RESUMO
Radiation monitoring is an important radiation safety measure implemented at the hydrometallurgical plant of the Stepnogorsk mining and chemical combine (HMP SMCC, Republic of Kazakhstan). Follow-up of the workers and their regular medical examinations has laid the basis to create a cohort with the potential to be used in radiation epidemiology. The aim of current pilot study was to analyze the dose forming factors for workers of HMP SMCC. For this, bioassays samples collected from 54 workers employed at eight HMP workshops were measured using the "Agilent 7800 ICP-MS" mass spectrometer. Three years later, measurements were repeated for four workers with the highest concentrations of uranium in urine. The results of site-specific measurements of dose rates, long-lived alpha-particle activity concentrations and equivalent equilibrium volume activity of radon were derived from the archive of the HMP SMCC Service of Radiation and Toxic Safety and analyzed to fully evaluate the radiation situation at those workplaces. Maximum urine uranium concentrations were measured for workers at the extraction workshop and mechanical repair shop (up to 26.7 µg/L and 14.6 µg/L, respectively). Urinary uranium from workers employed at other sites was mainly (for about 72% of the samples) in the range of values that may occur in natural conditions (< 0.4 µg/L). A wide individual variability in uranium concentration in urine samples (from 60% to 200% of CV) was found. A linear dependence of cumulative effective dose on work experience was found with a slope of 7.5 mSv per year. This slope did not depend on working place. For the investigated workers, cumulative effective doses of workers were found in the range of low (< 100 mSv) and medium doses (100-500 mSv). It is concluded that the newly created cohort of HMP SMCC workers has the potential to improve the knowledge on health effects from low- and medium doses of ionizing radiation.