Cesium [Cs, 55]
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10.7 HUMANS
The amount of Cs found in the human body (average 70 kg) is approximately 6 mg,
of which in the blood, 4 μg/L; in the bone, 10–50 μg/kg; and in other tissues, up to
1 mg/kg (Emsley 2011). Its content in the rib bone is about 7.7 μg/kg (Zaichik et al.
2011). Humans may be exposed to Cs by breathing, drinking, or eating.
The monovalent alkali metal Cs behaves similar to K, after absorption in blood
and is accumulated in all cells. Higher concentrations of Cs have been reported in
muscle than in other tissues, but the differences are small. It is generally assumed
that Cs is distributed uniformly between and within body organs and tissues. After
entering the blood, it is cleared rapidly and deposited more or less uniformly in
the tissues. It is now well established that the rate of clearance is faster in women
than in men, and that clearance may be further accelerated during pregnancy. The
mean equivalent biological half-time of Cs ranges from about 47–152 days in men
and from about 30–141 days in women. Rate of clearance of Cs is faster in children
(IARC 2001).
The transfer of Cs isotopes to the fetus has been followed in both humans and
animals. The concentrations of 137 Cs arising from exposure to fall-out from nuclear
weapons were measured in nine newborn children, within three days of birth and in
their mothers; concentrations were similar (IARC 2001).
Exposure to radioisotopes of Cs is of a great human health concern. Energy
released by radioactive isotopes can result in significant damage to living cells. Both
134 Cs and 137 Cs emit β particles and γ rays, which may ionize molecules within cells;
penetrations by these emissions resulted in tissue damage and disruption of cellular
functions. The most important exposure routes for radioisotopes of Cs are external
exposure to the radiation released by the radioisotopes and ingestion of radioactive
Cs-contaminated food sources. Inhalation and dermal exposure routes may also present a health hazard. The hazards of external exposure to 134 Cs and 137 Cs are similar to
those of other γ- and β-emitting radionuclides. Signs and symptoms of acute toxicity
from external and internal exposure to high levels of radiation from 134 Cs or 137 Cs are
typical of those observed in cases of high exposure to ionizing radiation in general.
Depending on the radiation dose, symptoms may include typical of acute radiation
syndrome (vomiting, nausea, and diarrhea), skin and ocular lesions, neurological
signs, chromosomal abnormalities, compromised immune function, and death.
Acute or repeated exposure of humans or animals to ionizing radiation may result
in reduced male fertility, abnormal neurological development following exposure
during critical stages of fetal development, and genotoxic effects such as increased
frequencies of chromosomal aberrations, T-lymphocyte point mutations, dominant lethal mutations, and reciprocal translocations. Animal studies have indicated
increased risk of cancer following external or internal exposure to relatively high
doses of radiation from 137 Cs sources. These studies showed that Cs is of relatively
low toxicity (ATSDR 2004a).
The amount of Cs in foods and drinks depends upon the emission of radioactive
Cs through nuclear power plants, mainly due to accidents. Impact of Chernobyl
nuclear explosion on radionuclides in the U.K. foods is illustrated by the average
level of the 137 Cs detected in Scottish milk. In 1985, it was 0.1 Bq/L, and after the