YSK rice commonly contains arsenic, but most of it can be removed by boiling in water (4:1 ratio) for 5 minutes, and discarding that water before starting the regular cook cycle.
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.
Details are in the study, linked in the title of this post. Here's a diagram from the abstract:
The real question. Apple seeds have naturally occurring cyanide, but you would have to eat something like 30 to 300 apples worth of seeds to maybe have a health issue.
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.