Trimethoxy(methyl)silane

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2007-06-08 to 2007-06-15

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Mortality at the intermediate concentrations may be related to the physical mixture of the solvent and test article.

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Measurement of test concentrations in one replicate test chamber of each treatment group at test initiation and test termination.

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Test solutions were prepared by direct addition of the test article to dilution water (100 and 200 mg/L treatment groups) or by addition of stocks prepared in DMF (13, 25 and 50 mg/L treatment groups).  The solvent solutions were used in the lower concentration treatments in order to facilitate accurate delivery of smaller amounts of the tests substance in the diluter system. The solvent control, 13, 25 and 50 mg/L treatment groups contained 0.1 mL/L DMF.  No solvent was delivered in the 100 and 200 mg/L treatment groups.  The diluter flow rate provided 32 volume additions/day.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source, supplier, any pretreatment, breeding method:  Dow Corning in-house Cultures. The cultures were initiated with organisms obtained from Aquatic Biosystems Inc., Fort Collins, Colorado.      

- Age at study initiation:  <24 hours old

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

Hardness 105 mg/L as CaCO3, Alkalinity 65 mg/L as CaCO3

Test temperature:

19.5 to 21.0ºC

pH:

7.5-7.8

Dissolved oxygen:

7.8-8.9 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: Negative Control, Solvent Control, 13, 25, 50, 100 and 200 mg/L 

Mean measured concentrations:
Recoveries of methyltrimethoxysilane were low because the hydrolysis half-life is approximately 2.2 hours.

The results are reported with reference to mean measured concentrations.

Details on test conditions:

TEST SYSTEM

- Exposure vessel type:  The test compartments were 300-mL glass beakers with 2 holes on opposite sides covered with nylon screen.  The test chambers were placed in 7.5-L polyethylene aquaria containing 3.4 L of test solution.  

- Dilution water source:  Dechlorinated Municipal Water

- Dilution water chemistry (hardness, alkalinity, pH, TOC, TSS, salinity, Ca/Mg ration, Na/K ratio):  Hardness 105 mg/L as CaCO3, Alkalinity 65 mg/L as CaCO3, pH 7.6, Conductivity 319  mhos/cm and Total Residual Chlorine <10  g/L

- Lighting (quality, intensity, and periodicity):  Wavelength similar to natural sunlight, 55 to 66 foot-candles, 16 hours light:8 hours dark

- Water chemistry in test:  DO, pH and temperature measured in each test chamber daily

- Element (unit) basis (i.e., immobilization):  Mortality and immobilization

- Test design (number of replicates, individuals per replicate, concentrations):  Two replicates/treatment, 10 individuals/replicate

- Method of calculating mean measured concentrations:  Arithmetic mean.

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 122 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

>= 122 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

>= 200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

- Immobilisation of control: 0

Reported statistics and error estimates:

No significant mortalities were recorded in the highest treatment. An EC50 value could therefore not be determined.

Table 1. Test results

Nominal concentration (mg/L)	Mean measured concentration (mg/L)	Percentage immobilisation after 24 hours	Percentage immobilisation after 48 hours
0 (Control)	-	0	0
0 (Vehicle control)	-	0	0
13	6	0	0
25	15	0	35
50	31	0	75
100	56	0	0
200	122	0	0

Was control response satisfactory: Yes

The effects observed in the 15 and 31 mg/L treatments were thought to relate to physical interaction with the test substance and solvent.

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 value of >122 mg/L and NOEC of ≥122 mg/L have been determined for the effects of the substance on mobility of Daphnia magna. Under the flow-through conditions used in the test the results reflect exposure to the test substance.

Description of key information

Short-term toxicity to aquatic invertebrates: 48-hour EC₅₀ >122 mg/l (measured concentration), mobility of Daphnia magna.

Additional information

A 48-hour EC₅₀ value of >200 mg/l, based on nominal concentration (highest concentration tested), and >122 mg/l, based on measured concentration, has been determined for the effects of the registered substance on mobility of Daphnia magna (Dow Corning Corporation 2007). The test was carried out in accordance with test guideline OECD 202 and in compliance with GLP. Under the flow-through conditions used in the test it is likely that the Daphnia were exposed to a mixture of the parent substance and its hydrolysis products. This is reflected in the nominal versus measured test concentrations.

To support the chemical safety assessment of the hydrolysis product, methylsilanetriol (CAS 2445-53-6; EC No. 219-489-9), data have been read-across from a structural analogue which rapidly hydrolyses to methylsilanetriol. A 96-hour EC₅₀ value of >500 mg/l (nominal concentration) (highest concentration tested) has been determined for the effects of triethoxy(methyl)silane (CAS 2031-67-6; EC No. 217-983-9) on mobility of Daphnia magna (Hazelton, 1994), carried out in accordance with EU test Method C.3 and in compliance with GLP.

In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, methylsilanetriol, by applying a molecular weight correction: (MW of silanol = 94.14 / MW of parent = 178.31) * (CONCENTRATION OF PARENT = >500) = >264 mg/l as methylsilanetriol.

Refer to Section 6 endpoint summary, Section 7.0 of CSR, for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.