Biological Effects of Uranium and Its Decay Products on Soil Microbes, Plants, and Humans

Abstract

In this atomic age, exposure to toxins in the environment ranges from radioactive heavy metals to chemical pesticides, and detoxification has become an issue of considerable importance. Recently, many parts of the world have been contaminated with radioactive waste from depleted uranium bombs and projectiles including the Arabian Gulf, Iraq, Syria, Bosnia, Serbia, and Afghanistan. In addition, other areas of the globe have been contaminated by nuclear testing sites and accidents at nuclear power plants involving radioactive uranium and its decay products. There are three naturally occurring uranium isotopes that are of major significance with regard to mining of this element and the nuclear industry. These include uranium-238 (U-238), which comprises the majority of this element in the Earth’s crust, uranium-235 (U-235), and uranium-234 (U-234), which together comprise a much smaller portion. The half-lives of these isotopes are approximately 4500 million years, 703 million years, and 246,000 years, respectively. The transfer of radionuclides of the uranium decay series through the environment is important for assessing the impact of nuclear weapons use, nuclear power plant leaks, and the mining and milling of uranium ores. The pathway from soil through plants to humans contributes significantly to the overall radiation dose. The transfer of mobilized radionuclides within the environment is determined by weathering rate, which, in turn, depends on particle composition and chemical conditions such as pH of the soil after deposition. Specific geographical sites that have been contaminated with uranium attract specific bacterial species that display resistance to the metal. Moreover, various plant species exhibit substantial differences in the soil-plant transfer factor for uranium and other related radionuclides. The biological effects of environmental radionuclides in humans (particularly depleted uranium) have been documented as part of the Gulf War syndrome and Balkan syndrome and comprise a complex set of seemingly unrelated symptoms. Some of these include incapacitating fatigue, musculoskeletal and joint pains, headaches, neuropsychiatric disorders, confusion, visual problems, changes of gait, loss of memory, lymphadenopathies, respiratory impairment, impotence, and urinary tract morphological and functional alterations. Moreover, the overall incidence of breast and lung cancer, leukemia, and lymphoma has doubled or tripled in certain areas of Iraq contaminated with depleted uranium during the Gulf War. An association with lung cancer has also been found in uranium miners. Thus, soil remediation, plant selection, phytoremediation, and human detoxification are the main issues to be considered in relation to environmental contamination with uranium and its decay products.