Radiobiological Aspects and Radiation Levels Associated With the Milling of Monazite Sand

Abstract

One of the chief problems in industrial radiological health in Brazil concerns 420 people in a plant processing monazite sand, a rare earth mineral containing up to 6 per cent ThO₂ and 0.3 per cent U₃O₈. Radiation hazards associated with ore concentration and chemical treatment were assessed by sampling and measurement of airborne radioactivity, 210Po bioassay in urine and chromosomal analysis in peripheral blood lymphocytes collected from plant personnel. Results showed that ²¹²Pb (t 1/2 = 10.64 hr) airborne concentrations range from 0.002 up to 3.9 pCi/l. A size distribution analysis showed that in 88 per cent of ²¹²Pb-bearing aerosols the mean count diameter is below 0.4 μm. Calculated values of airborne long-lived activity as ²³²Th ranged from 6 × 10⁻⁶ up to 1 × 10⁻⁴pCi/l. A few workers had a slight increase in the urinary concentration of ²¹⁰Po, although results did not show a statistically significant difference between these values and those found in control population. Chromosomal analysis revealed a statistically significant difference in the yield of aberrations for the ore mill workers in one of the plant sections, showing the highest airborne ²¹²Pb concentration.