Sodium metasilicate gets an F from EWG and a green circle from EPA. Both are right, because they grade different things. EWG grades the raw ingredient, which is corrosive at full strength. EPA rates it for its job in a product. Here is why it is in our dishwasher and laundry powders, and how diluted it gets.
Quick facts
- What it is: the sodium salt of metasilicic acid (Na2SiO3), a strongly alkaline silicate
- Its job in our products: alkaline builder
- Where it comes from: made from silica sand and soda ash
- EPA Safer Choice: green circle
- EWG grade: F, for the raw ingredient (see the EWG page)
- CAS number: 6834-92-0
Two ratings, two questions
EWG's F is the lowest grade in its cleaners database. It grades the raw ingredient, not our finished products, and the concentrated material is corrosive: it can burn skin and seriously damage eyes. The detergent industry's HERA risk assessment of soluble silicates agrees that their one critical hazard is irritation or corrosion of skin and eyes from their alkalinity, and metasilicate is among the more alkaline ones. We show the grade as it stands.
EPA's green circle answers a different question: is the ingredient of low concern for its job in a product, based on experimental and modeled data? It does not mean the concentrated powder is mild. More on how we vet ingredients.
What it does in the wash
Fats and oils break down much faster in strongly alkaline water: some react to form soap, and the rest loosen and lift more easily. Sodium metasilicate pushes the wash into that range and buffers it, holding the pH up as acidic food soils try to pull it down. According to HERA, silicates also tie up hard-water minerals so the surfactants can work, a job shared with sodium citrate in the same powders.
It is made by fusing soda ash (sodium carbonate) with silica sand at high temperature. The raw materials are minerals, but the result is industrially manufactured, so we call it mineral-based rather than natural.
How diluted is it, really?
HERA estimated that hand-wash laundry and cleaning solutions contain about 0.2 to 2.5 mg of silicate per milliliter, generally too low to irritate skin. With no measured data on what stays behind after rinsing, HERA modeled a worst case (5 percent left on fabric, plus the water film left on dishes). Even then, exposure came out about 63,000 times below the no-effect level in animal studies for clothes, and 140,000 times below it for dishes.
As a mineral, it does not biodegrade. It ends up as dissolved silica, which rivers already carry naturally (European rivers average about 7.5 mg per liter), and HERA found detergent use is not expected to harm aquatic ecosystems.
Handling and safety
Concentrated, it is corrosive to skin and eyes and can irritate airways. Avoid contact with eyes, do not leave damp powder on your hands or the scoop, and wash your hands afterward. Put a tablet into the dispenser with dry hands and close it right away, and keep little ones away from an open, loaded dishwasher door. If any gets in eyes, rinse cautiously with water for several minutes and call Poison Control at 1-800-222-1222. If any is swallowed, call Poison Control right away. Store powders and tablets dry and sealed in their pouch, up high or in a latched cabinet, out of reach of children and pets.
Where you'll find it
- Laundry: EWG Verified Max Strength Laundry Powder
- Dish: EWG Verified Dishwasher Tabs, EWG Verified Dishwasher Powder
- Kits and bundles: Home Kitchen Kit, Dish Starter Kit, Ultimate Home Bulk Bundle, Expert Home Cleaner Kit
All are fragrance-free, except that the Expert Home Cleaner Kit also includes scented sprays. Each product page has the full ingredient list.
Sources
- America's Poison Centers. (n.d.). Poison Help. https://poisoncenters.org/
- Environmental Working Group. (n.d.). EWG's Guide to Healthy Cleaning: Sodium metasilicate. https://www.ewg.org/cleaners/substances/5615-SODIUMMETASILICATE/
- HERA Project. (2005). Soluble silicates. Human and Environmental Risk Assessment on Ingredients of Household Cleaning Products. https://www.heraproject.com/substance/alkali-silicates/
- National Center for Biotechnology Information. (n.d.). PubChem compound summary: Sodium metasilicate. https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-metasilicate
- U.S. Environmental Protection Agency. (n.d.). Safer Choice: Safer Chemical Ingredients List. https://www.epa.gov/saferchoice/safer-ingredients
