Magnesium hydroxide

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:

2010-02-17 to 2010-07-02

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Qualifier:

according to guideline

Guideline:

ISO 8692 (Water Quality - Fresh Water Algal Growth Inhibition Test with Scenedesmus subspicatus and Selenastrum capricornutum)

Qualifier:

according to guideline

Guideline:

other: OECD series on testing and assessment number 23

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Test substance: Magnesium hydroxide
CAS Number: 1309-42-8
Purity: 99.90 %

Analytical monitoring:

yes

Details on sampling:

- Singular samples for analysis were taken from the undiluted filtrate (100 mg/L) and the control according to the schedule below:
- Frequency: at t=0, t=24 and t=72h
- Volume: 4.8mL
- Storage: Samples were stored in a freezer until analysis
- Handling: On the day of analysis, the frozen samples were defrosted at room temperature. The test samples were diluted with 0.2ml HNO3 and analysed. If neccesary, the samples were further diluted with 4%(v/v) aqueous HNO3 to obtain concentrations with the calibration range.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Preparations of test solutions started with an aqueous dispersion of 100 mg/L applying 3 days of magnetic stirring. The pH of the medium was adjusted from 8.9 to 6.5 using hydrochloric acid before the start of stirring. Magnetic stirring resulted in a dispersion. The dispersion was then filtered through a 0.45µm membrane filter to remove the undissolved material.
- Test concentration separation factor: 10
- Evidence of undissolved material: no
- Other relevant information: no

Test organisms (species):

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

Details on test organisms:

- Common name: Fresh water Algae
- Strain: NIVA CHL 1
- Source: In-house laboratory culture
- Reason for selection: This system is an unicellular algal species sensitive to toxic substances in the aquatic ecosystem and has been selected as an internationally accepted species.

ACCLIMATION
- Stock culture: Algae stock cultures were started by inoculating growth medium with algal cells from a pure culture on agar.The suspensions were continuously aerated and exposed to light in a climate room at a temperature of 21-24°C.
- Culturing media and conditions: 3 days before the start of the test, cells from the algal stock culture were inoculated in culture medium at a cell density of 1 x 10^4 cells/mL. The pre-culture was maintained under the same conditons as used in the test.
- Appearance of the cells: At the end of the final test microscopic observations were performed on the limit concentration to verify a normal and healthy appearance of the innoculum culture and to observe for any abmormal appearance of the algae.

Test type:

static

Water media type:

not specified

Limit test:

yes

Total exposure duration:

72 h

Test temperature:

21.7 - 24.1°C

pH:

6.5 - 7.1

Nominal and measured concentrations:

Nominal concentrations: 0.10, 1, 10 and 100 mg/L
Measured concentrations of nominal 100 mg/L: after 24h 95 mg/L, after 48h 96 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass vessels
- Material, size, fill volume: glass, 100 mL, 50 mL
- Aeration: no
- Initial cells density: 1 x 10^4 cells/mL
- Control end cells density: 103.4 x 10^4 cells/mL
- No. of vessels per concentration (replicates): 6 fro 100 mg/L, 3 for the other concentrations
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Stock Culture Medium: M1, according to the NPR 6505 formulated using Milli-RO water.
- Pre-culture medium: M2, according to the OECD 201 Guideline, formulated using Milli-Q water and subsequently passed over activated carbon and ion-exchange cartridges preventing precipitation.

OTHER TEST CONDITIONS
- Adjustment of pH: yes, during preparation of solutions
- Photoperiod: continous
- Light intensity and quality: TLD lamps of the type "Cool-white" of 30 Watt with a light intenstiy within the range of 65 to 73 µE/m2s

EFFECT PARAMETERS MEASURED
- Determination of cell concentrations: [counting chamber; electronic particle counter; fluorimeter; spectrophotometer; colorimeter]
- Chlorophyll measurement:
- Other: pH: at the beginning and at the end of the test; Temperature: continously

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

- Exponential growth in the control (for algal test): yes. In the controls, cell density increased by an average factor of > 16 within two days
- Observation of abnormalities: no
- Unusual cell shape: no
- Colour differences: no
- Flocculation: no
- Adherence to test vessels: no
- Aggregation of algal cells: no
- Any stimulation of growth found in any treatment: no
- Any observations that might cause a difference between measured and nominal values: no, after filtration at preparation of solutions
Analyses of samples taken from the filtered 100mg/l solution showed that the measured concentration was in agreement with the nominal throughout the test period(95-96%). Hence, the precipitate that was removed from the solution before the start of the test was not test substance related.
The mean coefficient of variation for section-by-section specific growth rates in the control cultures did not exceed 35%.

Results with reference substance (positive control):

- The EC50 of the reference substance potassium dichromate for growth rate reduction (ErC50: 0-72h) was 1.2 mg/l with a 95% confidence interval ranging from 0.77 to 2.0 mg/l. The historical ranges for growth rate reduction lie between 0.82 and2.3 mg/l. hence, the ErC50: 0-72h for the present batch corresponds with this range.
- The EC50 of the reference substance potassium dichromatefor yield inhibition (EyC50:0-72h) was 0.44 mg/l with a 95% confidence interval ranging from 0.37 to 0.54 mg/l. The historical ranges of the 72h EC50 for yield inhibition lie between 0.43 and1.1 mg/l. Hence, the EyC50: 0-72h for the present batch corresponds with this range.

Table 1 : Mean cell densities (x 10⁴ cells/mL)

Concentration Magnesium Hydroxide (mg/L)	Exposure time(hours)
	0	24	48	72
Control	1.0	6.6	24.2	103.4
0.10	1.0	6.2	22.6	99.9
1.0	1.0	6.5	23.7	103.7
10	1.0	6.7	23.0	99.9
100	1.0	5.7	19.4	71.0

 

Table 2: Percentage reduction of growth rate (total test period) and percentage inhibition of yield

Concentration Magnesium hydroxide (mg/L)	Mean growth rate		Yield (0-72 h)
	µ (0-72 h)	Reduction (%)	X10^4cells/ml	Inhibition (%)
Control	0.06440		102.42
0.10	0.06392	0.7	98.92	3.4
1.0	0.06445	-0.1	102.72	-0.3
10	0.06391	0.8	98.93	3.4
100	0.05915	8.2	70.00	31.7

  

Table 3: Percentage reduction of growth rate at different time intervals

Concentration Magnesium Hydroxide (mg/L)	Mean growth rate
	µ(0-24h)	Reduction (%)	µ (24-48h)	Reduction (%)	µ (48-72 h)	Reduction (%)
Control	0.07833		0.05444		0.06044
0.10	0.07576	3.3	0.05409	0.6	0.06192	-2.4
1.0	0.07818	0.2	0..05357	1.6	0.06159	-1.9
10	0.07929	-1.2	0.05623	-3.3	0.06120	-1.3
100	0.07220	7.8	0.05128	5.8	0.05396	10.7

 

 

 

Validity criteria fulfilled:

yes

Conclusions:

During the aquatic ecotoxicity test with green algea the EC50 for growth rate and yield inhibition was >100 mg/L for the test substance. The NOEC is 100 mg/L.

Executive summary:

In a 72 hour acute toxicity study, cultures of Pseudokirchneriella subcapitata were exposed to magnesium hydroxide at nominal concentrations of 0, 0.1, 1, 10 and 100 mg/L under static conditions in accordance with the OECD 201 guideline. The growth rate and yield inhibition were slightly reduced at 100 mg/L but 50% effect level were not reached. Analytical measurements were done for the highest concentrations (100 mg/L). The following values were obtained: 95 mg/L (24h) and 96 mg/L (48h). In conclusion: During the aquatic ecotoxicity test with green algea the EC50 for growth rate and yield inhibition was > 100 mg/L for the test substance, the NOEC is 100 mg/L.

Description of key information

According to the key study, both the EC50 for growth rate reduction (ErC50: 0-72h) and the EC50 for yield inhibition (EyC50: 0-72h) exceeded an analytically confirmed concentration of 100 mg/L, the NOEC is 100 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

In a 72 hour acute toxicity study, cultures of Pseudokirchneriella subcapitata were exposed to magnesium hydroxide at nominal concentrations of 0, 0.1, 1, 10 and 100 mg/L under static conditions in accordance with the OECD 201 guideline. The growth rate and yield inhibition were slightly reduced at 100 mg/L but 50% effect level were not reached. Analytical measurements were done for the highest concentrations (100 mg/L). The following values were obtained: 95 mg/L (24h) and 96 mg/L (48h). In conclusion: During the aquatic ecotoxicity test with green algea the EC50 for growth rate and yield inhibition was > 100 mg/L for the test substance, the NOEC is 100 mg/L.