Dimethoxydimethylsilane

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

Please refer to the analogue approach justification provided in Section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 118 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 118 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Conclusions:

A 72-hour EC50 value of >118 mg/L and a NOEC of ≥118 mg/L have been determined for the effects of the source substance on growth rate of Pseudokirchnerella subcapitata (OECD 201, GLP). The source substance is the hydrolysis product of the target substance. Since the hydrolysis half life is < 1 h, the results derived for the source substance describe additionally the effects of the the target substance.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-08-05 to 2008-08-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

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: Samples of each test medium were taken at the start and end of the test. They received no further treatment prior to analysis.

Vehicle:

no

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Source (laboratory, culture collection): Test organisms were obtained from in-house cultures. The source of the original brood stock was strain UTEX 1648, from the University of Texas at Austin, The Culture Collection of Algae, Botany Department, Austin, Texas, in March 1998. The identity of the species was verified by the supplier.

- Method of cultivation: Algal cultures were maintained at 24+/-2ºC on a rotary shaker set at approximately 100 rpm, under continuous cool white fluorescent lighting at a range of 400 ± 100 foot candles (4300+/-1075 lux). The cultures were periodically transferred axenically to new AAM.

- Culture medium: Algal Assay Medium was prepared based on ASTM guideline E 1218-04. The final concentration of each nutrient in the medium is presented in Appendix A. All stocks used to prepare the medium were prepared with sterile distilled water and were filter sterilized (0.22 μm). Medium was prepared with commercially available distilled water that is analyzed annually for contaminants. No contaminants have been shown to be present which might adversely impact the viability of the cultures or study.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

Not reported

Test temperature:

23.8 to 24.0 °C

pH:

pH at test initiation ranged from 7.4 to 7.5. At test termination, pH in the flasks that contained algae ranged from 8.0 to 9.0 and pH of media blanks ranged from 7.6 to 7.8

Nominal and measured concentrations:

Nominal test concentrations: 0 (Control), 7.5, 15, 30, 60 and 120 mg/L

Mean measured test concentrations in treated media: 7.9, 18, 28, 57 and 118 mg/L; which is 105, 121, 93, 95 and 98% of nominal.

The results are expressed relative to mean measured concentrations.

Details on test conditions:

TEST SYSTEM

- Test Apparatus: Test vessels were sterile 250-mL Erlenmeyer flasks covered with a sponge closure containing approximately 100 mL of test solution. Test vessels were labeled with the study number, concentration, and replicate.

- Initial cell density: 10000 cells/ml

- Test Conditions: Test vessels were placed in a temperature controlled incubator and positioned on rotary shakers that were set at approximately 100 rpm. In addition, the incubator was set at a temperature of 24+/-2ºC and under continuous cool white fluorescent lighting at a range of 412 – 825 foot-candles (4440 - 8880 lux).

Temperature was measured in a beaker of water adjacent to the shakers in the incubator and light readings were recorded at five indiscriminate areas on the shaker tables daily during the test. Readings of pH were completed on bulk preparations of each treatment group at test initiation. To maintain axenic conditions, pH readings for each test vessel were measured only at 72 hours.

- Observations: Samples for cell counts were collected on Day 0 for the original culture and test inoculums. Samples for cell counts were also collected from each test vessel at 24, 48 and 72 hours (within 1 hour). Samples were diluted with Isoton® II diluent solution and counted immediately using a Coulter® Counter. Dilution volumes were recorded in the raw data. Dilution samples of the medium and diluent blanks were counted at 24, 48, and 72 hours to account for any interference of particles. At test termination, samples were pooled by treatment and visually inspected for atypical cell morphology. Visual examination showed no concentration-dependent changes in shape, color or size.

- Light intensity: 446 to 620 foot-candles

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 118 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 118 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

- Exponential growth in the control (for algal test): yes, Control cell density for this study increased 122 fold by 72 hours.

Reported statistics and error estimates:

ECx values at 72 hours were calculated using linear interpolation or estimated by visual examination of the data.

Yield (biomass) and growth rate data were analyzed for normality and homogeneity of variance using the Shapiro-Wilk’s test and Bartlett’s test, respectively. The no observed effect concentration (NOEC) values were determined for growth rate and yield at 72 hours using Dunnett’s test. All statistical analyses were performed using TOXSTAT Version 3.5 software

Table 1. Measurement of Test Concentrations

Nominal Concentration (mg/L)	Day 0 Measured Concentration  (mg/L)	Day 3 Measured Concentration (mg/L)	Mean Measured Concentration (mg/L)	Percent of Nominal
Control	ND	ND	--	--
7.5	5.9	10	7.9	105
15	18	19	18	121
30	25	31	28	93
60	55	60	57	95
120	114	122	118	98
ND = Not Detected

 

Table 2. Mean Cell Densities (cells/mL)

Mean Measured Concentration (mg/L)	0-hour	24-hour	48-hour	72-hour
Negative Control	~10000	43433	240424	1222333
7.9	~10000	41551	246551	1276867
18	~10000	37384	232924	1216000
28	~10000	38551	217216	1129333
57	~10000	42022	228560	1090778
118	~10000	35773	201429	990800

Algal cell growth in the control was exponential during the 72-h exposure period. Cell densities were used to calculate the average specific growth rates and yield for each test concentration. 

Validity criteria fulfilled:

yes

Conclusions:

A 72-hour EC50 value of >118 mg/L and a NOEC of ≥118 mg/L have been determined for the effects of the test substance on growth rate of Pseudokirchnerella subcapitata.

Description of key information

ErC50 (72 h) > 118 mg/L (meas. arithm. mean, OECD 201, P. subcapitata; read across from silanol hydrolysis product DMSD)
NOErC (72 h) ≥ 118 mg/L (meas. arithm. mean, OECD 201, P. subcapitata; read across from silanol hydrolysis product DMSD)

Key value for chemical safety assessment

EC50 for freshwater algae:

118 mg/L

EC10 or NOEC for freshwater algae:

118 mg/L

Additional information

Experimental data for dimethoxy(dimethyl)silane (CAS No. 1112-39-6) are not available. However, since dimethoxy(dimethyl)silane hydrolyses rapidly to dimethylsilanediol and methanol (DT50 < 0.6 h) the hydrolysis products rather than the parent substance should be considered for the assessment and read-across data for the hydrolysis product, dimethylsilanediol, are considered appropriate for the assessment. The other hydrolysis product, methanol, is well described in the public domain literature. It has a low environmental hazard profile and is therefore not considered contributory to the overall aquatic toxicity of the registered substance (OECD SIDS, 2004). Thus, the ecotoxicity assessment was based on the silanol hydrolysis product dimethylsilanediol (DMSD, CAS No. 1066-42-8).

The toxicity to aquatic algae was investigated according to OECD 201 (GLP). In a static test, Pseudokirchneriella subcapitata was exposed to dimethylsilanediol at concentrations of 7.5, 15, 30, 60, and 120 mg/L (nominal) including a control (Dow Corning, 2009c). The actual exposure concentrations were measured by HPLC/RID analysis. Mean measured concentrations were 93 - 121% of nominal. Thus, the effect concentrations were based on the measured concentrations. The ErC50 (72 h) was estimated to be >118 mg/L, the highest concentration tested. The NOEC (72 h) for growth rate is ≥118 mg/L.

 

Reference
OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.