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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Reference
Endpoint:
bioaccumulation in aquatic species: fish
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance has a low potential to cross biological membranes
Conclusions:
Due to the inherent chemico-physical properties of synthetic amorphous silica (SAS), such as absence of lipophilicity, as well as the capability of the organism to excrete absorbed SAS particles, its bioaccumulation potential in aquatic organisms (e.g. fish) is assumed to be negligible. However, SAS can be accumulated in some aquatic organisms (e.g. diatoms, radiolarians, and sponges), which exploit it as a construction material to build up their skeletons in natural processes. Hydrophobic (surface treated) silica is stable against hydrolysis and the water solubility is lower than that of untreated amorphous silica. It does not possess lipophilicity either. For this reason bioavailability of hydrophobic silica is very low and no bioaccumulation is also assumed in aquatic organisms.
Basically, amorphous silica is a naturally occurring substance. Silica and silicic acid (silicate) are found throughout the Earth’s lithosphere and the ocean contains a huge sink of them. The synthetic form (SAS) is of higher purity than the naturally occurring amorphous silica and does not contain contaminants. Once released and dissolved in the environment no distinction can be made between SAS and naturally occuring amorphous silica due to its chemical analogy in natural environmental processes (i.e. enviornmental fate and pathways).

Description of key information

Due to the inherent chemico-physical properties of synthetic amorphous silica (SAS), such as absence of lipophilicity, as well as the capability of the organism to excrete absorbed SAS particles, its bioaccumulation potential in aquatic organisms (e.g. fish) is assumed to be negligible. However, SAS can be accumulated by some aquatic organisms (e.g. diatoms, radiolarians, and sponges), which exploit it as a construction material to build up their skeletons in natural processes. Hydrophobic (surface treated) silica is stable against hydrolysis and the water solubility is lower than that of untreated amorphous silica. It does not possess lipophilicity either. For this reason bioavailability of hydrophobic silica is very low and no bioaccumulation is also assumed in aquatic organisms.

Basically, amorphous silica is a naturally occurring substance. Silica and silicic acid (silicate) are found throughout the Earth’s lithosphere and the ocean contains a huge sink of them. The synthetic form (SAS) is of higher purity than the naturally occurring amorphous silica and does not contain contaminants. Once released and dissolved in the environment no distinction can be made between SAS and naturally occuring amorphous silica due to its chemical analogy in natural environmental processes (i.e. environmental fate and pathways).

Key value for chemical safety assessment

Additional information