Studies of workers employed at the Mayak complex in the Russian Federation offer a unique opportunity, because of the magnitude of the doses received (mean cumulative external dose of 1.2 Gy among monitored workers hired before 1959), to obtain reasonably precise estimates of risk from medium- to high-dose protracted external exposures. Substantial doses from plutonium have also been received by a number of these workers. Estimates of the radiation-related risks of leukemia; solid cancers; and lung, liver, and bone cancer have been derived from this cohort. Uncertainties in external dose estimates and in plutonium doses to specific organs must be considered in the interpretation of these results. Further studies of this population will be important to understand the effects of protracted exposure.


The Chernobyl accident resulted in widespread radioactive contamination of areas populated by millions of people in the three most affected countries of Belarus, the Russian Federation, and Ukraine. The populations at risk can be separated into the following groups (see Table 8-9):

  1. the “liquidators,” also referred to as “cleanup workers,” include persons who participated in the cleanup of the accident (cleanup of the reactor; construction of the sarcophagus; decontamination; building of roads; destruction and burial of contaminated buildings, forests, and equipment), as well as many others, including physicians, teachers, cooks, and interpreters who worked in the contaminated territories;

TABLE 8-9 Estimates of Collective Effective Doses for Chernobyl Population Groups of Interest



Collective Effective Dose (Sv)




Liquidators (1986–1987)



Persons living in contaminated areasa



Deposition density of 137Cs >15 Ci km−2



Deposition density of 137Cs >1 to 15 Ci km−2



aDoses are for 1986–1995; over the longer term (1996–2056) the collective dose will increase by approximately 50%.

SOURCE: Cardis and others (1996).

  1. the “evacuees” who were evacuated from the town of Pripyat and the 30 km zone around the Chernobyl reactor in April–May 1986;

  2. the residents of the “strict control zones”—those members of the general population who have continued to live in the more heavily contaminated areas (with levels of 137Cs deposition greater than 555 kBq m−2), typically within a few hundred kilometers of the Chernobyl Nuclear Power Plant (NPP). Within these areas, radiation monitoring and preventive measures have been taken to maintain doses within permissible levels; and

  3. the general population of the contaminated territories in the three countries.

The “liquidation” of the consequences of the Chernobyl accident lasted for about 3 years (1986–1989). During that time, different tasks were carried out, including the initial localization of the catastrophe (firefighting; closing down unaffected units of the power plant); evacuation of Pripyat and the population in the 30 km zone; decontamination of the inside of the Chernobyl NPP buildings, as well as the roofs of nearby buildings and nearby territories; renovation and maintenance of the other blocks of the power plant; construction of the sarcophagus; actions to decrease the spread of radioactive materials in the environment; safeguard of the 30 km zone and settlements and miscellaneous activities in the 30 km zone (health care, ecological monitoring, bringing in food, water, etc., for the liquidators). Different groups of liquidators were involved in these tasks; they worked under differing conditions of radiation monitoring and safety and were exposed to various types and levels of radiation. From 600,000 to 800,000 persons took part in the cleanup activities to liquidate the consequences of the Chernobyl accident. The exposure level was highest for those (approximately 200,000 liquidators) who worked in the 30 km zone in 1986–1987.


In 1987, an “All-Union Distributed Registry” was established following a directive of the Ministry of Public Health of the USSR (Tsyb and others 1989). The objective was to set up a comprehensive registration and active follow-up system for the persons most affected by the Chernobyl accident, including the liquidators. This system foresees an annual medical examination in which individuals are examined systematically by a general practitioner and a number of different specialists. All data on diseases diagnosed during the annual medical examination, as well as any other time during the year, are sent to the Chernobyl Registry for inclusion in the registry database. A study in Russia (Cardis and Okeanov 1996) indicates that the diagnostic information in the Chernobyl Registry is not always completely accurate. The lack of verification and quality control is actively being remedied but must be kept in mind when interpreting results

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