Radiotoxicity

the harmful effect of chemical substances as a result of their content of radioactive elements in various concentrations. The effect of ionizing radiation emitted by the elements leads to changes in the metabolism and structure of living organisms.

Radioactive substances contaminate the environment, equipment, and work areas. Contamination by radioactive substances in the air and water is expressed in curies, whereas the contamination of surfaces is expressed in the number of alpha or beta particles emitted from a unit surface per minute or the number of pulses recorded by radiometric instruments per minute per square centimeter. Existing radiometric methods permit the detection of even insignificant amounts of a radioactive substance. In a number of cases, radioactive substances have two types of toxicity: (1) chemical toxicity, caused by the chemical properties of the elements and compounds in the given substance, and (2) radiotoxicity proper.

The radioactive elements are divided into five groups, depending on toxicity:

(1) Group A—isotopes with particularly high radiotoxicity: ²¹⁰Pb, ²¹⁰PO, ²²⁶Ra, ²²⁸Th, ²³⁰Th, ²³²Th, ²³²U, ²³⁷Np, ²³⁸pu, ²³⁹Pu,²⁴¹Am, and ²⁴²Cm.

(2) Group B—isotopes with high radiotoxicity: ⁹⁰Sr, ¹⁰⁶Ru, ¹²⁴Sb, ¹²⁶I, ^l29I,¹³¹I, ^l44Ce, ¹⁷⁰Tm, ²¹⁰Bi, ²²³Ra, ²²⁴Ra, ²²⁷Th, ²³⁴Th, ²³⁰U, ²³³U, ²³⁴U, ²³⁵U, and ²⁴¹Pu.

(3) Group C—isotopes with moderate radiotoxicity: ²²Na, ²⁴Na, ³²P, ³⁵S, ³⁶Cl, ⁵⁴Mn, ⁵⁶Mn, ⁵⁹Fe, ⁶⁰Co, ⁸²Br, ⁸⁹Sr, ⁹¹Y, ⁹⁰Y, ⁹⁵Nb, ⁹⁵Zr, ¹⁰⁵Ru, ¹²⁵Sb, ¹³²I, ¹³³I, ¹³⁴I, ¹³⁴Cs, ¹³⁷Cs, ¹⁴¹Ce, ¹⁷¹Tm, ²⁰³Pb, ²⁰⁶Bi, ²³¹Th, and ²³⁹Np.

(4) Group D—isotopes with low radiotoxicity: ^l4C, ³⁸C1, ⁵⁵Fe, ⁶⁴Cu, ⁶⁹Zn, ^7lGe, ^91mY, ⁹⁷Zr, ^96mTc, ^99mTc, ¹³¹Cs, ^134mCs, and ¹³⁶Cs.

(5) Group E—isotopes with minimal radiotoxicity: ³H (tritium).

The degree of danger of a radioactive element is defined as the maximum amount of the element that does not require permission from the health and epidemiological service for its handling.

A distinction is made between external and internal irradiation of an organism. External irradiation is caused by sources of radiation outside the organism. Internal irradiation is produced by the action of ionizing radiation of radioactive substances that enter the organism (radioactive contamination of human skin is a mixed effect). Permissible doses of external and internal irradiation for each group of human organs that are especially sensitive to radiation are established individually for persons working with radioactive substances and for the general populace.

In working with radioactive substances, service personnel come into contact with all types of ionizing radiation emitted by radioactive elements. In light of the possible consequences of the effect of radioactive substances on the body, three categories of individuals exposed to radiation have been established: those working with radioactive substances, individuals in the population, and the population as a whole. Maximums for permissible doses of radiation and for entry of radioactive substances into the body are established according to these categories. Important factors in providing for safe handling of radioactive substances are proper organization of the work area and the establishment of measures that would protect individuals from radiation by preventing radioactive substances from entering the body. Work with radioactive substances is carried out under the supervision of a medical and public-health service and a dosimetry service, which determines the radioactivity of the air and contamination of equipment, the work area, special clothing, and exposed parts of the hands and face. Upon discovering a violation of established permissible standards for contamination, decontamination measures are taken in accord with the Basic Health Rules for Work with Radioactive Substances. Radioactive wastes and contaminated equipment are sources for the spread of radioactive substances, which are removed from work areas according to existing rules.

Aspects of toxicity and the establishment of safety norms for protection from irradiation are studied by the special International Commission on Radiological Protection (ICRP). On the basis of the work of the ICRP and of Soviet scientists, standards have been developed in the USSR for radiation safety (NRB-69), which are mandatory for all individuals working with radioactive substances.