Calcium oxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-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. No reproduction assessed. 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

Principles of method if other than guideline:

Toxicity test was conducted by a standard method developed by the laboratory. Test organisms were exposed, 14 d, to different concentrations of the test item in test solutions, prepared in natural seawater.

GLP compliance:

not specified

Analytical monitoring:

no

Details on sampling:

Temperature was checked daily. Water quality was measured three timed a week.

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:

- common name: sand shrimp
- source: collected from Kouchibouguac Bay, NB, Canada
- wet weight: mean 3.00 +/- 1.307 mg (n = 20)

Test type:

semi-static

Water media type:

saltwater

Limit test:

no

Total exposure duration:

14 d

Post exposure observation period:

not applicable

Hardness:

no data

Test temperature:

no data

pH:

7.95-9.78

Dissolved oxygen:

no data

Salinity:

no data

Nominal and measured concentrations:

nominal concentrations: 0, 3.2, 10, 32, 100, 320 mg/L

Details on test conditions:

- 20 replicates per test concentration
- water renewal: 80 % of test solution replaced 3 times a week with fresh solution
- feeding frequency: 3 times a week
- feed: 100 mg frozen brine shrimp with some live brine shrimp for the first week, and 200 mg frozen brine shrimp in week two
- after 14 days each sand shrimp was weighed (dry weight).

Reference substance (positive control):

not specified

Duration:

14 d

Dose descriptor:

LC50

Effect conc.:

53.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: 95% CL: 48.3-58.4 mg/L

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

32 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Details on results:

- at concentrations of 100 and 320 mg/L a 100 % mortality was observed
- at other concentrations mortality ranged between 5 and 15 %
- no effects on growth were observed.

Results with reference substance (positive control):

not applicable

Reported statistics and error estimates:

- LC50s were calculated following Stephan (1977)
- Analysis of variance was used to examine the effect of treatments on sand shrimp weights (log-transformed to normalize) (JMP version 4, SAS Institute 2000)

Validity criteria fulfilled:

not specified

Conclusions:

In the current test with sand shrimp, the 14d-LC50 for hydrated lime was 53.1 mg/L. Based on pH values measured at t=0 this is equivalent to 9.20 (9.12-9.28) pH units. No effects on growth were observed.

Description of key information

Klimisch 2 study (Locke et al., 2009): nominal 14d-NOEC value for mortality of Crangon septemspinosa = 32 mg Ca(OH)2/L
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.
An acute toxicity study to Daphnia magna was performed according to OECD 202 with a saturated solution (100% v/v) of calcium carbonate (nano) (Priestly, 2010). No immobilisation or toxic effects were observed in any of the Daphnia magna exposed. As a result, calcium carbonate is considered not acutely toxic to aquatic invertebrates and hence long term testing is considered to be unnecessary.

Key value for chemical safety assessment

Marine water invertebrates

Marine water invertebrates

Effect concentration:

32 mg/L