Diiron trioxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

GLP compliance:

no

Analytical monitoring:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Remarks on exposure duration:

Permanent aeration

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 10 000 mg/L

no effect on test microorganisms

Validity criteria fulfilled:

yes

Remarks:

The validity of the test was checked on the basis of a graphic analysis of the reference item.

Conclusions:

Following the guideline ISO 8192 a 3-hour EC50 of > 10000 mg/L for Iron(III)oxide was obtained on activated sludge of a predominantly domestic sewage.

Executive summary:

Following the guideline ISO 8192 (Test for Inhibition of Oxygen Consumption by Activated Sludge) a 3-hour EC50 of > 10000 mg/L for Iron(III)oxide was obtained on activated sludge of a predominantly domestic sewage. Nominal concentrations of 100 mg/L, 1000 mg/L and 10000 mg/L were used. No chemical analysis was performed. The validity of the test was checked on the basis of a graphic analysis of the reference item (3,5 -Dichlorophenol).

Description of key information

Based on a study with iron hydroxide oxide/diiron trioxide (75:25) in nanoform, diiron trioxide is not toxic to STP microorganisms. A 3-hour EC50 of > 10000 mg/L for iron hydroxide oxide/diiron trioxide (75:25) nanoparticles was obtained for activated sludge of a predominantly domestic sewage.

Additional information

Applying read-across to micro- and nano-sized iron (hydr)oxides (see attachment "Read-across justification-environ assessment-iron oxides" in section 13), micro-sized iron (hydr)oxides are not considered toxic to aquatic microorganisms. Based on studies with activated sewage sludge exposed to micro- and nano-sized iron (hydr)oxides, unbounded 3-h EC50 values of >10,000 mg/L were derived, a concentration that is 10-fold above the corresponding OECD test limit.

Table: Toxicity of iron (hydr)oxides to aquatic microorganisms

Endpoint	Test species	Test results	Test material/form	Reliability: Reference
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

For micro- and nano-sized iron (hydr)oxides, three reliable studies on toxicity to aquatic microorganisms are available. Toxicity was not observed in activated sludge exposed to micro- and nano-sized iron (hydr)oxide forms, and unbounded 3-h EC50 values of > 10 g/L were derived.

In a guideline study with activated sludge exposed to micro-sized triiron tetraoxide according to OECD 209 (Bruns, 1989), adverse effects on respiration rate were not observed after 3 h and an unbounded 3 h EC50 value of > 10 g/L was derived. Further, an unbounded 3-h EC50 value of > 10 g/L was derived for micro-sized manganese ferrite black spinel in a guideline study with activated sludge according to OECD 209.

Toxicity of nano-sized iron (hydr)oxides to aquatic microorganisms was investigated in a study using activated sludge of a predominantly domestic sewage exposed to iron hydroxide oxide/diiron trioxide (75:25) alpha nanoparticles, following ISO guideline 8192 (Test for Inhibition of Oxygen Consumption by Activated Sludge). An unbounded 3-h EC50 value of > 10 g/L was derived, as adverse effects were not observed at the highest concentration tested.

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 indicate a low potential for toxicity of iron(hydr)oxidesto activated sludge microorganisms (see table below). Toxicity ofmicro- and nano-sized iron (hydr)oxidesto aquatic microorganisms was not observed up to 10 g/L (Bruns, 1989; Bruns, 2004), a concentration that is 10-fold above the corresponding OECD test limit for toxicity to microorganisms.