Urinary silicon excretion by rats following oral administration of silicon compounds

Abstract

The rate and extent of urinary excretion of silicon was determined in rats after oral administration of magnesium trisilicate, food-grade sodium aluminosilicate, sodium silicate or Zeolite type increased rapidly after dosing and peak excretion rates occurred within 24 hr in all test groups. Zeolite A had the most rapid urinary excretion rate (half-life, 6–8 hr) followed by magnesium trisilicate (half-life, 16–20 hr), sodium silicate (half-life, 24 hr) and sodium aluminosilicate (half-life, 38 hr). First-order excretion kinetics were followed for all four materials. When expressed as a percentage of dose the total urinary silicon excreted was roughly equal for magnesium trisilicate, sodium silicate and Zeolite A but considerably less for sodium aluminosilicate. Urine of rats dosed with sodium aluminosilicate or Zeolite A did not show any detectable increase in aluminium, indicating that the silicon that was excreted was a breakdown product of the parent molecule. Since it is known that aluminuim when administered either ip or iv is excreted in urine, this is evidence for decomposition of the test material in the gastro-intestinal tract. For all four test materials urinary silicon excretion increased with dose level. However, the magnitude of this increase (two- to eightfold) was not as great as the increase in the amount dosed (25-fold) so that the percentage of silicon excreted decreased as the dose was increased. This suggested that some process in the absorption or excretion of silicon was becoming saturated. These results are discussed with respect to the comparative safety of these four silicates.