Calcium sulfate

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

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study performed according to GLP and guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes (incl. QA statement)

Details on test solutions:

An amount of test material (2000 mg) was dissolved in water with the aid of ultrasonication for approximately 60 minutes and the volume adjusted to 1 litre to give a 2000 mg/l stock solution from which serial dilutions were made to give 200 and 20 mg/l stock solutions. An aliquot (250 ml) of the 20 mg/l stock solution was dispersed with synthetic sewage (16 ml), activated sewage sludge (200 ml) and water, to a final volume of 500 ml, to give the required concentration of 10 mg/l. Similarly, aliquots (80 and 250 ml) of the 200 mg/l stock solution and aliquots (80 and 250 ml) of the 2000 mg/l stock solution were used to prepare the test concentrations of 32, 100, 320 and 1000 mg/l. The volumetric flasks containing the stock solutions were inverted several times to ensure homogeneity of the stock solutions.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The activated sewage sludge sample was maintained on continuous aeration in the laboratory at a temperature of approximately 21ºC and was used on the day of collection. The pH of the sample was 7.1 measured using a WTW pH/Oxi 340I pH and dissolved oxygen meter. Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 ml) of the activated sewage sludge by suction through a pre-weighed GF/A filter paper using a Buchner funnel which was then rinsed 3 times with 10 ml of deionised reverse osmosis water and filtration continued for 3 minutes. The filter paper was then dried in an oven at approximately 105ºC for at least 1 hour and allowed to cool before weighing. This process was repeated until a constant weight was attained. The suspended solids concentration was equal to 3.9 g/l prior to use.

Limit test:

no

Total exposure duration:

3 h

Test temperature:

21±1°C.

pH:

The pH values measured during the test period are given in table 2

Nominal and measured concentrations:

32, 100, 320 and 1000 mg/L (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: 250 mL darkened glass Biological Oxygen Demand (BOD) bottle
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2



TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The test water used for the definitive test was laboratory tap water dechlorinated by passage through an activated carbon filter (Purite Series 500) and partly softened (Elga Nimbus 1248D Duplex water softener) giving water with a total hardness of approximately 140 mg/l as CaCO3. After dechlorination and softening the water was then passed through a series of computer controlled plate heat exchangers to achieve the required temperature


OTHER TEST CONDITIONS
- Light intensity: Normal laboratory lighting


EFFECT PARAMETERS MEASURED : The rate of respiration for each flask was measured over the linear portion of the oxygen consumption trace (where possible between approximately 6.5 mg O2/L and 2.5 mg O2/L).

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol (Sigma-Aldrich Batch No. 04621CJ)

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: respiration

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: respiration

Results with reference substance (positive control):

The reference material gave a 3-Hour EC50 value of 7.6 mg/L, 95% confidence limits 6.0 – 9.6 mg/L.

Table1     Oxygen Consumption Rates and Percentage Inhibition Values after 3 Hours Contact Time

Nominal Concentration (mg/l)		Initial O2 Reading (mg O2/l)	Measurent Period (minutes)	Final O2Reading (mg O2/l)	O2Consumption Rates (mg O2/l/min)	% Inhibition
Control	R1	7.3	10	3.3	0.40	-
	R2	7.0	10	2.9	0.41	-
Test Material	10	6.7	10	2.6	0.41	[1]
	32	6.1	8	2.7	0.43	[6]
	100	6.9	10	2.9	0.40	1
	320	6.7	10	2.7	0.40	1
	1000	6.7	10	2.5	0.42	[4]
3,5-dichlorophenol	3.2	7.3	8	4.8	0.31	23
	10	7.8	10	6.3	0.15	63
	32	8.4	10	7.9	0.05	88

Increase in respiration rate as compared to controls]

R₁– R₂= Replicates 1 to 2

Table 2: pH Values of the Test Preparations at the Start and End of the Exposure Period

Nominal Concentration (mg/l)		pH
		0 Hours	3 Hours
Control	R1	7.3	7.9
	R2	7.6	7.9
Test Material	10	7.6	7.8
	32	7.6	7.9
	100	7.7	7.9
	320	7.5	7.8
	1000	7.5	7.7
3,5-dichlorophenol	3.2	7.4	8.1
	10	7.5	8.0
	32	7.5	8.2

R₁– R₂= Replicates 1 to 2

Table 3: Observations on the test preparations throughout the test period

Nominal Concentration (mg/l)		Observations on Test Preparations
		0 Hours	30 Minutes Contact Ti	3 Hours Contact Ti
Control	R1	Dark brown dispersion	Dark brown dispersion	Dark brown dispersion
	R2	Dark brown dispersion	Dark brown dispersion	Dark brown dispersion
Test Material	10	Clear colourless solution*	Dark brown dispersion, no undissolved test material visible	Dark brown dispersion, no undissolved test material visible
	32	Clear colourless solution*	Dark brown dispersion, no undissolved test material visible	Dark brown dispersion, no undissolved test material visible
	100	Clear colourless solution*	Dark brown dispersion, no undissolved test material visible	Dark brown dispersion, no undissolved test material visible
	320	Clear colourless solution*	Dark brown dispersion, no undissolved test material visible	Dark brown dispersion, no undissolved test material visible
	1000	Clear colourless solution*	Dark brown dispersion, no undissolved test material visible	Dark brown dispersion, no undissolved test material visible
3,5-dichlorophenol	3.2	Dark brown dispersion, no undissolved reference material visible	Dark brown dispersion, no undissolved reference material visible	Dark brown dispersion, no undissolved reference material visible
	10	Dark brown dispersion, no undissolved reference material visible	Dark brown dispersion, no undissolved reference material visible	Dark brown dispersion, no undissolved reference material visible
	32	Dark brown dispersion, no undissolved reference material visible	Dark brown dispersion, no undissolved reference material visible	Dark brown dispersion, no undissolved reference material visible

R₁– R₂= Replicates 1 to 2

*Observations made prior to the addition of synthetic sewage and activated sewage sludge.

Validity criteria fulfilled:

yes

Conclusions:

The effect of the test material on the respiration of activated sewage sludge micro-organisms gave a 3-Hour EC50 of greater than 1000 mg/L. The No Observed Effect Concentration (NOEC) after 3 hours exposure was 1000 mg/L.

Description of key information

Calcium sulfate has no inhibitory effect on sewage sludge microorganisms.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

An reliable OECD guideline Activated Sludge Respiration Inhibition (ASRI) study has been performed on calcium sulfate dihydrate. Sewage sludge microorganisms were exposed to nominal concentrations of 32, 100, 320 and 1000 mg/L for 3 h. The 3 h EC50 value was >1000 mg/L and the NOEC was 1000 mg/ (the highest dose tested)