How can i make items that entities hold react with the environment?

I am working on a Chemistry based mod and trying to figure out how to make zombies explode if they walk into water and have magnesium ingot or blocks in their inventory. I would also like to make it so when they hold Uranium, plutonium, and other radioactive metals ingots they will glow and make others around them lose health due to radioactivity. I assume that I would want to use wither for this effect? I am also curious about how to make it so when they hold fluorine ingots that they can make glass blocks shatter causing injury to others around them due to the shards in addition to wither effect.