Dodecamethylcyclohexasiloxane

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:

2007-08-28 to 2009-02-13

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: Stability and concentration verification of the samples was determined daily. Samples were collected from one analytical replicate of each treatment group.

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 5.1 μg/L. A preliminary stock solution was prepared by adding 0.102 g of the substance to a 200 mL volumetric flask (stock concentration 0.51 mg/mL). The flask was then brought to volume with dimethyl formamide (DMF) and inverted to mix. From the preliminary stock, 1 mL was removed and added to a 10 mL volumetric flask and brought to volume with DMF (0.051 mg/mL). The flask was inverted to mix. Four additional stock solutions were prepared at concentrations of 0.026, 0.013, 0.0064 and 0.0032 mg/mL by 50% serial dilution of the primary stock with DMF. DMF 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 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:

24.2 to 24.4 ºC

pH:

7.0 - 7.2 at start of test

7.3 - 7.7 on Day 1

7.4 to 7.9 on Day 2

8.7 to 9.5 on Day 3

pH of test media blanks ranged between 7.1 and 7.4

Dissolved oxygen:

Not reported

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 0 (Solvent control), 0.32, 0.64, 1.3, 2.6 and 5.1 μg/L.

Geometric mean measured concentrations: -, -, 0.15, 0.35, 0.60, 1.1 and 2.0 μg/L

The test results are reported and interpreted with reference to the 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 cells density: 875222 (Control), 760111 (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 - 835 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.:

> 2 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.:

> 2 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.:

>= 2 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.:

>= 2 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)	Measured concentration Day 0 (μg/L)	Measured concentration Day 1 (μg/L)	Measured concentration Day 2 (μg/L)	Measured concentration Day 3 (μg/L)	Geometric mean (μg/L)	Percent of nominal
0 (Control)	BLQ*	BLQ	BLQ	BLQ	-	-
0 (Solvent control)	BLQ	BLQ	BLQ	BLQ	-	-
0.32	0.29	0.19	BLQ	BLQ	0.15	45
0.64	0.45	0.36	0.34	0.26	0.35	54
1.3	0.70	0.67	0.55	0.50	0.60	46
2.6	1.1	1.2	1.1	1.1	1.1	43
5.1	1.5	2.1	2.5	2.1	2.0	40

*BLQ = Below Limit of Quantification

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	18624	124424	875222	-2.8	-15
0 (Solvent control)	5000	19816	115962	760111	0	0
0.15	5000	18407	125891	655089	3.0**	14**
0.35	5000	19927	122480	732244	0.77	3.7
0.60	5000	17067	122711	821467	-1.5	-8.1
1.1	5000	18153	111004	725000	0.95	4.6
2.0	5000	18636	116064	802933	-1.1	-5.7

**Significantly different from Control (p<0.05)

Validity criteria fulfilled:

yes

Conclusions:

A 72-hour EC50 value of >2.0 μg/L and NOEC of ≥2.0 μg/L have been determined for the effects of the test substance on growth rate of Pseudokirchneriella subcapitata.

Description of key information

Algae: (72 hour): EC₅₀ >2.0 μg/l; NOEC ≥2.0 μg/l, effects of the test substance on growth rate of Pseudokirchneriella subcapitata.

Additional information

Reliable test results are available for toxicity to aquatic algae.

A 72 hour EC₅₀ value of >2.0 μg/l and NOEC of ≥2.0 μg/l have been determined for the effects of the test substance on growth rate of Pseudokirchneriella subcapitata in accordance with OECD TG 201 and in compliance with GLP (Dow Corning, 2009). The results have been obtained under static conditions and are expressed relative to geometric mean measured concentrations of the substance.

In view of the hydrolysis half-life of the test substance and the exposure period of the test, it is likely that the test organisms were exposed primarily to the tested substance rather than its degradation products.