Triethoxypropylsilane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

2 mg/L

Assessment factor:

50

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

2.12 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.2 mg/L

Assessment factor:

500

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

10 mg/L

Assessment factor:

10

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

96 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

9.6 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

18.02 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

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).

triethoxypropylsilane and its silanol hydrolysis product are part of a category of organosilicon substances containing only alkyl, halogen or alkoxy groups attached to the Si atom. The category (containing approx. 40 substances with reliable data on toxicity to aquatic organisms) has a low hazard profile and data are consistent with a simple non polar narcosis mechanism, the potency of which is usually related to log Kow It is considered this justifies a reduction of the assessment factor from the normal value of 1000. A value of 500 is used, to reflect the increased confidence in the individual values due to the low variability across the category. This is discussed further in PFA, 2010.

Short-term ecotoxicity data for three trophic levels are available for (3-chloropropyl)triethoxysilane. The relevant values are:

Fish:LC50 (96 h): 80 mg/l; NOEC: 58 mg/l

Daphnia: EC50 (48 h): 21.2 mg/l; NOEC: 2.15 mg/l (Mitterer, K.-E. 2002)

Daphnia: EC50 (48 h): 140 mg/l; NOEC: 100 mg/l (Hüls 1993)

Algae: EC50 (72 h): >819 mg/l; NOEC 237 mg/l

 

In addition, a 21-day NOEC value of ≥100 mg/L has been determined for the effects of (3-chloropropyl)triethoxysilane on mortality and reproduction of Daphnia magna when expressed in terms of nominal concentrations. The result has been reinterpreted by the reviewer in terms of the mean measured concentration of the test substance to give a NOEC of ≥ 66 mg/l.

The PNEC is based on taking the NOECs derived in the algal test and long-term test with invertebrates into account and applying an assessment factor of 50. It is noted that the NOEC derived in the long-term invertebrate test is higher than the EC50 values derived in the short-term invertebrate and fish tests. The long-term invertebrate result has however been used as the basis for setting the PNEC for the following reasons:

Both invertebrate tests are assigned reliability 1 but the test design used in the long-term test is more robust in terms of the numbers organisms that are exposed in each treatment.

The apparent discrepancy in the relationship between the two results can be explained to a large degree by the shallow nature of the dose-response relationships in both tests which means that there is scope for overlap of the EC50 and NOEC values when other sources of variability in the test results are taken into account.

There is no significant difference in the susceptibility of fish and invertebrates indicated in the short-term tests; therefore, there is no reason to expect that a long-term fish test would give a lower NOEC than the long-term invertebrate study.

Therefore, PNEC_aquatic is ≥ 100/50 =≥ 2 mg/l.

PNECaquatic(marine water) is derived from the freshwater short-term 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 500.

Where releases are intermittent, it is appropriate to reduce the assessment factor to 50.

Conclusion on classification

Triethoxypropylsilane is expected to hydrolyse (half-life = 1.4 days at 20 °C) and the silanol hydrolysis product is not readily biodegradable.

Triethoxypropylsilane is not classified for the environment in the EU according to Regulation (EC) No 1272/2008 because measured data for structurally analogous substance ((3-chloropropyl)triethoxysilane (5089-70-3)) indicate that both the parent substance and the silanol hydrolysis product are not toxic. Short and long term data are available for the read across substance ((3-chloropropyl)triethoxysilane (5089-70-3)): A 21 day NOEC value of > 66 mg/l (measured data) and NOEC of >= 100 mg/l (nominal).