3-trimethoxysilylpropane-1-thiol

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil macroorganisms except arthropods: short-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1996-02-29 to 1996-03-14

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study was conducted according to an EU method, and in compliance with GLP, however no analytical monitoring was undertaken.

Qualifier:

according to guideline

Guideline:

EU Method C.8 (Toxicity for Earthworms: Artificial Soil Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Details on test organisms:

TEST ORGANISM

- Common name: Earthworm, Eisenia foetida foetida

- Source: Eisenia GmbH und Co, Wiesbaden, Germany

- Age at test initiation (mean and range, SD): 2 months

- Weight at test initiation (mean and range, SD): 300 - 600 mg

Study type:

laboratory study

Substrate type:

other: quartz sand

Limit test:

yes

Total exposure duration:

14 d

Test temperature:

20 +/-2 ºC

pH:

5.7

Moisture:

40%

Details on test conditions:

TEST SYSTEM

- No. of organisms per container (treatment): 10

- No. of replicates per treatment group: 4

- No. of replicates per control: 4

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)

- Composition (if artificial substrate): Quartz sand

OTHER TEST CONDITIONS

- Photoperiod: Daylight

- Light intensity: ca. 400 Lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Mortality after 7 and 14 days exposure

VEHICLE CONTROL PERFORMED: no

TEST CONCENTRATIONS

- Limit test at 1000 mg/kg

Nominal and measured concentrations:

Nominal: 1000 mg/kg

Reference substance (positive control):

no

Key result

Duration:

14 d

Dose descriptor:

LC50

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Key result

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Details on results:

- Mortality at end of exposure period: 0

Reported statistics and error estimates:

No toxic effects on survival and growth were observed in the test and therefore statistical analysis of the results was not required.

Validity criteria fulfilled:

yes

Conclusions:

A reliable 14-day LC50 of >1000 mg/kg dry weight has been reported for the test substance to Eisenia foetida. A NOEC of ≥1000 mg/kg dry weight was also determined in the test.

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Reason / purpose for cross-reference:

data waiving: supporting information

Reason / purpose for cross-reference:

data waiving: supporting information

Reason / purpose for cross-reference:

data waiving: supporting information

Reason / purpose for cross-reference:

data waiving: supporting information

Description of key information

A 14-day LC₅₀ value of >1000 mg/kg dry weight has been determined for the effects of 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) on the mortality of Eisenia fetida, based on nominal concentrations. This value is equivalent to >786 mg/kg dry weight when expressed in terms of the silanol hydrolysis product 3-(trihydroxysilyl)propanethiol.

Additional information

A short-term toxicity to earthworms test is available with the registered substance:

 

A 14-day LC₅₀ value of >1000 mg/kg dry weight has been determined for the effects of 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) on the mortality of Eisenia fetida, based on nominal concentrations of the substance (Scholz, 1996). The result was obtained under static test conditions. In view of the test media preparation method and 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 the concentration of the hydrolysis product, 3-(trihydroxysilyl)propanethiol, by applying a molecular weight correction (MW of silanol = 154.26/ MW of parent = 196.34) * (concentration of parent = 1000 mg/kg dry weight) = >786 mg/kg dry weight

 

The study was considered to be reliability 2 (reliable with acceptable restrictions)

No long-term terrestrial toxicity tests are available. Testing does not need to be conducted for the following reasons:

The registered substance, 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0, EC No. 224-588-5), will hydrolyse rapidly (2.6 hours at pH 7 and 20-25°C (QSAR)) in contact with water and atmospheric moisture to form 3-(trihydroxysilyl)propanethiol and methanol.

 

3-(Trihydroxysilyl)propanethiol is soluble in water (1.0E+06 mg/l at 20°C (QSAR)) and has low log K_ow (-1.4 (QSAR)).

 

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. Therefore, in accordance with REACH guidance, the terrestrial chemical safety assessment for 3-(trimethoxysilyl)propane-1-thiol is based on its silanol product 3-(trihydroxysilyl)propanethiol. The non-silanol hydrolysis product, methanol, is not expected to contribute to toxicity to terrestrial organisms. 

 

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long or short-term terrestrial toxicity to invertebrates/higher plants study because, as indicated in guidance R.7.11.6 (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1 and therefore the risk is already adequately controlled and further testing is not justifiable.

 

The substance is highly water soluble and is not readily biodegradable but has low potential for bioaccumulation and low potential for adsorption (based on log K_ow <3 (-1.4) and low log K_oc 0.29). The environmental compartment of concern is therefore expected to be the aquatic compartment.

 

Toxicity was observed in short-term aquatic toxicity tests, with Daphnia being the most sensitive. The occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in the aquatic studies would be considered unlikely.

 

3-(Trihydroxysilyl)propanethiol is classed as hazard category 3 for the terrestrial environment (Table R.7.11-2 of ECHA guidance R.7c, 2017) based on potential for high persistence (DT₅₀ >180 days), lack of ready biodegradability and low toxicity to aquatic organisms (EC/LC₅₀ not <1 mg/l).

 

In this situation, a screening approach is applied: a confirmatory long-term terrestrial test is usually appropriate, in addition to the equilibrium partitioning approach with an extra factor of ten in order to determine whether further full tests are necessary.

 

A confirmatory test would be conducted with the most sensitive organism group based on short-term aquatic testing. For this substance, invertebrates were the most sensitive organisms, indicating a preference to conduct a confirmatory test with terrestrial invertebrates.

 

The current PNECscreen(EQPM) for 3-(trihydroxysilyl)propanethiol is derived from the short-term test results with invertebrates and has a value of 0.0009 mg/kg dwt. For the purpose of the screening assessment comparison only, an extra factor of ten is applied (PECx10/PNECscreen (EQPM)). Based on the exposure assessment, the highest PECx10/PNECscreen(EQPM) for 3-(trihydroxysilyl)propanethiol is 5.53.

 

This high RCR would usually trigger the requirement for long-term terrestrial toxicity tests in accordance with Annex X testing requirements.However, there is an ongoing long-term toxicity to aquatic invertebrates study being conducted with the analogue substance 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1), in accordance with an appropriate test guideline and GLP. The results from this study will be read across to the 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0). The PNECs, including the PNECscreen(EQPM) will be updated when the new data become available.

 

In the event that terrestrial invertebrate and plant studies were to be conducted, the definitive terrestrial risk characterisation would use a PNECsoil based on the lower of the two test results with an assessment factor (AF) of 50 (unless soil microorganism data are available as well, in which case, the assessment factor would be 10). This PNEC would only be more conservative than the current value of PNECscreen(EQPM) if standard testing in terrestrial plants or invertebrates exhibited a dose response with a NOEC/EC₁₀ ≤ 0.045 mg/kg dw (current PNEC of 0.0009 mg/kg * AF 50 for two long-term tests). There is no basis to expect such toxicity in the terrestrial compartment for 3-(trihydroxysilyl)propanethiol based on the absence of significant toxicity observed in aquatic tests (EC/LC₅₀ not <1 mg/l). Additionally, no toxicity was observed in a short-term toxicity to Eisenia fetida test with the registered substance (14-day LC₅₀ >1000 mg/kg soil dry weight (Scholz, 1996)).

 

In the case of 3-(trihydroxysilyl)propanethiol, the registrants consider that a long-term terrestrial study is unlikely to affect the outcomes of the chemical safety assessment. As such, the registrants propose that further testing (including the confirmatory study) is not necessary.

 

Overall, it is concluded that the risk characterisation conclusion is sufficiently conservative and therefore further in vivo testing is not considered necessary.

 

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0, and Section 7, 9 and 10 of the Chemical Safety Report.