Gear Guy

Is it dangerous to swallow the rocky particles in glacial meltwater?

I'm going trekking around Mont Blanc and have been told not to drink any glacial meltwater because it contains tiny sharp particles of rock, called talc, which can shred one's insides. I have an Aquira water bottle with a two-micron filter, which is supposed to remove microscopic pathogens. Will it stop talc? Hal Berkeley, California

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Somebody told you what? That little pieces of glacial flour (another term for the same thing you’re talking about) will grind up your stomach and intestines? That isn’t the silliest thing I’ve ever heard, but it’s darned close.

First, some geology. Any stream flowing from glacial melt will look murky. That’s because the glaciers are busily grinding up all the rocks in their pack, turning big rocks into little, tiny rocks that are easily washed away by water. The makeup of that water-borne sediment will depend on what the surrounding mountains are made of. Mont Blanc is mostly granite, so the dust that results from its destruction contains feldspar, quartz, mica, and several other minerals. Talc is often found in association with quartz, so I suppose there is talc in the runoff.

Technically, talc is “Magnesium Silicate Hydroxide,” a soft mineral that is used in a wide variety of everyday things, including paint and in some electrical equipment. It is, of course, also the main ingredient in talcum powder. Talc is also used as a filler in some medicines.Anyway, I suppose if you added talc to your hamburger every day, in time you might feel some ill effects (mainly, it would grind down your teeth). But the tiny bits of it—or other granite by-products—in Mont Blanc water pose no risk at all. The stuff will just pass right through your system.

As for filtering the water, you should do that anyway to ensure you get rid of giardia and other parasites. Here, minerals in the water can cause problems by clogging your filter. So if you scoop water from a murky glacial stream, let it sit in a bottle or small bucket for several minutes, until it clarifies as the rock dust settles. Then filter.

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