinc cations and the fatty acid anions.

Based on the measured content of zinc (approximately 14% by weight) in zinc dilaurate and the reference values for zinc ion toxicity, derived from tests on soluble zinc compounds (see hazard assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006 below), zinc dilaurate may be classified for the aquatic hazard (Category Acute 1, Category Chronic 3 ), according to measured zinc concentrations in a highly reliable transformation / dissolution protocol study and ecotoxicity reference values for the zinc ion as derived in the hazard assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006:

Loading 100 mg/L OECD medium: -after 1 day at pH 8, the pH that maximises transformation/dissolution: 0.98 – 1.19 mg/L Zn

 

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

Acute

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

for the 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 the neutral/high pH:8.0: 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 zinc dilaurate 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 zinc ion toxicity.

Based on toxicity scores of the most senistive trophic level, i.e. EL10 value (3.73 mg/L) and EL50 value (12.87 mg/L) derived for growth rate of the alga P. subcapitata in a standard test medium, zinc dilaurate does not require classification for acute and chronic aquatic hazard. In addition, zinc dilaurate is considered to be readily biodegradable (based on read-across of ready biodegradability observed for shorter-chained (C8) and longer-chained (C16-18) fatty acids in OECD 301 studies). Therefore, zinc dilaurate is not expected to bioaccumulate as fatty acids degrade by the ß-oxidation pathway.

The classification and labelling decision for zinc dilaurate is based on substance-specific studies, 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 dilaurate does not need to be classified for the environment according to Regulation (EC) No 1272/2008 and Directive 67/548/EEC.

Nevertheless, as only limited environmental toxicity data are available for zinc dilaurate, 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 carried over to zinc dilaurate in a worst-case approach.

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 dilaurate 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."