Cytogenetic investigation in a Brazilian population living in an area of high natural radioactivity.

This paper presents a cytogenetic survey of the inhabitants from Guarapari, a small village on the coast of the state of Espirito Santo, Brazil, who live permanently exposed to high levels of radiation. The geological, physical, and radiochemical aspects of the survey in this area have been published [1-4]. Guarapari is a village of 12,000 inhabitants located on patches of black sand composed of ilmenite, rutile, and monazite. Monazite is a combination of rareearth phosphates with 6% thorium and 0.3%o uranium impurities. The beaches in the area contain 25%o-30%o monazite. External radiation levels within Guarapari range between 0.05 and 0.2 mR/hr, with peaks up to 0.6 mR/hr in houses where black sand has been used in the buildings and up to 2 mR/hr on some beaches. The average dose of 640 mR/year for the inhabitants was determined by a lithium fluoride dosimeter. The dosimeters, enclosed in medals to be hung from the neck, were distributed to about 500 persons [5, 6]. Attempts to detect above-normal body burdens of long-lived radionuclides by whole-body counting, measurements of thoron in breath, and radiochemical analysis of teeth and placentas were entirely negative. Thus this population, living in an abruptly changing radiation field, is exposed to external doses of 10-100 times the normal background level and to the possibility of internal contamination by radionuclides from the thorium and uranium series. This survey was performed in order to detect possible biological effects of chronic natural radiation exposure.