Hydrogen iodide

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

Study period:

24.06.2019 - 01.10.2019

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:

adopted March 23, 2006, corrected July 28, 2011

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Version / remarks:

Commission Regulation (EC) No 761/2009, August 24, 2009

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Remarks:

ion chromatography with conductivity detection

Details on sampling:

- Sampling method:
Duplicate samples from the freshly prepared test media (containing algae) of all test concentrations and from the control were taken at the start of the test.
For the determination of the stability of the test item under the test conditions and of the maintenance of the test item concentrations during the test period, duplicate samples from the test media of all test concentrations and the control (containing algae) were taken at the end of the test (after the 72 hours test period) by pouring together the contents of the test beakers of each treatment.
- Sample storage conditions before analysis:
All samples were stored in a freezer (≤ -20 °C), protected from light until analysis was performed.

Vehicle:

no

Details on test solutions:

A stock solution of 100 mg Hydroiodic acid/L was prepared by dissolving 170.6 mg test item into 10064.9 mL test water by intense stirring for 10 minutes. Adequate volumes of this stock solution were diluted with test water to prepare the test media of the desired test concentrations.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: green algae
- Strain: No. 61.81
- Origin: „Sammlung von Algenkulturen, Albrecht-von-Haller-Institut für Pflanzen-wissenschaften, Universität Göttingen", 37073 Göttingen, Germany
- Breeding conditions: The algae were cultivated in the laboratories of the testing facility under standardised conditions according to the test guidelines.
- Age of inoculum (at test initiation): 4 days

ACCLIMATION
- Acclimation period: no acclimation needed

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

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

Test temperature:

22.3 - 23.6 °C

pH:

7.8 - 9.1

Nominal and measured concentrations:

Nominal concentrations: control, 100, 31.3, 9.77, 3.05, 0.954, 0.298, 0.093, 0.0291 and 0.0091 mg Hydroiodic acid/L, corresponding to 169, 53.1, 16.6, 5.17, 1.62, 0.505, 0.158, 0.0493 and 0.0154 mg test item/L
Measured concentrations: control, mean of 107 % of the nominal concentrations (valid for 100, 31.3, 9.77, 3.05, 0.954, 0.298, 0.093 mg Hydroiodic acid/L), the lowest two concentrations (0.0493 and 0.0154 mg test item/L) were

Details on test conditions:

TEST SYSTEM
- Test vessel: Erlenmeyer flasks
- Type: covered with air permeable glass dishes
- Material, size, fill volume: glass, 50 mL size, 50 mL fill volume
- Aeration: none
- Initial cells density: 5000 algal cells per mL
- Control end cells density: 92.4E4 cells/mL, 184.8-fold increase from the initial cell density
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: OECD medium, prepared according to OECD 201

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuous illumination
- Light intensity and quality: mean light intensity: 5327 lx (4810 to 5600 lx)

EFFECT PARAMETERS MEASURED
- Determination of cell concentrations: The cell density on each observation time was determined by spectrophotometric measurement. Therefore, defined volumes of the algal suspensions from all replicates and from the blanks were sampled after 24, 48 and 72 hours of exposure, and were not replaced.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

1.58 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Remarks on result:

other: 95 % conf. interval: 1.47 – 1.69 mg/L

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

0.462 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: yield

Remarks on result:

other: 95 % conf. interval: 0.429 – 0.498 mg/L

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

0.384 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Remarks on result:

other: 95 % conf. interval: 0.329 – 0.439 mg/L

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

0.151 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: yield

Remarks on result:

other: 95 % conf. interval: 0.128 – 0.173 mg/L

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.298 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.093 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: yield

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

0.093 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

0.029 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: yield

Results with reference substance (positive control):

The most recent test with the reference item resulted in 72-h EC50 of 0.445 mg/L (95 % CI: 0.437 - 0.453 mg/L) for yield and 72-h EC50 of 0.941 mg/L for growth rate (95 % CI: 0.910 - 0.973 mg/L), respectively. The EC10 for yield was 0.192 mg/L (95 % CI: 0.184 - 0.199 mg/L) and for growth rate - 0.479 mg/L (95 % CI: 0.440 - 0.514 mg/L), respectively.

Appearance of the test item in the test medium

The two highest test item concentrations of 31.3 and 100 mg Hydroiodic acid/L showed a yellow colouration at test start. After 24, 48 and 72 hours the test item was floating at the surface of the test beaker at 9.77, 31.3 and 100 mg Hydroiodic acid/L.

Biological results

The 72-hour EyC50 was calculated to be 0.462 mg Hydroiodic acid/L and the ErC50 1.58 mg Hydroiodic acid/L. The 72-hour EyC10 was calculated to be 0.151 mg Hydroiodic acid/L and the ErC10 0.384 mg Hydroiodic acid/L. The 72-hour NOEyC was determined to be 0.029 mg Hydroiodic acid/L and the associated 72-hour LOEyC is 0.093 mg Hydroiodic acid/L. The 72-hour NOErC was determined to be 0.093 mg Hydroiodic acid/L and the associated 72-hour LOErC is 0.298 mg Hydroiodic acid/L.

Table 1. Summary of the Biological Results

Parameter	Yield [mg Hydroiodic acid/L]	Growth rate [mg Hydroiodic acid/L]
72-hour EC50	0.462	1.58
95 % conf. interval	0.429 – 0.498	1.47 – 1.69
72-hour EC20	0.222	0.625
95 % conf. interval	0.196 – 0.246	0.556 – 0.691
72-hour EC10	0.151	0.384
95 % conf. interval	0.128 – 0.173	0.329 – 0.439
72-hour NOEC	0.093	0.298
72-hour LOEC	0.029	0.093

Values refer to nominal test concentrations.

Microscopic Observations:

The microscopic examination of the shape of the algal cells after 72 hours of test duration did not show any differences between the algae that had been growing up to a nominal test concentration of 100 mg Hydroiodic acid/L and the algal cells in the control. Thus, the shape of the algal cells was not obviously affected up to this test concentration, the highest concentration tested.

Table 2. Yield y and Percentage Inhibition of y during the Test Period

Nominal concentration [mg Hydroiodic acid/L]	Yields y [10000 cells/mL] and % inhibition of y
	0 – 24 hours		0 – 48 hours		0 – 72 hours
	y	%	y	%	y	%
Control	2.530	-	17.772	-	91.896	-
0.0091	2.571	-1.6	17.534	1.3	88.600	3.6
0.0291	2.652	-4.8	17.534	1.3	89.394	2.7
0.093	2.081	17.7*	14.675	17.4*	79.151	13.9*
0.298	2.081	17.7*	13.325	25.0*	67.876	26.1*
0.954	0.775	69.4*	1.970	88.9*	15.866	82.7*
3.05	0.449	82.3*	0.065	99.6*	2.129	97.7*
9.77	0.136	94.6*	0.000	100.0*	0.000	100.0*
31.3	0.150	94.1*	0.000	100.0*	0.000	100.0*
100	0.204	91.9*	0.000	100.0*	0.000	100.0*

negative values in ‘% inhibition’ indicate an increase in growth relative to that of the control

* mean value significantly different from the control (tested with Williams t-test,a = 0.05, one-sided smaller)

 

 

Table 3. Growth Rates µ and Percentage Inhibition of µ during the Test Period

Nominal concentration [mg Hydroiodic acid/L]	Growth rates µ [1/day] and % inhibition of µ
	0 – 24 hours		0 – 48 hours		0 – 72 hours
	µ	%	µ	%	µ	%
Control	1.801	-	1.799	-	1.739	-
0.0091	1.814	-0.7	1.790	0.5	1.727	0.7
0.0291	1.839	-2.1	1.791	0.4	1.730	0.5
0.093	1.637	9.1	1.703	5.3*	1.690	2.9
0.298	1.640	8.9	1.655	8.0*	1.637	5.9*
0.954	0.932	48.2*	0.789	56.2*	1.149	33.9*
3.05	0.641	64.4*	0.061	96.6*	0.532	69.4*
9.77	0.228	87.3*	0.000	100.0*	0.000	100.0*
31.3	0.214	88.1*	0.000	100.0*	0.000	100.0*
100	0.342	81.0*	0.000	100.0*	0.000	100.0*

negative values in ‘% inhibition’ indicate an increase in growth relative to that of the control
* mean value significantly different from the control (tested with Williams t-test,a = 0.05, one-sided smaller)

 

Analytical results

In case of the lowest test concentration of nominal 0.0091 mg Hydroiodic acid/L all measured values were below the limit of detection or the limit of quantification of the analytical method.

In case of the second lowest test concentration of nominal 0.0291 mg Hydroiodic acid/L all measured values were slightly below the limit of quantification of the analytical method, apart from one replicate of the aged test media where 113 % of the nominal were found.

In the nominal test concentrations of 100, 31.3, 9.77, 3.05, 0.954, 0.298 and 0.093 mg Hydroiodic acid/L an average of 104 % of nominal was found at the start of the test. After 72 hours test duration, an average of 110 % of the nominal value was determined. During the test the algae were exposed to a mean of 107 % of nominal in these treatment groups.

Table 4. Summary of Analytical Results

Sample Description [mg Hydroiodic acid/L]	% of nominal*	RSD[%]	n
Control	n.a.	n.a.	4
0.0091	n.a.	n.a.	4
0.0291	113	n.a.	1
0.093	102	14	4
0.298	106	3	4
0.954	105	1	4
3.05	106	2	4
9.77	109	2	4
31.3	109	2	4
100	109	2	4

* mean value of all measured samples per treatment group
RSD: relative standard deviation per treatment group
n: number of analysed samples; n.a.: not applicable

Validity criteria fulfilled:

yes

Conclusions:

The 72-hour EyC50 was calculated to be 0.462 mg Hydroiodic acid/L and the 72-hour ErC50 value was calculated to be 1.58 mg Hydroiodic acid/L. The 72-hour NOEyC was determined to be 0.029 mg Hydroiodic acid/L and the associated 72-hour LOEyC was 0.093 mg Hydroiodic acid/L. The 72-hour NOErC was determined to be 0.093 mg Hydroiodic acid/L and the associated 72-hour LOErC was 0.298 mg Hydroiodic acid/L.

Executive summary:

The influence of the test item on the growth of the freshwater green algae Pseudokirchneriella subcapitata was assessed in a static concentration-response test performed according to OECD 201 and Regulation (EC) No. 226/2016 Method C.3 under GLP. The algae were exposed to test item concentrations of control, 100, 31.3, 9.77, 3.05, 0.954, 0.298, 0.093, 0.0291 and 0.0091 mg Hydroiodic acid/L, corresponding to 169, 53.1, 16.6, 5.17, 1.62, 0.505, 0.158, 0.0493 and 0.0154 mg test item/L under static conditions for 72 hours. The cell density of the algae was determined spectrophotometrically every 24 hours. The 72-hour EyC50 was calculated to be 0.462 mg Hydroiodic acid/L and the 72-hour ErC50 value was calculated to be 1.58 mg Hydroiodic acid/L. The 72-hour NOEyC was determined to be 0.029 mg Hydroiodic acid/L and the associated 72-hour LOEyC was 0.093 mg Hydroiodic acid/L. The 72-hour NOErC was determined to be 0.093 mg Hydroiodic acid/L and the associated 72-hour LOErC was 0.298 mg Hydroiodic acid/L.

The initial concentrations and the maintenance of the exposure concentrations during the test were sufficiently verified in the analytical part. All reported results refer to nominal values since the concentrations of the test item were within ± 20 % of the nominal concentrations (for all treatment levels above and equal NOEC) during the test.

Description of key information

The 72-hour EyC50 was calculated to be 0.462 mg Hydroiodic acid/L and the 72-hour ErC50 value was calculated to be 1.58 mg Hydroiodic acid/L. The 72-hour NOEyC was determined to be 0.029 mg Hydroiodic acid/L and the associated 72-hour LOEyC was 0.093 mg Hydroiodic acid/L. The 72-hour NOErC was determined to be 0.093 mg Hydroiodic acid/L and the associated 72-hour LOErC was 0.298 mg Hydroiodic acid/L.

Key value for chemical safety assessment

EC50 for freshwater algae:

1.58 mg/L

EC10 or NOEC for freshwater algae:

0.384 mg/L

Additional information

The influence of the test item on the growth of the freshwater green algae Pseudokirchneriella subcapitata was assessed in a static concentration-response test performed according to OECD 201 and Regulation (EC) No. 226/2016 Method C.3 under GLP. The algae were exposed to test item concentrations of control, 100, 31.3, 9.77, 3.05, 0.954, 0.298, 0.093, 0.0291 and 0.0091 mg Hydroiodic acid/L, corresponding to 169, 53.1, 16.6, 5.17, 1.62, 0.505, 0.158, 0.0493 and 0.0154 mg test item/L under static conditions for 72 hours. The cell density of the algae was determined spectrophotometrically every 24 hours. The 72-hour EyC50 was calculated to be 0.462 mg Hydroiodic acid/L and the 72-hour ErC50 value was calculated to be 1.58 mg Hydroiodic acid/L. The 72-hour NOEyC was determined to be 0.029 mg Hydroiodic acid/L and the associated 72-hour LOEyC was 0.093 mg Hydroiodic acid/L. The 72-hour NOErC was determined to be 0.093 mg Hydroiodic acid/L and the associated 72-hour LOErC was 0.298 mg Hydroiodic acid/L.

The initial concentrations and the maintenance of the exposure concentrations during the test were sufficiently verified in the analytical part. All reported results refer to nominal values since the concentrations of the test item were within ± 20 % of the nominal concentrations (for all treatment levels above and equal NOEC) during the test (reference 6.1.5-1).