Arsenic is one of many components that make up the earth's crust, and it is naturally present in soil and rocks all over the world. Arsenic is a toxic substance in its inorganic form, and it can be found in the air, water, and land. We typically take in small amounts of arsenic from the air we breathe and the food we eat. We can also ingest it from the water we drink. In small amounts, it doesn't appear to have adverse health effects.