Why you should know:
Arsenic is a carcinogen and has various other negative health effects; enough to warrant exposure limits in various jurisdictions. A five minute boil-and-discard step before cooking is a simple way to reduce your exposure, especially if you eat a lot of rice.
How much arsenic do you define as useful? I had a similar thought and could probably figure it out, but I really don’t want to dig my old chem and bio texts out of my garage.