Reaction mass of decamethyltetrasiloxane; dodecamethylpentasiloxane; hexamethyldisiloxane; octamethyltrisiloxane

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Guideline study but it is not certain whether the study was conducted in accordance with GLP.

Qualifier:

according to guideline

Guideline:

other: Environment Canada EPS 1/RM/45, February 2005

GLP compliance:

not specified

Remarks:

The data is from a publication and this information was not included.

Analytical monitoring:

yes

Details on sampling:

Soil samples were collected throughout the initial treatment, preparation (i.e., at manure amendment, following the 2-h equilibrium period, and following mixing of the amended biosolid with the Gr10 soil) for the range-finding tests to confirm the analytical methodology used, as well as to evaluate the loss of D5 over time. For the definitive tests, samples were taken for analysis only on day 0 of the test (i.e., when the test organisms were added) to confirm dose concentrations in the test soil. All samples were immediately frozen and stored at -20°C prior to analysis. All samples were analyzed for cVMS D4, D5 and D6 concurrently by Quebec Laboratory for Environmental Testing of Environment Canada (Montreal, Quebec).

Triplicate 1.0g (+/-0.2) (wet weight) samples were then measured into glass tubes and well mixed to ensure solids are homogenized. To extract the soil samples, 5 mL of acetonitrile was added to each sample and vortexed followed by the addition of 5 mL of pentane (also vortexed). The sample was then sonicated in an ice bath for 10 min followed by centrifugation at 1500 RPM for 10 min at 15°C. The pentane phase was then transferred to a clean GC vial and 75 μL of naphthalene-D8 solution(lfi) ng/μL in pentane) was added as an internal standard.

Vehicle:

no

Details on preparation and application of test substrate:

A sandy loam soil (Gr10) was obtained from Greely Sand and Gravel (Ottawa Ontario (ON)) in June 2010 and was dried, sieved (4-mm mesh) and homogenized prior to use. The negative control treatment consisted of a formulated artificial soil (AS) comprising 10% air-dried pre-sieved Sphagnum sp. peat, 20% kaolin clay, and 70% silica sand, with calcium carbonate added to standardize the soil pH.

For the toxicity tests, the soil was amended with either an uncontaminated or contaminated surrogate biosolid. Although available, the use of an actual biosolid produced from a water treatment facility was not pursued as an option for use in the toxicity tests as the potential for other contaminants or toxicants present in the sample may have confounded toxicity test results. As a result, mushroom compost and organic cow manure were both considered as options for a surrogate biosolid. Both alternative biosolids were analyzed in conjunction with a real biosolid (obtained from the Robert O. Picard Water Treatment facility in Ottawa, ON) for comparison of their physical and chemical characteristics. Based on these characteristics. the organic cow manure was selected for its similarity in percent organic matter to the actual biosolid.

To prepare test samples, the surrogate biosolid was amended with D5 (97% pure liquid; Sigma-Aldrich) to create a contaminated test substance; subsequently, the amended biosolid was manually mixed for 2 min, covered to prevent volatilization, and allowed to equilibrate for 2 h. Following the 2 h equilibration period, the amended biosolid was added to the Gr10 soil at a rate of 5 g/kg (on a dry weight basis), equivalent to 8 t/ha, a common application rate for biosolids on agricultural soils in Ontario to create the test soil. Each test concentration was prepared independently. The average moisture content of the test soil was 38± 3%, with an average pH of 7.55±0.15 for all test set-ups.

Species:

Hordeum vulgare

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

All seeds were purchased from commercial suppliers and underwent in-house germination and emergence evaluations, as well as reference toxicant testing prior to use.

Species:

Trifolium pratense

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

All seeds were purchased from commercial suppliers and underwent in-house germination and emergence evaluations, as well as reference toxicant testing prior to use.

Test type:

other: Seedling emergence, shoot and root length and dry biomass

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

14 d

Test temperature:

25°C (day) and 15°C (night) +/-3°C

pH:

7.55 +/-0.15

Moisture:

38 +/-3%

Details on test conditions:

Test vessels were incubated for 14d on a light/dark cycle of 16 h/8 h at 25°C and 15°C (+/-3°C), respectively. The mean light intensity during 'day' hours was 307 +/-24 and 275 +/-43 μmol (m2t)-1 for T. pratense and H. vulgare respectively: these were within the range specified in the method. Upon completion of the test, the number of emerged seedlings was counted, and the shoot and root length and dry biomass measured and recorded.

Nominal and measured concentrations:

H . vulgare test: Nominal/measured concentrations of D5 at time 0 were 0/2.02, 143/39, 244/77, 414/218, 704/275, 1197/610, 2035/1357, 3460/1347, 5882/1561, and 10 000/3127 (mg/kg dry wt.). Measured values >0 mg/kg D5 in control soil were used as background values.

T. pratense: Nominal/measured concentrations of D5 at time 0 were 0/1.34, 143/41, 244/63, 414/67, 704/252, 1197/675, 2035/1018, 3460/1015, 5882/1918, and 10000/4054 (mg/kg dry wt.).

Reference substance (positive control):

not specified

Species:

Hordeum vulgare

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

> 3 127 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

seedling emergence

Species:

Hordeum vulgare

Duration:

14 d

Dose descriptor:

other: IC50

Effect conc.:

2 051 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: shoot length

Remarks on result:

other: 1675-2518

Species:

Hordeum vulgare

Duration:

14 d

Dose descriptor:

other: IC50

Effect conc.:

> 3 127 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: root length

Species:

Hordeum vulgare

Duration:

14 d

Dose descriptor:

other: IC50

Effect conc.:

248 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: shoot dry mass

Remarks on result:

other: 201-307

Species:

Hordeum vulgare

Duration:

14 d

Dose descriptor:

other: IC50

Effect conc.:

209 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: root dry mass

Remarks on result:

other: 150-292

Species:

Trifolium pratense

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

> 4 054 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

seedling emergence

Species:

Trifolium pratense

Duration:

14 d

Dose descriptor:

other: IC50

Effect conc.:

> 4 054 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: shoot and root length

Species:

Trifolium pratense

Duration:

14 d

Dose descriptor:

other: IC50

Effect conc.:

> 4 054 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: shoot and root dry mass

Details on results:

Emergence was not affected by the D5 concentrations chosen for testing regardless of plant species. However, differences in sensitivity between the two plant species were evident in that H. vulgare was significantly more sensitive for the given growth endpoints. There was no effect observed for any of the test endpoints for T. pratense. For H. vulgare, shoot and root biomass endpoints were significantly more affected than length.

Reported statistics and error estimates:

The effective concentration (i.e., EC50s) was calculated for plant emergence using the EPA Probit Analysis Program {version 1.5) of the EPA Trimmed Spearman-Karber (TSK) Program (version 1.5). Inhibitory concentrations (i.e., lC50s) were estimated for plant shoot and root length and dry biomass using nonlinear regression analysis via SYSTAT (version 13) software, ensuring that model assumptions (normality and homoscedasticity) were met. When regression models were unable to calculate the IC50, or model assumptions were not met, a "Linear Interpolation for Sublethal Toxicity: The Inhibition Concentration (ICp) Approach" (ICPIN) (version 2.0) was used. ln cases where a 50% effect was not observed, an ANOVA was performed to determine if there was a significant difference in the measured endpoint across treatments. lf a significant difference was found. then Fishers least significant difference test was used to determine where the difference was among treatments.

Validity criteria fulfilled:

yes

Conclusions:

A 14-day IC50 value of 209 mg/kg dry weight has been determined for the effects of the test substance on root dry mass of Hordeum vulgare. IC50/EC50 values for effects on seedling emergence, root and shoot length and shoot dry mass determined in the same test were ≥248 mg/kg dry weight. 14-day EC50 values of >4054 mg/kg dry weight have been determined for the effects of the test substance on seedling emergence, root and shoot length and root and shoot dry mass of Trifolium pratense. NOECs were not determined in the tests.

Description of key information

L4: IC₅₀ (14-day): 209 mg/kg dry weight, root dry mass, Hordeum vulgare, read-across from D5 CAS 541-02-6.

EC₅₀ (14-day): >4054 mg/kg dry weight, seedling emergence, root and shoot length and root and shoot dry mass, Trifolium pratense, read-across from D5 CAS 541-02-6.

 

L5: IC₅₀ (14-day): 209 mg/kg dry weight, root dry mass, Hordeum vulgare, read-across from D5 CAS 541-02-6.

EC₅₀ (14-day): >4054 mg/kg dry weight, seedling emergence, root and shoot length and root and shoot dry mass, Trifolium pratense, read-across from D5 CAS 541-02-6.

Additional information

Constituents HMDS and L3

No data are available for the effects of Constituent HMDS or Constituent L3 on terrestrial plants. Data is waived on the basis that the test substance is too volatile to maintain adequate concentrations in the test system.

 

Constituents L4 and L5

There are no data describing the toxicity of L4 and L5 to terrestrial plants. However, data are available for the siloxane decamethylcyclopentasiloxane (D5, CAS 541-02-6). These data are read across to Constituents L4 and L5.

A short-term (14-day) IC₅₀ value of 209 mg/kg dry weight has been determined for the effects of D5 on root dry mass of Hordeum vulgare. IC₅₀/EC₅₀ values for effects on seedling emergence, root and shoot length and shoot dry mass determined in the same test were ≥248 mg/kg dry weight. 14-day EC₅₀ values of >4054 mg/kg dry weight have been determined for the effects of D5 on seedling emergence, root and shoot length and root and shoot dry mass of Trifolium pratense. NOECs were not determined in the tests.

Testing proposal for Constituent L4

An OECD TG 208 toxicity to terrestrial plants study is proposed for L4. The need for this study will be re-assessed once the results of the OECD TG 222 with L4 are available. If there is no indication of risk from the OECD TG 222 study, the OECD TG 208 will not be conducted.

Read-across of the terrestrial toxicity data for D5 to L4 is considered to be suitable to derive an interim hazard and risk assessment under REACH for L4.

 

Test proposal for Constituent L5

An OECD TG 208 toxicity to terrestrial plants study is proposed for L5. The need for this study will be re-assessed once the results of the OECD TG 222 with L5 are available. If there is no indication of risk from the OECD TG 222 study, the OECD TG 208 will not be conducted.

Read-across of the terrestrial toxicity data for D5 to L5 is considered to be suitable to derive an interim hazard and risk assessment under REACH for L5.