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Sediment toxicity

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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:
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.
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:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
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:
Remarks:
(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:
39 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 Siloxane Category report (PFA, 2017a). The hypothesis for read-across of sediment ecotoxicity evidence within the Siloxanes Category is that no structure-based or property-based pattern is evident from the category dataset of existing studies, although patterns are identifiable associated with extrinsic aspects of test design to which effects may be attributed. The approach will be revisited in the event that reliable new data become available. With this in mind, a single overall interpretation is made across the category. To fulfil the requirements of REACH, a conservative approach is made by reading across on a nearest-neighbour basis the reliable data within the category.

In the context of the RAAF, Scenario 6 is expected to apply to this endpoint. It is considered that effects observed in benthic organisms are associated primarily with extrinsic factors associated with test design and not to structural similarities as such.

A total of twenty-four sediment toxicity studies for siloxanes are available and nineteen results from studies of standard duration in standard test species 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 the studies which are not suspected to be confounded by extrinsic factors show relatively minimal effects across the dataset.

READ-ACROSS JUSTIFICATION

Data available for the substance:

No data are available for the effects of the registration substance on sediment organisms. Data are read-across from the structural analogue octamethyltrisiloxane (L3; 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-L3 and 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 Kow and 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 Section 6 Ecotoxicological Information.

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 sediment incorporated test substance 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 under semi-static water replenishment conditions (Wildlife International, 2009a).

A 28-day LC50 and NOEC value of >70 and ≥70 mg/kg, respectively, (>95 and ≥95 mg/kg dwt, respectively, 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 (Smithers Viscient, 2013b).

Two studies with Lumbriculus variegatus are available for 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 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, 2009b). 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).

Outlier analysis was performed on the four NOEC values obtained from these studies (Dow Corning Corporation, pers. comm., August 2015). The scores of the lowest L3 benthic invertebrate NOEC value (i.e., 1.1 mg/kg dw on artificial sediment) showed the largest deviation from the whole distribution and the datum is an outlier via both the Dixon Q test and Grubbs’ (z) test. In addition, differences between measured and nominal concentrations were observed at the start and over the course of this study. Measured concentrations at the start of the test showed that they were in the range of approximately 13-25% (more generally 22-25%) of nominal. Over the course of the test they declined further to between approximately 12 and 20% (more generally 12-14%) of nominal. These difference might be explained as follows:

-        The relatively high vapour pressure and Henry’s Law Constant of the substance would suggest that volatile losses from the test system are likely even during the media preparation phase.

-       Under the test conditions (pH 8.2-8.4 and temperature 22-24°C), the hydrolysis half-life of approximately 4 days would explain the further decline in measured concentration of parent substance over the duration of the study.

In view that a second study with the same species (L. variegatus), is also available, using natural sediment and at a lower pH, this outlier value 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 C. riparius (Wildlife International, 2009a). This value is used as the key value for the CSA.