**5. Sensitivity of organisms to radioactivity**

There is a wide range of sensitivity of organisms to radioactivity. Mammals are most sensitive while bacteria are most resistant especially as spores. Moreover there is a wide range of tolerance to radiation during the life cycle of an organism. Radiation sickness in

Sparrow (1962), Sparrow and Evans (1961), Sparrow and Woodwell (1962), and Sparrow et al (1963) have demonstrated that sensitivity of ionizing radiation is directly proportional to the size of the cell nucleus or chromosome volume. The larger the chromosome volume the more sensitive the material is to radiation. There are also differences in radiation tolerance between wild and laboratory rodent populations. Gambino and Lindberg (1964) and Golley et al (1965) have reported that the lethal dose for 50% of some wild rodent populations is roughly twice that of laboratory white mice or white rats, likely due to the reduced variation

Radioactivity has been successfully used to sterilize certain male insect pests. Sterile males are introduced to natural populations in large numbers which mate with females. A female mates only once, and once mated with a sterile male produces no young. Introducing radiated sterile male screw-worm flies in areas where they occur successfully reduced the number of screw-worm flies, a major pest in the southern United States. For those seeking more general information on this topic see Baumhover et al (1955) Bushland (1960),

Since the early 1960's there have been numerous studies on the effect of gamma radiation on ecosystems. These studies were fueled by the arms race between the Soviet Union and the United States (Stalter and Kincaid 2009). After lengthy negotiations between the two powers the SALT (Strategic Arms Limitation Treaty) was signed in 1971 and extended in 1977. With the signing of the treaty, less funding for irradiation studies was available (Stalter and Kincaid 2009). Thus most studies cited in this paper are those conducted prior to the SALT agreement of 1971. The gamma source that has been used has been either cesium 137 or cobalt 60. These include the studies of Woodwell (1962, 1965a) at Brookhaven National Laboratory, Long Island, New York, a tropical rain forest , Puerto Rico (Odum and Pigeon 1970) and the desert of Nevada (French 1965). Additional studies have been conducted in the fields and forests of Georgia (Odum and Kuenzler 1963) (Platt 1965), and Oak Ridge, Tennessee (Witherspoon 1965, 1969). Much additional work involving a portable gamma source on plant communities has been conducted at the Savanna River Ecology Laboratory, Aiken, South Carolina (McCormick and Platt 1962, McCormick and Golly 1966, Monk 1966,

 Stalter and Kincaid (2009) investigated community development following gamma radiation at a pine-oak forest, Brookhaven National Laboratory, Long Island, New York. The objective of this study was to compare vascular plant community change at five vegetation zones the site of Woodwell's (1962) gamma irradiated forest (Figure 1). The zones were: the dead zone where all vegetation was killed; a gramminoid *Carex pensylvanica* zone; an ericaceous zone; an oak dominated zone; and a control, the original oak pine forest. Radiation greater than 63,000 roentgens killed all vegetation. *Carex* dominated the zone receiving 27,000 to 63,000 roentgens, ericaceous shrubs, *Vaccinium* spp. and *Gaylussacia baccata* were dominant at the zone receiving 11,000 to 27,000 roentgens while oaks survived at the zone receiving 3600 to 11,000 roentgens. Upon completion of the Woodwell study in the 1970's, pitch pine (*Pinus rigida*) has invaded the total kill zone as bare mineral soil favors pine regeneration (Stalter and Kincaid 2009). *Carex* remained the dominant taxon in the

Cutcomp (1967), Knipling ( 1960,1964, 1965, 1967) and Lawson (1967).

**6. Radiation effects on ecosystems** 

in the latter.

McCormick 1969).

humans can be caused by as little as 0.35 Gy while a dose of 6-8 Gy is lethal to nearly 100% of individuals (Donnelly et al 2010). A dose of 2 Gy may kill some insect embryos while a dose of 100 Gy is necessary to kill all adult individuals (Odum 1971). Dividing cells are generally more susceptible to radiation than resting cells. The toxicity of radionuclides depends on the absorption, distribution in the body, half-life, elimination half-time, type of radiation emitted, and their energy.


Table 1. Naturally occurring gamma emitting isotopes which contribute to background radiation (Odum 1971).


Table 2. Elements important in fission products entering the environment through fallout or waste disposal.

humans can be caused by as little as 0.35 Gy while a dose of 6-8 Gy is lethal to nearly 100% of individuals (Donnelly et al 2010). A dose of 2 Gy may kill some insect embryos while a dose of 100 Gy is necessary to kill all adult individuals (Odum 1971). Dividing cells are generally more susceptible to radiation than resting cells. The toxicity of radionuclides depends on the absorption, distribution in the body, half-life, elimination half-time, type of

Table 1. Naturally occurring gamma emitting isotopes which contribute to background

Half-Life Radiations Emitted

7 x 108 yrs. Alpha3 Gamma0 1620 yrs. Alpha3 Gamma0 1.3 x 109 yrs. Beta2 Gamma2

Half-Life Radiations Emitted

33 yrs. Beta2 Gamma 2.6 min Beta Gamma1 2.3 yrs. Beta1 Gamma2

285 days Beta1 Gamma0 17 min. Beta2 Gamma2 33 days Beta1 Gamma1

30 sec. Beta3 Gamma2 40 days Beta1 Gamma1 65 days Beta1 Gamma1 35 days Beta0 Gamma1 12.8 days Beta1 Gamma1 40 hrs Beta2 Gamma2 11.3 days Beta1 Gamma1 2.6 yrs. Beta1 Gamma 61 days Beta2 Gamma1 2.4 x 104 yrs. Alpha3 Gamma1 8 days Beta1 Gamma1 7 x 108 yrs. Alpha3 Gamma0

1 yr. Beta2

Table 2. Elements important in fission products entering the environment through fallout or

radiation emitted, and their energy.

Element

Element

(137Pr)

Uranium-235(235U) Radium-226 (226Ra) Potassium-40 (40K) Carbon-14 (See Table 3.)

radiation (Odum 1971).

The cesium group Cesium-137 (137Cs) and daughter barium-137 (137Ba)

Cesium-134 (134Cs)

Cerium-141 (141Ce)

The ruthenium group Ruthenium-106 (106Ru) and daughter rhodium-106 (106Rh)

Ruthenium-103 (103Ru)

 lanthanium-140(140La) Neodymium-147 (147Nd) and daughter promethium-147(147Pm)

niobium-95(95Nb)

 Yttrium-91 (91Y) Plutonium-239 (239Pu) Iodine-131 (131I) Uranium-235 (235U)

waste disposal.

daughter praseodymium-144

Zirconium-95 (95Zr) and daughter

Barium-140 (140Ba) and daughter

The cerium group Cerium-144 (144Ce) and Sparrow (1962), Sparrow and Evans (1961), Sparrow and Woodwell (1962), and Sparrow et al (1963) have demonstrated that sensitivity of ionizing radiation is directly proportional to the size of the cell nucleus or chromosome volume. The larger the chromosome volume the more sensitive the material is to radiation. There are also differences in radiation tolerance between wild and laboratory rodent populations. Gambino and Lindberg (1964) and Golley et al (1965) have reported that the lethal dose for 50% of some wild rodent populations is roughly twice that of laboratory white mice or white rats, likely due to the reduced variation in the latter.

Radioactivity has been successfully used to sterilize certain male insect pests. Sterile males are introduced to natural populations in large numbers which mate with females. A female mates only once, and once mated with a sterile male produces no young. Introducing radiated sterile male screw-worm flies in areas where they occur successfully reduced the number of screw-worm flies, a major pest in the southern United States. For those seeking more general information on this topic see Baumhover et al (1955) Bushland (1960), Cutcomp (1967), Knipling ( 1960,1964, 1965, 1967) and Lawson (1967).
