As a consequence of the Chernobyl accident, about 50,000 people were evacuated from the settlements in the 30-km zone around the reactor in the period 3-11 d after the accident. As no countermeasures were implemented in the early phase, people continued to consume milk and some leafy vegetables. In this paper, average effective ingestion doses are modeled for evacuees. Input data for the assessment are the 137Cs activity per unit area, the ratios of the radionuclides relative to 137Cs, the mean day of evacuation, and intake rates for milk and green vegetables. The transfer of radionuclides from deposition to humans is estimated by modeling radionuclide interception by vegetation, weathering, and the time-dependent transfer of radionuclides to milk taking into account site-specific agricultural practices. Depending on the evacuation day and site, the estimated ingestion doses for the settlements are in the range of 20 to 1,300 mSv and 3 to 180 mSv for infants and adults, respectively. 131I is by far the most important isotope, the ingestion dose due to 133I is more than one order of magnitude lower. The most exposed organ is the thyroid, inducing more than 80% and 50% of the ingestion dose for infants and adults. The ingestion doses are compared to the doses due to inhalation and external exposure. The internal dose exceeds the external by a factor of about 2-10 for adults and 2-40 for 1-y-old infants depending on site and evacuation day. The thyroid doses assessed for the evacuees are consistent with results achieved in studies performed in areas outside the 30-km zone.
Due to lack of measurements of activity concentrations in air, the assessment of the inhalation dose of the population evacuated from the 30-km zone after the Chernobyl accident is not possible from continuous filter measurements. Since the evaluation of the inhalation dose in each settlement of the zone is of great interest for epidemiological purposes, an approach was chosen that utilizes the available data on ground deposition of 137Cs, a recently performed best estimate of the radionuclide vector and its spatial distribution as well as the radionuclide dependent deposition velocity. The derived inhalation dose values in the 30-km zone range between 3 mSv to 150 mSv effective dose for adults depending on the distance to the reactor site and the day of evacuation. For 1-y-old infants the values range between 10 to 700 mSv. In Chernobyl town, an effective inhalation dose of 25 mSv until evacuation day was assessed. Thyroid doses due to inhalation ranged from 0.02 to 1 Sv for adults, for 1-y-old infants from 0.02 to 6 Sv. The inhalation dose in each settlement of the 30-km zone is approximately 8-13 times higher than the external exposure in each settlement if evacuation of the settlement occurred at an early stage. For settlements with evacuation at a later stage (day 10 or later) the inhalation dose was about 50-70% higher than the external dose. The dominant contribution to the effective inhalation dose comes from 131I (about 40%) and tellurium and rubidium isotopes (about 20-30%). Despite high zirconium and cerium ground depositions, zirconium and cerium isotopes contribute rather little to the inhalation dose which is mainly due to the great particle sizes to which they are attached. The relative contribution of short-lived radionuclides is, despite higher activities than at greater distances, less than 5%.
Comment In: Health Phys. 2003 Jul;85(1):110-1; author reply 111-212852478