Octamethyltrisiloxane

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2007-08-07 to 2009-01-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Water samples were daily from each test chamber. Water samples (10 mL) were collected using a 10 mL volumetric pipette and placed in a 20-mL glass scintillation vial.

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: The nominal test concentrations were selected on the basis of the reported water solubility of the test substance 34 μg/L. A preliminary stock solution was prepared by adding 0.00333 g of the substance to a 10 mL volumetric flask (stock concentration 333 mg/L). The flask was then brought to volume with acetone. The specific activity of the primary stock solution was determined to be 173.4 μCi/mg. Four additional stock solutions were prepared at concentrations of 167, 83, 42 and 21 mg/L by 50% serial dilution of the primary stock with acetone. Acetone only (0.1 mL/L) was used for the solvent control.

To prepare the test solutions, 0.5 mL of the appropriate stock was added to 5 L algal assay medium in a 5 L volumetric flask. The flask was then inverted to mix. The resulting solutions were clear and colourless. Approximately 300 mL of test solution was added to each of thirteen replicates and the media blank for each treatment group. Remaining test solution in the volumetric flasks was used for initial water quality measurements.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM

- Strain: UTEX 1648, obtained in March 1998 from the University of Texas at Austin

- Source (laboratory, culture collection): In-house cultures

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

Not reported

Test temperature:

24.0 to 24.1 ºC

pH:

7.0 - 7.3 at start of test

7.1 - 7.5 on Day 1

7.2 to 7.5 on Day 2

8.9 to 9.7 on Day 3

pH of test media blanks ranged between 7.2 and 7.3

Dissolved oxygen:

Not reported

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 0 (Solvent control), 2.1, 4.3, 8.5, 17 and 34 μg/L.

Geometric mean measured concentrations: -, -, 0.5, 1.2, 2.3, 4.6 and 9.4 μg/L

The geometric mean measured concentrations in the treated media were 24, 28, 27, 27 and 28% of the nominal values respectively

The test results are reported and interpreted with reference to the geometric mean measured concentrations.

Details on test conditions:

TEST SYSTEM

- Test vessel: 300 mL BOD bottles

- Type (delete if not applicable): sealed with a glass stopper

- Material, size, headspace, fill volume: glass, 300 mL, completely full and containing two glass marbles to aid continuous suspension of the algae throughout the test.

- Aeration: None

- Initial cells density: 5000 cells/mL

- Control end cell density: 755844 (Control), 699756 (solvent control)

- No. of vessels per concentration (replicates): 13

- No. of vessels per control (replicates): 13

- No. of vessels per vehicle control (replicates): 13


GROWTH MEDIUM

- Standard medium used: yes


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Algal assay Medium (AAM) based on ASTM Guideline E 1218-04 except that the concentration of NaHCO3 was increased from 15 mg/L to 300 mg/L to supply the CO2 needed in the closed bottle test system.

- Culture medium different from test medium: No

- Intervals of water quality measurement: Daily


OTHER TEST CONDITIONS

- Sterile test conditions: yes

- Adjustment of pH: yes

- Photoperiod: Continuous

- Light intensity and quality: Continuous cool fluorescent white lighting at a range of 412 - 825 foot-candles (4440 to 8880 Lux).


EFFECT PARAMETERS MEASURED: Cell concentrations measured daily

- Determination of cell concentrations: Coulter Counter


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 9.4 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 9.4 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

other: yield (equivalent to biomass)

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 9.4 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 9.4 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

other: yield (equivalent to biomass)

Details on results:

- Exponential growth in the control (for algal test): yes

Reported statistics and error estimates:

The NOEC concentrations were determined using Dunnett's test. The analysis was performed using TOXSTAT Version 3.5 software.

Table 1. Results of analysis of test media

Nominal concentration (μg/L)	Geometric mean (μg/L)	Percent of nominal
0 (Control)	<LoQ*	-
0 (Solvent control)	<LoQ*	-
2.1	0.50	24
4.3	1.2	28
8.5	2.3	27
17	4.6	27
34	9.4	28

*Limit of Quantitation

Table 2. Test results

Geometric mean measured concentration (μg/L)	Mean cell density at start of test (cell/mL)	Mean cell density after 24 hours (cell/mL)	Mean cell density after 48 hours (cell/mL)	Mean cell density after 72 hours (cell/mL)	Inhibition of growth rate (%)*	Inhibition of yield (biomass) (%)*
0 (Control)	5000	12109	102562	755844	-	-
0 (Solvent control)	5000	16647	92947	699756	-	-
0.50	5000	16527	106527	662889	1.1	5.3
1.2	5000	17698	108558	662978	1.1	5.3
2.3	5000	16489	111276	648533	1.6	7.4
4.6	5000	15196	105311	654933	1.3	6.5
9.4	5000	14084	98676	774267	-2.0	-11

*Compared with solvent control

Validity criteria fulfilled:

yes

Conclusions:

A 72-hour EC50 value of >9.4 μg/L and NOEC of ≥9.4 μg/L have been determined for the effects of the test substance on growth rate and biomass (yield) of Pseudokirchnerella subcapitata based on mean measured concentrations.

Description of key information

Short-term toxicity to algae: 72 hr EC₅₀ (>9.4 μg/L (measured, growth rate and biomass (yield), highest concentration tested); 72 hr NOEC: ≥9.4 μg/L: (measured, growth rate and biomass (yield), highest concentration tested) (OECD 201).

Additional information

A 72-hour EC₅₀ value of >9.4 μg/L and NOEC of ≥9.4 μg/L (measured, highest concentration tested) have been determined for the effects of the test substance on growth rate and biomass (yield) of Pseudokirchneriella subcapitata based on mean measured concentrations.