Page 363 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

330 SECTION | III Nanoparticles, Radiation and Carcinogens

VetBooks.ir TABLE 19.1 Target Tissues and Physical and Biological Half-Lives for Selected Radionuclides Commonly Associated

With Radiological Incidents
Radionuclide Target Tissue(s) Physical Half-Life Biological Half-Life
Cesium-134 ( 134 Cs) Muscle and whole body 2 years 70 days
Cesium-137 ( 137 Cs) Muscle and whole body 31 years 70 140 days
Iodine-131 ( 131 I) Thyroid and breast 8 days 12 138 days
90
Strontium-90 ( Sr) Bone and lung 28 years 18 50 years
Source: Adapted from Nussbaum, R.H., Ko ¨hnlein, W., 2003. Ionizing radiation. In Greenberg, M.I., Hamilton, R.J., Phillips, S.D., McCluskey, G.J. (Eds.),
Occupational, Industrial, and Environmental Toxicology (2nd ed.). Mosby. Philadelphia, (pp. 702-715).

50% and is specific to the radioisotope. Biologic half-life through ground litter and in the soil for animals and
is determined by physical half-life and also the body’s plants, had radiocesium levels .500 Bq/kg. Muscle
ability to excrete the radioisotope. Excretion varies among radiocesium levels in wild Japanese monkeys were signif-
the different tissue types in the body and also between icantly related to levels of soil contamination (Hayama
animal species and individuals. Both physical and biologi- et al., 2013). Cattle fed contaminated rice straw also
cal half-lives vary from hours to years (Table 19.1). resulted in radiocesium concentrations .500 Bq/kg
Like stable or nonradioactive elements, radioisotopes (Povinec et al., 2013). In March 2011, the Japanese
can accumulate in plant and animal tissues, and exposures Ministry of Health, Labor, and Welfare adopted a provi-
to multiple radioisotopes are additive. Radioisotopes sional regulation level of radioactive substances in foods
accumulate in tissues using the same pathways as their of ,5 mSv/year (Hosono et al., 2013). Under this regula-
stable analogs. This is why 137 Cs accumulates in muscle, tion the upper radiocesium limits were set at 200 Bq/kg
90 131
Sr in bone, and I in the thyroid. Animal food pro- for drinking water and dairy products, and 500 Bq/kg for
ducts would be expected to be most commonly contami- meat, vegetables, and grains. In April 2012 a new stan-
nated with 131 I (mainly milk) and 134 Cs and 137 Cs (mainly dard of 1 mSv/year was established, along with new upper
meat) (Beresford and Howard, 2011). The International limits of radiocesium of 100 Bq/kg for general food pro-
Atomic Energy Agency published a handbook of parame- ducts and 50 Bq/kg for milk. Studies on the distribution
ter values that predict transfer of radionuclides to animal of radiocesium in cattle suggest that when suspicious
products (IAEA, 2010). levels of 50 100 Bq/kg are detected in the neck tissues,
Iodine is completely absorbed from the gastrointestinal where radioactivity inspection is generally conducted at
tract, concentrates in the thyroid, and transfers to milk and slaughter, another portion of muscle should be reinspected
eggs (Crout et al., 2000). High concentrations of 131 I and (Okada et al., 2013).
radiocesium were detected in raw milk sampled in Ibaraki
prefecture following the Fukushima accident (Povinec ACUTE EFFECTS OF RADIATION
et al., 2013). Because of the relatively short physical half- EXPOSURE IN ANIMALS
life of 131 I, contaminated milk could be processed into
food products that are then held until the 131 I has decayed Acute radiation syndrome (ARS) was first described in
to acceptable levels (Beresford and Howard, 2011). human victims of Hiroshima and Nagasaki. Whole-body
Cesium absorption varies with the form involved and irradiation doses associated with ARS in people generally
is distributed throughout soft tissues (Beresford et al., exceed 1 Gy, or about 160 times an average annual expo-
2000). Its rate of loss from meat is faster for smaller ani- sure (Rella, 2015). The sequence of events observed with
mals, such as 1 2 days for chickens (Po ¨schl et al., 1997), ARS varies with the severity of the exposure (Waselenko
compared to 60 days for a larger animal like a beef cow et al., 2004). The effects of radiation exposure, including
(Voight et al., 1989). In wild boar collected around the time until death occurs following whole-body irradiation,
site of the Chernobyl accident, highest concentrations of vary among animal species and are determined by the
137
Cs were detected in muscle and kidneys, sometimes at exposure duration and the radioisotope(s) involved
levels .660 kBq/kg, and 90 Sr concentrated mainly in the (Sample and Irvine, 2011; von Zallinger and Tempel,
bone (Gulakov, 2014). Wild boar hunted in Fukushima 1998). Survival times for lethally exposed animals vary
and its neighboring prefectures had detectable levels of from minutes for an absorbed dose of 1000 Gy to 3 5
134 137
Cs and Cs in their muscle (Ishida, 2013). More than days for 10 100 Gy and up to 30 60 days for 2 10 Gy
50% of Fukushima prefecture’s boars, animals that forage (Coggle, 1983). LD 50/30 is defined as the radiation dose