Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1 June - 18 December 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 208 (Terrestrial Plants, Growth Test)

GLP compliance:

yes

Remarks:

Test substance was characterised prior to the study but not in accordance with GLP standards. Routine soil and water screening analyses were conducted using standard US EPA procedures, but not in accordance with GLP standards.

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Tier I testing:
Triplicate samples were collected from the control and treatment levels on day 0.
One composite sample from the control and treatment levels were sampled on days 7 and 14; for the composite sample, all replicates per treatment level and control for each species were sampled and combined into one sample.
Tier II testing:
One sample was collected from each treatment level and control on day 0.
One composite sample from each control and treatment level was sampled on days 7 and 14; for the composite sample, all replicates per treatment level and control for each species were sampled and combined into one sample. For the 4.1 mg/kg treatment level, samples were collected at the termination of the cabbage exposure, which was the only species that contained that low level in the Tier II exposure. As that species terminated two days prior to the final species termination, that sample was held refrigerated until termination of the final species and analyzed with the other treatment levels.
In addition, subsamples of the soil were also collected at each sampling interval and stored frozen as archive samples.
- Sampling method: Soil was sampled approximately 0.5 inch from the surface as to not disturb developing seeds and roots.
- Sample storage conditions before analysis: Most samples were processed and analyzed on the same day alongside quality control samples. When samples were analyzed at a later date, data quality and integrity are ensured by the preparation of QC samples which serve as an indication of stability during storage. The exposure and QC samples were initially processed and analyzed on the sampling day. On occasion, the original results were not reportable due to standard curve failures or known processing issues. As a result, some samples were reprocessed and re-analyzed at a later date. Separate stability-indicating QC samples were re-processed with each set of soil samples. The recoveries of these stability QC samples all met acceptance criteria which serves as confirmation of stability during storage. As a result of the confirmation of stability, the delay in the analysis of these samples has minimal impact on the results of this testing.
All primary and secondary stock solutions for the test substance were stored refrigerated (2 to 8 °C) in amber glass bottles fitted with Teflon-lined caps. All primary and secondary stock solutions for the internal standard were stored in a freezer (-25 to -10 °C) in amber glass bottles fitted with Teflon-lined caps. Diluent solutions were prepared fresh on the day of use and discarded after use.

Vehicle:

no

Details on preparation and application of test substrate:

- Method of mixing into soil (if used): The test substance was added to the soil directly and mixed in a Hobart mixer for 10 minutes.
- Controls: The control soil was not treated with the test substance

The appropriate amount of reaction mass of 3,3 diphenylhexamethyltrisiloxane and 3,3,5,5 tetraphenylhexamethyltetrasiloxane was dispensed volumetrically to the support medium (soil) directly; the control support medium was not treated with the test substance. The support medium was then mixed using a Hobart mixer for 10 minutes. In previous studies involving chemical analysis of core subsamples, 10 minutes of mixing has demonstrated homogeneous distribution of the test substance using this technique.
After preparation, approximately 1.2 kg dry weight of support medium for each concentration was added to the corresponding replicate pots. For each plant species in the Tier I testing, 10 replicates for the control and 1000 mg/kg dry soil treatment level, and three replicates for the 10 and 100 mg/kg dry soil range findings treatment levels, were established.
After preparation, approximately 1.0 kg dry weight of support medium for each concentration was added to the corresponding replicate pots. For each plant species in the Tier II testing, 10 replicates for the control and each treatment level were established.

Species:

Lycopersicon esculentum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: tomato
- Plant family:
- Variety: Celebrity F1
- Source of seed: Johnny's Selected Seeds, Winslow, Maine
- Prior seed treatment/sterilization: Seeds had not been pretreated with fungicides or insecticides before use in testing
- Historical germination of seed (germination of seed lot tested): not reported
- Seed storage: Seeds were stored refrigerated in the dark until use in testing

Species:

Glycine max (G. soja)

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Soybean
- Plant family:
- Variety: Viking
- Source of seed: Johnny's Selected Seeds, Winslow, Maine
- Prior seed treatment/sterilization: Seeds had not been pretreated with fungicides or insecticides before use in testing
- Historical germination of seed (germination of seed lot tested): not reported
- Seed storage: Seeds were stored refrigerated in the dark until use in testing

Species:

Brassica oleracea var. capitata

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Cabbage
- Plant family:
- Variety: Stonehead hybrid
- Source of seed: Park Seed Company, Hodges, South Carolina
- Prior seed treatment/sterilization: Seeds had not been pretreated with fungicides or insecticides before use in testing
- Historical germination of seed (germination of seed lot tested): not reported
- Seed storage: Seeds were stored refrigerated in the dark until use in testing

Species:

Zea mays

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: corn
- Plant family:
- Variety: Field
- Source of seed: Carolina Biological Supply Company, Burlington, North Carolina
- Prior seed treatment/sterilization: Seeds had not been pretreated with fungicides or insecticides before use in testing
- Historical germination of seed (germination of seed lot tested): not reported
- Seed storage: Seeds were stored refrigerated in the dark until use in testing

Species:

Cucumis sativus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: cucumber
- Plant family:
- Variety: Marketmore
- Source of seed: Johnny's Selected Seeds, Winslow, Maine
- Prior seed treatment/sterilization: Seeds had not been pretreated with fungicides or insecticides before use in testing
- Historical germination of seed (germination of seed lot tested): not reported
- Seed storage: Seeds were stored refrigerated in the dark until use in testing

Species:

Allium cepa

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: onion
- Plant family:
- Variety: Zoey F1 OG
- Source of seed: Johnny's Selected Seeds, Winslow, Maine
- Prior seed treatment/sterilization: Seeds had not been pretreated with fungicides or insecticides before use in testing
- Historical germination of seed (germination of seed lot tested): not reported
- Seed storage: Seeds were stored refrigerated in the dark until use in testing

Test type:

seedling emergence and seedling growth test

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

14 d

Remarks:

Study was conducted in two phases: Please see "Any other information on materials and methods" free text field.

Test temperature:

Tier I: 20-36 degrees C. Mean temperature during the day: 27 degrees C, and night: 23 degrees C
Tier II: 15-38 degrees C. Mean temperature during the day: 25 degrees C, and night: 19 degrees C

pH:

Not reported

Moisture:

Tier I: 5.54%
Tier II: 6.45% for the soil used for the control group. 8.09% for soil used for the treatment groups.

Details on test conditions:

TEST SYSTEM
- Testing facility: Smithers, 790 Main Street, Wareham, Massachusetts 02571-1037
- Test container (type, material, size): Polypropylene pots
- Amount of soil: approximately 1.2 kg
- Method of seeding: Seeds were impartially selected and planted at a depth of approximately 1 cm below the surface of the soil in each pot.
- No. of seeds per container: 4 (for both Tier I and II tests)
- No. of plants (retained after thinning): Not reported
- No. of replicates per treatment group: Tier I: 10 replicates for the control and 1000 mg/kg dry soil treatment level, and three replicates for the 10 and 100 mg/kg dry soil range findings treatment levels; Tier II: 10 for the control and each treatment level.
- No. of replicates per control: Tier I: 10, Tier II: 10


SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographic location: Not reported
- Pesticide use history at the collection site: Routine analyses for the presence of pesticides, PCBs, and toxic metals were conducted periodically. None of these compounds were detected at concentrations that would compromise the results of the study, in agreement with ASTM, 2007 standard practice.
- Collection procedures:
- Sampling depth (cm): 1 cm
- Soil texture (if natural soil)
- % sand: 91%
- % silt: 6%
- % clay: 3%
- Soil taxonomic classification: Not reported
- Soil classification system: Not reported
- Composition (if artificial substrate): 70% washed silica sand, 30% loamy sand
- Organic carbon (%): 1.7%
- Maximum water holding capacity (in % dry weight): Not reported
- CEC: Not reported
- Pretreatment of soil: Not reported
- Storage (condition, duration): Not reported

NUTRIENT MEDIUM (if used)
- Description: Approximately twice weekly, plants were watered with 400 mg/L of nutrient solution, prepared in dechlorinated well water.

GROWTH CONDITIONS
- Photoperiod: 16 hour light: 8 hour dark cycle
- Light source: Sodium vapor lights supplemented natural light when necessary to maintain ≥ 50 PAR (μmol/m2/sec) during the light period.
- Light intensity and quality: Tier I: mean 260 μmol/m2/sec, range 100-890 μmol/m2/sec. Tier II: mean 200 μmol/m2/sec, range 100-470 μmol/m2/sec
- Day/night temperatures: Tier I: 20-36 degrees C. Mean temperature during the day: 27 degrees C, and night: 23 degrees C
Tier II: 15-38 degrees C. Mean temperature during the day: 25 degrees C, and night: 19 degrees C
- Relative humidity (%): Tier I: Relative humidity ranged from 36-88% with mean humidity of 73%
Tier II: Relative humidity ranged from 19-97% with mean humidity of 63%
- Wind velocity: Not reported
- Air exchange rate: Not reported
- Watering regime and schedules: After test substance application, the first watering occurred on the support medium surface to support capillary action, and all subsequent waterings were by sub-irrigation. All additional watering was provided using dechlorinated Town of Wareham well water.
- Water source/type: Dechlorinated Town of Wareham well water
- Volume applied: Not reported
- Interval of applications: Not reported
- Method of application: sub-irrigation
- Any pest control method/fertilization (if used): Approximately twice weekly, plants were watered with 400 mg/L of nutrient solution, prepared in dechlorinated well water.

ACCLIMATION PERIOD: Not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Seed emergence was observed on days 0, 7, 14. Observations of morphological abnormalities (e.g. chlorosis, necrosis or leaf blotching) were recorded as the percentage of plants exhibiting the abnormality. Shoot dry weights were measured to the nearest 0.0001g. Weight data was not collected for shoots that died during the exposure.

- Phytotoxicity rating system (if used): Not reported

VEHICLE CONTROL PERFORMED: not applicable as no vehicle used.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3x
- Justification for using less concentrations than requested by guideline: Not applicable

Nominal and measured concentrations:

Nominal: Tier I: 0 and 1000 mg/kg. Tier II for cabbage: 0, 4.1, 12, 37, 110, 330 and 1000 mg/kg. Tier II for onion and tomato: 0, 12, 37, 110, 330 and 1000 mg/kg
Measured: Tier I: 0 and 930 mg/kg. Tier II: 0, 2.9, 26, 48, 96, 240, 870 mg/kg.
Tier I testing:
Triplicate samples were collected from the control and treatment levels on day 0.
One composite sample from the control and treatment levels were sampled on days 7 and 14; for the composite sample, all replicates per treatment level and control for each species were sampled and combined into one sample.
Tier II testing:
One sample was collected from each treatment level and control on day 0.
One composite sample from each control and treatment level was sampled on days 7 and 14; for the composite sample, all replicates per treatment level and control for each species were sampled and combined into one sample. For the 4.1 mg/kg treatment level, samples were collected at the termination of the cabbage exposure, which was the only species that contained that low level in the Tier II exposure. As that species terminated two days prior to the final species termination, that sample was held refrigerated until termination of the final species and analyzed with the other treatment levels.

Reference substance (positive control):

no

Key result

Species:

Allium cepa

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:

other: Seedling emergence, survival and shoot dry weight

Key result

Species:

Brassica oleracea var. capitata

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:

other: Seedling emergence, survival and shoot dry weight

Key result

Species:

Zea mays

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:

other: Seedling emergence, survival and shoot dry weight

Key result

Species:

Cucumis sativus

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:

other: Seedling emergence, survival and shoot dry weight

Key result

Species:

Glycine max (G. soja)

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:

other: Seedling emergence, survival and shoot dry weight

Key result

Species:

Lycopersicon esculentum

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:

other: Seedling emergence, survival and shoot dry weight

Reported statistics and error estimates:

Data were analysed by Shapiro Wilk's test and Bartlett's test for normality and homogeneity of variance, respectively. See Table 1 for analysis of treatment data for NOECs.

Table 1. Decision strategy for statistical analysis

Endpoint	Normal distribution	Equal variance	Comparison test for Tier I	Comparison test for Tier II
Emergence and Survival	N/a	N/a	Fisher’s Exact test	Monotonic: Cochran-Armitage’s step-down test Non-monotonic: Fisher’s exact test with Bonferroni-Holm’s adjustment
Shoot dry weight	Yes	Yes	Equal Variance test	Monotonic: Williams’ multiple comparison test Non-monotonic: Dunnett’s multiple comparison test
Shoot dry weight	Yes	No	Unequal Variance t-test	Monotonic: Jonckheere-Terpstra’s step-down test Non-monotonic: Dunnett’s T3 multiple comparison test
Shoot dry weight	No	Yes and no	Wilcoxon Rank-Sum Two-sample test	Monotonic: Jonckheere-Terpstra’s step-down test Non-monotonic: Wilcoxon’s test with Bonferroni-Holm’s adjustment

Table 2. Emergence rates, survival and shoot dry weight of different plant species after 14-days' exposure to the test substance

Species	Tier	Nominal concentration (mg/kg dry soil)	Number of non-emerged seeds	% Emerged	% Survival	Mean weight (g)
Brassica oleracea	I	Control	10 / 40	75	100	0.1538
		10	5 / 16	69	100	0.1375
		100	1 / 16	94	100	0.1122
		1000	20 / 40	50	100	0.0914
	II	Control	10 / 40	75	100	0.0563
		4.1	4 / 40	90	100	0.0803
		12	6 / 40	85	100	0.0671
		37	1 / 40	98	100	0.0918
		110	4 / 40	90	100	0.0955
		330	1 / 40	98	100	0.0941
		1000	5 / 40	88	100	0.1496
Zea mays	I	Control	3 / 40	93	100	0.4403
		10	1 / 16	94	100	0.4467
		100	0 / 16	100	100	0.3667
		1000	1 / 40	98	100	0.4077
Cucumis sativus	I	Control	2 / 40	95	100	0.3735
		10	0 / 16	100	100	0.3482
		100	0 / 16	100	100	0.2897
		1000	1 / 40	98	100	0.3343
Allium cepa	I	Control	3 / 40	93	100	0.0076
		10	2 / 16	88	94	0.0090
		100	2 / 16	88	100	0.0099
		1000	12 / 40	70	92	0.0114
	II	Control	5 / 40	88	98	0.054
		12	11 / 40	73	100	0.0042
		37	11 / 40	73	100	0.0062
		110	14 / 40	65	92	0.0066
		330	8 / 40	80	100	0.0081
		1000	12 / 40	70	95	0.0117
Glycine max	I	Control	5 / 40	88	100	0.3906
		10	3 / 16	81	100	0.3581
		100	3 / 16	81	100	0.4854
		1000	5 / 40	88	100	0.4910
Lycopersicon esculentum	I	Control	1 / 40	98	100	0.1681
		10	7 / 16	56	100	0.1623
		100	1 / 16	94	100	0.1373
		1000	2 / 40	95	100	0.1185
	II	Control	7 / 40	83	97	0.0376
		12	1 / 40	98	100	0.0376
		37	1 / 40	98	100	0.0339
		110	8 / 40	80	100	0.0458
		330	5 / 40	88	100	0.0359
		1000	1 / 40	98	100	0.0520

Table 3. Morphological observations of different plant species after 14 days' exposure to the test substance

Species	Tier	Nominal concentration (mg/kg dry soil)	Number of healthy plants	Number of necrotic plants	Number of dead plants
Brassica oleracea	I	Control	30	0	0
		10	11	0	0
		100	15	0	0
		1000	20	0	0
	II	Control	30	0	0
		4.1	36	0	0
		12	34	0	0
		37	39	0	0
		110	36	0	0
		330	39	0	0
		1000	35	0	0
Zea mays	I	Control	37	0	0
		10	15	0	0
		100	16	0	0
		1000	39	0	0
Cucumis sativus	I	Control	38	0	0
		10	16	0	0
		100	16	0	0
		1000	39	0	0
Allium cepa	I	Control	37	0	0
		10	12	1	1
		100	13	1	0
		1000	25	1	2
	II	Control	34	0	1
		12	28	1	0
		37	27	2	0
		110	21	3	2
		330	31	1	0
		1000	25	1	2
Glycine max	I	Control	35	0	0
		10	13	0	0
		100	13	0	0
		1000	35	0	0
Lycopersicon esculentum	I	Control	35	0	0
		10	9	0	0
		100	15	0	0
		1000	38	0	0
	II	Control	32	0	1
		12	39	0	0
		37	39	0	0
		110	32	0	0
		330	35	0	0
		1000	39	0	0

Validity criteria fulfilled:

yes

Remarks:

All OECD TG 208 criteria were met. Mean control seedling emergence and survival were ≥75% and ≥97% respectively, and no phytotoxic effects were observed. Environmental conditions were identical.

Conclusions:

14-day NOEC values of ≥1000 mg/kg dry weight were determined for the effects of the test substance on the survival, emergence and dry shoot weight of various plant species, based on nominal concentrations. Species tested were cabbage (Brassica oleracea), corn (Zea mays), cucumber (Cucumis sativus), onion (Allium cepa), soybean (Glycine max) and tomato (Lycopersicon esculentum). The NOEC values are equivalent to ≥1176 mg/kg dry weight when normalised to 2% organic carbon content.

Description of key information

14-day NOEC ≥1000 mg/kg dry weight, effects of the test substance on the survival, emergence and dry shoot weight of cabbage (Brassica oleracea), corn (Zea mays), cucumber (Cucumis sativus), onion (Allium cepa), soybean (Glycine max) and tomato (Lycopersicon esculentum).  

Additional information

An OECD TG 208 seedling emergence and growth test has been conducted with the registered substance in accordance with ECHA final decision TPE-D-2114497761-36-01/F.

14-day NOEC values of ≥1000 mg/kg dry weight were determined for the effects of the test substance on the survival, emergence and dry shoot weight of six plant species, based on nominal concentrations (Smithers, 2020). The species tested were cabbage (Brassica oleracea), corn (Zea mays), cucumber (Cucumis sativus), onion (Allium cepa), soybean (Glycine max) and tomato (Lycopersicon esculentum).  No effects were observed. The test was conducted in accordance with OECD TG 208 and in compliance with GLP.

The NOEC values are equivalent to ≥1176 mg/kg dry weight when normalised to 2% organic carbon content.

EC₂₅ and EC₅₀ values were all determined to be >1000 mg/kg dry weight.

Analytically verified test concentrations confirmed that the test substance was relatively stable in the soil throughout the duration of the test.

An initial OECD TG 208 test was carried out with the six species reported above: cabbage, corn, cucumber, onion, soybean and tomato. The test was carried out as a limit test at a concentration of 1000 mg/kg dry weight (Tier I test).

No effects on corn, cucumber and soybean were observed during the limit test therefore no further testing was carried out with these species and NOEC values of ≥1000 mg/kg dry weight were concluded.

However, effects on cabbage, onion and tomato were observed at the 1000 mg/kg dry weight concentration. A full dose response test was therefore conducted with the three species (Tier II test). During the full dose response test, no effects were observed at the highest concentration tested of 1000 mg/kg dry weight. NOEC values of ≥1000 mg/kg dry weight for cabbage, onion and tomato were consequently concluded.