Accumulation of Radioactive Substances in the Biosphere

the buildup of radioactive matter in all the components of the biosphere, both living (bacteria, plants, animals, and man) and nonliving (soil and fresh and salt water). Accumulation of radioactive substances is particularly active in living organisms. Certain radioactive substances become stably attached to various tissues—for example, plutonium and strontium in animal and human bones. Others, such as cesium, are readily eliminated. Radioactive substances that temporarily leave the biological cycle are accumulated primarily in bottom sediments and in the soil on dry land. Part of the radioactive substances entering the soil are accumulated by plants and enter animal and human organisms along with plant food; after death the substances return to the soil. Thus flora and fauna—particularly creatures found in large numbers, such as insects and worms—are an important factor in the transfer of radioactive substances in the soil. A measure of the accumulation of radioactive substances in living organisms is provided by the accumulation coefficient (build-up factor)—that is, the ratio of the concentration of radioactive substance in the organism to the concentration in the environment and water (for water-dwelling organisms) or soil solution. The accumulation coefficient depends on the type and state of the organism, on the properties and concentration of the radioactive substances, on the degree to which the latter are bound to the environment, and so forth. The accumulation coefficient is relatively high for water-dwelling organisms, on the order of 10² to 10⁴. For strontium-90 in green algae it is 1.6 • 10³; for niobium-95 in shellfish, 3 • 10³; and for yttrium-91 in fish, 5 • 10². The result of accumulation of radioactive substances is irradiation of the organism, which may cause radiation sickness, malignant tumors, harmful genetic effects, and death. Therefore it is important to forbid testing of nuclear weapons, which increase radioactive contamination of the environment.