Trichlorosilane

Toxicity to terrestrial arthropods

Administrative data

Endpoint:

toxicity to terrestrial arthropods: short-term

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

Please see the cross-referenced supporting information to justify the waiving of terrestrial toxicity data.
Further discussion on the ecotoxicity of silicic acid producers can be found in the attached report “PFA, 2013x Analogue report Ecotoxicity of (poly)silicic acid producers_20130516”.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Adsorption/desorption: Low potential for adsorption to organic carbon.

Testing is waived in accordance with Column 2 of REACH Annex IX. The substance has a low potential for adsorption.

The substance hydrolyses very rapidly in contact with water, generating HCl and silanetriol. Further hydrolysis of silanetriol is then expected to occur rapidly to monosilicic acid and hydrogen. Both silanetriol and monosilicic acid exist only in dilute aqueous solutions and readily condense at concentrations above approximately 100 -150 mg/L as SiO₂ to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid. These hydrolysis products are inorganic substances which enter natural biogeochemical cycles; adsorption/desorption studies are not relevant. Based on their structure and predicted water solubilities, the hydrolysis products will have a high affinity for water and a low affinity for organic carbon and so a low potential for adsorption to the organic carbon. However, they may interact with the mineral content of soil. Amorphous polysilicic acid is a constituent of most soils.

Cross-reference 2

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Bioaccumulation: aquatic/sediment: Low potential for bioaccumulation

Testing is waived in accordance with Column 2 of REACH Annex IX. Direct or indirect exposure of aquatic organisms to the registered substance is very limited due to the instability of the substance in water. The substance hydrolyses very rapidly to monosilicic acid [Si(OH)₄], hydrochloric acid and hydrogen.

Silicic acid condenses at concentrations above approximately 100-150 mg/L as SiO₂ to give insoluble amorphous polysilicic acid. These hydrolysis products are inorganic substances which enter natural biogeochemical cycles.

Silicic acidis the bioavailable form of silica that can be absorbed by certain organisms in the environment. In these organisms, silicic acid, precipitated as insoluble amorphous silica, plays a structural and defensive role. In animals, silica is a trace nutrient.

Cross-reference 3

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2004-05-06 to 2004-05-08

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with GLP but no analysis of exposure concentrations

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Principles of method if other than guideline:

OECD. 2000. Guideline for Testing of Chemicals. Daphnia sp., Acute Immobilization Test. Revised Proposal tor Updating Guideline #202. October 2000.
U.S. EPA. 1975. Methods for Acute Toxicity Tests with Fish, Macroinvertebrates and Amphibians. Ecological Research Series (EPA-660/3-75-009). 61 pp.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 100 mg a.i./L stock solution was prepared by adding 0.215 mL of trimethoxysilane to 2.0 L of dilution water (based on a purity of 97.1% and a density of 0.957 g/mL). The solution was mixed overnight with a magnetic stir plate and Teflon®-coated stir bar.  Each test concentration was prepared by adding the appropriate amount of the 100 mg a.i./L stock solution to an intermediate vessel and bringing it to a final volume of 1.0 L with dilution water.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source: Springborn Smithers culture facility. 

- Method of culture: Daphnids were cultured in 1.0-L glass vessels containing 0.80 L of water. Water used to culture the daphnids was prepared in the same manner and has the same characteristics as the dilution water. Daphnids were fed a unicellular green algae, Ankistrodesmus falcatus (4 x 10E7cells/mL) and YCT (yeast, cereal leaves and flaked fish food) suspension daily, at a rate of 2.0 mL algae and 0.5 mL YCT solution per vessel per day. Daphnids were obtained by removing all immature daphnids from the culture vessel, thus isolating mature gravid daphnids <24 hours prior to initiating the test. Young produced by these organisms were subsequently pipetted into the test beakers.

- Age at study initiation: < 24 hours

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

Total hardness and alkalinity: 180 mg/L and 110 mg/L as CaCO3

Test temperature:

20 to 22ºC

pH:

7.7-8.0

Dissolved oxygen:

7.6-9.0 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 13, 22, 36, 60 and 100 mg a.i./L. (nominal)

Details on test conditions:

TEST SYSTEM

- Test vessel: The toxicity test was conducted in 250-mL glass beakers, each containing 200 mL of test solution.  

- Aeration: No aeration was provided to the test vessels.


TEST DESIGN

- Replication: Four replicate test vessels were established for each treatment lever and a dilution water control.

- Number of daphnids per treatment: Twenty daphnids were impartially selected and distributed to each concentration and the control (five daphnids per replicate vessel). 

- Control group: Dilution water control


TEST MEDIUM / WATER PARAMETERS

- Dilution water source: Fortified well water based on the formula for hard water (U.S. EPA, 1975).

- Dilution water chemistry (hardness, alkalinity. pH, TOC): The dilution water had a total hardness and alkalinity as CaCO3 of 180 mg/L and 110 mg/L, respectively, a pH range of 7.9 to 8.0 and a specific conductivity of 500 umhos/cm. The TOC concentration of the dilution water source was 0.40 mg/L for the month of May 2004.


OTHER TEST CONDITIONS

- Light intensity: The test area was illuminated with fluorescent bulbs at an intensity range of 65 to 83 footcandles at the solutions' surface. 

- Photoperiod: The test area received a regulated photoperiod of 16 hours of light and 8 hours of darkness. Sudden transitions from light to dark and vice versa were avoided. Light intensity was measured once during the test.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Immobilization . 

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

- Range finding study

- Test concentrations: 1, 10 and 100 mg/L

- Results used to determine the conditions for the definitive study: No immobilisation in any treatment

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

- Was control response satisfactory: Yes. No immobilization or adverse effects were observed among daphnids exposed to the control.

Reported statistics and error estimates:

No treatment level resulted in any immobilisation. The EC50 and NOEC values were therefore empirically estimated to be ≥the highest test concentration.

Table 1. Test results

Nominal concentration (mg/L)	Mean percentage immobilisation after 24 hours	Mean percentage immobilisation after 48 hours
0 (Control)	0	0
13	0	0
22	0	0
36	0	0
60	0	0
100	0	0

The highest concentration producing 0% immobilization was 100 mg a.i./L.   The lowest concentration producing 100% immobilization was > 100 mg a.i./L. Biological observations: - Number immobilized as compared to the number exposed: Number immobilized: 0, Number exposed: 120 (includes control) o Was control response satisfactory (yes/no/unknown): Yes. No immobilization or adverse effects were observed among daphnids exposed to the control.

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 of >100 mg/L and NOEC of ≥100 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Cross-reference 4

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2004-05-06 to 2004-05-10

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with GLP but no analysis of exposure concentrations

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Principles of method if other than guideline:

ASTM. 2002. Standard practice for conducting acute toxicity tests with fishes, macroinvertebrates and amphibians. Standard E729-96. American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428.

OECD. 1992. Guideline for Testing of Chemicals. Fish Acute Toxicity Test. Guideline #203. Adopted 17 July 1992.

U.S. EPA. 1975. Methods for Acute Toxicity Tests with Fish, Macroinvertebrates and Amphibians. Ecological Research Series (EPA-660/3-75-009). 61 pp.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)

- Method: A 100 mg a.i./L stock. solution was prepared by adding 4.3 mL of trimethoxysilane to 40 L of dilution water (based on a purity of 97.1% and a density of 0.957 g/mL). The solution was mixed overnight and was observed to be clear and colorless with no undissolved test substance visible following mixing. Each test concentration was prepared by adding the appropriate amount of the 100 mg a.i./L stock solution to the test vessel and bringing it to a final volume of 15 L with dilution water.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Common name: Rainbow trout

- Source: Test organisms were obtained from Trout Lodge, Sumner, Washington. 

- Length at study initiation (length definition, mean, range): 40 mm (range 38 to 42 mm)

- Weight at study initiation (mean and range): 0.62 g (range 0.47 to 0.74 g)

- Holding conditions: during the 14-day period prior to testing, rainbow trout were held in a 500-L fiberglass tank under a photoperiod of 16 hours light and 8 hours dark. The temperature in the holding tank ranged from 13 to 15 °C during this 14-day period. The water which flowed into the fish holding tank and was characterized as having a total hardness and alkalinity as CaCO3 of 36 mg/L and 24 mg/L, respectively, a pH of 7.5, and a specific conductivity of 130 umhos/cm. The fish were fed a dry commercial flaked fish food and brine shrimp, ad libitum,daily. Fish were not fed during the 48-hour period prior to test initiation or during the exposure period.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

Total hardness and alkalinity: 44 mg/L and 28 mg/L as CaCO3

Test temperature:

13 to 15 ºC

pH:

6.1-7.0

Dissolved oxygen:

5.1-9.8 mg/L

Salinity:

not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 13, 22, 36, 60 and 100 mg a.i./L

Details on test conditions:

TEST SYSTEM

- Test vessel: The toxicity test was conducted in 20.8-L aquaria constructed entirely of glass and silicone sealant impartially placed in a temperature-controlled water bath designed to maintain exposure solution temperatures at 14± 1°C. A single aquarium was established for each treatment level and the control with the aquaria containing 15 L of test solution. Gentle, oil-free aeration was initiated at the 48-hour observation interval to raise and maintain dissolved oxygen levels at or above 60% of saturation.

- Test design (number of replicates, individuals per replicate, concentrations): Ten rainbow trout were impartially selected and distributed to each exposure vessel. Fish were added two at a time to each test vessel until each test vessel contained ten fish. A total of 10 organisms were exposed to each treatment level and the control.


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Laboratory well water.

- Dilution water chemistry (hardness, alkalinity, pH, TOC): The dilution water had a total hardness and alkalinity as CaCO3 of 44 mg/L and 28 mg/L, respectively, a pH of 7.6 and a specific conductivity of 130 umhos/cm. The TOC concentration of the dilution water source was 0.40 mg/L for the month of May 2004.

- Water chemistry in test (D.O., pH), in the control, and at least one concentration where effects were observed: The dilution water control vessel had a measured DO concentration of 9.7 mg/L at test initiation and 9.4 mg/L at test termination. The pH measured in the dilution water control was 6.8 at test initiation and test termination.


OTHER TEST CONDITIONS

- Lighting (quality, intensity, and periodicity): The test area was illuminated with fluorescent bulbs at an intensity range of 32 to 57 footcandles at the solutions' surface. The test area received a regulated photoperiod of l6 hours of light and 8 hours of darkness. Sudden transitions from light to dark and vice versa were avoided. Light intensity was measured once during the test.


EFFECT PARAMETERS MEASURED: Mortality

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 1.6

- Range finding study

- Test concentrations: 1, 10 and 100 mg/L

- Results used to determine the conditions for the definitive study: 20% mortality in 100 mg/L after 24 hours. No effects in other treatments or Control

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 100 mg/L

Details on results:

- Mortality of control: 0

Reported statistics and error estimates:

No effects were observed in the test. The results were therefore not subject to statistical analysis

Sublethal observations / clinical signs:

Table 1. Test results

Nominal concentration (mg/L)	Percentage mortality after 96 hours
0 (Control)	0
13	0
22	0
36	0
60	0
100	0

24-, 48-, 72-, and 96-hour LC50: > 100 mg a.i./L.

NOEC through 96 hours 100 mg a.i./L.

The highest concentration producing 0% mortality was 100 mg
a.i./L.  The lowest concentration producing 100% mortality
was > 100 mg a.i./L.

Biological observations:

- Number of mortalities as compared to the number exposed:
Number of mortalities: 0, Number exposed: 60 (includes
control)

- Concentration response with 95% confidence limits: > 100
mg a.i./ L (empirically estimated), corresponding 95%
confidence intervals could not be calculated.

- Cumulative mortality: 0% mortality was observed among fish
exposed to all treatment levels tested.

- Was control response satisfactory (yes/no/unknown): Yes.

No mortality or adverse effects were observed among fish
exposed to the control.

Validity criteria fulfilled:

yes

Conclusions:

A 96-hour LC50 of >100 mg/L and NOEC of ≥100 mg/L have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Cross-reference 5

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2004-05-06 to 2004-05-09

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with GLP but no analysis of exposure concentrations

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 100 mg a.i./L. (mg active ingredient/L) stock solution was prepared by adding 215 µL of trimethoxysilane (0.1998 g based on a purity of 97.1% and a density of 0.957 g/mL) to 2000 mL of dilution water. The solution was mixed overnight with a magnetic stir plate and Teflon-coated stir bar. Each test concentration was prepared by adding the appropriate amount of the 100 mg a.i./L stock solution to an intermediate vessel and bringing it to a final volume of 1000 mL with dilution water.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM

- Strain: Psuedokirchneriel/a  subcapitata, formerly Selenastrum capricornutum, strain 1648,Class Chlorophyceae

- Source (laboratory, culture collection): The alga was obtained from the University of Texas, Austin, Texas and was maintained in stock culture at Springborn Smithers Laboratories. 

- Method of cultivation: The stock cultures were maintained within the following conditions: shaking rate of 100+/- 10 rpm, a temperature of 24 ± 1 °C and continuous illumination at the surface of the medium with an intensity of 6300 to 9600 lux (590 to 890 foot candles). Lighting was supplied by fluorescent bulbs. Culture flasks were agitated continuously on an orbital shaker. 


ACCLIMATION

- Culturing media and conditions (same as test or not): no

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

No data

Test temperature:

24°C

pH:

7.0 to 7.1 at start of test

8.6 to 9.3 at end of test

Dissolved oxygen:

No data

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 6.3, 13, 25, 50 and 100 mg/L

Details on test conditions:

TEST SYSTEM

- Test vessel: The test was conducted in sterile 250-mL Erlenmeyer flasks containing 100 mL of test solution. All test vessels were fitted with stainless steel caps which permitted gas exchange.

- Test Design: One hundred milliliters of the appropriate exposure solution was placed in each replicate flask. A 0.226mL inoculum of Psuedokirchneriella subcapitata cells, at a density of approximately 443 x 10(4) cells/mL, was aseptically introduced into each flask. This inoculum provided the required initial (0 hour) cell density of approximately 1.0 x 10(4)cells/mL. Three replicate test vessels were established for the treatment levels and the dilution water control.

- Water chemistry in test: TOC concentration of the AAP sample collected in May 2004 was 0.46 mg/L. Conductivity of the exposure and control solutions measured at test initiation and termination was maintained at 80 umhos/cm.  

GROWTH MEDIUM

- Standard medium used: yes

- Detailed composition if non-standard medium was used: The culture medium used was Algal Assay Procedure (AAP) medium prepared with sterile, deionized water. AAP medium used to prepare the exposure solutions was formulated in the same manner as the culture medium.


OTHER TEST CONDITIONS

- Light intensity and quality: 6500 to 8600 lux (600 to 800 footcandles). The photosynthetically-active radiation (PAR) of the test area measured at test initiation ranged from 98 to 128 µE/m2/s.

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

- Range finding study

- Test concentrations: 0.01, 0.1, 1. 10 and 100 mg/L

- Results used to determine the conditions for the definitive study: No significant difference in cell densities compared with the Control after 72 hours

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 6.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth rate and biomass

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth rate and biomass

Details on results:

After 72 hours of exposure, cells exposed to all the treatment levels tested and the control were observed to be normal.  The 72 hour cell density in the control averaged 154.00 x 10 (4) cells/mL. Cell densities in the 6.3, 13, 25, 50 and 100 mg a.i./L treatment levels averaged 104.75, 117.58, 104.33, 117.72 and 119.14 x 10(4) cells/mL, respectively.

Reported statistics and error estimates:

Average-specific growth rates and Areas under the growth curves were determined for each treatment level in accordance with OECD guidance. No test concentration resulted in >50% effect on growth and therefore the EC50 values were estimated empirically from the data as being >than the highest treatment.

After checking for homogeneity of variance with Bartlett's test and Shapiro-Wilks' test, the NOECs were determined by Williams' test at p≤5%.

Table 1. Test results

Nominal test substance concentration (mg/L)	Initial cell concentration (cells/mL) (SD)	Mean cell concentration after 24 hours (cells/mL) (SD)	Mean cell concentration after 48 hours  (cells/mL) (SD)	Mean cell concentration after 72 hours  (cells/mL) (SD)
0 (Control)	10000	47500 (18900)	280000 (47500)	1540000 (237500)
6.3	10000	47500 (4300)	167500 (25400)	1047500 (218800)
13	10000	52500 (2500)	160000 (10900)	1175800 (143700)
25	10000	40000 (10000)	181700 (36400)	1043300 (110000)
50	10000	38300 (15900)	200000 (26500)	1177200 (206900)
100	10000	43300 (22700)	127500 (69300)	1191400 (231900)

Biomass:  The total biomass in the control averaged 101.37 x 10(4) cells-days/mL. Total biomass in the 6.3, 13, 25, 50 and 100 mg a.i./L treatment levels averaged 67.53, 73.38, 67.92, 75.81 and 70.15 x 10(4) cells-days/mL, respectively.  Williams' Test determined a significant difference in the control (101.37 x 10(4) cells-days/mL). The NOEC for total biomass was determined to be <6.3 mg a.i./L, the lowest nominal concentration tested.  Since no concentration tested resulted in ≥50% inhibition, the 72-hour EbC50 was empirically estimated to be >100 mg a.i./L, the highest nominal concentration tested. Growth rate:  The 0 to 72 hour growth rate in the control averaged 1.72 days-1.  The 0-72 hour growth rate in the 6.3, 13, 25, 50 and 100 mg a.i./L treatment levels averaged 1.58, 1.63, 1.59, 1.63 and 1.63 days-1, respectively.  Statistical analysis (Williams' Test) determined a significant reduction in all treatment levels tested when compared to the growth rate in the control (1.72 days-1).  The 72 hour NOEC for growth rate was determined to be <6.3 mg a.i./L, the lowest nominal concentration tested.  Since no concentration tested resulted in ≥50% inhibition, the 72-hour EC50 was empirically estimated to be >100 mga.i./L, the highest nominal concentration tested.

Validity criteria fulfilled:

yes

Conclusions:

A 72-hour EC50 of >100 mg/L and a NOEC of <6.3 mg/L have been determined for the effects of the test substance on growth rate and biomass of Pseudokirchnerella subcapitata. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Cross-reference 6

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

There are no in vivo or in vitro data on the toxicokinetics of trichlorosilane.

The following summary has therefore been prepared based on the physicochemical properties of the substance itself and its hydrolysis products. The main input variable for computer-based toxicokinetic prediction models is log Kow which is not relevant for inorganic substances such as trichlorolsilane.

Trichlorosilane is a moisture-sensitive, volatile liquid that hydrolyses very rapidly in contact with water (half-life approximately 5 seconds at pH 7), generating HCl and silicic acid; hydrogen gas is a further by-product of the hydrolysis reaction. At concentrations above about 100 -150 mg/l (measured as SiO2 equivalents), condensation products of monosilicic acid can also form. At concentrations >100 -150 mg/l of SiO2, monomeric monosilicic acid condenses into insoluble colloidal particles of polysilicic acid (silica sol) or a highly cross-linked network (silica gel). These forms of polysilicic acid are equivalent to synthetic amorphous silica. Most, if not all, hydrolysis will have occurred before absorption into the body, therefore relevant systemic exposure is limited to the hydrolysis products.

Human exposure can occur via the inhalation or dermal routes. Relevant inhalation exposure would be to the hydrolysis products (hydrolysis would occur rapidly when inhaled, even if a mixture of parent and hydrolysis products were present in air). The substance would also hydrolyse rapidly in contact with moist skin. The resulting HCl hydrolysis product would be severely irritating or corrosive.

Potential systemic exposure to hydrochloric acid is not discussed.

Absorption

Oral

Significant oral exposure is not expected for this corrosive substance.

However, oral exposure to humans via the environment may be relevant for the hydrolysis product, silicic acid and then silica. When oral exposure takes place, it is necessary to assume that except for the most extreme of insoluble substances, that uptake through intestinal walls into the blood takes place. Uptake from intestines can be assumed to be possible for all substances that have appreciable solubility in water or lipid. Other mechanisms by which substances can be absorbed in the gastrointestinal tract include the passage of small water-soluble molecules (molecular weight up to around 200) through aqueous pores or carriage of such molecules across membranes with the bulk passage of water (Renwick, 1993).

As silica is water soluble (approximately 100 - 150 mg SiO2/l with condensation occurring at higher concentrations) and has a molecular weight of approximately 60.08 g/mol it meets both of these criteria, so should oral exposure occur it is reasonable to assume systemic exposure will occur also. Gastrointestinal absorption of insoluble silica will be insignificant as compared to the absorption of the soluble species (Carlisle, 1986).

Dermal

Trichlorosilane hydrolyses rapidly on the skin, thus producing silicic acid and HCl. The molecular weights of the hydrolysis products favour absorption across the skin. However, silica is water soluble (approximately 100 - 150 mg SiO2/l with condensation occurring at higher concentrations), which suggests that it is too hydrophilic to cross the lipid rich stratum corneum.  Since the other hydrolysis product, HCl is corrosive to the skin, damage to the skin might increase penetration. Absorption of the insoluble condensation products is not expected.

Available dermal studies did not show evidence of systemic availability, as effects (such as those on body weights) are generally thought to be secondary to corrosion of the skin.

Inhalation

Inhalation exposure would be to the hydrolysis products as trichlorosilane would hydrolyse rapidly when inhaled, even if a mixture of parent and hydrolysis products were present in air. Once hydrolysis has occurred, significant uptake would be expected into the systemic circulation, as the silicic acid hydrolysis product is highly soluble (approximately 100 - 150 mg SiO2/l with condensation occurring at higher concentrations). Due to the hydrophilic nature of silicic acid, it is likely that some will be retained within the mucous of the lungs and thus absorption will be limited. Condensation to silica might lead to some precipitate being retained in the lining of the respiratory tract, although this cannot be confirmed from results of the only reliable experimental animal study available.

As with dermal exposure, damage to membranes caused by the corrosive nature of the hydrochloric acid hydrolysis product might enhance the uptake. In the available acute inhalation toxicity studies, the only adverse effects appeared to be secondary to corrosive effects of the test substance.

Distribution

All absorbed material is likely to be in the form of the hydrolysis products, HCl and silicic acid, which rapidly precipitates to insoluble silica (SiO2) when the concentration is sufficiently high. Silicic acid is a small molecule, and therefore has potential to be widely distributed, but its hydrophilic nature  will limit its diffusion across membranes (including the blood-brain and blood-testes barriers) and its accumulation in fatty tissues. Human blood contains 1 mg SiO2/l of monosilicic acid (Iler RK, 1979).  Hydrogen and chloride ions will enter the body’s natural homeostatic processes.

Metabolism

Trichlorosilane is rapidly hydrolysed to HCl and silicic acid, which rapidly precipitates to insoluble silica (SiO2) when the concentration is sufficiently high. Most if not all of this will have occurred before absorption into the body. Silicic acid is not metabolised, but forms a precipitate, as previously described. Silicon is an essential trace element participating in the normal metabolism of higher animals. It is required in bone, cartilage and connective tissue formation as well as participating in other important metabolic processes. The silicon is present almost entirely as free soluble monosilicic acid (Carlisle, 1986). Genetic toxicity tests in vitro showed no observable differences in effects with and without metabolic activation.

Excretion

A determinant of the extent of urinary excretion is the soluble fraction in blood. Given the hydrophilic nature of the hydrolysis product, silicic acid, the soluble fraction of silicic acid in blood is extremely high suggesting it is likely to be effectively eliminated via the kidneys in urine and accumulation is very unlikely.

Following oral ingestion precipitated silica will be eliminated in faeces. The low molecular weight and high water solubility of silicic acid suggest that it is likely to be rapidly eliminated via the kidneys in urine. There is therefore no evidence to suggest that this substance will accumulate in the body.

References

Renwick A. G. (1993) Data-derived safety factors for the evaluation of food additives and environmental contaminants. Fd. Addit. Contam. 10: 275-305.

Iler, Ralph K. (1979) The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties and Biochemistry of Silica, Wiley, p. 13.

Carlisle EM. Silicon as an essential trace element in animal nutrition. Ciba Found Symp. 1986;121:123-39.

Cross-reference 7

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

The substance hydrolyses very rapidly to give silanetriol and HCl. The Si-H bonds of trichlorosilane also react in water (assumed half-life <12 hours at pH 7 and 25°C) to produce hydrogen and monosilicic acid. Both silanetriol and monosilicic acid exist only in dilute aqueous solutions and readily condense at concentrations above approximately 100-150 mg/L as SiO₂ to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid.

These hydrolysis products are inorganic substances which enter natural biogeochemical cycles. Monosilicic acid and its condensation products are ubiquitous in the environment.

A comparison of the total flux of dissolved silica into rivers can be compared with the input from manufacture and use of trichlorosilane, and indicates that the input is considered negligible in comparison with the natural flux of silica/silicic acid in the environment.

Therefore, it is not appropriate to calculate Predicted Environmental Concentrations (PECs) for the hydrolysis product monosilicic acid.

Cross-reference 8

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no hazard identified

Hazard assessment conclusion:

no potential for bioaccumulation

The hydrolysis half-life of trichlorosilane (CAS 10025-78-2) is approximately 5 seconds at 25°C and pH 4, 7 and 9 (based on read-across data); the substance will therefore undergo very rapid hydrolysis in contact with water. This half-life relates to hydrolysis of the Si-Cl bonds to give silanetriol and hydrochloric acid. The Si-H bond is also expected to react rapidly, forming monosilicic acid (Si(OH)₄) and hydrogen as the ultimate hydrolysis products. The precise rate of this reaction is uncertain but the half-life for Si-H reactivity of trichlorosilane is estimated as <12 hours (possibly much less than 12 hours) at pH 7 and 25°C.

Monosilicic acid (Si(OH)₄) exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100-150 mg/l as SiO₂ to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid.

 

The water solubility is approximately 100-150 mg/l (limited by condensation reactions) (see Section 4.8 of IUCLID for further discussion).

 

The consideration of the non-silanol hydrolysis product, hydrochloric acid, is discussed below.

 

REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT₅₀ is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. ECHA Guidance Chapter R.7b (ECHA 2017) states that where degradation rates fall between >1 hour and <72 hours, testing of parent and/or degradation product(s) should be considered on a case-by-case basis.

 

The substance will be exposed to the environment through wastewater treatment plant (WWTP) effluent only. The minimum residency time in the wastewater treatment plant is approximately 7 hours (although this is a conservative figure and wastewater treatment time may be hours longer) with an average temperature of 15°C (assumed to be at neutral pH). Significant degradation by hydrolysis would be expected before the substance is released to the receiving waters.

 

The environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is therefore based on the properties of the silanol hydrolysis product, in accordance with REACH guidance.

 

As described below and in Section 4.8 of IUCLID, condensation reactions of the monosilicic acid are possible.

 

READ-ACROSS JUSTIFICATION

No measured data are available for the registration substance. Data have therefore been read across from relevant substances to assess the toxicity of the silanol hydrolysis product to aquatic organisms.

 

In order to reduce testing, read-across is proposed to fulfil up to REACH Annex X requirements for the registration substance from substances that have similar structure and physicochemical properties. Ecotoxicological studies are conducted in aquatic medium or in moist environments; therefore the hydrolysis rate of the substance is particularly important since after hydrolysis occurs the resulting product has different physicochemical properties and structure.

 

In moist medium, trichlorosilane (CAS 10025-78-2) hydrolyses very rapidly (half-life approximately 5 seconds at 20-25°C and pH 7), with the final hydrolysis products being monosilicic acid and hydrochloric acid. The non-silanol hydrolysis product hydrochloric acid is not expected to contribute to any adverse effects at the relevant dose levels. This is discussed further below.

 

The registration substance and the substances used as surrogate for read-across are part of a class of chlorosilane and alkoxysilane compounds which hydrolyse rapidly or moderately rapidly to produce monosilicic acid (Si(OH)₄) and another non-Si hydrolysis product. Si(OH)₄ has not been isolated and only exists in dilute aqueous solution. It readily and rapidly (within minutes) condenses to give amorphous polysilicic acid. Depending on the pH and concentration, solutions will contain varying proportions of monosilicic acid, cyclic and linear oligomers and polysilicic acid of three-dimensional structure. Further details are given in supporting reports (PFA 2015ao and PFA 2013x) attached in Section 13 of the IUCLID dataset.

 

Reliable data have been read across from trimethoxysilane (CAS 2487-90-3). This substance, like trichlorosilane (CAS 10025-78-2), hydrolyses very rapidly (t_1/2 <0.3 min at pH 4, 7 and 9 and 2°C) to form silanetriol. Methanol is also produced. Silanetriol then reacts further to monosilicic acid. Under neutral conditions of the environment and buffered test media, neither hydrogen chloride nor methanol will significantly influence the hydrolysis and condensation reactions of the silanetriol species formed by initial hydrolysis of both trichlorosilane (CAS 10025-78-2) and trimethoxysilane (CAS 2487-90-3). Although there is some uncertainty around the rate of reaction from silanetriol to monosilicic acid, the reaction is expected to be fairly rapid (<12 hours) and the final silicon-containing products of trimethoxysilane and trichlorosilane hydrolysis are equivalent and produced on an equivalent timescale.

Short-term toxicity studies with fish, invertebrates and algae have been read across from trimethoxysilane (CAS 2487-90-3).

LC₅₀ or EC₅₀ values for the three organisms are all >100 mg/l indicating that the substance is not acutely toxic to aquatic organisms. These data are used as key data.

 

Short-term toxicity data are also available with tetraethyl orthosilicate (CAS 78-10-4) which rapidly hydrolyses (t_1/24.4 h at 25°C and pH 7) to produce monosilicic acid and ethanol.

As discussed above, trichlorosilane (CAS 10025-78-2) also rapidly hydrolyses (half-life approximately 5 seconds at 20-25°C and pH 7) to produce monosilicic acid as the silanol hydrolysis product. Tetraethyl orthosilicate (CAS 78-10-4) and trichlorosilane (CAS 10025-78-2) are considered part of the same analogue group as they both react in water to produce (poly)silicic acid. The non-silicon hydrolysis products, ethanol and hydrochloric acid, respectively, do not cause effects in aquatic organisms at relevant concentrations as discussed below.

Short-term toxicity data for fish and algae with tetraethyl orthosilicate (CAS 78-10-4) indicate that this substance is of low toxicity to aquatic organisms (E(L)C₅₀values >100 mg/l). These data are used as supporting data.

 

Silicic acid producers analogue group

Silicic acid is a naturally-occurring substance which is not harmful to aquatic organisms at relevant concentrations. Silicic acid is the major bioavailable form of silicon for aquatic organisms and plays an important role in the biogeochemical cycle of silicon (Si). Most living organisms contain at least trace quantities of silicon. For some species Si is an essential element that is actively taken up. For example, diatoms, radiolarians, flagellates, sponges and gastropods all have silicate skeletal structures (OECD SIDS 2004c, silicates). Silicic acid has been shown to be beneficial in protection against mildew formation in wheat and to be non-phytotoxic in non-standard studies (Côte-Beaulieu et al. 2009).

 

Silicic acid is therefore not expected to be harmful to organisms present in the environment. To support this view, all the available studies with aquatic organisms report no effects at 100 mg/l nominal loading in short-term toxicity studies (see Table 2 in PFA 2013x for key studies).

 

Given that all substances produce silicic acid and no toxicity is observed, it is possible to read-across freely within the analogue group. (Reference PFA 2013x).

 

Please see the attached report in IUCLID Section 13 for the analogue approach to address ecotoxicity of trichlorosilane (CAS 10025-78-2).

 

Considerations on the non-silanol hydrolysis product:

Hydrogen chloride

Chloride ions occur naturally (typically at levels 40 – 160 mg/l in environmental fresh waters). Standard test media contain chloride salts at levels equivalent to approximately 20 – 64 mg Cl-/l.

Effects on aquatic organisms arising from exposure to hydrochloric acid are thought to result from a reduction in the pH of the ambient environment (arising from an increase in the H+ concentration) to a level below their tolerable range. Aquatic ecosystems are characterized by their ambient conditions, including the pH, and resident organisms are adapted to these conditions. The pH of aquatic habitats can range from 6 in poorly-buffered ‘soft’ waters to 9 in well-buffered ‘hard’ waters. The tolerance of aquatic ecosystems to natural variations in pH is well understood and has been quantified and reported extensively in ecological publications and handbooks (e.g. OECD SIDS 2002 for CAS No. 7647-01-0, hydrochloric acid). It is not considered appropriate or useful to derive a single aquatic PNEC for hydrochloric acid because any effects will not be a consequence of true chemical toxicity and will be a function of, and dependent on, the buffering capacity of the environment. Physical hazards related to pH effects are considered in the risk management measures (e.g. neutralisation) for effluents/aqueous waste.

 

It is not appropriate for this substance to discuss the combined ecotoxicological potency of the silicon and non-silicon hydrolysis products because:

•            effects arising from exposure to HCl are related to changes in pH and not true chemical toxicity;

•            monosilicic acid has a predicted first dissociation constant around 10 and so does not significantly affect the pH of an aqueous solution;

•            the silicon-containing hydrolysis products are not toxic to aquatic organisms at 100 mg/l in short-term studies.

 

Methanol and Ethanol

Methanol and ethanol are well-characterised in the public domain literature and are not hazardous at the concentrations relevant to the studies; the short-term EC₅₀ and LC₅₀ values for these substances are in excess of 1000 mg/l (OECD 2004a and OECD 2004b, respectively).

 

References:

Côté-Beaulieu C, Chain F, Menzies JG, Kinrade SD, Bélanger RR (2009). Absorption of aqueous inorganic and organic silicon compounds by wheat and their effect on growth and powdery mildew control. Environ Exp. Bot 65: 155–161.

ECHA (2016). REACH Guidance on Information Requirements and Chemical Safety Assessment Chapter R16: Environmental Exposure Assessment Version: 3.0. February 2016.

ECHA (2017). European Chemicals Agency. Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7b: Endpoint specific guidance. Version 4.0 June 2017.

OECD SIDS (2002). SIDS Initial Assessment Report for SIAM 15, Boston, USA, 22-25th October 2002, Hydrochloric acid, CAS 7647-01-0.

OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1

OECD (2004b): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

OECD SIDS (2004c). SIDS Initial Assessment Report for SIAM 18, Paris, France, 20-23 April, 2004, Soluble Silicates, CAS 1344-09-8 Silicic acid, sodium salt; CAS 6834-92-0 Silicic acid (H2SiO3), disodium salt; CAS 10213-79-3 Silicic acid (H2SiO3), disodium salt, pentahydrate; CAS 13517-24-3 Silicic acid (H2SiO3), disodium salt, nonahydrate; CAS 1312-76-1 Silicic acid, potassium salt.

PFA, 2013x, Peter Fisk Associates. Analogue report - Ecotoxicity of (poly)silicic acid generating compounds , PFA.300.003.001.

PFA, 2015ao, Peter Fisk Associates. The aquatic chemistry of inorganic silicic acid generators, PFA.404.001.001.

Reliable data are read across from analogous substances (on the basis of common hydrolysis product). On this basis it

is proposed that trichlorosilane should not be classified in the EU under EC Regulation No 1272/2008 (CLP Regulation, as adapted) for acute or chronic toxicity on the grounds that reliable studies read-across for the silanol hydrolysis product indicate that it would not be toxic at a loading rate of 100 mg/l. The substance very rapidly hydrolyses to hydrogen chloride and inorganic silicate moieties. Hydrolysis product hydrogen chloride has a harmonised classification in Annex VI of Regulation No 1272/2008 and does not require classification for the environment. Hydrolysis product monosilicic acid is a naturally-occurring substance which is not harmful to aquatic organisms at relevant concentrations. All available studies with aquatic organisms report no effects at 100 mg/L in short-term toxicity studies (reference PFA 2013x).

Cross-reference 9

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Assessed substance:

transformation product

Composition of assessed substance:

Trichlorosilane

PBT status of the assessed substance:

PBT assessment does not apply