Diiron trioxide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Version / remarks:

2006

Deviations:

yes

Remarks:

Performed in 24-well microplates

Principles of method if other than guideline:

A 72 h study according to OECD guideline 201 was conducted to evaluate the potential effects of nano-Fe2O3 on the growth of the green alga Raphidocelis subcapitata.

GLP compliance:

not specified

Remarks:

not specified in publication

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Samples were taken from suspensions at the highest test concentration.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: NM suspensions were prepared by vigorously mixing the NM in the corresponding medium through magnetic stirring.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Stock culture: Maintained in Woods Hole MBL growth medium at 20±2°C, under continuous
illumination (100 μE/m/s).
- Method of cultivation: According to OECD guideline 201 with adaptation to 24-well microplates.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

not reported

Test temperature:

20±2°C

pH:

not reported

Dissolved oxygen:

not reported

Nominal and measured concentrations:

Nominal: 0, 8.2, 10.2, 12.8, 16.0, 20.0 mg Fe2O3-NPs/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 24-well microplates
- Volume: 1 mL
- Aeration: Twice a day by repetitive pipetting to promote active gas exchange and prevent cell clumping
- Initial cells density: 10^4 cells/mL

GROWTH MEDIUM
- Standard medium used: yes, OECD conform

OTHER TEST CONDITIONS
- Photoperiod: Continuous
- Light intensity and quality: 100 μE/m/s

EFFECT PARAMETERS MEASURED: Growth (photometric measurement of cell density at 440 nm absorbance)

Reference substance (positive control):

no

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 20 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 20 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Reported statistics and error estimates:

The non-linear least squares regression procedure supplied by the software package Statistica 8.0 was used. One-way ANOVAs followed by Dunnett tests were also employed to find out potential significant differences in the endpoints assessed between the control and tested concentrations of each NM suspension, using the software Sigmaplot version 11.0. No observed effect concentration (NOEC) and low observed effect concentration (LOEC) values were taken from ANOVA significant results, reported for a significance level of 0.05.

Table 1: Data from DLS and ELS for Fe2O3 nanoparticles in MBL medium

Conc. (mg/L)	Soluble metal ions (mg/L)	pH	Zeta potential (mV)	Cond (mS/cm)	Z average diameter (nm)	Average diameter by number distribution	PdI
20	8.75±0.04	7.03	−22.9±8.4	0.537±0.007	1545±20	595±115	0.529±0.34

Validity criteria fulfilled:

yes

Remarks:

stated by the authors

Conclusions:

A 72 h algae growth inhibition test was performed according to OECD 201 to assess the potential effects of Fe2O3 nanoparticles (average particle size 85×425 nm). No significant effect on the growth rate of Pseudokirchneriella subcapitata was observed at the applied concentrations of 8.2 to 20.0 mg/L and thus an unbounded 72 h NOEC ≥ 20 mg/L (nominal) was derived.

Description of key information

Based on a study with diiron trioxide in nanoform, diiron trioxide is not toxic to aquatic algae. In a reliable 72 h algae growth inhibition test according to OECD 201 with Fe2O3 nanoparticles, no significant effect on the growth rate of Pseudokirchneriella subcapitata was observed at the applied concentrations of 8.2 to 20.0 mg/L and thus an unbounded 72 h NOEC≥20 mg/L (nominal) was derived.

Additional information

A 72-h algae growth inhibition test was performedby Nogueira et al. (2015)according to OECD 201 to assess the potential effects of Fe2O3 nanoparticles (average particle size 85 × 425 nm). A significant effect on the growth rate of Pseudokirchneriella subcapitata was not observed at the applied concentrations ranging from 8.2 to 20.0 mg/L. Thus, an unbounded 72-h NOEC of ≥ 20 mg/L (nominal) and 72-h EC50 of > 20 mg/L were derived for the growth inhibition of P. subcapitata.

Based on read-across to 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 ofmicro-sized iron (hydr)oxidesto aquatic algae (see table below).

 

Table: Toxicity of nano-sized iron (hydr)oxides to aquatic algae.

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

In a supporting, non-guideline study, effects of diiron trioxide nanoparticles (α-Fe2O3-NP) on the freshwater algae Chlorella pyrenoidosa were assessed (Lei et al., 2016). Based on the obtained results a 96 h IC50 and IC10 forα-Fe2O3 of 71.0 and ~20 mg/L (graphical estimate, extrapolated value) were assessed, respectively. The study is considered as supporting only since it cannot be considered reliable due to a number of methodological shortcomings. It is not clear whether growth rates were calculated from cell counts (only % inhibition is presented) and the growth of the control cannot be checked (validity criteria not assessable).