Calcium oxide

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

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

Adequacy of study:

key study

Study period:

19 - 21 June 2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

GLP study, according to the OECD 202 guideline Rationale for read-across: in the environment, lime substances rapidly dissociate or react with water. These reactions, together with the equivalent amount of hydroxyl ions set free when considering 100mg of the lime compound (hypothetic example), are illustrated below: Ca(OH)2 <-> Ca2+ + 2OH- 100 mg Ca(OH)2 or 1.35 mmol sets free 2.70 mmol OH- CaO + H2O <-> Ca2+ + 2OH- 100 mg CaO or 1.78 mmol sets free 3.56 mmol OH- From these reactions it is clear that the effect of calcium oxide will be caused either by calcium or hydroxyl ions. Since calcium is abundantly present in the environment and since the effect concentrations are within the same order of magnitude of its natural concentration, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions. Furthermore, the above mentioned calculations show that the base equivalents are within a factor 2 for calcium oxide and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of calcium oxide is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to calcium oxide is justified.

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

yes

Remarks:

Although the pH increased significantly, it was not neutralized.

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Control, and all test solutions were sampled in duplicate. The duplicate sample was kept separately as a reserve. Immediately after sampling, the samples were superposed with nitrogen.

Vehicle:

not specified

Details on test solutions:

Elendt Medium M4 was used to dilute the test item and to keep the daphnids during the period of the test. The preparation of medium M4 is described in the Standard Operation Procedure (SOP) A 5.6.
The required amount of Medium M4 was prepared not longer than 4 weeks before it was used.
During storage Medium M4 was aerated.

CHARACTERISTICS OF THE BATCH MEDIUM M4:
Water hardness: 250 mg/l as CaCO3.
pH: 7.6
Temperature: 21.3 °C
Dissolved oxygen: 98%
Dissolved oxygen: 8.6 mg/l
Conductivity: 600 µS/cm

Test organisms (species):

Daphnia magna

Details on test organisms:

Daphnia magna (Straus), clone 5, cultured at ECT Oekotoxikologie GmbH since October 11, 2000.
The organisms were originally supplied by Aventis, Frankfurt a.M.
The age of the daphnids at the beginning of the test: 6 - 24 h.

CULTURING OF DAPHNIA MAGNA:
Material of stock vessel: glass
Amount of medium per stock vessel: 1.8 l
Depth of medium in the stock vessel: 14 - 15 cm
Number of daphnids kept as stock per culture vessel: approximately 20
Separation of adult and young daphnids: 1 to 4 times per week
Medium: medium M4
Renewal of medium: approximately 2 times per week
Temperature: 20 ± 2°C
Photoperiod (light/dark): 16/8 h
Light intensity: 50 - 1000 lx
Aeration: none
Food: Algae (Desmodesmus subspicatus, Pseudokirchneriella subcapitata), TetraMin, instant baker's yeast suspension
Feeding frequency: 3 times a week

One day before starting the exposure, all young daphnids were removed from selected holding vessels which contained adult daphnids aged 15 to 45 days. Al least 6 hours before placing young daphnids into the test vessels the newborn daphnids were separated from the parental daphnids which were kept in the selected holding vessels.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Post exposure observation period:

not applicable

Hardness:

250 (mean) mg/l CaCO3

Test temperature:

19.1-21.7°C

pH:

7.7-11.1

Dissolved oxygen:

8.5-8.7 mg/l O2

Salinity:

not applicable

Nominal and measured concentrations:

Nominal: 0.0, 14.8, 22.2, 33.3, 50.0 and 75.0 mg/l.

Details on test conditions:

Number of replicates per test concentration: 4
Number of organisms per test vessel: 5
Test units: 300 ml glass beaker, covered by glass lids
Amount of test solution per test vessel: 150 - 200 ml
Test medium: Medium M4
Aeration of test vessel: none
Adjustment of pH in the test solutions: none
Renewal of the rest solution during the test: none
Feeding during exposure: none
Light regimen: 16 h light : 8 h dark
Light intensity: 354 lx (247 - 453 lx)

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Duration:

48 h

Dose descriptor:

EC50

Remarks:

from regression curve

Effect conc.:

49.1 mg/L

Nominal / measured:

estimated

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

mobility

Remarks on result:

other: calculated pH 10.9

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

33.3 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

mobility

Remarks on result:

other: initial pH 10.1

Duration:

48 h

Dose descriptor:

EC100

Effect conc.:

75 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

mobility

Remarks on result:

other: initial pH 11.1

Details on results:

- Behavioural abnormalities: some daphnids sticking to the water surface were observed at all concentrations, except the control and the highest test concentration. Daphnids with reduced swimming activities compared to controls were observed at the 50 mg/L level.
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: with increasing test item concentrations, precipitates formed over time. The formation of precipitates is likely the result of the reaction between Ca(OH)2 and CO2 dissolved in the medium yielding poorly soluble CaCO3.

Results with reference substance (positive control):

24h-EC50 is 2.06 mg/L, which is in the range between 0.6 and 2.1 mg/L (OECD, April, 2004). Therefore the results with the reference substance are acceptable.

Initial pH values: 7.7 (control), 9.5 (14.8 mg/L), 9.7 (22.2 mg/L), 10.1 (33.3 mg/L), 10.7 (50 mg/L) and 11.1 (75 mg/L).

Using nonlinear regression analysis of the initial OH- concentration against the % inhibition, resulted in an equation (r2=0.992) from which the EC50 was derived: OH- concentration of 0.000717 mol/L (i.e. 49.1 mg/L) and pH 10.9.

Validity criteria fulfilled:

yes

Remarks:

Immobilised daphnids in the control: 0%. Dissolved oxygen concentration at the end of the test in control and test vessels: 8,5 mg/l.

Conclusions:

A clear concentration-response relationship was observed.
The biological findings (immobilisation of the daphnids) were closely related to the initial pH and the corresponding OH- concentrations in the test solutions. At the test item concentration used in this study, the pH values were in the range of the control pH within 24 hours. Therefore the initial pH is considered to be the main reason for the effects of the test item on the test organisms.

Reference 2

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Acceptable, well-documented publication, which meets basic scientific principles. Rationale for read-across: in the environment, lime substances rapidly dissociate or react with water. These reactions, together with the equivalent amount of hydroxyl ions set free when considering 100mg of the lime compound (hypothetic example), are illustrated below: Ca(OH)2 <-> Ca2+ + 2OH- 100 mg Ca(OH)2 or 1.35 mmol sets free 2.70 mmol OH- CaO + H2O <-> Ca2+ + 2OH- 100 mg CaO or 1.78 mmol sets free 3.56 mmol OH- From these reactions it is clear that the effect of calcium oxide will be caused either by calcium or hydroxyl ions. Since calcium is abundantly present in the environment and since the effect concentrations are within the same order of magnitude of its natural concentration, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions. Furthermore, the above mentioned calculations show that the base equivalents are within a factor 2 for calcium oxide and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of calcium oxide is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to calcium oxide is justified.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Toxicity test was conducted by a standard method developed by the laboratory.`Test organisms were exposed, 96 h, to different concentrations of the test item in test solutions, prepared in natural seawater.

GLP compliance:

not specified

Analytical monitoring:

no

Details on sampling:

Water quality was measured daily

Vehicle:

no

Details on test solutions:

Test solutions were prepared for the samples in natural seawater, acclimated to 15+/-1°C, and initial water quality was measured.

Test organisms (species):

Crangon septemspinosa

Details on test organisms:

TEST ORGANISM
- Common name: sand shrimp
- Strain: Say, 1818
- Source: collected from Kouchibouguac Bay, NB, Canada

Test type:

static

Water media type:

saltwater

Limit test:

no

Total exposure duration:

96 h

Post exposure observation period:

not applicable

Hardness:

no data

Test temperature:

15 ± 1 °C

pH:

7.68 (in control) - 12.46 (at highest dose)

Dissolved oxygen:

no data

Salinity:

no data

Nominal and measured concentrations:

Nominal concentrations: 0, 5, 50, 500, 5000, 50000 mg/L

Details on test conditions:

Ten replicate 1 L mason jars were filled with each test concentration and acclimated to 15+/-1°C. One sand shrimp was introduced into each test vessel. The tests were checked for mortality and water quality daily.

Reference substance (positive control):

not specified

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

158 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

hydrated lime

Basis for effect:

mortality

Remarks on result:

other: 95% CL: 50-500 mg/L

Details on results:

There was no mortality in control (pH 6.60-8.03) to 50 mg/L (pH 8.17-9.12) treatments, but 100% mortality in treatments with concentrations of 500 mg/L (pH 8.58-10.32) to 50000 mg/L (pH 12.39-12.61).

Results with reference substance (positive control):

No data

Reported statistics and error estimates:

The NOEC was approximated from the concentrations resulting in <=10% mortality in fish.

Validity criteria fulfilled:

not specified

Conclusions:

In the current test with sand shrimp, the 96h-LC50 for hydrated lime was 158 mg/L. Based on pH values measured at t=0 this is equivalent to 9.70 (9.12-10.3) pH units.

Description of key information

Klimisch 1 study: nominal 48h-EC50 value for the immobility of Daphnia magna = 49.1 mg Ca(OH)2 /L (Egeler et al., 2007)
Klimish 2 study: 96h-LC50 for marine water crustacean Crangon septemspinosa Say = 158 mg Ca(OH)2 /L (Locke et al., 2009)
Rationale for read-across: in the environment, lime substances rapidly dissociate or react with water. These reactions, together with the equivalent amount of hydroxyl ions set free when considering 100mg of the lime compound (hypothetic example), are illustrated below:
Ca(OH)2 <-> Ca2+ + 2OH-
100 mg Ca(OH)2 or 1.35 mmol sets free 2.70 mmol OH-
CaO + H2O <-> Ca2+ + 2OH-
100 mg CaO or 1.78 mmol sets free 3.56 mmol OH-
From these reactions it is clear that the effect of calcium oxide will be caused either by calcium or hydroxyl ions. Since calcium is abundantly present in the environment and since the effect concentrations are within the same order of magnitude of its natural concentration, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions. Furthermore, the above mentioned calculations show that the base equivalents are within a factor 2 for calcium oxide and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of calcium oxide is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to calcium oxide is justified.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

49.1 mg/L

Marine water invertebrates

Marine water invertebrates

Effect concentration:

158 mg/L

Additional information

The short-term toxicity test with Daphnia magna (Egeler et al., 2007) was carried out according to the OECD 202 guidance taking into account GLP and thus resulting in a Klimish 1 score. The biological findings for Daphnia magna (immobility) were closely related to the initial pH of the test solutions, which ranged from 7.7 in the controls to 9.5, 9.7, 10.1, 10.7 and 11.1 at 14.8, 22.2, 33.3, 50 and 75 mg Ca(OH)2 /L, respectively. Therefore the initial pH is considered to be the main reason for the effects of calcium dihydroxide on Daphnia magna (Egeler et al., 2007).

The short-term toxicity test with the marine species Crangon septemspinosa Say (Locke et al., 2009) was conducted by a standard methodology developed by the laboratory. Test conditions are well described, a dose-response relationship was established (96h-LC50 = 158 mg/L); no statistics were reported. This resulted in a Klimish 2 score.

The acute toxicity to daphnia of calcium carbonate (nano) was assessed in a study performed according to OECD TG 202 under GLP (Priestly, 2010). In this study Daphnia magna were exposed to a 100 %v/v saturated solution of calcium carbonate. No toxic effects were seen in the study. Hence the 48 h EC50 was >100% v/v saturated solution and the NOEC was 100% v/v saturated solution. The concentration of calcium carbonate (nano) that might cause acute toxicity is therefore greater than the maximum solubility of calcium carbonate in water.

Based on the results of the studies performed on the read-across substance calcium dihydroxide and on calcium carbonate, it may be concluded that the acute toxicity to daphnia of grades of calcium oxide containing up to 35% calcium carbonate will be driven by the calcium oxide content and hence the results available for the read-across substance calcium dihydroxide represent the worse-case for all grades of calcium oxide.