Arsenic is well-known poison that occurs naturally in many rocks, minerals, and soils.
Several industrial processes require its use, but most man-made pollution comes from the application of arsenic-containing pesticides.
The toxicity of arsenic is well known. Like lead, even very small amounts build up in the body over time causing a condition known as chronic arsenosis.
Arsenic is also known to cause cancer, and affects the liver and heart.
Arsenic is effectively removed by reverse osmosis, distillation and activated carbon filtration.