I agree with Dogfish - boiling temps will kill most critters.
Are you planning on using this in a freshwater tank? if so, you may want to keep an eye on your ph/hardness. Odds are most of those are silicates, but there are probably going to be some carbonates and shell bits and stuff in there.
May not be an issue, depending on your setup.
If your concerned about seaweed and such, I would think swirling/swishing it in a bucket a few times would rinse out most of the stuff.
It should look really good, I think the mixed colors of the grains looks a lot more natural then the completely uniformly colored gravels in the petshops.
let us know how it turns out.