Chlorine is ubiquitous in the environment and is an essential element for higher plants and animals. The primary radioactive isotope is 36Cl, which has a half-life of 3.01 × 105 years and which is produced both naturally and as a result of anthropogenic nuclear activity. This article considers the important sources of 36Cl in the environment and the subsequent behavior of the radionuclide. The chemistry of radio- and stable chlorine is discussed with particular emphasis on its ability to not only exist as the chloride ion but also as organic chlorine. Procedures for the fractionation/speciation and analytical determination of 36Cl in environmental samples are also reported. Owing to the high solubility of the chloride ion, the potential for a large degree of 36Cl migration within soils, and from soils into plants is described. The most significant source of 36Cl is likely to be nuclear waste buried in underground rock repositories. Over extended time periods, if such a repository were to leak, 36Cl has the potential to move upward with the flow of water into soils and plants. The article describes risk modeling that assesses this important pathway by which humans may become exposed to 36Cl. Such modeling suggests that 36Cl leaked from a buried nuclear waste repository has the potential to eventually contaminate soils, plants, well water, and surface waters. However, the radioactive dose associated with this contamination would apparently be relatively low.
Keywords: chlorine; chlorine-36; 36Cl; radioactivity; soil; plant; organic chlorine; speciation; nuclear waste