Sulphur trioxide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

72 hours

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Samples taken at 0 and 72 hours.

Vehicle:

no

Details on test solutions:

125.0 mg of the test item was added to 1 litre of dilution water. The pH was measured to be pH 2.9 and was adjusted to pH 8.1 with 1 M sodium
hydroxide solution. 80 mL of the stock solution were taken and diluted with 10 mL nutrient medium and 10 mL algal inoculum with a cell density of 5000 cells/mL resulting in a final concentration of 100 mg/L. For each test item concentration and control 6 replicates were prepared.

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

The test species were obtained from 'The Collection of Algal Cultures' of the Institute of Plant Physiology at the University of Göttingen (Germany).
Exponentially-growing stock cultures were maintained in the test facility under constant temperature conditions (23 +/- 2°C) at a light intensity in the range 60 – 120 µE. x m-2 x s-1 (measured in the range 400 to 700 nm using a spherical quantum flux meter). The nutrient medium (according to BRINGMANN & KÜHN (1977) was renewed once a week. Cell density measurements were made using a microcell counter.

Pre-cultures were prepared up to three days before the start of a test. They were grown under identical exposure conditions as the stock cultures, except from the use of a different nutrient medium (annex 1).

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Post exposure observation period:

Not applicable

Hardness:

Not stated

Test temperature:

A temperature in the range 21°C to 25°C was maintained at +/- 2°C.

pH:

The test solution was altered to pH 8.1

Dissolved oxygen:

Not stated

Salinity:

Not stated

Nominal and measured concentrations:

Test item concentration was 100 mg/L.

Details on test conditions:

Light intensity: At the average of the test solutions, a light intensity in the range 60 to 120 µE. x m-2 x s-1, or an equivalent range of 4000 to 8000 lux, was used.

Reference substance (positive control):

yes

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:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Analysis of the yield and growth rate of the algal population within the 72 h exposure period gave the following results:

Results [mg/L]:
ErC 50 (0-72 h) : > 100
EyC 50 (0-72 h): > 100

There were no toxic effects on algae observed at a limit test concentration of 100 mg/L. Growth curves were plotted for each test concentration and control which showed both curves to overlap indicting no effect on growth.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Not reported

The results (cell density measurements, yields and growth rates) were tabulated according to the concentration of the test item and the time of measurement. Growth curves were plotted for each test concentration and control. The percentage inhibition of both, yield [b] and growth rate [r], were calculated for each test concentration. The growth rate [r] was calculated for each test culture. Below in tables 1-3 are the results. The cell number, growth rate and yield are an average result of the 6 test samples and 6 control samples collected.

Table 1; Cell number (C) and its inhibition relative to control (%) as computed from the raw data for test intervals selected.

Treatment	0-24 h		0-48 h		0-72 h
[mg/L]	C	%l	C	%l	C	%l
Control	2.167	0.0	8.333	0.0	44.500	0.0
100.000	2.167	0.0	8.333	0.0	45.833	-3.0

Table 2; Yield (Y) and its inhibition relative to control (%) as computed from the raw data for test intervals selected.

Treatment	0-24 h		0-48 h		0-72 h
[mg/L]	Y	%l	Y	%l	Y	%l
Control	1.667	0.0	7.833	0.0	44.000	0.0
100.000	1.667	0.0	7.833	0.0	45.333	-3.0

Table 3: Growth rate (G) and its inhibition relative to control (%) as computed from the raw data for test intervals.

Treatment	0-24 h		0-48 h		0-72 h
[mg/L]	G	%l	G	%l	G	%l
Control	1.454	0.0	1.406	0.0	1.495	0.0
100.000	1.454	0.0	1.406	0.0	1.505	-0.7

Validity criteria fulfilled:

yes

Remarks:

The coefficient of variation of the mean specific growth rate replicates in the control between 0 and 72 h was: 2.0%. The factor of the biomass parameter, measured in the control between 0 and 72 h was 89.0. The test fulfills the validity criterion.

Conclusions:

Following exposure of Desmodesmus subspicatus to sulfuric acid both the 72 hour ErC50 (0-72h) and EyC50 (0-72 h) were >100 mg/L (the highest concentration tested).

Executive summary:

A study was performed to assess the adverse effects of Sulfuric acid on the yield (= biomass at time t minus initial biomass) and the growth rate (= rate of increase in cell density with time) of the planktonic freshwater algal species Desmodesmus subspicatus (former name:Scenedesmus subspicatus) over several generations.

The study was conducted in accordance with OECD Guideline for Testing of Chemicals No. 201 'Alga, Growth Inhibition Test' (2006). This method succeeded the previous OECD Guideline No. 201 'Alga, Growth Inhibition Test' (1984) and EU Method C.3 'Algal inhibition test' (1992).

Exponentially growing algal cells were exposed for a period of 72 hours to a limit test concentration of nominally 100 mg/L of Sulfuric acid dissolved in water adjusted to pH 8.1 of the OECD growth medium.

The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions. The following values were determined:

 

E_rC 50 (0-72 h): > 100 mg/L with the corresponding NOEC [r] of 100 mg/L

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

72 hours

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Sulphur trioxide readily reacts with water to form sulphuric acid. The reaction is instantaneous, to the extent that SO3 will react with water vapour in the atmosphere to form fumes of sulphuric acid. This reaction forms the basis of the manufacturing process of H2SO4. The read-across hypothesis is therefore that SO3 will instantaneously transform into H2SO4 upon contact with water (i.e. in aquatic ecotoxicology tests), thus any observed effects will be directly attributable to sulphuric acid. It is therefore justifiable to derive hazard conclusions from sulphuric acid data, with regard to ecotoxicological endpoints.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Available study data for sulphuric acid is being used for read-across to the target substance, sulphur trioxide.

Analytical monitoring:

yes

Details on sampling:

Samples taken at 0 and 72 hours.

Vehicle:

no

Details on test solutions:

125.0 mg of the test item was added to 1 litre of dilution water. The pH was measured to be pH 2.9 and was adjusted to pH 8.1 with 1 M sodium
hydroxide solution. 80 mL of the stock solution were taken and diluted with 10 mL nutrient medium and 10 mL algal inoculum with a cell density of 5000 cells/mL resulting in a final concentration of 100 mg/L. For each test item concentration and control 6 replicates were prepared.

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

The test species were obtained from 'The Collection of Algal Cultures' of the Institute of Plant Physiology at the University of Göttingen (Germany).
Exponentially-growing stock cultures were maintained in the test facility under constant temperature conditions (23 +/- 2°C) at a light intensity in the range 60 – 120 µE. x m-2 x s-1 (measured in the range 400 to 700 nm using a spherical quantum flux meter). The nutrient medium (according to BRINGMANN & KÜHN (1977) was renewed once a week. Cell density measurements were made using a microcell counter.

Pre-cultures were prepared up to three days before the start of a test. They were grown under identical exposure conditions as the stock cultures, except from the use of a different nutrient medium (annex 1).

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Post exposure observation period:

Not applicable

Hardness:

Not stated

Test temperature:

A temperature in the range 21°C to 25°C was maintained at +/- 2°C.

pH:

The test solution was altered to pH 8.1

Dissolved oxygen:

Not stated

Salinity:

Not stated

Nominal and measured concentrations:

Test item concentration was 100 mg/L.

Details on test conditions:

Light intensity: At the average of the test solutions, a light intensity in the range 60 to 120 µE. x m-2 x s-1, or an equivalent range of 4000 to 8000 lux, was used.

Reference substance (positive control):

yes

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:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Analysis of the yield and growth rate of the algal population within the 72 h exposure period gave the following results:

Results [mg/L]:
ErC 50 (0-72 h) : > 100
EyC 50 (0-72 h): > 100

There were no toxic effects on algae observed at a limit test concentration of 100 mg/L. Growth curves were plotted for each test concentration and control which showed both curves to overlap indicting no effect on growth.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Not reported

The results (cell density measurements, yields and growth rates) were tabulated according to the concentration of the test item and the time of measurement. Growth curves were plotted for each test concentration and control. The percentage inhibition of both, yield [b] and growth rate [r], were calculated for each test concentration. The growth rate [r] was calculated for each test culture. Below in tables 1-3 are the results. The cell number, growth rate and yield are an average result of the 6 test samples and 6 control samples collected.

Table 1; Cell number (C) and its inhibition relative to control (%) as computed from the raw data for test intervals selected.

Treatment	0-24 h		0-48 h		0-72 h
[mg/L]	C	%l	C	%l	C	%l
Control	2.167	0.0	8.333	0.0	44.500	0.0
100.000	2.167	0.0	8.333	0.0	45.833	-3.0

Table 2; Yield (Y) and its inhibition relative to control (%) as computed from the raw data for test intervals selected.

Treatment	0-24 h		0-48 h		0-72 h
[mg/L]	Y	%l	Y	%l	Y	%l
Control	1.667	0.0	7.833	0.0	44.000	0.0
100.000	1.667	0.0	7.833	0.0	45.333	-3.0

Table 3: Growth rate (G) and its inhibition relative to control (%) as computed from the raw data for test intervals.

Treatment	0-24 h		0-48 h		0-72 h
[mg/L]	G	%l	G	%l	G	%l
Control	1.454	0.0	1.406	0.0	1.495	0.0
100.000	1.454	0.0	1.406	0.0	1.505	-0.7

Validity criteria fulfilled:

yes

Remarks:

The coefficient of variation of the mean specific growth rate replicates in the control between 0 and 72 h was: 2.0%. The factor of the biomass parameter, measured in the control between 0 and 72 h was 89.0. The test fulfills the validity criterion.

Conclusions:

Following exposure of Desmodesmus subspicatus to sulfuric acid both the 72 hour ErC50 (0-72h) and EyC50 (0-72 h) were >100 mg/L (the highest concentration tested).

Executive summary:

Data on the effects to freshwater algae is available for sulphuric acid and is considered suitable for read-across (based on the analogue approach) to the target substance, sulphur trioxide. Sulphur trioxide readily reacts with water to form sulphuric acid. The reaction is instantaneous, to the extent that SO₃ will react with water vapour in the atmosphere to form fumes of sulphuric acid. This reaction forms the basis of the manufacturing process of H₂SO₄. The read-across hypothesis is therefore that SO₃ will instantaneously transform into H₂SO₄ upon contact with water (i.e. in aquatic ecotoxicology tests), thus any observed effects will be directly attributable to sulphuric acid. It is therefore justifiable to derive hazard conclusions from sulphuric acid data, with regard to ecotoxicological endpoints.

A study was performed to assess the adverse effects of Sulfuric acid on the yield (= biomass at time t minus initial biomass) and the growth rate (= rate of increase in cell density with time) of the planktonic freshwater algal species Desmodesmus subspicatus (former name:Scenedesmus subspicatus) over several generations.

The study was conducted in accordance with OECD Guideline for Testing of Chemicals No. 201 'Alga, Growth Inhibition Test' (2006). This method succeeded the previous OECD Guideline No. 201 'Alga, Growth Inhibition Test' (1984) and EU Method C.3 'Algal inhibition test' (1992).

Exponentially growing algal cells were exposed for a period of 72 hours to a limit test concentration of nominally 100 mg/L of Sulfuric acid dissolved in water adjusted to pH 8.1 of the OECD growth medium.

The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions. The following values were determined:

 

E_rC 50 (0-72 h): > 100 mg/L with the corresponding NOEC [r] of 100 mg/L

Description of key information

An OECD 201 Guideline study on the toxicity of sulphuric acid on the freshwater algal species Desmodesmus subspicatus is available, which showed no observed toxic effect at the limit concentration of 100 mg/L after 72 hours.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

A study was performed to assess the adverse effects of Sulfuric acid on the yield (= biomass at time t minus initial biomass) and the growth rate (= rate of increase in cell density with time) of the planktonic freshwater algal species Desmodesmus subspicatus (former name:Scenedesmus subspicatus) over several generations.

The study was conducted in accordance with OECD Guideline for Testing of Chemicals No. 201 'Alga, Growth Inhibition Test' (2006). This method succeeded the previous OECD Guideline No. 201 'Alga, Growth Inhibition Test' (1984) and EU Method C.3 'Algal inhibition test' (1992).

Exponentially growing algal cells were exposed for a period of 72 hours to a limit test concentration of nominally 100 mg/L of Sulfuric acid dissolved in water adjusted to pH 8.1 of the OECD growth medium.

The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions. The following values were determined:

 

E_rC 50 (0-72 h): > 100 mg/L with the correspondingNOEC [r] of 100 mg/L