MCL: 15 pCi/L
Source: Contaminates water by alpha decay of naturally occurring elements.
Summary: Alpha particles are comprised of two protons and two neutrons and are produced from radioactive decay of atoms such as polonium, radium, and uranium. These elements are naturally occurring, and their radioactive decay may cause water contamination. This is known as alpha decay, where an atom emits the alpha particle and loses two protons, becoming a new element. Alpha particles have a positive charge. Although alpha particles do not possess energy great enough to penetrate skin, they are hazardous to cells, DNA, and tissue if they are consumed in water supplies. They have high ionization energy.