Iridium

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:

supporting study

Study period:

16 Dec 2019 - 11 May 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

28 July 2011

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Ir content: 41.43%

Analytical monitoring:

yes

Details on sampling:

Test substance was analysed in samples of freshly prepared test solutions and controls prior to filling it into the test vessels.
After 72-hours, samples were taken from representative replicates per treatment level and control.
All samples were stabilised by acidification and stored at 4 ± 3 °C until further analysis

Vehicle:

no

Details on test solutions:

An amount of 100.1mg of the test item was transferred into a sterile glass flask filled up to the 1L with growth medium (sterile) to obtain a stock solution. The test media was stirred for 24 hours at room temperature (about 20°C). Since there was undissolved test item after 24 hours, the test media was ultrasonicated for 30 minutes followed by stirring of the test media for further 30 minutes. Afterwards, the test media was filtered through a 0.22 µm polyethersulfone filter. The stock solution then was diluted with sterile growth medium to obtain the highest test concentration. The other test concentrations were prepared by serial dilution.
For the control growth medium without test item was used.

Test organisms (species):

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

Details on test organisms:

Species: Raphidocelis subcapitata, Chlorophycea, Chlorophyta.
Origin: SAG, Culture Collection of Algae at Pflanzenphysiologisches Institut of the University at Göttingen, Albrecht von Haller Institut, Untere Klarspüle 2, 37073 Göttingen.
Strain number: Catalog No 61.81 SAG.
Cultivation: The stock cultures were maintained fulfilling the criteria of the OECD guide-line (culture medium recommended by Bringmann und Kühn (1980) [6]). Prior to testing a pre-culture was established in OECD growth medium (as described below) to obtain exponentially-growing algae for the test. The culture duration of the pre-cultures was 3 days.
cell numbers: cell concentrations were determined in the inoculum culture prior to the addition to the test vessels at test start and after 24, 48 and 72 h in the test cultures.
The cell density was measured using an electronic particle counter (CASY TT, OMNI Life Science GmbH & Co. KG, Bremen, Germany).

Test type:

static

Water media type:

freshwater

Remarks:

sterilised synthetic growth medium (OECD medium) according to OECD 201

Limit test:

no

Total exposure duration:

72 h

Test temperature:

22.0°C during the test

pH:

pH of controls: increased during the test from 7.13 at test start to a mean value (n = 8) of 7.94 at test end
pH of treatments: initial pH in the treatments ranged from 7.10 to 7.23 and the mean pH value was between 7.94 and 8.03 at the end of the test

Nominal and measured concentrations:

Nominal test concentrations: control, 0.050, 0.158, 0.501, 1.58 and 5.00 mg test item/L (corresponding to control, 0.021, 0.066, 0.207, 0.656, 2.07 mg Ir/L)
At test initiation: measured concentrations were At test termination: measured concentrations were Measured concentrations were within a range of 80 – 120% of the nominal concentrations, and the evaluation of biological results was based on the nominal concentrations.

Details on test conditions:

light intensity: OSRAM Standard “cool white”, 60 - 120 µE m-2 s-1 (4440 - 8880 lux), light intensity as measured daily using a cosine (2 π) receptor (LI-250A, LI-COR) in µE m-2 s-1 at level of the test media surface and at different positions in the incubation chamber. measured value: 93.75 to 96.96 µE m-2 s-1
During the course of the test all test vessels were kept on a laboratory shaker (Incubation Shaker Multitron®, INFORS Typ HT, Switzerland) shaking continuously at 150 rpm.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

1.4 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat. (dissolved fraction)

Remarks:

measured equals 80-120% of nominal

Basis for effect:

growth rate

Remarks on result:

other:

Remarks:

95% CI 1.04-1.71

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

3.28 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat. (dissolved fraction)

Remarks:

measured is 80-120%of nominal

Basis for effect:

growth rate

Remarks on result:

other:

Remarks:

95%CI 2.89-3.7

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

0.3 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat. (dissolved fraction)

Basis for effect:

other: yield

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

1.32 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat. (dissolved fraction)

Basis for effect:

other: yield

Details on results:

A concentration-dependent inhibiting effect on the growth of the freshwater green algae was observed over the range of the tested concentrations.
Microscopic examinations were performed to verify a normal and healthy appearance of the inoculum culture and to detect any abnormal appearance of the algae (as may be caused by the exposure to the test substance) at the end of the test.

Results with reference substance (positive control):

Sensitivity of the test organism is routinely checked using 3,5-dichlorophenol as primary standard following internal SOPs in a non-GLP test twice a year. The latest (March 2020) ErC50 value of 2.92 mg/L (nominal; 95% confidence limits: 2.64 – 3.24 mg/L) is in good agreement with the results of an international ring test with an ErC50 of 3.38 ± 1.30 mg/L.

Reported statistics and error estimates:

Four replicates of each test concentration and eight replicates for the control were prepared.

Validity criteria fulfilled:

yes

Remarks:

cell number in control cultures increased by a factor of 93.7, mean of replicate CV % in controls was 19.5 %, coefficient of variation of average specific growth rate at test end in replicate control cultures was 4.5 %

Conclusions:

The 72-hour toxicity of diammonium hexachloroiridate to the unicellular green alga Raphidocelis subcapitata was determined in a static system (OECD 201). The 72-hour ErC50 for the inhibition of growth rate was determined to be at 3.28 mg test item/L. The ErC10 was determined to be at 1.40 mg test item/L.

Executive summary:

A study was performed to determine the toxicity of Diammonium hexachloroiridate on the growth of the unicellular freshwater green algaRaphidocelis subcapitata.

Exponentially-growing cultures of the green alga were exposed to five concentrations of the test item plus a control over several generations under defined conditions for 72 hours according to the OECD guideline 201.

The nominal test concentrations were prepared with sterile growth medium under sterile conditions. For the examination of the inhibition of alga growth, eight replicates of the control (test medium only) and four replicates of each treatment were tested at the following nominal concentrations: 0.050, 0.158, 0.501, 1.58 and 5.00 mg test item/L, equivalent to 0.021, 0.066, 0.207, 0.656 and 2.07 mg Ir/L (factor: 3.16).

The concentrations of test test item in the media were confirmed by ICP-OES measurements of iridium at test initiation and test termination. The LOQ was at 0.0035 mg Ir/L.

At test initiation, the measured concentrations ranged from 95.9 to 105% of nominal concentrations and therefore were within a range of 80 to 120% of the nominal concentrations. The measured concentrations did remain stable within ± 20% throughout the test period of 72 hours (% of initial: 85.7 to 99.6%; % of nominal: 89.4 to 95.5%). Therefore, the evaluation of biological results was based on the nominal test item concentrations.

A concentration-dependent inhibiting effect on the growth of the freshwater green algae was observed over the range of the tested concentrations.

The respective 72-hour E_rC₅₀for the inhibition of growth rate was determined to be at 3.28 mg test item/L and the E_rC₁₀at 1.40 mg test item/L. The NOEC for growth rate was at 0.50 mg test item/L. For yield, an E_yC₅₀of 1.32 mg test item/L was determined. The EC₁₀values for yield was at 0.30 mg test item/L and the NOEC was at 0.16 mg test item/L.

Description of key information

No experimental study is required for iridium based on the outcome of a full TDp assay (cfr.

IUCLID Section 4 'Water solubility') and the identified acute and chronic threshold values with other

water soluble iridium(IV) substances.

Based on mean measured iridium concentrations the EC50 was 1.36 mg Ir L^-1 and the EC10 was 0.58 mg Ir L^-1.

This is the lowest acute and chronic threshold identified with iridium(IV) substances, and this value serves as basis for acute and chronic ERV derivation.

Key value for chemical safety assessment

EC50 for freshwater algae:

1.36 mg/L

EC10 or NOEC for freshwater algae:

0.58 mg/L

Additional information

No experimental study is required for iridium based on the outcome of a full TDp assay (cfr.

IUCLID Section 4 'Water solubility') and the identified acute and chronic threshold values with other

water soluble iridium(IV) substances.

The 72-hour toxicity of diammonium hexachloroiridate to the unicellular green alga Raphidocelis subcapitata was determined in a static system (OECD 201) (Schlich, 2020). The  72-hour ErC50 for the inhibition of growth rate was determined to be at 3.28 mg test item/L (corresponding to 1.36 mg Ir/L). The ErC10 was determined to be at 1.40 mg test item/L (corresponding to 0.58 mg Ir/L).