MCL: 4 (millirems/yr)
Source: Contaminates water by beta decay of naturally occurring elements.
Summary: Beta particles are negatively charged particles emitted from radioactive decay. Beta decay takes place in unstable isotopes of elements such as hydrogen and strontium. Beta decay may take place by positron emission, electron capture, or electron emission. Beta particle radiation may be stopped by a layer of clothing or an aluminum sheet, but skin contact may cause a burn. Consuming water contaminated with beta particles may lead to damage of tissue and DNA. The elements that undergo beta decay may be naturally occurring, and their decay may cause direct contamination into groundwater or surface water supplies.