Calcium oxide

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil macroorganisms except arthropods: short-term

Type of information:

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

Adequacy of study:

supporting study

Study period:

June 26, 2007 - July 10, 2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

According to OECD 207. Well documented GLP study. Validity criteria fulfilled. 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 207 (Earthworm, Acute Toxicity Tests)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

14 d

Duration:

14 d

Dose descriptor:

LC50

Effect conc.:

> 5 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

mortality

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

other: biomass

Validity criteria fulfilled:

yes

Remarks:

Adult mortality: ≤ 10% (being 0% after 14 days).

Conclusions:

After 14 days of exposure to Calcium dihydroxide in artificial soil the LC50 for Eisenia fetida was estimated to be higher than 5000 mg Calcium dihydroxide/kg soil d.w. The NOEC was determined to be 5000 mg Calcium dihydroxide/kg soil d.w.

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Type of information:

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

Adequacy of study:

key study

Study period:

August 16, 2007 - October 11, 2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

According to OECD 222. Well documented. Validity criteria fulfilled. 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 222 (Earthworm Reproduction Test (Eisenia fetida/Eisenia andrei))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Details on sampling:

Not applicable.

Vehicle:

no

Details on preparation and application of test substrate:

- approx. 24 h before test start, artificial soil was prepared
- deionized water was added to dry components to adjust water content to approx. 40 - 60 % of WHC
- test item incorporated directly into the soil by mixing with a small quantity of finely ground quartz sand (10 g of vessel), such that the required test concentration was achieved once mixed with the artificial soil

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Details on test organisms:

- Eisenia fetida andrei
- source: original breeding animals were purchased from "W. Neudorff GmbH KG", An der Mühle 3, D-31860 Emmertal
- test animals: reared under ambient laboratory conditions in the test facility
- age of animals used in the test: adult worms (approximately 3 months old with clitellum)
- weight of animals used in the test: 313 - 466 mg/worm
- feeding: weekly during first 4 weeks, by adding ground hourse manure on the soil surface (last feeding at 4 weeks)

ACCLIMATION
- period: approx. 24 h in artificial soil (with food)

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

4 wk

Remarks:

4 weeks for adult mortality

Post exposure observation period:

4 weeks for juvenile development

Test temperature:

18-22 °C

pH:

test start: 6.23 - 8.17
test end: 6.05 - 7.71

Moisture:

test start: 34.8-35.0 %
test end: 34.7-35.1 %

Details on test conditions:

- light conditions: light/dark 16/8 h, artificial light (590 lx)
- food: air-dried and ground horse manure (5 g at test start)
- feeding frequency/amount: weekly, amount of manure depended on feeding activity
- test vessels: plastic, 18.3 x 13.6 x 6.4 cm, with lid pervious to air and light
- number of animals/vessel (= replicate): 10
- number of replicates/control group: 8
- number of replicates/treated group: 4
- number of animals/control group: 80
- number of animals/treated group: 40
- amount of soil/test vessel: 556 g dry weight (corresponding to approx. 750 g moist soil)
- total carbon content (%): 4.51 %
- total organic carbon content (%): 4.47 %
- light conditions:
* source: artificial light
* intensity: 590 lx
* duration: 16:8 light:dark

Nominal and measured concentrations:

nominal concentrations: 0, 250, 500, 1000, 2000, 4000 and 5000 mg test item/kg soil d.w.

Reference substance (positive control):

yes

Remarks:

Benlate

Duration:

4 wk

Dose descriptor:

NOEC

Effect conc.:

2 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

reproduction

Duration:

4 wk

Dose descriptor:

EC50

Effect conc.:

4 180 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

reproduction

Remarks on result:

other: 95% CL: 3346-4665 mg/kg soil d.w.

Duration:

4 wk

Dose descriptor:

NOEC

Effect conc.:

5 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

Ca(OH)2

Basis for effect:

mortality

Details on results:

Validity criteria for control group:
- adult mortality after 4 weeks: <= 10 %
- number of juveniles per replicate: >= 30
- coefficient of variation of reproduction: <= 30%

- Mortality at end of exposure period: 0% in all dose groups
- Total mass of adults at beginning of test: mean between 378.1 and 384.1 mg
- Changes in body weigth of live adults (% of initial weight) at end of exposure period: 31.8% (control), 29.1% (250 mg/kg), 28.8% (500 mg/kg), 32.8% (1000 mg/kg), 29.4% (2000 mg/kg), 26.8% (4000 mg/kg), 22.6% (5000 mg/kg)
- No. of offspring produced: mean numbers:129.5 (control), 123 (250 mg/kg), 126.5 (500 mg/kg), 125.3 (1000 mg/kg), 118 (2000 mg/kg), 77.3 (4000 mg/kg), 32.8 (5000 mg/kg)

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- Relevant effect levels: The number of juveniles was reduced by 67% and 100% compared to control at concentrations of 5 and 10 mg Benlate/kg soil d.w., respectively.

Reported statistics and error estimates:

- probit analysis according to the maximum likelihood methods was used for the calculation of EC50 (software ToxRat Professional 2.09)

Validity criteria fulfilled:

yes

Remarks:

Adult mortality: ≤ 10% (being 0% after 4 weeks). Number of juveniles per replicate: ≥ 30 (being 158, 144, 97, 128, 119, 135, 109 and 146). Coefficient of variation of variation of reproduction: ≤ 30% (being 15.8%).

Conclusions:

Calcium dihydroxide did not show significant adverse effects on survival and growth of the earthworm Eisenia fetida in artificial soil up to 5000 mg Calcium dihydroxide/kg soil dry weight, i.e. the highest rate tested.
The test item showed statistically significantly adverse effects on reproduction at 4000 and 5000 mg Calcium hydroxide/kg soil d.w. Therefore, the NOEC for reproduction was determined to be 2000 mg Calcium dihydroxide/kg soil dry weight. The EC50 for number of juveniles was calculated to be 4180 mg Calcium dihydroxide/kg soil dry weight.

Description of key information

Klimisch 1 study: short-term toxicity of calcium dihydroxide on mortality and biomass of the earthworm Eisenia fetida (Friedrich, 2007b).
Klimisch 1 study: chronic study on the effect of Ca(OH)2 on the reproduction of the earthworm Eisenia fetida in an artificial soil (Friedrich, 2007a).
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

Long-term EC10, LC10 or NOEC for soil macroorganisms:

2 000 mg/kg soil dw

Additional information

The short-term toxicity of calcium dihydroxide on mortality and biomass of the earthworm Eisenia foetida (Friedrich, 2007b) was carried out according to OECD test guideline 207. The study is well-documented, all validity criteria are fulfilled. As such a Klimisch 1 score was assigned to the study. After 14 days, no significant effect on both mortality and biomass was observed up to the highest tested dose (5000 mg Ca(OH)2 /kg dw).

The chronic study on the effect of calcium dihydroxide on the reproduction of the earthworm Eisenia foetida (Friedrich, 2007a), was carried out according to OECD test guideline 222. The study is well-documented, all validity criteria are fulfilled. As such a Klimisch 1 score was assigned to the study. The study resulted in a 4w-EC50 of 4180 mg Ca(OH)2 /kg soil dw and a 4w-NOEC of 2000 mg Ca(OH)2 /kg soil dw.

The acute toxicity to earthworms of calcium carbonate (nano) was assessed in a study performed according to OECD TG 207 under GLP (Goodband, 2010). Eisenia foetida were exposed to calcium carbonate in a limit test at 1000 mg/kg in soil for 14 days. There were no significant mortalities or sub-lethal effects observed. Hence, the 14 day LC50 value was >1000 mg/kg soil dw and the NOEC was 1000 mg/kg soil dw. Calcium carbonate is therefore not toxic to earthworms up to a concentration of 1000 mg/kg soil dw.

Long term toxicity tests are not available for calcium carbonate, but given the ubiquitous nature of calcium and carbonate ions in the environment it is considered that calcium carbonate will not have a detrimental effect on soil macroorganisms over an extended time period and it would be expected that any potential toxicity will be limited by its solubility when compared to calcium dihydroxide.

In conclusion, both calcium dihydroxide and calcium carbonate show no effects when tested up to limit doses of 5000 mg/kg dw and 1000 mg/kg dw, respectively in acute tests. In a chronic study, calcium dihydroxide did show significant adverse effects on reproduction at 4000 and 5000 mg/kg soil dw and the NOEC was determined to be 2000 mg/kg soil dw. No explanation for the toxicity observed is given in the study report, however, given the large difference in solubility between calcium dihydroxide/ calcium oxide and calcium carbonate, it would be expected that such effects will be mitigated when exposure to high concentrations of calcium carbonate occurs. On this basis, it may be concluded that the results for the read-across substance calcium dihydroxide represent a worse-case for grades of calcium oxide containing up to 35% calcium carbonate.