Dodecamethylpentasiloxane

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

fish early-life stage toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 210 (Fish, Early-Life Stage Toxicity Test)

Version / remarks:

(1992)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: alternate replicates at each treatment level and in controls.
- Sampling method: sample removed from approximate midpoint of aquarium, using a pipette.
- Sample storage conditions before analysis: not reported

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: diluter system using solvent stock (DMF)
- Differential loading: yes, proportional diluter system
- Controls: blank control and solvent control
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): dimethylformamide, CAS 68-12-2
- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): 1.0 ul/l
- Evidence of undissolved material (e.g. precipitate, surface film, etc): none

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM
- Common name: rainbow trout
- Source: Troutlodge Inc. (commercial supplier) - embryos and sperm obtained

METHOD FOR PREPARATION AND COLLECTION OF FERTILIZED EGGS
On the day of exposure initiation, two bags containing the unfertilized gametes were warmed in a water bath to 10 ºC gradually over a one-hour period. Fertilization was achieved by adding cold fertilization buffer solution, consisting of 3.75 g/L glycine, 2.42 g/L TRIS and 5 g/L sodium chloride, to the bag containing the embryos. The bag was rocked gently back and forth a few times and then placed in a water bath at test temperature (approximately 10 ºC) for approximately 30 minutes. This procedure was used to rinse away any ovarian fluid sealing the embryos, preventing fertilization. Following the rinsing procedure, the embryos were removed from the water bath and most of the buffer solution was poured off. Sperm and an aliquot of buffer solution were added to the bag containing the embryos. The bag was then rocked gently back and forth and placed in a water bath for 15 minutes to complete the fertilization process. The sperm was then poured off of the embryos and the embryos were then gently rinsed of excess sperm using cold dilution water. The embryos were then placed in a stainless steel bowl containing cold dilution water and allowed to water-harden for approximately 45 minutes. During the water hardening period, the eggs were maintained at a temperature of 10 ºC.

After the water hardening period, the embryos were then impartially distributed to the embryo incubation cups in the following manner: twenty-eight labelled embryo incubation cups were set in a shallow water bath maintained at 10 ºC. The embryos were then counted into each incubation cup, sequentially, five at a time, until each cup contained five embryos. This procedure was repeated until each embryo cup contained 30 embryos. To initiate the exposure, the incubation cups, each containing 30 embryos, were then placed on the rocker arm apparatus in the respective exposure aquarium (one cup per replicate vessel). The embryos were approximately one hour old (post-fertilization) at exposure initiation.

POST-HATCH FEEDING
- Start date: day 14 post-hatch
- Type/source of feed: live brine shrimp nauplii (Artemia salina)
- Amount given: ad libitum
- Frequency of feeding: three times daily

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

60 d

Remarks on exposure duration:

post-hatch (92 day total duration)

Post exposure observation period:

n/a

Hardness:

20-24 mg/l as CaCO3

Test temperature:

9.9-13 ºC

pH:

6.8-8.0

Dissolved oxygen:

67 - 130% saturation

Salinity:

n/a

Nominal and measured concentrations:

Nominal concentrations: 0.42, 0.84, 1.7, 3.4, 6.7 µg/l

Measured concentrations (time weighted mean): 0.52, 1.1, 1.8, 4.5, 7.9 µg/l

Details on test conditions:

TEST SYSTEM
- Embryo cups (if used, type/material, size, fill volume): glass jars, 5 cm diameter x 8 cm height
- Test vessel: aquaria 30 * 15 * 20 cm made from glass and silicone sealant.
- Type (delete if not applicable): open / closed
- Material, size, headspace, fill volume: fill volume 6.5 l, headspace (calculated by reviewer) 2.5 l
- Aeration:
- Type of flow-through (e.g. peristaltic or proportional diluter): proportional diluter
- Renewal rate of test solution (frequency/flow rate): 90% replacement per 7 h (7.7 aquarium volumes per 24 h)
- No. of fertilized eggs/embryos per vessel: 15
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- No. of vessels per vehicle control (replicates): 4
- Biomass loading rate: During the 92-day exposure period, biomass loading (based on control organism wet weight at test termination) did not exceed 0.2 g/L under the exposure's flow through conditions or 1.5 g/L at any time in any replicate exposure aquarium.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: well water
- Total organic carbon: 0.1 - 0.44 mg/l
- Particulate matter:
- Metals: analysed but not presented
- Pesticides: analysed but not presented
- Chlorine: n/a
- Alkalinity: 56 to 76 mg/l as CaCO3
- Ca/mg ratio: n/a
- Conductivity: 290-420 µS/cm
- Salinity: n/a
- Culture medium different from test medium: no
- Intervals of water quality measurement: weekly

OTHER TEST CONDITIONS
- Adjustment of pH: not reported
- Photoperiod: 16 h/d once all larvae reached swim-up stage
- Light intensity: 680-1100 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

VEHICLE CONTROL PERFORMED: yes

RANGE-FINDING STUDY PERFORMED: no

POST-HATCH DETAILS
- Begin of post-hatch period: day 32
- No. of hatched eggs (alevins)/treatment released to the test chamber: 15
- Release of alevins from incubation cups to test chamber on day no.: not reported

FERTILIZATION SUCCESS STUDY
- Number of eggs used: 30 embryos
- Removal of eggs to check the embryonic development on day no.: n/a

Reference substance (positive control):

no

Duration:

60 d

Dose descriptor:

NOEC

Effect conc.:

>= 0.008 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

other: Hatching, larval survival, abnormal appearance and behaviour

Remarks on result:

other: This concentration represents the limit of solubility in the test medium.

Details on results:

- Mortality/survival at embryo, larval, juvenile, and adult stages: embryo hatching success 93-99%; live normal larvae at hatch 99-100%; larval survival 82-100%
- Days to hatch or time to release of young: hatch complete after 32 d
- Numbers hatched, Numbers of offspring produced, or Number of offspring per live female per day: embryo hatching success 93-99%
- Observations on body length and weight of young and/or exposed parents at one or more time periods: body length of young 43 - 45.3 mm; body weight of young 0.114-0.134 g (based on mean values per dose level, after 60 d post-hatch)
- Number of healthy fish at end of test: larval survival 82-100% after 60 d post-hatch
- Type of and number with morphological abnormalities: 1 live, deformed larva at an intermediate treatment level, not interpreted as significant.
- Type of and number with behavioural abnormalities: not reported
- Type and number of developmental effects: not reported
- Type and magnitude of hormonal changes: not reported
- Other biological observations: not reported
- Effect concentrations exceeding solubility of substance in test medium: no
- Incidents in the course of the test which might have influenced the results: none

Results with reference substance (positive control):

n/a

Table : Sub-lethal effect of L4 on rainbow trout

Treatment (mg/l) nominal (measured) concentration		% deformed larvae
Control (dilution water only)	Replicate #1	0
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
Solvent control	Replicate #1	0
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
0.42 mg/l	Replicate #1	0
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
0.84 mg/	Replicate #1	0
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
1.7 mg/l	Replicate #1	0
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
3.4 mg/l	Replicate #1	1/30 = 3.3%
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
6.7 mg/l	Replicate #1	0
	Replicate #2	0
	Replicate #3	0
	Replicate #4	0
	Replicate #4	0

 

Table : Effect of L4} on growth (mean±SD) of juvenile rainbow trout in the FELS test

Treatment concentration(unit)		Growth - Length			Growth - Dry Weight
Measured	Rep	Mean per fish (mm)	+SD	Treatment Mean(mm)	Mean per fish (mg)	+SD	Treatment Mean(mg)
Dilution control	A	44.1	2.53	44.0 ± 0.63	0.125	0.0259	0.122 ± 0.0078
	B	44.1	2.09		0.124	0.0234
	C	44.6	2.69		0.127	0.0255
	D	43.1	1.47		0.110	0.0186
Solvent control	A	46.2	2.23	44.1 ± 1.30	0.139	0.0294	0.124 ± 0.0105
	B	43.8	1.52		0.119	0.0179
	C	43.7	2.44		0.124	0.0263
	D	43.3	2.84		0.114	0.0352
0.52	A	42.7	3.67	43.6 ± 0.83	0.110	0.0376	0.123 ± 0.0093
	B	44.2	2.38		0.121	0.0221
	C	44.3	2.20		0.131	0.0293
	D	43.0	3.15		0.129	0.0414
1.1	A	45.2	3.27	45.3 ± 0.84	0.135	0.0280	0.134 ± 0.0162
	B	44.4	1.43		0.119	0.0145
	C	46.5	2.07		0.157	0.0294
	D	45.2	2.00		0.126	0.0150
1.8	A	44.5	5.34	43.6 ± 0.79	0.138	0.0444	0.124 ± 0.0107
	B	44.1	1.67		0.124	0.0142
	C	43.1	1.87		0.113	0.0191
	D	42.9	1.56		0.120	0.0184
4.5	A	43.6	1.99	43.7 ± 0.44	0.122	0.0215	0.121 ± 0.0069
	B	43.2	1.15		0.112	0.0121
	C	44.3	1.69		0.129	0.0207
	D	43.6	3.15		0.120	0.0350
7.9	A	43.1	2.16	43.0 ± 0.71	0.115	0.0205	0.114 ± 0.0038
	B	43.5	1.61		0.119	0.0211
	C	42.0	2.60		0.110	0.0264
	D	43.5	2.30		0.113	0.0255

 

Validity criteria fulfilled:

yes

Remarks:

Dissolved Oxygen exceeded the threshold of 60% ASV throughout the test; water temperature variation limited; analytical work appropriate; hatching success and post-hatch success in the controls and solvent controls exceeded the threshold of 75%.

Conclusions:

A 60-d (post-hatch) NOEC of ≥0.0079 mg/L (limit of solubility) was determined for effects (hatching, larval survival, abnormal appearance or behaviour) of decamethyltetrasiloxane (L4) in rainbow trout. This result was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Long-term toxicity to fish: 60 day post-hatch NOEC ≥7.9 µg/l (time weighted mean measured) (highest concentration tested) (OECD 210), based on hatching, larval survival, abnormal appearance and behaviour in Oncorhynchus mykiss, read-across from an analogous/structurally related substance, decamethyltetrasiloxane (CAS 141-62-8).

 

This is supported by 35 day LC₅₀: >39 μg/l (mean measured) and NOEC: ≥39 μg/l (mean measured) (OECD 305) based on mortality in Pimephales promelas.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

7.9 µg/L

Additional information

A 60 day post-hatch NOEC of ≥7.9 µg/l (time weighted mean measured) has been determined for the effects of the analogous substance, decamethyltetrasiloxane (L4, CAS 141-62-8) on hatching, larval survival, abnormal appearance and behaviour in Oncorhynchus mykiss in the fish early-life stage test (OECD 210). In view of the exposure regime it is likely that the test organisms were exposed primarily to the tested substance rather than its degradation products.

Supporting evidence is provided by mortality data in a bioconcentration study. A 35 day LC₅₀ value of >39 ng/l and NOEC of ≥39 ng/l have been determined for the effects of the test substance on mortality of Pimephales promelas. The results have been obtained under flow-through conditions and are expressed relative to mean measured concentrations of the substance.