The Estonian study of Chernobyl cleanup workers: I. Design and questionnaire data.

Nearly 2% of the male population of Estonia aged 20-39 years were sent to Chernobyl to assist in the cleanup activities after the reactor accident. A cohort of 4,833 cleanup workers was assembled based on multiple and independent sources of information. Information obtained from 3,704 responses to a detailed questionnaire indicated that 63% of the workers were sent to Chernobyl in 1986; 54% were of Estonian and 35% of Russian ethnicity; 72% were married, and 1,164 of their 5,392 children were conceived after the Chernobyl disaster. The workers were less educated than their counterparts in the general population of Estonia, and only 8.5% had attended university. Based on doses entered in worker records, the mean dose was 11 cGy, with only 1.4% over 25 cGy. Nearly 85% of the workers were sent as part of military training activities, and more than half spent in excess of 3 months in the Chernobyl area. Thirty-six percent of the workers reported having worked within the immediate vicinity of the accident site; 11.5% worked on the roofs near the damaged reactor, clearing the highly radioactive debris. The most commonly performed task was the removal and burial of topsoil (55% of the workers). Potassium iodide was given to over 18% of the men. The study design also incorporates biological indicators of exposure based on the glycophorin A mutational assay of red blood cells and chromosome translocation analyses of lymphocytes; record linkage with national cancer registry and mortality registry files to determine cancer incidence and cause-specific mortality; thyroid screening examinations with ultrasound and fine-needle biopsy; and cryopreserved white blood cells and plasma for future molecular studies. Comprehensive studies of Chernobyl cleanup workers have potential to provide new information about cancer risks due to protracted exposures to ionizing radiation.