**8. Radioactive fallout**

Radioactive particles that fall to the earth after above ground nuclear tests and nuclear power plant accidents are called radioactive fallout. Radioactive particles mix with the dust in the atmosphere and eventually fall to earth often thousands of miles from the initial explosion.

There are two types of nuclear weapons, the fission bomb and fusion bomb or thermonuclear weapon. In thermonuclear devices, deuterium fuses to form a heavier element with the release of energy and neutrons. A fission bomb is needed to trigger the fusion reaction. The thermonuclear weapon produces more neutrons which induce radioactivity in the environment than a fission device per unit of energy released. Roughly ten percent of the energy of a nuclear weapon is in residual radiation which may become dispersed in the atmosphere (Glasstone 1957). The amount of fallout produced depends on the type of weapon, size of the weapon and also on the amount of naturally occurring material that is mixed with the radioactive material released in the explosion. Fallout patterns and intensity depend upon the direction of the wind, speed and direction of the jet stream, presence and amount of precipitation.

Atomic explosions carry radioactive material high in the atmosphere where the radioactive material becomes fused with silica dust and other material present in the vicinity of the explosion. These particles are largely insoluble. The fallout particles may adhere to vegetation where they enter food chains at the primary consumer level. Fallout from Chernobyl in 1986 was deposited in Lappland (Sweden) where caribou consumed contaminated vegetation. Shifting winds also carried Chernobyl radiation particles to northern Italy where rabbit growers fed their rabbits vegetation contaminated with

original *Carex* zone demonstrating again that different plant species vary in their tolerance

Herbaceous plant communities may be more resistant to radiation than mature forests because many early successional species have small nuclei (Sparrow and Evans 1961) and also because herbaceous taxa like *Carex pensylvanica* have more below ground plant material which is shielded from gamma radiation. Sparrow (1962), Sparrow and Evans (1961), and Sparrow et al (1963) present detailed information on the relationship between nuclear

Radioactive material may become concentrated or "biologically magnified" during food chain transfer. Numerous biology and ecology text books include information on how living organisms take up nutrients pesticides and radioactive material and concentrate them. Because this concept is well known, we direct the reader to several early studies involving the concentration of radioactive material (See the work of Foster and Rostenbach, 1954; Hanson and Kornberg 1956; Davis and Foster 1958). Ophel (1963) reported a concentration of strontium 90 in perch flesh as 5x that of lake water while that in perch bone was 3000x! Additional information on radioecological concentration can be found in Auberg and

Radioactive particles that fall to the earth after above ground nuclear tests and nuclear power plant accidents are called radioactive fallout. Radioactive particles mix with the dust in the atmosphere and eventually fall to earth often thousands of miles from the initial

There are two types of nuclear weapons, the fission bomb and fusion bomb or thermonuclear weapon. In thermonuclear devices, deuterium fuses to form a heavier element with the release of energy and neutrons. A fission bomb is needed to trigger the fusion reaction. The thermonuclear weapon produces more neutrons which induce radioactivity in the environment than a fission device per unit of energy released. Roughly ten percent of the energy of a nuclear weapon is in residual radiation which may become dispersed in the atmosphere (Glasstone 1957). The amount of fallout produced depends on the type of weapon, size of the weapon and also on the amount of naturally occurring material that is mixed with the radioactive material released in the explosion. Fallout patterns and intensity depend upon the direction of the wind, speed and direction of the jet

Atomic explosions carry radioactive material high in the atmosphere where the radioactive material becomes fused with silica dust and other material present in the vicinity of the explosion. These particles are largely insoluble. The fallout particles may adhere to vegetation where they enter food chains at the primary consumer level. Fallout from Chernobyl in 1986 was deposited in Lappland (Sweden) where caribou consumed contaminated vegetation. Shifting winds also carried Chernobyl radiation particles to northern Italy where rabbit growers fed their rabbits vegetation contaminated with

volumes, chromosome numbers and relative radiosensitivity.

**7. Biological magnification of radioactive material** 

Crossley (1958), Auberg and Hungate (1967) and Polikarpov (1966).

of radiation.

**8. Radioactive fallout** 

stream, presence and amount of precipitation.

explosion.

radioactive fallout from Chernobyl. Ultimately the rabbits were destroyed because of the high concentration of radioactive material in their flesh.

There are differences in the kind of radionuclides that enter terrestrial and marine food chains. Soluble fission products, strontium 90 and cesium 137, are generally found in the highest amounts in land plants and animals. In marine systems fallout that forms strong complexes with organic matter such as cobalt 60, iron 59, zinc 65, and manganese 54 are most likely to be concentrated in marine organisms. In addition, those found in colloidal form such as cesium 134 and zirconium 95 are also found in high concentration in marine organisms. Cesium 134 is mostly from the fission products of a power reactor whereas cesium 137 can be formed during atomic power plant accidents or as a product of nuclear bomb explosions.

There are additional considerations/problems associated with concentrating radioactive material entering food chains as the concentration of radioactivity is also a function of nutrient richness, and the exchange and storage capacity of soils. Nutrient poor soils and thin soils such as those found on granite outcrops act as a nutrient trap providing more radionuclides to the vegetation. For example, sheep grazing on hill pastures in England accumulated 20x as much strontium 90 in their bones than sheep pastured in deep valleys where calcium content of the soil was higher and the grasses taller (Bryant et al 1957). For additional radiological work on tracers in food chains and trophic levels see Odum and Golley (1963), Odum and Kuenzler (1963), de la Cruz (1963), Ball and Hooper (1963), Foster (l958), and Foster and Davis (1956).
