Inorganic arsenic compounds are mainly used to preserve wood. They are also used to make insecticides and weed killers. You can check the labels of treated wood and insecticides to see if they contain arsenic. Copper and lead ores contain small amounts of arsenic. It doesn't evaporate.
Most arsenic compounds can dissolve in water.
It gets into air when contaminated materials are burned. It settles from the air to the ground. It doesn't break down, but can change from one form to another. Fish and shellfish build up organic arsenic in their tissues, but most of the arsenic in fish isn't toxic. Inorganic arsenic is a human poison.