Magnesium hydroxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18-01-2010 to 22-01-2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Batch No.: 20BR0026
Purity: 99.90%

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Magnesium hydroxide is hardly soluble in water so test concentrations were prepared separately in Milli-RO water. Two 1-litre test bottles were filled with 250 ml of test substance mixtures with initial loading rates of 200 mg/l. These mixtures were stirred in closed dark glass bottles for approximately 25 hours. Subsequently, 16 ml synthetic sewage feed, 200 ml sludge and Milli-RO water up to 500 ml were added resulting in a loading rate of 100 mg/l. Optimal contact between the test substance and test organisms was ensured applying continuous aeration and stirring.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: Municipal sewage treatment plant: Waterschap de Maaskant, ´s-Hertogenbosch, The Netherlands (predominantly domestic sewage)
- Pretreatment: The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105 °C to determine the amount of suspended solids (4.0 g/l of sludge, as used for the test). The pH was 7.8 on the day of testing. The batch of sludge was used one day after collection. Therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18.4 - 19.1 °C

pH:

7.8 - 8.0

Nominal and measured concentrations:

Nominal concentration: 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass vessels
- Type (delete if not applicable): open / closed
- Material, fill volume: galss, 1L
- Aeration: yes
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 4
- No. of vessels per abiotic control (replicates): 1
- Sludge concentration (weight of dry solids per volume): not available
- Weight of dry solids per volume of reaction mixture per unit of time: not available
- Nutrients provided for bacteria: sythetic sewage feed (peptone, meat extract, urea, NaCl, CaCl2x2H2O, MgSO4x7H2O, K2HPO4 in Milli-Q water)
- Nitrification inhibitor used: none

TEST MEDIUM / WATER PARAMETERS
- Source of dilution water: Adjusted ISO medium, folmulated usin RO-water (tab-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q))

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: not available
- Light intensity: not available

EFFECT PARAMETERS MEASURED
Oxygen consumption was measured and recorded for approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer. The pH and temperature were determined in the remaining part of the reaction mixture.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

No inhibition of respiration rate of the sludge was recorded at a loading rate of 100 mg magnesium hydroxide per litre. The duplicate measurement confirmed the result of the first measurement.

Results with reference substance (positive control):

The EC50 of 3,5-dichlorophenol was in the accepted range of 5-30 mg/L (9.0 mg/L).

Table 1. Controls (C) and Magnesium hydroxide (T): pH, oxygen concentration. oxygen consumption and percentage inhibition of the respiration rate

Flask	Loading Rate (mg/l)	Oxygen conc. at the start (≡mg O2/l)	Oxygen consumption (mg O2/l/h)	% Inhibition respiration rate	pH
Cstart	0	7.2	66	-	7.8
Cend	0	6.8	70	-	7.9
			Δ 6%
T 1	100	7.0	68	0	7.9
T 2	100	6.5	69	-1	8.0

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this present test, magnesium hydroxide was not toxic to waste water (activated sludge) bacteria at a loading rate of 100 mg/l. The 3-hour EC50 of magnesium hydroxide exceeded a loading rate of 100 mg/l.

Executive summary:

The influence of magnesium hydroxide on the respiration rate of activated sludge was investigated after a contact time of 3 hours. The study procedure was based on OECD guideline 209 (adopted April 4, 1984), Commission Regulation (EC) No. 440/2008 of 30 May 2008, Part C 11: Biodegradation and ISO Standard 8192 (2007).

The batch of the test material was a white powder with a purity of 99.9 wt %. Since magnesium hydroxide was hardly soluble in water the test concentrations were prepared separately in Milli-RO water. Two 1 -liter test bottles were filled with 250 mL of test substance mixtures and stirred in closed dark glass bottles for approximately 25 hours. A concentration of 100 mg/L of the test material was tested in duplicate. Optimal contact between the test substance and test medium was ensured applying continuous aeration and stirring.

No significant inhibition of the respiration rate of the sludge was recorded at 100 mg test material per liter. The duplicate measurement confirmed the result of the first measurement. Therefore, no further testing was needed.Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, under the conditions of this present test, the test substance was not toxic to waste water (activated sludge) bacteria at a concentration of 100 mg/L. EC50 > 100 mg/L, NOEC = 100 mg/L.

Description of key information

Magnesium hydroxide was not toxic to waste water (activated sludge) bacteria at a loading rate of 100 mg/l. The 3-hour EC50 of magnesium hydroxide exceeded a loading rate of 100 mg/l, the NOEC = 100 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

The influence of magnesium hydroxide on the respiration rate of activated sludge was investigated after a contact time of 3 hours. The study procedure was based on OECD guideline 209 (adopted April 4, 1984), Commission Regulation (EC) No. 440/2008 of 30 May 2008, Part C 11: Biodegradation and ISO Standard 8192 (2007).

The batch of the test material was a white powder with a purity of 99.9 wt %. Since magnesium hydroxide was hardly soluble in water the test concentrations were prepared separately in Milli-RO water. Two 1 -liter test bottles were filled with 250 mL of test substance mixtures and stirred in closed dark glass bottles for approximately 25 hours. A concentration of 100 mg/L of the test material was tested in duplicate. Optimal contact between the test substance and test medium was ensured applying continuous aeration and stirring.

No significant inhibition of the respiration rate of the sludge was recorded at 100 mg test material per liter. The duplicate measurement confirmed the result of the first measurement. Therefore, no further testing was needed.Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, under the conditions of this present test, the test substance was not toxic to waste water (activated sludge) bacteria at a concentration of 100 mg/L. EC50 > 100 mg/L, NOEC = 100 mg/L.