Radium is a radioactive, alkaline, earth metal that occurs naturally, almost everywhere, in trace amounts in rocks and soils. It has a chemical symbol of RA with an atomic number of 88. As radium decays, it releases energy into the environment until a stable, non-radioactive substance is formed. This emitted energy becomes part of the natural background radiation to which we are exposed. The radioactive half-life of radium is about 1600 years.
Radium is usually found in surface water supplies only in very small amounts. However, in certain geological formations it can be readily dissolved by slowly flowing groundwater where acidic conditions (low pH) are found. This can result in significant levels of contamination in affected groundwater. There are a number of locations in the United States in which radium contamination of groundwater is a significant problem. Some of these areas are in New Jersey and Northern Anne Arundel County in Maryland, Wisconsin and Florida. Such naturally-occurring contamination poses a potential health risk from both municipal water supplies and individual wells.
Radium can be present in several forms, called isotopes. The most common isotopes in groundwater are Ra-226 and Ra-228. The primary form of radiation emitted by the radium isotopes is the alpha particle. An alpha particle consists of two neutrons and two protons ejected from the nucleus of an atom. The alpha particle is, therefore, identical to the nucleus of a helium atom. Other examples of alpha emitters are radon, thorium, and uranium.
Because alpha particles are charged and relatively heavy, they interact intensely with atoms in materials they encounter, giving up their energy over a very short range. In air, their travel distances are limited to only a few centimeters. In general, it is easy to shield against alpha particle radiation. In fact, this radiation can be stopped by a single sheet of paper.
Since alpha particles cannot penetrate the outer layer of the skin, they present little hazard from exposures that are outside of the body. However, due to the very large number of ionizations they produce in a very short distance, alpha emitters can present a serious hazard when they are in close proximity to cells and tissues. If alpha emitters are inhaled, ingested (swallowed) or absorbed into the blood, sensitive tissues can be exposed to alpha radiation. The resulting biological damage increases the risk of cancer. In particular, alpha radiation is known to cause lung cancer in humans when alpha emitters are inhaled and bone cancers when ingested. Exposure to high levels of radium has also been associated with an increased risk of liver and breast cancers. The greatest exposure to alpha radiation for average citizens comes from the inhalation of radon and its decay. However, another potential route of exposure to alpha emitters is from ingestion of radium in the drinking water.
