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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Endpoint:
bioaccumulation in aquatic species: fish
Data waiving:
other justification
Justification for data waiving:
other:
Justification for type of information:
A study on bioaccumulation is scientifically not necessary, because the crystalline structure of layered delta-sodium disilicate is completely destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8). Upon dilution of concentrated commercial amorphous sodium silicate solutions with water, the highly cross-linked polysilicate ions depolymerize rapidly to monosilicate ions (see section 5.2.1 study report on hydrolysis by Hirschen, 2009). The resulting water glass is identical to naturally occuring silicate. Thus, it can be concluded that disodium disilicate (delta-crystalline) is degraded hydrolytically to a naturally occurring substance, which is widespread in nature. In addition, the concentration related silicate-release from disodium disilicate (delta-crystalline) is not expected to be significantly higher than natural fluctuations in silicate levels.
The substance is unlikely to pose a risk to predatory organisms or humans exposed via the environment since silicate is a known beneficial mineral element for humans. Internal concentrations will be well-regulated at the expected exposure concentrations. The excretion of sodium silicate - the main hydrolysis product of disodium disilicate (delta-crystalline) – and silicate in general is described in the SIDS Initial Assessment Report 2004 (see supporting study entry). Based on the current state of knowledge no bioaccumulation is expected.
Endpoint:
bioaccumulation in sediment species: invertebrate
Data waiving:
other justification
Justification for data waiving:
other:
Justification for type of information:
A study on bioaccumulation is scientifically not necessary, because the crystalline structure of layered delta-sodium disilicate is completely destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8). Upon dilution of concentrated commercial amorphous sodium silicate solutions with water, the highly cross-linked polysilicate ions depolymerize rapidly to monosilicate ions (see section 5.2.1 study report on hydrolysis by Hirschen, 2009). The resulting water glass is identical to naturally occuring silicate. Thus, it can be concluded that disodium disilicate (delta-crystalline) is degraded hydrolytically to a naturally occurring substance, which is widespread in nature. In addition, the concentration related silicate-release from disodium disilicate (delta-crystalline) is not expected to be significantly higher than natural fluctuations in silicate levels.
The substance is unlikely to pose a risk to predatory organisms or humans exposed via the environment since silicate is a known beneficial mineral element for humans. Internal concentrations will be well-regulated at the expected exposure concentrations. The excretion of sodium silicate - the main hydrolysis product of disodium disilicate (delta-crystalline) – and silicate in general is described in the SIDS Initial Assessment Report 2004 (see supporting study entry). Based on the current state of knowledge no bioaccumulation is expected.
Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
other: Secondary source
Adequacy of study:
supporting study
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Principles of method if other than guideline:
The OECD SIDS report on soluble silicates reviews data for physicochemical properties, toxicology, ecotoxicology and environmental fate. Concerning bioaccumulation the SIDS report refers to publications on feeding studies with rats, dogs, cats and guinea pigs. The urinary excretion of silica was analysed by sampling urine and feaces after feeding silica.
GLP compliance:
no
Specific details on test material used for the study:
The following soluble silicates are subject of the present SIDS report:
1344-09-8 Silicic acid, sodium salt
6834-92-0 Silicic acid (H2SiO3), disodium salt
0213-79-3 Silicic acid (H2SiO3), disodium salt, pentahydrate
13517-24-3 Silicic acid (H2SiO3), disodium salt, nonahydrate
1312-76-1 Silicic acid, potassium salt
Route of exposure:
feed
Validity criteria fulfilled:
not applicable
Conclusions:
Soluble silicates are not bioaccumulating.
Executive summary:

In several publications referred to in the OECD SIDS report (2004) it is shown that ingested silicates are excreted via urine and to a lesser extent via the faeces. Markedly increased and rapid urinary excretion of silica was observed when soluble sodium silicates were administered to rats, dogs, cats and guinea pigs. The urinary silicon excretion half-life after administration of sodium silicate to rats via stomach tube was 24 h. The studies demonstrate that soluble silicates are fully excreted and no bioaccumulation is to be expected.

Description of key information

Bioaccumulation is not expected.

Key value for chemical safety assessment

Additional information

Disodium disilicate (delta-crystalline) is degraded hydrolytically to a naturally occurring substance, which is widespread in nature. In addition, the concentration related silicate-release of disodium disilicate (delta-crystalline) is not expected to be significantly higher than natural fluctuations in silicate levels. The substance is unlikely to pose a risk to predatory organisms or humans exposed via the environment: Silicate is a known beneficial mineral element for humans, and internal concentrations will be well-regulated at the expected exposure concentrations. The excretion of sodium silicate – the main hydrolysis product of disodium disilicate (delta-crystalline) – and silicate in general is described in the OECD SIDS Initial Assessment Report 2004 (see supporting study entry). Based on the current state of knowledge no bioaccumulation is expected.