Potassium superoxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

other: evidence from degradation product

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Justification for type of information:

Refer to the section 13 of IUCLID dataset for details. The chronic toxicity study with the degradation product is considered sufficient to fulfil the information requirements as further explained in the provided endpoint summary.

Reason / purpose for cross-reference:

read-across source

Principles of method if other than guideline:

The study objective was to determine the hydrogen peroxide concentrations that have no effect on the time to death, growth, production, and gender ratio of young produced from Daphnia magna during 21 days of continuous exposure.

GLP compliance:

no

Analytical monitoring:

yes

Vehicle:

no

Details on test solutions:

Working solutions containing hydrogen peroxide were prepared in 19-L glass jars with purified deionized water to a specific resistance of N17.8mΩcm−1 with a Barnstead E-pure water purification system, Dubuque, IA). The test system was operated for 2 days to stabilize 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 hydrogen peroxide concentrations in pooled samples from each test group were verified.

Test organisms (species):

Daphnia magna

Details on test organisms:

24 h old D.magna.

Test type:

flow-through

Total exposure duration:

21 d

Post exposure observation period:

OBSERVATIONS/MEASUREMENTS:

- First generation daphnid length measurement

A wet mount of each first generation daphnid surviving to the end of the trial was prepared. Daphnid length was determined by first making an image of the Daphnia with a digital camera (Coolpix 5000; Nikon) through a microscope (E600; Nikon). The image was then loaded into an imaging software (Image ProExpress) designed to measure microscopic and macroscopic organisms. Length (top of the head to the base of the spine) was measured using the software. The software was calibrated from an image of a micrometer. Accuracy of the calibration was verified periodically during measurement sessions. Daphnia were preserved in the 4% formalin–sucrose solution for 4 months at about 21°C before length was determined.

- Determination of progeny gender

The gender of a brood was determined by inspecting a subsample of 10 to 20 second generation Daphnia from each brood. Gender was determined for each daphnid with the aide of a dissecting scope. Daphnia were preserved in the 4% formalin–sucrose solution for 4 months at about 21°C before brood gender was determined.

Hardness:

CaCO3 and total hardness ranged from 168 to 172 mg/L. Alkalinity ranged from 123 to 127 mg/L.

Test temperature:

The mean temperature was 20.1°C.

pH:

The daily pH values ranged from 7.45 to 7.99.

Dissolved oxygen:

The daily dissolved oxygen concentrations ranged from 7.93 to 10.0 mg/L.

Nominal and measured concentrations:

exposure concentrations: 0.0, 0.32, 0.63, 1.25, 2.5, and 5.0 mg/L

Details on test conditions:

CONDITIONS:

Daphnia were maintained in the following conditions: water temperature, 20°C; lighting, 16 h of incandescent light and 8 h of darkness; and light intensity, b600 lx.

Daphnia food was prepared by following:
Bread machine yeast (8.5 g), 12 g of Spirulina microfine dry powder microalga, 150 mL of Micro•Vert™ invertebrate food, and 500 mL of deionized water were mixed in a blender at medium high speed for 3 min. After blending, the mixture was poured into a glass flask, the blender cup rinsed with 500 mL of deionized water, and the water added to the flask. The food was stored at about 4°C for no more than 10 days. The food was mixed on a stir plate for more than 3 min before offering to Daphnia.

EXPERIMENTAL DESIGN:
A flow-through, continuous exposure test system was developed to expose Daphnia magna to an unstable compound 35% Perox-Aid®.
The experimental design included 6 test groups with each group represented with one of the following exposure concentrations: 0.0, 0.32, 0.63, 1.25, 2.5, and 5.0 mg/L. There were 10 test chambers per test group. Each chamber was assigned to 1 of 10 blocks. A block was a 2×3 configuration of test chambers. Test chambers were randomly assigned to blocks so that each of the 6 test groups were represented in each block (a randomized block design in a 2×3 configuration). A mobile, 24-h old Daphnia was transferred to each test chamber upon study initiation.
The mean flow rate through all chambers was 5.0 mL/min.

Exposure system
The experimental phase was conducted in an environmental chamber where the air temperature was maintained at about 20 °C. The exposure system consisted of test chambers supported on a platform elevated above a fiberglass tank. Each test chamber was a 250-mL glass beaker with a 12-mm hole drilled through the bottom. A holewas drilled through a silicone stopper (size 16D), a glass standpipe inserted through the stopper, and the stopper inserted into the hole at the bottom of the test chamber. Polyethylene tubing delivering well water from a glass distribution box to the test chamber was secured to the rim with a tubing clip. Six distribution boxes were mounted above test chambers. The bottom of each box had 10 silicone stoppers plugging 10 holes and 1 hole pluggedwith a stopper and glass standpipe for overflow. The 10 silicone stoppers were pierced with a 2-cm piece of 18 gauge stainless steel tubing. The PE160 tubing delivering water to the test chamber was slipped over the piece of 18 gauge tubing protruding from the stopper. A head box (a 37.9-L glass aquarium) was mounted above the distribution boxes. The temperature of well water flowing into the head box was controlled by a thermocouple and electronic mixing valve. A teflon stopcock attached to tubing controlled flow into the distribution box. A second length of tubing was attached to the effluent end of the teflon stopcock. A polycarbonate three-way stopcock was attached to the effluent end of the tubing. Hydrogen peroxide solution entered the flow stream through the three-way stopcock where it mixed with well water from the head box, flowed into the distribution box, and then to test chambers through the PE160 tubing at about 5.0 mL min−1 producing about 35 volume exchanges per 24 h.

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

< 0.63 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks:

no significant effect on the total number of young produced

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.32 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth

Details on results:

First generation Daphnia survival
- From the concentration of 1.25 mg/L there were treatment-related effects on D. magna survival (one Daphnia died, by study day 15).
- 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 test 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.

Body length
- The length of Daphnia was inversely related to hydrogen peroxide concentration (P=0.01). The length of Daphnia from the 0 mg/L test group was significantly greater than the lengths of Daphnia from the 0.32, 0.63, and 1.25 mg/L test groups. The lengths of Daphnia from the 0.32 and 0.63 mg/L test groups were significantly greater than the length of Daphnia from the 1.25 mg/L test group (p=0.01), but were not significantly different from each other.

Daphnia production time
- Test substance significantly impacted the time for Daphnia to produce their first brood (p=0.0030).
- Test substance significantly reduced the total number of broods produced (p=0.04). The total numbers of broods produced in the 0, 0.32, 0.63, and 1.25 mg/L test 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 test group (P 0.01).

Number of young individuals
- The total number of young produced was inversely related to the test substance concentration (p=0.04).
-The total numbers of young produced in the 0, 0.32 and 0.63 mg/L test groups were significantly greater than the total numbers of young produced in the 1.25 and 2.5 mg/L test groups (P 0.05).
- Significantly more young were produced in the 1.25 mg/L test group than in the 2.5 mg/L test group (P=0.01).
- The test substance had no significant effect on the gender ratio of young produced.

Validity criteria fulfilled:

not specified

Conclusions:

Under the study conditions, the 21 d NOEC of the substance for reproduction and growth in Daphnia magna were determined to be 0.63 and 0.32 mg/L respectively.

Executive summary:

A study was conducted to determine the chronic toxicity of the degradation product hydrogen peroxide to the growth and reproduction in Daphnia magna. A flow-through, continuous exposure test system was developed to expose Daphnia magna to an unstable compound. The study design consisted of 6 treatment groups (10 test chambers each) with target test substance concentrations of 0.0, 0.32, 0.63, 1.25, 2.5, and 5.0 mg/L. The study was initiated with 24 h old Daphnia (1 daphnid per chamber) that were exposed to the test substance for 21 days. Under the study conditions, concentrations ≤1.25 mg/L had no significant effect on the time to death compared to controls and no significant effect on the time to first brood production and the number of broods produced. Concentrations ≤0.63 mg/L had no significant effect on the total number of young produced. Concentrations ≥0.32 mg/L had a negative effect on Daphnia growth. The test substance had no significant effect on the gender ratio of young produced. Under the study conditions, the 21 d NOEC of the substance for reproduction and growth in Daphnia magna were determined to be 0.63 and 0.32 mg/L respectively (Meinertz, 2008).

Description of key information

Under normal use conditions, potassium superoxide is not anticipated to be exposed to the aquatic environment. Exposure to the water is only possible if KO2 is accidentally released. However, when exposed, potassium superoxide reacts rapidly with water to produce potassium hydroxide (KOH), oxygen (O2) and potassium hydrogen peroxide (KHO2), which slowly degrades to KOH, H2O2 (hydrogen peroxide) and O2. Therefore, aquatic toxicity of KO2 could be anticipated to be due, in part, to the degradation product H2O2. KOH further dissociates into potassium and hydroxyl ions which constitute normal ion pool of the medium. On the other hand, hydrogen peroxide is likely to degrade within a short time in aquatic medium due to many alternative and competitive degradation pathways. As a result, the contribution of toxicity from hydrogen peroxide is likely to be low. Overall, the aquatic toxicity of potassium superoxide is likely to be low and a quantitative estimation of the hazard potential will not be appropriate due to its rapidly changing degradation kinetics.

Additional information

A study was conducted to determine the chronic toxicity of the degradation product hydrogen peroxide to the growth and reproduction in Daphnia magna. A flow-through, continuous exposure test system was developed to expose Daphnia magna to an unstable compound. The study design consisted of 6 treatment groups (10 test chambers each) with target test substance concentrations of 0.0, 0.32, 0.63, 1.25, 2.5, and 5.0 mg/L. The study was initiated with 24 h old Daphnia (1 daphnid per chamber) that were exposed to the test substance for 21 days. Under the study conditions, concentrations ≤1.25 mg/L had no significant effect on the time to death compared to controls and no significant effect on the time to first brood production and the number of broods produced. Concentrations ≤0.63 mg/L had no significant effect on the total number of young produced. Concentrations ≥0.32 mg/L had a negative effect on Daphnia growth. The test substance had no significant effect on the gender ratio of young produced. Under the study conditions, the 21 d NOEC of the substance for reproduction and growth in Daphnia magna were determined to be 0.63 and 0.32 mg/L respectively (Meinertz, 2008).