destillation fraction of chlorosilanes

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.2 mg/L

Assessment factor:

500

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.02 mg/L

Assessment factor:

5 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

66.7 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.54 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.054 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

equilibrium partitioning method

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.34 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

16.7 mg/kg food

Assessment factor:

300

Additional information

PNEC Aqua

No data are available for the toxicity of the MS-Silane components to aquatic organisms. However, the substance hydrolyses very rapidly (half life at pH 7 << 1 min) in contact with water to produce silanols and hydrogen chloride. Therefore, it is appropriate to assess the hazard to the aquatic environment of the substance in terms of the properties of the hydrolysis products.

Aquatic ecosystems are characterized by, among other factors, their pH; the organisms of the ecosystem are adapted to these conditions.The pH of aquatic habitats can range from 6 in poorly buffered ‘soft’ waters to 9 in well buffered ‘hard’ waters. The tolerance of aquatic ecosystems to natural variations in pH is well understood and has been quantified and reported extensively in ecological publications and handbooks (e.g. OECD SIDS for CAS No. 7647-01-0).Effects on aquatic organisms arising from exposure to hydrogen chloride are thought to result from a reduction in the pH of the ambient environment (arising from an increase in the H⁺concentration) to a level below their tolerable range.

 

It is not considered appropriate or useful to derive a single aquatic PNEC for hydrogen chloride because any effects will not be a consequence of true chemical toxicity and will be a function of, and dependent on, the buffering capacity of the environment. Physical hazards related to pH effects are considered in the risk characterisation and risk management measures.

 

The aquatic toxicity of MS-Silane is assessed on the basis of reliable acute toxicity tests results for the hydrolysis products dimethylsilanediol, trimethylsilanol, and tetraethylorthosilicate for freshwater fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchnerella subcapitata)). LC50 or EC50 values for the three organisms are all >100 mg/L respectively.

Measured acute data at three trophic levels are available for constituents of MS-Silane. However, these are limit values only, showing no effects at the highest concentration tested. This means that a true PNEC cannot be calculated; only a value indicative of the lower limit of possible values for PNEC can be derived.

The standard approach to PNEC calculation when acute data are available for three trophic levels is to apply an assessment factor of 1000 to the lowest lethal or effect concentration (E(L)C50). However, this assessment factor may be reduced by up to a factor of 10 if this is justified by the available data, for example:

- Evidence from structurally similar compounds which may demonstrate that a higher or lower factor may be appropriate.

- Knowledge of the mode of action as some substances by virtue of their structure may be known to act in a non-specific manner. A lower factor may therefore be considered. Equally a known specific mode of action may lead to a higher factor (ECHA 2009).

The lowest L(E)C50 value is for the constituent hydrolysis product dimethylsilanediol (>100 mg/L) for aquatic invertebrates. Therefore, PNECaquatic derived from measured acute data is >100/500 = >0.20 mg/L.

The current preferred value for PNECaquatic is based on short-term data and is 0.20 mg/L. The predictions are sufficiently robust, and are not limit values. This PNEC is considered adequate for the present REACH risk characterisation, however, it may be possible to refine it further and it should not be used for other regulatory purposes without further consideration.

PNECaqua-marine is derived from the freshwater acute aquatic toxicity data as no data are available for marine species. An additional assessment factor of 10 is applied to account for possible differences between marine and freshwater environments, giving an overall assessment factor of 5000.

The documented PNECs are considered adequate for the present REACH risk characterisation. They have been calculated using the current ECHA guideline, including the most conservative assessment factors, and are used for the registration under the regulation 1907/2006 dated June 1st 2007 (REACH) only. They should not be used for other regulatory purposes (e.g., OELs) without further consideration and evaluation.

	Value	Assessment factor	Remarks/justification
PNEC aqua – freshwater (mg/l)	0.20	500	An assessment factor of 500 is applied acute data from three trophic levels. See above text for justification.
PNEC aqua - marine water (mg/l)	0.02	5000	An additional assessment factor of 10 is applicable for extrapolation from freshwater to marine species.
PNEC aqua – intermittent releases (mg/l)			Intermittent releases are not applicable to the identified uses of the substance.

PNEC Sediment

No toxicity test data are currently available for sediment-dwelling organisms; therefore, it is not possible to determine a PNECsed based on measured data. A PNECsediment can however be calculated by the equilibrium partitioning method using the following equation: PNECsed = Ksusp-water/RHOsusp * PNECwater * 1000

For MS-Silane this is: PNECsed = 3.13/1150 * 0.20 * 1000 = 0.544 mg/kg wwt

Hence PNECsediment = 0.544 mg/kg wwt will be used for risk characterisation.

The substance hydrolyses rapidly and exposure will be to the silanol hydrolysis product, therefore, the calculations of Ksusp-water and RHOsusp used the physicochemical properties of the silanol hydrolysis product of the substance. In the absence of measured data, it is not appropriate to use additional assessment factors when determining a PNECsediment by the equilibrium partitioning method. Furthermore, the Log KOW is <<5, therefore, no additional assessment factor is needed to account for possible uptake via sediment ingestion.

The documented PNECs are considered adequate for the present REACH risk characterisation. They have been calculated using the current ECHA guideline, including the most conservative assessment factors, and are used for the registration under the regulation 1907/2006 dated June 1st 2007 (REACH) only. They should not be used for other regulatory purposes (e.g., OELs) without further consideration and evaluation.

PNEC Soil

No toxicity test data are currently available for soil-dwelling organisms; therefore, it is not possible to determine a PNECsoil based on measured data. A PNECsoil can however be calculated by the equilibrium partitioning method using the following equation: PNECsoil = Ksoil-water/RHOsoil * PNECwater * 1000

For MS-Silane this is: PNECsoil = 2.88/1700 * 0.20 * 1000 = 0.339 mg/kg wwt

Hence PNECsoil = 0.339 mg/kg wwt will be used for risk characterisation.

The substance hydrolyses rapidly and exposure will be to the silanol hydrolysis product, therefore, the calculations of Ksoil-water and RHOsoil used the physicochemical properties of the silanol hydrolysis product of the substance. In the absence of measured data, it is not appropriate to use additional assessment factors when determining a PNECsoil by the equilibrium partitioning method. Furthermore, the Log KOW is <<5, therefore, no additional assessment factor is needed to account for possible uptake via soil ingestion.

The documented PNECs are considered adequate for the present REACH risk characterisation. They have been calculated using the current ECHA guideline, including the most conservative assessment factors, and are used for the registration under the regulation 1907/2006 dated June 1st 2007 (REACH) only. They should not be used for other regulatory purposes (e.g., OELs) without further consideration and evaluation.