1,1,1,3,5,5,5-heptamethyltrisiloxane

Sediment toxicity

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

sediment toxicity: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-04-29 to 2009-05-27

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 218 (Sediment-Water Chironomid Toxicity Test Using Spiked Sediment)

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

SEDIMENT

- Sampling interval: Sediment samples were collected from the analytical replicates from each test concentration and control shortly after the introduction of the organisms on Day 0, on Day 7 and at test termination on Day 28.

Vehicle:

no

Details on sediment and application:

SEDIMENT

- Formulated sediment: The sediment used in the study was a formulated sediment based on the recommendations of OECD Guideline 218. The sediment was composed of approximately 10% sphagnum peat moss, 20% silt and clay (kaolin clay) and 70% industrial quartz sand. The sand and clay were mixed in a PK Twinshell mixer for 20 minutes without the peat, since the peat was added later. The targeted organic carbon content of the final mixture was 5.0 ± 1.0%. The dry soil was stored under ambient conditions until used. The final pH of the sediment was 7.0. The percent organic carbon of the sediment was found to be 2.2.

Test organisms (species):

Chironomus riparius

Details on test organisms:

TEST ORGANISM

- Source: Egg masses were obtained from Environmental Consulting and Testing, Superior, Wisconsin. The organisms were held for five days prior to the start of the test at approximately the same temperature and in water from the same source as the water used during the test. At test initiation, the midges were collected from the culture and impartially added one and two at a time to test chambers. All transfers were made below the air/water interface using wide-bore pipettes.

Study type:

laboratory study

Test type:

semi-static

Water media type:

freshwater

Type of sediment:

artificial sediment

Limit test:

no

Duration:

28 d

Exposure phase:

total exposure duration

Hardness:

136-144 mg/L as CaCO3

Test temperature:

20 ± 2 ºC

pH:

pH ranged from 8.1 to 8.6

Dissolved oxygen:

≥7.1 mg/L (79% of saturation)

Salinity:

not applicable

Ammonia:

<0.17 to 6.28 mg/L (Ammonia levels exceeded 4.0 mg/L in the overlying water of some replicates on Days 7 and 14; therefore, the overlying water was partially renewed on those days in each replicate to prevent toxicity caused by high levels of ammonia).

Nominal and measured concentrations:

Nominal concentrations in mg/Kg: 0 (Control), 31, 63, 125, 250, 500 and 1000

Arithmetic mean measured concentrations in mg/Kg in the treated sediments: 7.4, 14, 39, 84, 210 and 435

The mean measured concentrations in the treated sediments are equivalent to 24, 23, 32, 34, 42 and 44% of nominal.

The results are interpreted with reference to the mean measured concentrations.

Details on test conditions:

TEST SYSTEM

- Test container (material, size): Test chambers were 2000-mL glass beakers containing approximately 2 cm of sediment and 8 cm of overlying water

- Aeration: yes

- Overlying water renewal: Overlying water was partially renewed on Days 7 and 14 of the test to prevent the build-up of ammonia concentrations to toxic levels

- Aeration frequency and intensity: Loose plastic covers were placed over each test chamber. Each test chamber was gently aerated through a glass pipette that did not extend to a depth closer than 2 cm from the surface of the sediment. Air was bubbled into the test chamber at a rate greater than 1 bubble per second but not so great as to disturb the sediment.

EXPOSURE REGIME

- No. of organisms per container (treatment): Four replicates were tested in each treatment group with 20 midges in each replicate for a total of 80 midges per treatment group.

- Type and preparation of food: A 28-day ration of food (280 mg Tetramin flake food) was dry mixed into the sediment prior to the addition of the overlying water and 49 hours before adding the test organisms.

OVERLYING WATER CHARACTERISTCS

- Dilution water source: Well Water

- Dilution water chemistry: hardness 136-144 mg/L as CaCO3 , alkalinity 178-180 mg/L as CaCO3 and conductivity 371-393 mhos/cm

OTHER TEST CONDITIONS

- Lighting (quality, intensity, and periodicity): fluorescent lighting with wavelengths similar to natural lighting, intensity was 414 lux at the surface of the water at test initiation, photoperiod was 16 hours light:8 hours dark with a 30-minute transition period.

The sediment contained 72% sand, 10% silt and 18% clay. Textural class: sandy loam. Organic carbon: 2.2%, Organic matter: 3.9%

Reference substance (positive control):

no

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

166 mg/kg sediment dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: 84-435

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

84 mg/kg sediment dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

development rate

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

39 mg/kg sediment dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

development rate

Reported statistics and error estimates:

The 28-Day LC50 was calculated using the computer software of C.E. Stephan. The program is designed to calculate the LC50 value and 95% confidence interval by probit analysis, the moving average method, or binomial probability with nonlinear interpolation. In this study, the binomial method was used to calculate the LC50 value. The LC50 value was calculated using the mortality data collected at the end of the test. The no-observed-effect-concentration (NOEC) and the lowest-observed-effect-concentration (LOEC) were determined by visual interpretation of the dose-response pattern and statistical analyses of the mean development times, emergence ratios and development rates.

   Table 1. Results of analysis of sediment exposure concentrations

 

Nominal Test Concentration (mg/Kg)	Mean Measured Concentration (mg/Kg)	Mean Percent of Nominal
Negative Control	--	--
31	7.4	24
63	14	23
125	39	32
250	84	34
500	210	42
1000	435	44

 

 

Table 2. Test results

 

Mean Measured Concentration (mg/Kg)	Number Exposed	Percent Emergence	Percent Mortality	Mean Development Time (Days)	Emergence ratio	Development rate
Negative Control	80	88	13	17.7	0.88	0.0604
7.4	80	90	10	18.0	0.90	0.0588
14	80	94	6.3	17.4	0.94	0.0608
39	80	91	8.8	18.9	0.91	0.0588
84	80	71	29	20.3	0.71	0.0519*
210	80	43*	58	21.8*	0.43*	0.0486*
435	80	4*	96	23.8*	0.04*	0.0431*

^*There was a statistically significant difference (p<0.05) from the negative control using Dunnett’s t-test.

Validity criteria fulfilled:

yes

Conclusions:

A 28-Day LC50 value of 166 mg/kg dry weight has been determined for the effects of the sediment incorporated test substance on mortality of Chironomus riparius. A NOEC of 39 mg/kg dry weight for effects on development rate has been determined in the same test.

Reference 2

Endpoint:

sediment toxicity: long-term

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 endpoint summary for discussion of read-across.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

39 mg/kg sediment dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

development rate

Remarks on result:

other: 89 mg/kg dwt normalised to 5%OC

Description of key information

NOEC 39 mg/kg dwt (89 mg/kg dwt normalised to 5% OC)

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:

89 mg/kg sediment dw

Additional information

No sediment toxicity data are available for the registration substance H-L3.

A category approach is applied to this endpoint and is detailed in the updated extract from the Reconsile Siloxane Category report attached to the endpoint summary in IUCLID Section 6.3.

More than twenty-five sediment toxicity studies for siloxanes are available and have been reviewed in detail. There is a general trend for studies using natural sediment, which all have pH <~8, to show no effects, or higher NOECs than those with artificial sediment. No significant toxicity (NOEC <100 mg/kg) in any organism is found at pH near 7 with natural sediment. The data suggest that it is possible to read across sediment toxicity data between different siloxane structures, especially where natural sediment data are available, given that studies which are not suspected to be confounded by extrinsic factors show relatively minimal effects across the dataset.

In the use of the data set for hazard assessment and derivation of predicted no-effect concentration (PNEC), the following approaches are used:

- Where the hydrolysis half-life is >48 hours, the chemical safety assessment will focus on the parent form.

- Where data are available for a substance with natural sediment and with artificial sediment for the same species, the natural sediment data will be given preference over data obtained with artificial sediment.

- PNEC will be determined on a weight-of-evidence basis for each substance, including use of read-across. Equilibrium partitioning calculations will be used if necessary.

 

No measured data are available for the effects of the registration substance on sediment organisms. Data are read-across from the structural analogue octamethyltrisiloxane (L3, CAS 107-51-7).

The registered substance (H-L3) and read-across substance (L3, CAS 107-51-7) are members of the Reconsile Siloxanes Category.H-L3and the source substance L3 are linear siloxanes with three silicon atoms, alternated by oxygen atoms. In L3, the Si atoms are fully methyl substituted, whereas in H-L3 the central silicon atom is substituted with one hydrogen atom and one methyl group.The registration and read-across substances have similar physicochemical properties (low water solubility, high log K_owand slow hydrolysis rates), are not readily biodegradable and have high potential for adsorption to sediment.A summary of the relevant physicochemical properties of the registration and read-across substances are reported in the table in Section 6 of IUCLID.

Chironomus riparius

A 28-day LC₅₀ value of 166 mg/kg dry weight (377 mg/kg dwt normalised to 5% organic carbon (OC)) has been determined for the effects of the read-across test substance, L3, on mortality of Chironomus riparius. A NOEC of 39 mg/kg dry weight (89 mg/kg dwt normalised to 5% OC) for effects on development rate has been determined in the same test. The test was conducted in artificial sediment under semi-static water replenishment conditions (Wildlife International 2009b).

Hyalella azteca

28-Day LC₅₀ and NOEC values of >70 and ≥70 mg/kg (>95 and ≥95 mg/kg dwt normalised to 5% OC) have been reported for the effects of L3 on the mortality and growth rate of the freshwater amphipod Hyalella azteca. The results are based on mean measured concentrations. The study was conducted in natural sediment, under flow-through conditions (Smithers Viscient 2013b).

Lumbriculus variegatus

Three studies with Lumbriculus variegatus read across from L3.

In a 28-day study (using artificial sediment under flow-through water replenishment conditions), an EC₅₀ of >17 mg/kg sediment dry weight (>45 mg/kg dwt normalised to 5% OC) has been determined for the effects of the L3 on survival and reproduction of Lumbriculus variegatus. In the same study, a NOEC of 1.1 mg/kg sediment dry weight (2.9 mg/kg dwt normalised to 5% OC) was determined for the same endpoints (Wildlife International 2009a).

In a second study (using natural sediment under static conditions), no effects on reproduction or growth were observed in Lumbriculus variegatus at 38 mg/kg dw (measured, initial). The EC₅₀ is therefore >38 mg/kg dwt (61 mg/kg dwt normalised to 5% OC) and the NOEC ≥38 mg/kg dw (≥61 mg/kg dwt normalised to 5% OC; highest concentration tested) (Smithers Viscient 2013a).

In the third study (using artificial sediment under static conditions), no effects of L3 on biomass and reproduction (as total number of oligochaetes) were observed in Lumbriculus variegatus. The EC₅₀ is therefore >7.8 mg/kg dwt and the NOEC is ≥7.8 mg/kg dwt (both values normalised to 5% OC as >18.6 and ≥ 18.6 mg/kg dwt, respectively) (Smithers Viscient 2017).

The Wildlife International 2009a Lumbriculus study derives the lowest NOEC of all the sediment tests with L3. However, the results of this study are discounted for the following reasons:

- As discussed in the Reconsile Siloxane Category report extract, there are a number of possible contributing factors that could have caused higher toxicity in studies in artificial sediment, particularly the use of artificial sediment with a peat-based carbon source and elevated pH in the test system. The result is therefore disregarded because it is thought that the artificial sediment with peat based carbon source and high pH values in the study interfered with the test system to exhibit toxicity that is extrinsic to the actual toxicity of the substance.

- Two further studies of higher reliability with the same species (Lumbriculus variegatus) are available; one using natural sediment at a lower pH (Smithers Viscient 2013a), and one in artificial sediment with neutral pH (Smithers Viscient 2017). No effects were reported in either of these studies.

- In both the Smithers Viscient 2013a and Smithers Viscient 2017 studies, the worms were synchronised prior to testing, whereas the worms in the Wildlife International 2009a study were not. This can lead to variability in reproduction and difficulty in interpreting results.

- Reproduction was quite poor in the Wildlife International 2009a study, with the number of worms at the end of the study (day 28) in the control vessels not quite meeting the validity criteria outlined in the OECD TG 225 guidance (the average number of living worms per replicate in the controls should have increased by a factor of at least 1.8 at the end of exposure compared to the number of worms per replicate at the start of exposure; the worms in the Wildlife International 2009a study increased by a factor of 1.73). Although this slight difference in reproductive increase might not justify disregarding of the study, the combination of factors discussed above indicates that this study is less reliable than the Smithers Viscient 2013a and Smithers Viscient 2017 studies.

In view that two further studies with Lumbriculus variegatus are available with higher reliability, and one of the available studies uses natural sediment, the Wildlife International 2009a study with Lumbriculus variegatus is disregarded without detriment to the completeness of the data set. Hence, the lowest NOEC is taken as 39 mg/kg dwt (89 mg/kg dwt when normalised to 5% organic carbon content) from the study with Chironomus riparius (Wildlife International, 2009b). This value is used as the key value for the CSA.