Zinc ferrite brown spinel

Endpoint summary

Description of key information

Based on read-across to micro- and nano-sized iron (hydr)oxides (see attachment "Read-across justification-environ assessment-iron oxides" in section 13), available data for fish, invertebrates, algae and microorganisms indicate a low potential for acute and chronic aquatic toxicity of micro-sized iron (hydr)oxides.

Additional information

Data available on the short-term toxicity of different iron (hydr)oxides, including micro- and nano-sized iron hydroxide oxide yellow, diiron trioxide, triiron tetraoxide, zinc ferrite brown spinel and manganese ferrite black spinel, to fish (Danio rerio), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) indicate a low potential for acute toxicity. Respective unbounded EC/LC50 values amount for fish up to > 100 g/L, a concentration that is 1000-fold above the corresponding OECD test limit for acute toxicity, for invertebrates up to > 10 g/L, a concentration that is 100-fold above the corresponding OECD test limit for acute toxicity and > 20 mg/L for algae.

 

Iron (hydr)oxides are also not toxic to aquatic micro-organisms as 3-h EC50 values for the respiration inhibition of different iron (hydr)oxides, including micro- and nano-sized iron hydroxide oxide/diiron trioxide (75:25), manganese ferrite black spinel and triiron tetraoxide are > 10 g/L, a concentration that is 10-fold above the corresponding OECD test limit.

 

Furthermore, chronic toxicity data of diiron trioxide in nanoform indicate a low potential for aquatic toxicity since NOECs available for three trophic levels (algae, invertebrates, fish) are ≥ 10 mg/L, and thus above the corresponding OECD test limit of 10 mg/L for chronic toxicity.

 

Regarding differences in the particle size, the available data for the acute toxicity of diiron trioxide in powder and nano-form to fish further indicate that the particle size does not affect the toxicity potential to any detectable extent since effect concentrations of the powder and nano-form are up to 500-fold above the OECD test limit. In all acute and chronic toxicity studies with iron (hydr)oxides, effect concentrations were unbounded and/or above the OECD test limit (see Table below).

 

Table: Aquatic toxicity of iron (hydr)oxides.

Endpoint	Test species	Test results	Test material/form	Reliability: Reference
Short-term toxicity to fish	Danio rerio	LC50 (96h): > 50 g/L nominal LC0 (96h): >= 50 g/L nominal	diiron trioxide / powder	RL2: Bruns, 1989
.	Danio rerio	LC50 (96h): > 10 g/L nominal LC0 (96h): >= 10 g/L nominal	triiron tetraoxide / powder	RL2: Caspers, 2000
.	Danio rerio	LC50 (96h): > 10 g/L nominal LC0 (96h): >= 10 g/L nominal	triiron tetraoxide /powder	RL2: Bayer AG, 1989
.	Danio rerio	LC50 (96h): > 100 g/L nominal LC0 (96h): >= 100 g/L nominal	zinc ferrite brown spinel / powder	RL2: Weyers, 1989
.	Danio rerio	LC50 (96h): > 100 g/L nominal LC0 (96h): >= 100 g/L nominal	manganese ferrite black spinel / powder	RL2: Weyers, 1989
.	Danio rerio	LC50 (96h): > 10 g/L nominal LC0 (96h): >= 10 g/L nominal	diiron trioxide / nano, alpha	RL2: Weyers, 1985
.	Danio rerio	LC50 (96h): > 100 g/L nominal LC0 (96h): >= 100 g/L nominal	iron hydroxide oxide yellow / nano, alpha	RL2: Weyers & Caspers, 1989
Long-term toxicity to fish	Danio rerio	NOEC (168 h): 10 mg/L nominal	diiron trioxide / nano, alpha	RL3: Zhu et al., 2012
Short-term toxicity to aquatic invertebrates	Daphnia magna	EC50 (48h): > 100 mg/L nominal	diiron trioxide / powder	RL2: Neuhahn, 2008
.	Daphnia magna	EC0 (48 h): >= 10 g/L nominal	triiron tetraoxide /powder	RL2: Caspers, 2000
.	Daphnia magna	EC0 (48 h): >= 10 g/L nominal	zinc ferrite brown spinel / powder	RL2: Caspers, 1999
.	Daphnia magna	EC0 (48 h): >= 10 g/L nominal	manganese ferrite black spinel / powder	RL2: Caspers, 2000
.	Daphnia magna	EC50 (48h): > 100 mg/L nominal	iron hydroxide oxide yellow / nano, alpha	RL2: Neuhahn, 2008
Long-term toxicity to aquatic invertebrates	Daphnia magna	NOEC (21d): >= 20 mg/L nominal	diiron trioxide / nano	RL2: Nogueira et al., 2015
Toxicity to aquatic algae and cyanobacteria	Pseudokirchneriella subcapitata	NOEC (72 h): >= 20 mg/L nominal EC50 (72 h): > 20 mg/L nominal	diiron trioxide / nano	RL2: Nogueira et al., 2015
Toxicity to microorganisms	Activated sludge	EC50 (3 h): > 10 g/L nominal	triiron tetraoxide / powder	RL2: Bruns, 1989
.	Activated sludge	EC50 (3 h): >= 10 g/L nominal	manganese ferrite black spinel / powder	RL2: Bruns, 1989
.	Activated sludge	EC50 (3 h): > 10 g/L nominal	iron hydroxide oxide/diiron trioxide (75:25) / nano, alpha	RL2: Bruns, 2004

 

Soluble iron salts are also not considered toxic to the aquatic life, i.e. do not meet CLP classification criteria for acute (short-term) aquatic hazard and chronic (long-term) aquatic hazard.

 

Zinc ferrite can be considered environmentally and biologically inert due to the spinel structure in which atoms are tightly bound and not prone to dissolution in environmental and physiological media. This assumption is supported by available transformation/dissolution data (Klawonn, 2021) that indicate a very low release of metal ions at pH 6 and 8. Transformation/dissolution tests (according to OECD Series on Testing and Assessment Number 29) of zinc ferrite at a loading of 1 mg/L and pH 6 resulted in dissolved zinc concentrations of 9.2 µg Zn/L and 12.5 µg Zn/L after 7 and 28 days, and at pH 8 in 3.0 µg Zn/L and 8.0 µg Zn/L after 7 and after 28 days, respectively. Iron ion release of zinc ferrite after 7 and 28 days at 1 mg/L loading and pH 6 and 8 resulted in concentrations below the respective limit of detection (< 2.6 µg Fe/L). Thus, the rate and extent to which zinc ferrite produces soluble (bio)available ionic and other ion-bearing species in environmental media is limited. Hence, zinc ferrite can be considered as environmentally and biologically inert during short- and long-term exposure. The poor solubility of zinc ferrite is expected to determine its behaviour and fate in the environment, including the partitioning in soil, sediment and water.

 

The acute aquatic hazard potential of poorly soluble substance zinc ferrite is evaluated by comparing the dissolved metal ion levels resulting from the transformation/dissolution test after 7 days at a loading rate of 1 mg/L with the lowest acute ecotoxicity reference values (ERVs) as determined for the (soluble) metal ions. The ERVs are based on the lowest EC50/LC50 values for algae, invertebrates and fish. Acute ERVs were obtained from the Metals classification tool (MeClas) database (Version 5.9 accessed on 22.11.2021) as follows: Iron (hydr)oxides are not expected to have an ecotoxic potential as confirmed by the absence of acute ecotoxicity reference values for iron (ions) in the Metals classification tool (MeClas) database. According to ECHA Guidance on the Application of the CLP Criteria (Version 5.0, July 2017), “Where the acute ERV for the metal ions of concern is greater than 1 mg/L the metals need not be considered further in the classification scheme for acute hazard.” Thus, a concern for short-term (acute) toxicity of iron ions was not identified (no classification). The acute ERVs for zinc at pH 6 and 8 amount to 413 µg Zn/L and 136 µg Zn/L and are thus well above dissolved zinc concentration of 9.2 µg Zn/L and 3.0 µg Zn/L, measured at a loading of 1 mg/L and pH 6 and pH 8 after 7 days T/D, respectively. Due to the lack of an acute aquatic hazard potential for soluble iron ions and the fact that the dissolved zinc concentrations measured in the T/D test after 7 days at pH 6 and pH 8 are significantly lower than the respective lowest acute ERVs for zinc, it can be concluded that the substance zinc ferrite is not sufficiently soluble to cause short-term toxicity at the level of the acute ERVs (expressed as EC50/LC50).

 

The chronic aquatic hazard potential of poorly soluble substance zinc ferrite is evaluated by comparing the dissolved metal ion levels resulting from the transformation/dissolution test after 28 days at a loading rate of 1 mg/L with the lowest chronic ecotoxicity reference values (ERVs) as determined for the (soluble) metal ions. The chronic ERVs are based on the lowest NOEC/EC10 values for algae, invertebrates and fish. ERVs were obtained from the Metals classification tool (MeClas) database as follows: Iron (hydr)oxides are not expected to have an ecotoxic potential as confirmed by the absence of chronic ecotoxicity reference values for iron (ions) in the Metals classification tool (MeClas) database. According to ECHA Guidance on the Application of the CLP Criteria (Version 5.0, July 2017), “Where the chronic ERV for the metal ions of concern corrected for the molecular weight of the compound (further called as chronic ERV compound) is greater than 1 mg/L, the metal compounds need not to be considered further in the classification scheme for long-term hazard.” Thus, a concern for long-term (chronic) toxicity of iron (ions) was not identified (no classification). The chronic ERVs for zinc at pH 6 and 8 amount to 82 µg Zn/L and 19 µg Zn/L and are thus well above the dissolved zinc concentration of 12.5 µg Zn/L and 8.0 µg Zn/L, measured at a loading of 1 mg/L and pH 6 and pH 8 after 28 days T/D, respectively. Due to the lack of an chronic aquatic hazard potential for soluble iron ions and the fact that the dissolved zinc concentrations measured in the T/D test after 28 days at pH 6 and 8 are significantly lower than the respective lowest long-term ERVs for zinc, it can be concluded that the substance zinc ferrite (member of the poorly soluble iron oxide category substances) is not sufficiently soluble to cause long-term toxicity at the level of the chronic ERVs (expressed as NOEC/EC10).

 

The conclusion on a lack of an aquatic hazard potential of iron (hydr)oxides is in accordance with a Tier-1 assessment performed with MECLAS version 5.2 (http://www.meclas.eu/ accessed on 22.11.2021). The Metals Classification Tool (MECLAS) is a web enabled classification tool always updated to the latest classification guidance, legal ruling, information on toxicity references and available self-classifications.

 

In sum, iron (hydr)oxides (poorly soluble iron oxide category substances) do not meet classification criteria of an acute or long-term aquatic hazard of Regulation (EC) No 1272/2008.

 

“If there are ecotoxicity data showing effects in aquatic organisms, but the substance is not classified as dangerous for the aquatic environment, an aquatic PNEC can nevertheless be derived thus indicating a hazard to the aquatic environment (ECHA guidance on IR & CSA, Part B: Hazard Assessment (V. 2.1, December 2011).” For soluble iron salts and poorly soluble iron (hydr)oxides, there are not any reliable ecotoxicity data showing effects in aquatic organisms, soluble iron salts and iron (hydr)oxides are not classified as dangerous for the aquatic environment, an aquatic PNEC cannot be derived thus not indicating a hazard to the aquatic environment.

 

Micro-sized iron (hydr)oxides are not classified as harmful, toxic or very toxic to aquatic life or may cause long lasting harmful effects to aquatic life. Micro-sized iron (hydr)oxides are also not an unclassified hazard to the aquatic environment. Based on the poor solubility, bioavailability, lack of a potential for bioaccumulation and toxicity to aquatic organisms and considering ubiquitousness of iron (hydr)oxides in the aquatic compartment and essentiality of iron (as described in section "Nano-Environmental fate and pathways"), micro-sized iron (hydr)oxides are also not considered an unclassified hazard to the aquatic compartment.