Reaction mass of decamethyltetrasiloxane; dodecamethylpentasiloxane; hexamethyldisiloxane; octamethyltrisiloxane

Toxicity to terrestrial arthropods

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial arthropods: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Guideline study but it is not certain whether the study was conducted in accordance with GLP.

Qualifier:

according to guideline

Guideline:

other: Environment Canada 1/RM/47, June 2007

GLP compliance:

not specified

Remarks:

The data is from a publication and this information was not included.

Application method:

soil

Analytical monitoring:

yes

Details on sampling:

Soil samples were collected throughout the initial treatment, preparation (i.e., at manure amendment, following the 2-h equilibrium period, and following mixing of the amended biosolid with the Gr10 soil) for the range-finding tests to confirm the analytical methodology used, as well as to evaluate the loss of D5 over time. For the definitive tests, samples were taken for analysis only on day 0 of the test (i.e., when the test organisms were added) to confirm dose concentrations in the test soil. All samples were immediately frozen and stored at -20°C prior to analysis. All samples were analyzed for cVMS D4, D5 and D6 concurrently by Quebec Laboratory for Environmental Testing of Environment Canada (Montreal, Quebec).

Triplicate 1.0g (+/-0.2) (wet weight) samples were then measured into glass tubes and well mixed to ensure solids are homogenized. To extract the soil samples, 5 mL of acetonitrile was added to each sample and vortexed followed by the addition of 5 mL of pentane (also vortexed). The sample was then sonicated in an ice bath for 10 min followed by centrifugation at 1500 RPM for 10 min at 15°C. The pentane phase was then transferred to a clean GC vial and 75 μL of naphthalene-D8 solution(lfi) ng/μL in pentane) was added as an internal standard.

Vehicle:

no

Details on preparation and application of test substrate:

A sandy loam soil (Gr10) was obtained from Greely Sand and Gravel (Ottawa Ontario (ON)) in June 2010 and was dried, sieved (4-mm mesh) and homogenized prior to use. The negative control treatment consisted of a formulated artificial soil (AS) comprising 10% air-dried pre-sieved Sphagnum sp. peat, 20% kaolin clay, and 70% silica sand, with calcium carbonate added to standardize the soil pH.

For the toxicity tests, the soil was amended with either an uncontaminated or contaminated surrogate biosolid. Although available, the use of an actual biosolid produced from a water treatment facility was not pursued as an option for use in the toxicity tests as the potential for other contaminants or toxicants present in the sample may have confounded toxicity test results. As a result, mushroom compost and organic cow manure were both considered as options for a surrogate biosolid. Both alternative biosolids were analyzed in conjunction with a real biosolid (obtained from the Robert O. Picard Water Treatment facility in Ottawa, ON) for comparison of their physical and chemical characteristics. Based on these characteristics. the organic cow manure was selected for its similarity in percent organic matter to the actual biosolid.

To prepare test samples, the surrogate biosolid was amended with D5 (97% pure liquid; Sigma-Aldrich) to create a contaminated test substance; subsequently, the amended biosolid was manually mixed for 2 min, covered to prevent volatilization, and allowed to equilibrate for 2 h. Following the 2 h equilibration period, the amended biosolid was added to the Gr10 soil at a rate of 5 g/kg (on a dry weight basis), equivalent to 8 t/ha, a common application rate for biosolids on agricultural soils in Ontario to create the test soil. Each test concentration was prepared independently. The average moisture content of the test soil was 38 ± 3%, with an average pH of 7.55±0.15 for all test set-ups.

Test organisms (species):

Folsomia candida

Animal group:

Collembola (soil-dwelling springtail)

Details on test organisms:

Ten age-synchronized organisms {10-12 d old) were added to each test vessel at the test start (day 0).

Study type:

laboratory study

Limit test:

no

Total exposure duration:

28 d

Test temperature:

20+/-2°C

pH (if soil or dung study):

7.55 +/-0.15

Photoperiod and lighting:

8.3 +/-2.1 μmol(m2/s)

Details on test conditions:

Ten age-synchronized organisms {10-12 d old) were added to each test vessel at the test start (day 0). The test vessels were incubated at 20 +/-2°C with an average light intensity of 8.3 +/-2.1 μmol (m2t)-1, within the ranges specified in the method. The test vessels were aerated weekly, fed yeast bi-weekly, and the soil was hydrated with de-ionized water as necessary. At the end of the test, the test vessels were flooded with water, allowing the test organisms to float to the surface, and the number of live adults and juveniles was recorded.

Nominal and measured concentrations:

Nominal/measured concentrations (mg/kg dry wt.) of D5 used in the F. candida test were 0/0.10, 175/42, 279/65, 447/99, 715/239, 1144/377, 1831/363, 2930/1082, 4688/2053, 7500/2917. The measured value of 0.10 mg/kg D5 in the control soil was used as the background level.

Reference substance (positive control):

not specified

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

813 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: 457-1514

Duration:

28 d

Dose descriptor:

other: IC50

Effect conc.:

767 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks on result:

other: 471-1253

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

377 mg/kg soil dw

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

other: mortality and reproduction

Remarks on result:

other: based on visual evaluation of data by reviewer

Details on results:

An effect was observed for both adult survival and juvenile reproduction when F. candida was exposed to D5. There was no significant difference between the test endpoints, in that, as adults became affected by D5 in the soil, the juvenile production dropped of accordingly.

Reported statistics and error estimates:

The lethal concentration (i.e., LC50s) was calculated for invertebrate mortality using the EPA Probit Analysis Program {version 1.5) or the EPA Trimmed Spearman-Karber (TSK) Program (version 1.5). Inhibitory concentrations (i.e., lC50s) were estimated for invertebrate juvenile production using nonlinear regression analysis via SYSTAT (version 13) software.

A NOEC has been determined by the reviewer on the basis of a visual examination of the data.

Validity criteria fulfilled:

yes

Conclusions:

A 28-day LC50 value of 813 mg/kg dry weight and a 28 day IC50 value of 767 mg/kg dry weight have been determined for the effects of the test substance on mortality and reproduction of Folsomia candida. A NOEC of 377 mg/kg dry weight has been determined by the reviewer on the basis of a visual examination of the data for both mortality and reproduction.

Description of key information

L4: LC₅₀ (28-day): 813 mg/kg dry weight, mortality Folsomia candida, measured, read-across from D5 CAS: 541-02-6.

IC₅₀(28-day): 767 mg/kg dry weight reproduction, Folsomia candida, measured, read-across from D5 CAS: 541-02-6.

NOEC (28-day): 377 mg/kg dry weight mortality and reproduction, Folsomia candida, measured, read-across from D5 CAS: 541-02-6.

L5: LC₅₀ (28-day): 813 mg/kg dry weight, mortality Folsomia candida, measured, read-across from D5 CAS: 541-02-6.

IC₅₀(28-day): 767 mg/kg dry weight reproduction, Folsomia candida, measured, read-across from D5 CAS: 541-02-6.

NOEC (28-day): 377 mg/kg dry weight mortality and reproduction, Folsomia candida, measured, read-across from D5 CAS: 541-02-6.

Additional information

Constituents HMDS and L3

No data are available for the effects of Constituent HMDS or Constituent L3 on terrestrial arthropods. Data is waived on the basis that the test substance is too volatile to maintain adequate concentrations in the test system.

 

Constituents L4 and L5

There are no data describing the long-term toxicity of L4 and L5 to terrestrial arthropods. However, data are available with the siloxane decamethylcyclopentasiloxane (D5, CAS: 541-02-6). A 28-day LC₅₀ value of 813 mg/kg dry weight and a 28-day IC₅₀ value of 767 mg/kg dry weight have been determined for the effects of D5 on mortality and reproduction of Folsomia candida. A NOEC of 377 mg/kg dry weight has been determined by the reviewer on the basis of a visual examination of the data for both mortality and reproduction.

These data will be considered in the derivation of the PNECsoil for L4 and L5.

 

Testing proposal for Constituent L4

An OECD TG 222 earthworm reproduction study is under way for L4. The earthworm is the standard organism for soil macroorganisms and there is no indication that arthropods would be any more susceptible.

Read-across of the terrestrial toxicity data for D5 to L4 is considered to be suitable to derive an interim hazard and risk assessment under REACH for L4.

 

Testing proposal for Constituent L5

An OECD TG 222 Earthworm reproduction study is under way for L5. The earthworm is the standard organism for soil macroorganisms and there is no indication that arthropods would be any more susceptible.

Read-across of the terrestrial toxicity data for D5 to L5 is considered to be suitable to derive an interim hazard and risk assessment under REACH for L5.