Reaction mass of calcium dihydroxide and calcium peroxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: In accordance with the ASTM Designation E 1193-97 for conducting Daphnia magna life-cycle toxicity tests. High flow rate may have affected test results to some extent.

Qualifier:

according to guideline

Guideline:

other:

Deviations:

yes

Remarks:

Increased flow rate was necessary to maintain hydrogen peroxide concentration

Principles of method if other than guideline:

ASTM Designation E 1193-97: 21-day flow through bioassay

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

Hydrogen peroxide concentrations were measured each day in test chambers before feeding was initiated. Approximately 2.5 mL of water from each chamber of a common test group were pooled.

Vehicle:

no

Details on test solutions:

Working solutions containing hydrogen peroxide were prepared in 19-L glass jars with purified deinonised water (water deinoised to a specific resistance of > 17.8 mOhm/cm with a Barnstead E-pure water purification system). The test system was operated for 2 days to stabilise the system before the study was initiated. Peristaltic pumps delivered working solutions continuously to the test system through the duration of the study. On study day 0, target concentrations in pooled samples from each test group were verified.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water flea
- Source: no data
- Age of parental stock (mean and range, SD): no data
- Age at begin of experiment: < 24 hours
- Feeding during test
- Food type: Mixture of Red Star bread machine yeast (8.5 g), Spirulina platensis microfine dry powder microalga (12 g), MicroVert invertebrated food (150 mL) and deionised water (500 mL)
- Amount: 300 microliter
- Frequency: 5 times a day


ACCLIMATION
- Acclimation period: no data
- Acclimation conditions (same as test or not): no data

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Post exposure observation period:

Not applicable

Hardness:

Alkalinity: 123 – 127 mg/L as CaCO3 and total hardness: 168 – 172 mg/L

Test temperature:

20.1°C ranging from 19.7 to 20.4 °C

pH:

7.45-7.99

Dissolved oxygen:

7.93 – 10.0 mg O2/L

Salinity:

Not applicable

Nominal and measured concentrations:

The nominal treatment level of 0.32, 0.63, 1.25, 2.5 and 5.0 mg/L

Details on test conditions:

Adjustment of pH: No
Aeration of dilution water: No
Quality/Intensity of irradiation: Incandescent light/< 600 Lux
Photoperiod: 16 h illumination daily
Replacement of chambers: every 4 to 5 days
Flow rate: 5.0 mL/min (range from 4.6 to 5.4 mL/min) - approximately 35 volume exchanges per day
Test chambers: 10 test chambers per test group; each chamber assigned to 1 of 10 blocks consisting of 2 x 3 test chambers
No. of animals per chamber: 1

Reference substance (positive control):

no

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.63 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

1.25 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Details on results:

Exposure to hydrogen peroxide concentrations greater 1.25 mg/L significantly increased the probability of death and decreased the time to death of Daphnia. Nine of ten first generation Daphnia associated with the 5.0 mg/L test group were dead by study day 2. The final mortality for that group occurred by study day 9. All first generation Daphnia associated with the 2.5 mg/L test group were dead by study day 19. Only 1 Daphnia died in the 1.25 mg/L test group on study day 15. In this same test group, one chamber was found overflowing on day 21 and the Daphnia missing. The Daphnia seemed normal the previous day and exposure to hydrogen peroxide was not considered to be the cause of death. Only one daphnid died in the 0.32 and 0.63 mg/L groups.
The length of Daphnia was inversely related to hydrogen peroxide exposure concentration. The length of the control group was significantly greater than the lengths of Daphnia from the 0.32, 0.63 and 1.25 mg/L groups. The length of Daphnia from the 0.32 and 0.63 mg/L groups were significanty greater than the length of Daphnia from the 1.25 mg/L group.
Hydrogen peroxide significantly impacted the time for Daphnia to produce their first brood (though data between the groups were ssomewhat varible). The total number of broods produced in the 0, 0.32, 0.63 and 1.25 mg/L groups were not significantly different from each other but were significantly greater than the total number of broods produced in the 2.5 mg/L group. The total number of young produced was inversely related to the hydrogen perxoide concentration. They were significantly greater in the 0, 0.32 and 0.63 mg/L groups than in the 1.25 or 2.5 mg/L groups.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Mortality and reproduction data were analysed using SAS statistical analyses (P ≤ 0.05); effects on body length and number of broods were analysed using maximum-likelihood estimation (Chi-square test).

Table 1: Hydrogen peroxide concentrations in pooled samples from test chambers where D. magna were continuously exposed for 21 days

Nominal concentrations (mg/L)	n samples	Mean concentrations (mg/L)	SD (mg/L)	Minimum daily measurement (mg/L)	Maximum daily measurement (mg/L)
0.0	21	0.02	0.01	0.01	0.03
0.32	21	0.34	0.02	0.30	0.38
0.63	21	0.63	0.06	0.47	0.73
1.25	21	1.27	0.26	0.56	1.88
2.5	19	2.61	0.24	2.03	2.90
5.0	9	5.00	0.53	4.45	5.90

Table 2: Body length of the first generation D. magna continuously exposed for 21 days

Nominal concentration (mg/L)	Mean length (mm)	95 % confidence limits (mm)	Range (mm)
0.0	4.616 a	4.512, 4.721	4.408 to 4.791
0.32	4.455 b	4.344, 4.565	4.143 to 4.715
0.63	4.391 b	4.281, 4.502	4.052 to 4.662
1.25	3.901 c	3.784, 4.018	3.675 to 4.206
2.5	NA #	NA	NA
5.0	NA	NA	NA
Mean lengths with the same letter are not statistically different (p > 0.05)
# NA = not applicable

Table 3: Days to production of the first brood and number of young produced in the first brood of D. magna continuously exposed for 21 days

Nominal concentration (mg/L)	Mean and range of days to first brood	Mean and range of number of young in first brood
0.0	11 (8-13) a, b	20 (1-45)
0.32	12 (10-16) a, c	22 (1-44)
0.63	10 (9-13) b	16 (2-34)
1.25	10 (8-13) b	8 (1-32)
2.5	16 (none) c	1 (none)
5.0	NA #	NA
Mean days to first brood with the same letter are not statistically different (p > 0.05)
# NA = not applicable, no young produced

Table 4: Second generation production from D. magna continuously exposed for 21 days

Nominal concentration (mg/L)	Mean number of broods per test chamber	Total number of broods produced in the test group	Total number of young produced in the test group
0.0	4.1	41 a	1516 a
0.32	4.0	40 a	1564 a
0.63	3.9	39 a	1388 a
1.25	4.0	40 a	1000 b
2.5	0.1	1 b	1 c
Total number of broods and total number of young produced with the same letter are not statistically different (p > 0.05)

Validity criteria fulfilled:

yes

Conclusions:

A test on chronic toxicity of hydrogen peroxide to Daphnia magna resulted in a NOEC of 0.63 mg/L and a LOEC of 1.25 mg/L.

Executive summary:

The chronic toxicity of hydrogen peroxide to Daphnia magna was tested in a 21 - day flow-through test according to ASTM Designation E1193 - 97 for conducting Daphnia magna life-cycle toxicity tests. The concentrations in the test solutions ranged from 0.32 to 5 mg/L (nominal). Concentrations were analysed continuously and found to match the nominal concentrations to a sufficient extent. A control with no exposure to hydrogen peroxide was included. Exposure to 2.5 and 5.0 mg/L killed all first generation Daphnia magna before the end of the testing period. Continuous exposure to hydrogen peroxide was found to decrease the body length of first generation Daphnia magna in a dose-dependent manner. The days to production of first brood was increased and the number of second generation Daphnia decreased in a dose-dependent manner. The NOEC value established in the study was 0.63 mg/L and the LOEC was found to be 1.25 mg/L, respectively.

Description of key information

No experimental study on the long-term toxicity of “reaction mass of calcium dihydroxide and calcium peroxide” to aquatic invertebrates is available. Nevertheless, a 21d- NOEC value can be derived from reliable information on hydrogen peroxide which is the primary hydrolytic degradation product of the reaction mass. The 21d- NOEC value for the reaction is 1.67 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

1.67 mg/L

Additional information

No experimental study on the long-term toxicity of “reaction mass of calcium dihydroxide and calcium peroxide” to aquatic invertebrates is available. Nevertheless, for this endpoint reliable information is available for hydrogen peroxide (H2O2), the primary hydrolytic degradation product of the reaction mass. The chemical reactions of the reaction mass in water are as follows:

- CaO2 + 2 H2O -> Ca2 + + 2 (OH)- + H2O2

- H2O2 + H2O -> 2 H2O + O2

- Ca(OH)2 -> Ca2 + + 2 OH

Calcium peroxide (CaO2) goes into the chemical reactions above rapidly (i.e. within 24 hours) as evidenced by a water solubility study.  In the water solubility test, 100 mg/L of “reaction mass of calcium dihydroxide and calcium peroxide” was completely dissolved and hydrogen peroxide subsequently occurred within 24 hours. Therefore, the use of test results obtained for its primary hydrolytic degradation product “hydrogen peroxide” for the assessment of long-term toxicity to aquatic invertebrate is considered appropriate. It is also to be noted that hydrogen peroxide itself is further decomposed to form water and oxygen, which are of no concern.

The long-term toxicity of hydrogen peroxide to Daphnia magna was tested in a 21d- flow-through test according to ASTM Designation E1193 - 97. The 21- day NOEC value established in the study was 0.63 mg/L based on reproductive output. From this value, a corresponding  21d-NOEC value for assessing the long-term toxicity of the reaction mass to aquatic invertebrates can be calculated by considering the hydrolytic reaction involved in the formation of hydrogen peroxide from calcium peroxide and the composition of the reaction mass (i.e. the reaction mass contains ca. 80% calcium peroxide). The amount of hydrogen peroxide generated binds in equimolar ratio to the amount of calcium peroxide.

Accordingly, 100 mg of the reaction mass contains 80 mg of calcium peroxide, which corresponds to 1.11 mmol of calcium peroxide available for the hydrolytic reaction. Thus, 1.11 mmol (= 37.74 mg) of hydrogen peroxide is formed upon hydrolysis of 100 mg of calcium peroxide.

Therefore, the 21d-NOEC value for the reaction mass can be calculated from the 21d-NOEC value for hydrogen peroxide (0.63 mg/L) as follows:

- 100 mg of the reaction mass yields 37.74 mg hydrogen peroxide.

- 1.67mg  of the reaction mass yields 0.63 mg hydrogen peroxide.

Consequently, the extrapolated 21d-NOEC value for the reaction mass is 1.67mg /L.