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Long-term toxicity to aquatic invertebrates

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long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
23 Aug - 13 Sep 2017
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 211 (Daphnia magna Reproduction Test)
Version / remarks:
2 October 2012
Natural water instead of recommended medium was used.
according to guideline
EPA OPPTS 850.1300 (Daphnid Chronic Toxicity Test)
GLP compliance:
Analytical monitoring:
Details on sampling:
- Concentrations: control and 12 mg/L
- Sampling method: The bulk exposure solutions (lab dilution water (LDW) control and 12.0 mg/L solutions) were sampled for analytical confirmation of the fortified test material concentrations on days 0, 2, 7, 14, and 19. On days 0, 2, 7, 14, and 19, single aliquots (6 mL) of LDW control bulk exposure solution was collected using a glass pipette and transferred to a 20 mL vial. On days 0, 14, and 19, four aliquots (6 mL) of 12.0 mg/L bulk exposure solution were collected from random locations at mid depth using a glass pipette and transferred to 20 mL vials to evaluate exposure solution concentration and homogeneity. On days 2, 5, 9, 16, and 21, single aliquots (1.50 mL) of each test vessel were pooled in 20 mL glass vials via Eppendorf pipette. Vials were capped and briefly vortex-mixed. Aliquots (0.100 mL) from the bulk and pooled spent solutions were transferred to autosampler vials containing 0.900 mL of MS grade water.
Details on test solutions:
- Method: The 12 mg/L (nominal) test solution was prepared by adding 180 mg of the test material directly to the dilution water (15 L contained in a 20 L glass carboy) and was utilized for the duration of the study. Bulk solutions were maintained at ambient temperature covered with dark plastic and stirred at 60 rpm with Teflon lined stir bars. Slight aeration was provided.
- Differential loading: no
- Controls: only dilution water
- Evidence of undissolved material: no undissolved material observed
Test organisms (species):
Daphnia magna
Details on test organisms:
- Common name: water flea
- Source: laboratory culture
- Age of parental stock (mean and range, SD): less than 24 h old neonates (neonates were only used from daphnids which have had at least 3 broods).
- Feeding during test: yes
- Food type and amount: From test initiation through test day 6 Daphnids were fed with 0.4 mL Raphidocelis subcapitata and 0.1 mL YTC (yeast, wheat grass, finfish food suspension). On test days 7 through 20, the feeding ration was increased from 0.4 ml to 0.5 mL R. subcapitata with 0.1 mL YTC. . The total organic carbon (TOC) concentration was determined from representative samples of the two food types. The R. subcapitata and YTC suspensions contained 0.371 mg C/mL and 0.638 mg C/mL respectively. The final feeding ration level was approx. 0.2 mg C/daphnid/day.
- Frequency: daily (Daphnids were not fed on Day 21)
Test type:
Water media type:
Limit test:
Total exposure duration:
21 d
54-64 mg CaCO3/L
Test temperature:
20-21 °C
Dissolved oxygen:
7.4-8.9 mg/L (84-102% air saturation)
160-195 µS/cm (control)
157-200 µS/cm (test item vessel)
Nominal and measured concentrations:
Nominal: 0 (Control), 12 mg/L
Measured: < LOQ (Control), 12.6 mg/L (TWA)
Details on test conditions:
- Test vessel: 125 mL glass borosilicate jars
- Type: vessel were loosely covered
- Fill volume: 90 mL
- Renewal rate of test solution: renewal every Monday, Wednesday and Friday
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

- Source/preparation of dilution water: Dilution water was Lake Huron water. The water was obtained from the upper Saginaw Bay of Lake Huron off Whitestone Point and was limed and flocculated with ferric chloride. Before use in the laboratory, the water was sand-filtered, pH-adjusted with gaseous CO2, carbon-filtered, and UV-irradiated. Concentrations of contaminants were below levels of concern that may have interfered with the results of the test.
- Total organic carbon: 1.7 mg/L
- Total Suspended Solids: < 2 mg/L
- Alkalinity: 38-46 mg CaCO3/L (control) and 38-44 mg CaC0 3/L (test item vessel)
- Intervals of water quality measurement: Dissolved oxygen, temperature and pH were measured at test initiation and at each test solution renewal from the bulk water control and bulk test solution. Dissolved oxygen, temperature and pH were also measured from spent replicate solutions once per week and at exposure termination. Water temperature was continuously monitored from one surrogate vessel. Alkalinity, hardness, and conductivity were measured at least one time per week from the bulk water control and bulk test solution. Periodically, the water was monitored for total organic carbon (TOC), total suspended solids (TSS), and selected inorganic and organic compounds.

- Adjustment of pH: see source/preparation of dilution water
- Photoperiod: 16 hour light/8 hour dark
- Light intensity: 1042-1484 lux

EFFECT PARAMETERS MEASURED: Observations were made daily for parent mortality and neonate production (reproduction was quantified every M, W, and F). The time (days) to production of first brood was also recorded. Any sublethal effects (abnormal behavior or appearance) were recorded. On Day 21, lengths (distance measured from apex of helmet to base of the shell spine) were measured to the nearest 0.1 mm and recorded for all surviving parent Daphnia. Daphnids were then dried at 60°C for 24 h and dry weights was determined to the nearest 0.01 mg.

- Test concentrations: Definitive test concentrations were based on the 48 h EC50 value of > 117 mg/L, determined from the daphnid acute toxicity test with the same substance.
Reference substance (positive control):
21 d
Dose descriptor:
Effect conc.:
>= 12.6 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
21 d
Dose descriptor:
Effect conc.:
> 12.6 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
Reported statistics and error estimates:
- Analyses were conducted in SAS/STAT software, version 9.2 (SAS System, Copyright 2002-2008, SAS Institute Inc. SAS and all other SAS Institute Inc. products or services are registered trademarks or trademarks of SAS Institute Inc., Cary, North Carolina).

- The determination of a NOEC for offspring, weight and length was made by comparing the treated groups to the control group with a lower railed Dunnett ' s test, since the data met the normality and homogeneity assumptions.

- The statistically significant effect observed in weight was interpreted to be a result of the absence of neonate production of select control organisms (3 of 9) on day 21 (exposure termination) as compared to limit test level (1 of 9). This resulted in a higher mean dry weight for the control due to the suspected presence of unreleased progeny. Therefore an additional analysis was conducted removing the weight data for animals with an absence of neonate production on day 21 (exposure termination). The NOEC for weight was based on the analysis where the data were removed. This interpretation is supported by the absence of effects in reproduction, survival and the additional growth parameter (length).

- The survival data were not statistically analyzed as the percent survival was equal for the two concentrations.


The percent of measured concentration of bulk exposure solutions ranged from 100 - 109% of the nominal target values. The percent of measured concentration of corresponding spent (pooled replicate) solutions ranged from 96.9-108% of the nominal target values. This indicated that the test material was not degraded or otherwise lost from the test vessels over the course of the 21-day static-renewal exposure period.

Table 1: Results form analysis of the test substance.

Nominal Concentration [mg/L] Fresh Spent Fresh Spent Fresh Spent Fresh Spent Fresh Spent TWA % of Target
Day 0 Day 2 Day 2 Day5 Day 7 Day 9 Day 14 Day 16 Day 19 Day 21
Control < LOQ < LOQ < LOQ < LOQ < LOQ < LOQ < LOQ < LOQ < LOQ < LOQ < LOQ N/A
12 12.5 12.6 13.1 12.7 12.7 12.7 12 11.6 13.1 13 12.6 105%


Table 2: Summary of biological observations and results

Time Weighted Mean Measured Conc. [mg/L] % Survival Average Cumulative Offspring Per Surviving Adult Length [mm] Dry Weight [mg]
0 (Control) 90 120.7± 9.9 4.19± 0.06 0.53± 0.15
12 90 118.2± 11.6 4.17± 0.07 0.44± 0.07

Growth (Length)

LOEC, MATC: >12.6 mg/L (limit concentration tested)

NOEC: 12.6 mg/L (limit concentration tested)

Growth (Dry weight)

LOEC, MATC: >12.6 mg/L (limit concentration tested)

NOEC:12.6 mg/L(limit concentration tested)


Table 3: Results for statistical assumptions

Endpoint Shapiro's-Wilk's test for normality Levene's Test for Homogeneity of Variance Data transform Comparison test Procedure
Total Offspring 0.19519 0.7241 none Dunnett's 1-tailed
Weight (mg) 0.25169 0.2038 none Dunnett's 1-tailed
Length (mm) 0.035432 0.6106 none Dunnett's 1-tailed
Animals with absence of neonate production are removed from analysis
Weight 0.16889 0.2049 none Dunnett's 1-tailed

* Rejection criterion for normality is p<0.01; homogeneity of variance is p<0.05

Table 4: Statistical Results

Endpoint Test Run Significance a alpha=0.05
Total Offspring ANOVA p-value = 0.6374 none*
Weight (mg) ANOVA p-value = 0.0804


Length (mm) ANOVA p-value = 0.4829 none*
Survival N.A. N.A.
Animals with absence of neonate production are removed from analysis
Weight ANOVA p-value = 0.1646 none*

*Dunnett's test for test of control concentration versus treated groups

N.A.: not applicable as both concentration groups had the same percent survival.


Table 5: Validity criteria for OECD 211.

Criterion from the guideline


Validity criterion fulfilled

The mortality of the parent animals in the control (female Daphnia) does not exceed 20% at the end of the test.

The survival in the water control was 90%


The mean number of living offspring produced per parent animalsurvivingat the end of the test is ≥ 60 in the control.

The mean number of offspring per surviving adult female in the water control was 120.7 with a standard deviation of 9.9.


Validity criteria fulfilled:
For further details please refer to “Any other information on results incl. tables”.
The chronic toxicity concerning reproduction (NOEC) for Daphnia magna exposed to a limit concentration of the test item over a 21-day static-renewal exposure period and based on time-weighted mean measured concentrations was 12.6 mg/L. The respective LOEC was > 12.6 mg/L.

Description of key information

NOEC (21 d) ≥ 12.6 mg/L based on reproduction (OECD 211, Daphnia magna); read across from hydrolysis product (dimethylsilanediol)

Key value for chemical safety assessment

Additional information

Experimental data for dimethoxydimethylsilane (CAS 1112-39-6) are not available. However, since dimethoxydimethylsilane hydrolyses rapidly to dimethylsilanediol and methanol (DT50 < 0.6 h) the hydrolysis products rather than the parent substance should be considered for the assessment, read-across data for the hydrolysis product, dimethylsilanediol, are considered appropriate for the assessment.

The experimental study conducted with the hydrolysis product dimethylsilanediol was performed according to OECD 211 (GLP, Dow, 2017). Daphnia magna was exposed to the test item under semi-static conditions. Based on the result from the short-term study with an EC50 (48 h) of > 117 mg/L a limit concentration of 12 mg/L was tested. This concentration is sufficient to conclude the environmental hazard classification as well as the PBT/vPvB assessment. The actual exposure concentrations were verified by HPLC/MS with corresponding measured concentrations of the pooled replicates ranging from 96.9-108% of the nominal target values. After 21 d the reproduction as well as length and weight of Daphnids was measured. No effects on reproduction, growth and length were recorded resulting in a NOEC (21 d) ≥ 12.6 mg/L based on the time-weighted average of the measured concentrations. Thus, the silanol hydrolysis product is of low toxicity to aquatic invertebrates.