Sodium Metasilicate, Anhydrous [6834-92-0], Sodium Metasilicate Pentahydrate [10213-79-3], and Sodium Metasilicate Nonahydrate [13517-24-3] Review of Toxicological Literature

Toxicological summary for sodium metasilicate [6834-92-0] and its 01/2002 pentahydrate [10213-79-3] and nonahydrate [13517-24-3] i Executive Summary Basis for Nomination Sodium metasilicate was nominated for subchronic inhalation toxicity testing based on the large number of individuals occupationally exposed to the compound, evidence for biological activity, and the gaps in available toxicity data. Nontoxicological Data Sodium metasilicate, a very corrosive compound, is precipitated by acids and alkaline earth and heavy metal ions. When heated or acidified, solutions of the compound are hydrolyzed to free sodium ions and silicic acid. Sodium metasilicate is produced by the fusion of sodium carbonate with silicon dioxide or silica sand at about 1400 °C. It is commercially available in various grades and in both the anhydrous and pentahydrate forms from several U.S. companies. Annual capacities range from 50 to 806 million pounds. Sodium metasilicate is used in fireproofing mixtures; in laundry, dairy, metal, and floor cleaning; in deinking paper; in washing carbonated drink bottles; in insecticides, fungicides, and antimicrobial compounds; as a chemical intermediate for silica gel catalysts; as an additive in soaps and synthetic detergents; as an ingredient in adhesives; as a bleaching aid; and as a boiler compound. Combined with other salts such as sodium bicarbonate, it can be applied to aluminum as a paint stripper. In field experiments, compounds composed of sodium metasilicate, an alkali metal carbonate, and a preservative have been used as desiccants for forage crops. Sodium silicate solutions, reacted with solutions of many soluble salts to form complex gelatinous precipitates, have been used in soil stabilization. The pentahydrate form is considered generally recognized as safe (GRAS) by the Food and Drug Administration (FDA) for use in washing mixtures for fruits and vegetables, in sanitizing solutions for food-contact surfaces, in boiler water, as a denuding agent for tripe, as a hog scald agent for the removal of hair, and as a cooling and retort water agent for the prevention of staining of the outside surfaces of canned goods. Sodium metasilicate is also regulated by the Environmental Protection Agency (EPA). It has been Reregistration Eligibility Decision (RED) approved. Little information was found on actual cases of sodium metasilicate determination in environmental media or in potential releases to the environment. Potential human exposure to sodium metasilicate may occur from its use in cleaning products, fireproofing materials, pesticides, deinking paper, etc. For the general population, exposure is possible through the use of soaps, detergents, …