I'd go with the chemists recommendations. Pretty low concentrations.
Google search says the isotope labelled product has been fed to dogs (poor bloody dogs) to see where it goes:
http://www.inchem.org/documents/pims/chemical/pim500.htm But you'd have to track down the original paper to read methods (Clayton and Clayton 1993), almost certainly it was well above the concentrations you're talking about.
Excerpt:
6.1 Absorption by route of exposure
Radio-labelled 31Si sodium metasilicate, partially
neutralized, was given orally to dogs. It was rapidly
absorbed and excreted in the urine but a significant amount
was retained in the tissues (Clayton & Clayton, 1993).
6.2 Distribution by route of exposure
Radio-labeled 31Si sodium metasilicate, partially
neutralized, was given orally to dogs. It was rapidly
absorbed. A significant amount was retained in the tissues.
These findings are consistent with the recognition that
silicon is an essential trace element for bone formation in
animals (Clayton & Clayton, 1993).
6.3 Biological half-life by route of exposure
No data available
6.4 Metabolism
No data available
6.5 Elimination by route of exposure
Radio-labelled 31Si sodium metasilicate, partially
neutralized, was given orally to dogs. It was rapidly
excreted in the urine (Clayton & Clayton, 1993).