1H-Imidazole, hydrobromide (1:1)

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

2005-02-04 to 2005-02-16

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Negligible deviations to OECD 201 (2006): e.g. cell density of the inoculum was twice the recommended density; concentration of FeCl3 in test medium slightly above the recommended Fe concentration of the OECD 201 medium but within the range of Fe concentrations of other acceptable media. However, the deviations are not expected to influence the outcome of the study since the biomass in the control cultures increased exponentially by a factor of at least 16 within the 72-hour test period.

Justification for type of information:

Read-across from imidazole hydrobromide to imidazole hydroiodide is justified since both substances only differ in the respective counterion iodide or bromide. Both anions iodide and bromide are quite similar concerning ecotoxicological behaviour and thus do not influence the ecotoxicological results received.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Report date:

2005

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Version / remarks:

(1984)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Version / remarks:

(1992)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed March 2003

Test material

Test material information

Constituent 1

Reference substance name:

1H-Imidazole hydroiodide

Cas Number:

68007-08-9

Molecular formula:

C3H4N2*HI

IUPAC Name:

1H-Imidazole hydroiodide

Test material form:

solid

Details on test material:

- Name of test material (as cited in study report): Imidazolhydroiodid
- Solubility in water: > 500 g/L
- pH in aqueous solution: 3.5 - 4.5 at concentrations of 50 g/L

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: room temperature, protected from light

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Duplicates of test media samples from nominal concentrations of 1 to 100 mg/L were measured.
- Sampling method: HPLC-UV/VIS
- Sample storage conditions before analysis: all samples were deep-frozen at -20 °C

Test solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A stock solution (100 mg/L) was prepared in test water using intense stirring for 10 minutes at room temperature. Lower test concentrations were prepared by dilution.
- Differential loading: 5 dilutions of the stock solution were prepared with a spacing factor of approx. 3.2
- Controls: Test medium without test item
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): None, all solutions were clear throughout the test.

Test organisms

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: Desmodesmus subspicatus
- Strain: CHODAT, Strain No. 86.81 SAG
- Source (laboratory, culture collection): Culture collection, SAG, Institute for Plant Physiology, University of Göttingen, D-37073 Göttingen, Germany)
- Age of inoculum (at test initiation): 3 days old preculture
- Method of cultivation: The algae were cultivated in synthetic water, according to OECD 201, under standardized conditions.

ACCLIMATION
- Culturing media and conditions (same as test or not): yes

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test conditions

Hardness:

0.24 mmol/L (= 24 mg/L as CaCO3)

Test temperature:

23 - 24 °C

pH:

at test start: 7.5 - 8.1
at test end: 7.9 - 9.0

Dissolved oxygen:

No data

Salinity:

Not applicable

Conductivity:

No data

Nominal and measured concentrations:

Nominal concentrations: 0 (control). 0.32, 1.0, 3.2, 10, 32, and 100 mg/L corresponding to:
mean measured concentration: not detected, not measured, 0.914, 2.88, 9.38, 30.1, 95.7 mg/L, corresponding to a mean recovery of 90 to 96 % of nominal concentrations.

Details on test conditions:

TEST SYSTEM
- Test vessel: Erlenmeyer flask
- Type (delete if not applicable): covered with glass dishes
- Material, size, headspace, fill volume: glass, 50 mL flasks filled with 15 mL
- Agitation: continuously stirred by magnetic stirrers
- Initial cells density: 10^4 algal cells per mL
- Control end cells density: 153.5 x 10^4 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes, according to the guideline (OECD 201 medium, 1984).

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: according to the guideline (OECD 201 medium, 1984)
- Intervals of water quality measurement: At test start and end , the pH was determined in each test concentration and the control. The water temperature was measured daily.

OTHER TEST CONDITIONS
- Photoperiod: continuously illuminated
- Light intensity and quality: 7140 to 8520 lux

EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: Biomass and growth rate were determined via the cell density by counting with an electronic particle counter (Coulter Counter, Model ZM), with at least two measurements per sample after 24, 48, and 72 hours.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: Six concentrations were tested with a spacing of 3.2

RANGE-FINDING STUDY
Test concentrations were based on the results of a range-finding test (without GLP).

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Results and discussion

Effect concentrations

Effect concentrations 1

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

34 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

(analytically verified)

Basis for effect:

growth rate

Remarks on result:

other: 95%-CL: 17-105 mg/L

Effect concentrations 2

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

3.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

(analytically verified)

Basis for effect:

growth rate

Remarks on result:

other: 95%-CL: 0.59-7.7 mg/L

Effect concentrations 3

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

8.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

(analytically verified)

Basis for effect:

biomass

Remarks on result:

other: 95%-CL: 3.3-22 mg/L

Effect concentrations 4

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

(analytically verified)

Basis for effect:

biomass

Remarks on result:

other: 95%-CL: 0.14-3.6 mg/L

Details on results:

- Exponential growth in the control: yes
- Observation of abnormalities: none

Results with reference substance (positive control):

Potassium dichromate is tested at least once a year. The latest results showed that the toxic performance was valid and within the historical range in the laboratory.

Reported statistics and error estimates:

Inhibition of algal growth was determined from the area under the growth curves AUC (= biomass, b) and the specific growth rates (r) for exponentially growing cultures.
AUC and r were calculated for each test flask. Based on these values, the arithmetic mean area and the arithmetic mean growth rate were calculated for all test flasks per treatment. The tabulated values represent rounded results obtained by calculation using the exact raw data. The EbC5O and E,C50 values (the respective concentrations of the test item corresponding to 50% inhibition of algal biomass (b) and growth rate (r) compared to the control), and the corresponding EC1O value and E090 values and their 95%-confidence limits were calculated by Probit Analysis (Ref. 3, 4). For the determination of the LOEC and NOEC, the calculated mean biomass and the mean growth rate at the test concentrations were tested for significant differences when compared to the control values by a Dunnett-test (Ref. 5, 6).

Any other information on results incl. tables

Table 1: NOEC and LOEC were also calculated for algal biomass and growth rate after 72 hours test duration:

Parameter (0-72 h)	Biomass (mg/L)	Growth rate (mg/L)
NOEC	1.0	1.0
LOEC	3.2	3.2

 

Table 2: Results obtained for the concentrations of the test item in the test medium

Nominal concentration of test item [mg/L]	Test item measured (average)
	[mg/L]	[% of nominal]
Treatment samples
1.0	0.914	91
3.2	2.88	90
10	9.38	94
32	30.1	94
100	95.7	96
Biological control sample
0	n.d.	n.a.
Spiked test water samples
1.11	1.01	91
97.1	93.0	96
mean:		93
Analytic blank
0	n.d.	n.a.

n.d. = no test item detected; n.a. = not applicable

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

In an alga growth inhibition test according to OECD 201 (1984), the growth rate of Desmodesmus subspicatus was affected by imidazole hydroiodide; the 72-h EC50 for inhibition of specific growth rate amounts to 34 mg/L with a corresponding EC10 of 3.5 mg/L (all nominal, analytically verified).