Triethoxy(phenyl)silane

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:

calculation (if not (Q)SAR)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The result was obtained by an appropriate predictive method.

Principles of method if other than guideline:

The ECOSAR ‘neutral organics’ QSARs for acute data have been applied and the effect concentrations calculated using log Kow and molar mass as input variables. An additional factor of *0.2 has been applied to the results.


The USEPA model ECOSAR was used as the basis for the estimation. This method is well-validated for ‘neutral organics’, i.e. those which act by a general narcotic mechanism, the potency of which is usually related to log Kow. Its scope is acute and long-term effects for the three standard trophic levels.
The method was validated for use with organosilicon compounds with a high weight percent of Si and limited or no additional functionality. Many of the reliable data for the category are limit values, therefore, the data were considered in terms of the range of theE(L)C50, in accordance with normal classification bands:    
E(L)C50 < 1 mg/l;
E(L)C50 in the range > 1 mg/l to 10 mg/l;
E(L)C50 in the range > 10 mg/l to 100 mg/l;
E(L)C50 > 100 mg/l.

In broad terms ECOSAR predicted correctly for most substances for each trophic level. However, performance was improved significantly by application of a factor of 0.2 to each predicted value (expressed in mg/l). This is equivalent to saying that the organosilicon substances are slightly more toxic than the general ECOSAR ‘neutral organics’ regression lines, although still well within the range of each model. The factor of 0.2 is applicable to fish,Daphniaand algae, across the whole range of log Kowvalues.
It is concluded that the acute effects of the substances in the sub-category can therefore be predicted from ECOSAR, with a minor modification.

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

120 mg/L

Basis for effect:

growth rate

Conclusions:

A 96 h EC50 values of 120 mg/L was obtained for the hydrolysis product of the submission substance using an appropriate calculation method . The results are considered to be reliable.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-09-29 to 2009-10-02

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:

no

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Prior to test solution preparation, a dosing stock solution was prepared by mixing 1.52 mL of Trichloro(phenyl)silane (corresponding to 2 g) with 2 mL of tetrahydrofuran (THF) using Hamilton syringes. The solution was shaken by hand. A 100 mg test item/L stock solution
was prepared prior to test initiation by adding 176 μL of the dosing stock solution to 800 mL algal medium using a Hamilton syringe. Prior to addition of the dosing stock solution, the measurement flask containing the algal medium was placed on a magnetic stirrer. The spiked solution was stirred continuously over night. The pH of the solution was then adjusted to 7.0 with 0.1 N sodium hydroxide (NaOH). Thereafter, the stock solution was further diluted to a final volume of 1000 mL with algal medium, resulting in a solvent (THF) concentration of 0.10 mL/L. Nominal test concentrations of 6.25, 12.5, 25, 50 and 100 mg/L were prepared by dilution of the stock solution and addition of THF to a final concentration of 0.1 mL/L. All resulting test solutions were shaken by hand for 30 seconds and observed to be clear and colorless, with no visible undissolved test item.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM

- Source (laboratory, culture collection): The alga was originally obtained from Albrecht-v.-Haller-Institut, Göttingen, Germany, and was maintained in stock culture at Springborn Smithers Laboratories (Europe).

- Culture medium: The culture medium used was a synthetic algal assay growth medium (OECD, 2006), prepared by adding appropriate amounts of nutrient stock solutions to sterile, deionized water. Representative samples of the dilution water source used in the preparation of the culture medium were analyzed periodically for the presence of pesticides, PCBs and toxic metals conducted at Bachema, Schlieren, and Interlabor Belp AG, Belp, Switzerland. None of these compounds have been detected at concentrations that are considered toxic to algae in any of the water samples analyzed in agreement with ASTM guidelines.

- Preparation of starter culture: Four days prior to test start, the culture was maintained within the following conditions: a shaking rate of 120 rpm, a temperature of 23ºC and continuous illumination of 7091 to 7123 lux. Lighting was supplied by fluorescent bulbs. Culture flasks were shaken
continuously on an orbital shaker. Temperature was controlled using an environmental chamber. The inoculum used to initiate the toxicity test was taken from a stock culture that had been transferred to fresh medium four days before testing.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

Not reported

Test temperature:

23.4 to 23.7ºC

pH:

7.30 to 7.65 at test initiation

6.08 to 9.86 at end of test

Dissolved oxygen:

Not reported

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal test concentrations: 0 (Control), 0 (Solvent control), 6.25, 12.5, 25.0, 50.0 and 100 mg test item/L

Details on test conditions:

TEST SYSTEM

Test vessels: Three sterile 250-mL Erlenmeyer flasks (A to C) for the controls and the treatment levels were prepared. An aliquot of 100 mL of the appropriate test solution was placed in each replicate flask. All test vessels were fitted with stainless steel caps which permitted gas exchange.

- Inoculum: An aliquot of 0.25 mL of the preculture of Pseudokirchneriella subcapitata, at a density of 394 x 104 cells/mL, was then inoculated aseptically in each 250 mL volumetric flask. The resulting slight dilution from the inoculum was considered to be negligible. These volumes of inocula provided the required cell density of 1.0 x 104 cells/mL.

- Algal growth medium: The algal medium used to prepare the exposure solutions was the same as the culture medium. The medium was equilibrated to test temperature. The pH of the medium was 8.03.

- Test conditions: The test was conducted in a temperature-controlled room to maintain the test conditions specified in the study plan: a temperature of 24 ± 2ºC and continuous light intensity of 4400 to 8800 lux. An orbital shaker table provided a shaking rate of 100 rpm. Test flasks were randomly placed on the shaker table at test initiation. Following each observation interval the test flasks were assigned new random positions.

- Algal growth measurement: At each subsequent 24-hour interval, cell counts were conducted on each replicate vessel of the treatment levels and the control using a hemocytometer (Neubauer Improved) and a Leica DMLS microscope. One sample was removed from each flask for counting. One or more hemocytometer field(s), each 0.1 cm x 0.1 cm in size and 0.01 cm deep, containing 0.0001 mL of culture, were examined for each sample until at least 400 cells or a total of four fields were counted. Observations of the health of the algal cells were also made at each 24- hour interval.

- Monitoring culture conditions: Temperature was measured continuously with a minimum/maximum thermometer located in a flask of water adjacent to the test flasks in the environmental chamber. Minimum and maximum temperatures and the shaking rate of the orbital shakers (Gerhardt, 450625 R05) were recorded daily. Light intensity was measured with a Pancontrol LX 1308 at hour 0 and at each 24-hour interval during the exposure period. The pH of the test solutions and control was measured at test initiation and at the termination of the 72-hour exposure period. Test solution pH was measured using a Metrohm 691 pH-meter.

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

- Exponential growth in the control (for algal test): yes

Reported statistics and error estimates:

Definitive EC50 values could not be determined because they were above the highest treatment level.

ANOVA and William’s Test were used to determine the NOEC and LOEC values

Table 1. Test results

Nominal test concentration (mg/L)	Initial cell density (cells/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)	Perecntage inhibition in cell density*	Percentage inhibition in growth rate*	Percentage inhibition in biomass*
0 (Control)	10000	48000	247000	1070000	9.0	1.4	9.0
0 (Solvent control)	10000	59000	228000	1180000	-	-	-
6.25	10000	65000	279000	1240000	-5.3	-1.9	-5.4
12.5	10000	49000	254000	1140000	2.7	-0.03	2.7
25.0	10000	43000	240000	1050000	10.5	1.9	10.6
50.0	10000	33000	203000	1030000	12.6	2.0	12.7
100	10000	45000	248000	1030000	12.1	2.2	12.2

*Relative to solvent control. A negative (-) value indicates that growth was higher than in the solvent control.

Validity criteria fulfilled:

yes

Conclusions:

A 72-hour EC50 value of >100 mg/L and a NOEC of ≥100 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 primarily exposed to the hydrolysis products of the substance.

Reference 3

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 attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Description of key information

A 72-hour EC50 value of >100 mg/l and a NOEC of >=100 mg/l have been determined for the effects of the trichloro(phenyl) silane on growth rate and biomass of Pseudokirchnerella subcapitata. The substance is not harmful to algae.

Additional information

No experimental data were available for triethoxy(phenyl)silane (CAS 780-69-8) therefore read across from data available for the comparable substance trichloro(phenyl)silane (CAS 98-13-5) was considered suitable as both substances hydrolyse rapidly in contact with water to phenylsilanetriol. Due to rapid hydrolysis the algae are very likely exposed to both the parent substance and the hydrolysis products. Details on read across justifications can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.

A study according to the OECD guideline 201 is available for the read across substance trichloro(phenyl)silane (CAS 98-13-5). A 72-hur EC50 value of >100 mg/L and a NOEC of ≥100 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 algae were primarily exposed to the hydrolysis products of the substance, therefore a 72 h EC₅₀ value of 120 mg/L was obtained for the hydrolysis product using an appropriate calculation method. The results show that the substance is not harmful towards algae.