Are Silica Beads Poisonous?

Silica gel is a type of silicon dioxide that is used to control humidity. Although it is called a gel, silica gel actually is a solid. It's usually non-toxic, despite the warning label.
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Silica gel beads are found in those little packets accompanying shoes, clothing and some snacks. The packets contain round or granular bits of silica, which is called a gel but is really a solid. The containers typically carry dire "Do Not Eat" and "Keep Away from Children" warnings, so naturally one would assume they are poisonous -- but what really what happens if you eat silica?

What Happens If You Eat Silica Gel Beads?

Usually, nothing happens if you eat silica gel. In fact, you eat it all the time. Silica is added to improve flow in powdered foods. It occurs naturally in water, where it may help confer resistance against developing senility. Silica is just another name for silicon dioxide, the main component of sand, glass, and quartz. The "gel" part of the name means the silica is hydrated or contains water. If you eat silica, it won't be digested, so it will pass through the gastrointestinal tract to be excreted in feces.

Yet, if silica is harmless to eat, why do the packets carry the warning? The answer is that some silica contains toxic additives. For example, silica gel beads may contain poisonous and potentially carcinogenic cobalt(II) chloride, which is added as a moisture indicator. You can recognize silica containing cobalt chloride because it will be colored blue (dry) or pink (hydrated). Another common moisture indicator is methyl violet, which is orange (dry) or green (hydrated). Methyl violet is a mutagen and mitotic poison. While you can expect most silica you encounter will be non-toxic, ingestion of a colored product warrants a call to Poison Control. It's not a great idea to eat beads even if they don't contain toxic chemicals because the product is not regulated as a food, meaning there may easily be contaminants that you wouldn't want to eat.

How Silica Gel Works

In order to understand how silica gel is, let's take a closer look at what exactly it is. Silica is synthesized into a vitreous (glassy) form that contains nanopores. When it's made, it is suspended in a liquid, so it's truly a gel, much like gelatin or agar. When it's dried, you get a hard, granular material called a silica xerogel. The substance is used as granules or beads, where it can be packaged in paper or another breathable material to remove humidity.

The pores in the xerogel are about 2.4 nanometers in diameter. They have a high affinity for water molecules. Moisture gets trapped in the beads, helping to control spoiling and limit chemical reactions with water. Once the pores fill up with water, the beads are useless, except for decorative purposes. However, you can recharge them by heating them. This drives the water off so the beads can hold it once again.

How to Reuse Silica

Silica can be used in many interesting projects, plus you can recycle it to renew its desiccant properties. All you need to do it heat the gel in a warm oven (anything over the boiling point of water, which is 100°C or 212°F, so a 250°F oven is fine). Let the beads cool slightly and then store them in a water-proof container.

Fun Historical Fact

Silica gel was important in World War II. It was used to keep penicillin dry, as a catalyst to make high octane gasoline, to make synthetic rubber, and to absorb toxic gases in gas masks.