A Review of Scientific Literature on the Long-Term Effects of Part 1: Sodium Silicates on Human Consumption

At Velora Water Systems Inc., we believe informed decisions start with credible science. Today we launch the first in a three-part educational series examining common water additives and their potential impacts.

Sodium Silicate – What It Is and Why It’s Added

Sodium silicate is widely used by municipalities as a corrosion inhibitor. It forms a protective lining inside aging water distribution pipes to reduce leaching of metals such as lead and copper. While effective for infrastructure protection, questions remain about its long-term presence in drinking water for consumers.

Many homeowners observe a fleshy pink discoloration in toilet bowls and inside pipes (visible when pipes are cut), often mistaking it for iron. In reality, this is typically sodium silicate residue rather than iron from municipal sources.

Scientific Literature Summary

Scientific literature on the long-term effects of sodium silicates (including sodium metasilicate) via oral consumption (ingestion) is limited, particularly regarding direct human studies. Most available data derive from animal toxicology studies (primarily rats, mice, and dogs), regulatory safety assessments, and reviews by bodies such as the Cosmetic Ingredient Review (CIR), OECD High Production Volume (HPV) chemicals program, FDA, and others. No robust long-term epidemiological or chronic human consumption studies were identified in major databases.

Key Findings from Reviews and Animal Studies

• Absorption and Excretion: Orally administered sodium silicate is readily absorbed from the gastrointestinal tract and primarily excreted in the urine. Silicon from these compounds behaves similarly to natural dietary silica, with limited accumulation in the body.

  
  

• Acute vs. Subchronic/Chronic Toxicity:

  • Acute oral LD50 values in rats and mice range from approximately 770–1,350 mg/kg (moderately toxic at high doses), with primary effects including gastrointestinal irritation.

  • In repeated-dose studies (4 weeks to 180 days), No Observed Adverse Effect Levels (NOAELs) for sodium metasilicate were around 227–237 mg/kg body weight/day in rats and 260–284 mg/kg body weight/day in mice (highest doses tested in some studies). For sodium silicate, a NOAEL of approximately 159 mg/kg body weight/day was reported in a 180-day rat drinking water study.

  • At significantly higher doses (>1,000 mg/kg/day), observed effects included polydipsia (excessive thirst), polyuria, soft stools, kidney lesions (e.g., gross cortical changes in dogs at 2.4 g/kg/day for 4 weeks, without functional impairment), alterations in blood minerals (Ca, Mg, P, Cu, Zn), and reduced body weights in some cases.

    
    

• Reproductive/Developmental Effects: One older rat drinking water study (600–1,200 ppm added silica) reported reduced offspring numbers (67–80% of controls), though the study had methodological limitations. Other data, including in mice, showed no clear adverse effects on fertility or development at lower doses. There is no strong evidence of teratogenicity.

  
  

• Genotoxicity and Carcinogenicity: Results are generally negative in bacterial and in vitro/in vivo assays. No valid long-term carcinogenicity studies were identified.

  
  

• Human Data: Data for chronic oral exposure are very sparse. Sodium metasilicate is FDA GRAS (Generally Recognized as Safe) as a direct food ingredient. Limited dermal studies and patch tests indicate low concern for irritation at dilute concentrations used in products, though concentrated forms are corrosive. No significant long-term systemic toxicity has been reported from typical exposure levels.

  
  

Regulatory Conclusions

• The CIR Expert Panel (2005, with later amendments) concluded that sodium silicate and related compounds are safe for use in cosmetics when formulated to avoid irritation, citing limited absorption and their GRAS status for food applications.

  
  

• In the broader OECD, EFSA, and FDA context, there is low concern for long-term toxicity at typical exposure levels (e.g., as food additives, in water treatment, or as indirect additives). These compounds are poorly absorbed and align with natural dietary silica. Higher molar ratio silicates (higher silica content, lower alkalinity) tend to exhibit lower toxicity and irritation potential.

  
  

Context for Water Filtration and Drinking Water Applications

In municipal water treatment and filtration applications, residual levels of sodium silicates in drinking water are expected to be very low and are subject to regulatory oversight. Any potential effects would more likely relate to alkalinity (pH elevation) or unintended high exposure rather than chronic low-dose toxicity. Amorphous silica forms (as relevant here) are generally considered inert, unlike crystalline silica, which carries inhalation risks such as silicosis, an unrelated exposure route.

This review is based on available peer-reviewed and regulatory sources. While sodium silicates appear to have a favorable safety profile at typical environmental and consumer exposure levels, data gaps in long-term human studies underscore the value of informed water treatment choices for residential systems.

To continue to Part 2, where we will examine another common water additive, click on the following link below. https://www.velorawater.com/post/long-term-health-risks-and-benefits-of-water-chlorination-a-synthesis-of-toxicology-epidemiology