K. Dias da Cunha

Exposure of workers in mineral processing industries in Brazil

The mining, milling and processing of uranium and thorium bearing minerals may result in radiation doses to workers. A preliminary survey pilot program, that included six mines in Brazil (two coal mines, one niobium mine, one nickel mine, one gold mine and one phosphate mine), was launched in order to determine the need to control the radioactive exposure of the mine-workers. Our survey consisted of the collection and analysis of urine samples, complemented by feces and air samples. The concentrations of uranium, thorium and polonium were measured in these samples and compared to background data from family members of the workers living in the same dwelling and from residents from the general population of Rio de Janeiro. The results from the coal mines indicated that the inhalation of radon progeny may be a source of occupational exposure. The workers from the nickel, gold and phosphate mines that were visited do not require a program to control internal radiological doses. The niobium mine results showed that in some areas of the industry exposure to thorium and uranium might occur.

STUDY OF WORKER'S EXPOSURE TO THORIUM, URANIUM AND NIOBIUM MINERAL DUST

The aim of this study is to evaluate worker’s exposure to particles, with special attention to thorium, uranium and niobiumbearing particles. A cascade impactor (CI) with six stages was used to collect particles with aerodynamic diameter in the rangeof 0.64 to 19.4 μm. The elemental mass concentrations impacted in each stage of the CI were determined using the PIXE(Particle Induced X-ray Emission) technique. The Mass Median Aerodynamic Diameter (MMAD) and elemental mass concentration in the fine fraction of aerosol (0.5 to 2.5 μm) were determined.Personal air samplers were used by workers to collect fine particles of aerosol. The concentrations of 232Th and 228Th in these air samplers were measured by the alpha spectrometry technique. Faeces and urine samples from the workersand their wives were analyzed to determine the thorium, uranium and niobium mass concentration (mass spectrometry) and 232Th, 228Th, 238U and 234U concentrations (α spectrometry) and then compared to inhabitants of regions with low metal concentrations. The analysis of thefaecesand urine samples from workers and their wives indicated that themain pathway of thorium, uranium and niobium incorporation was byingestion. The observed concentrations of niobium and uranium inurine samples from workers showed a systemic incorporation of niobium and uranium.

PIXE and PDMS Methods Applied to Aerosols Analysis

The aim of this study was to apply the PIXE (Particle Induced X-ray Emission) and PDMS (Plasma Desorption Mass Spectrometry) techniques to characterize airborne dust particles containing metals. Aerosols generated at a mineral-sand processing plant were characterized in this study. The aerosol samples were collected at a plant that processes mineral sands to obtain rutile, ilmenite, zircon, and monazite concentrates. A cascade impactor with six stages was used to collect mineral dust particles with aerodynamic diameters in the range of 0.64 to 19.4 mum. The particles impacted on each stage of the cascade impactor were analyzed by PIXE, which permits the determination of the elemental mass air concentration and the MMAD (Mass Median Aerodynamic Diameter). The chemical compositions of the aerosol samples were identified by PDMS analysis. This study shows that, by using PIXE and PDMS techniques, it is possible to determine the chemical compounds in which the elements are associated in the aerosol particles. Based on the results of the PIXE analysis, the elemental mass concentrations and the MMADs were determined.

A cascade impactor for mineral particle analysis

ABSTRACT A cascade impactor (NCI) made of stainless steel with six stages was developed to collect particles using 50% cutpoints in the range of 0.64 to 19.4 μm. The sixth stage of the NCI was calibrated using monodisperse aerosols. The experimental MMAD (mass median aerodynamic diameter) was 0.634 μm, which agreed with the calculated MMAD. The NCI, stacked filter unit (SFU) and personal air samplers with the cyclone were used to characterize the workers exposure in two Brazilian plants where niobium minerals with thorium associated to the crystal lattice are processed. The Th, U, Nb, Zr, Pb, Fe, Sr, and Y air concentrations were determined. The MMAD of the particles containing these elements have shown the availability of mineral particles in the fine particles of aerosols. The Th concentration in the samples collected using SFU were in the same order of magnitude of those collected with the cascade impactor and are correlated.

Occupational exposure to thorium air monitoring

The occupational exposure to thorium of monazite processing plant workers is determined by characterizing the airborne particulates and the determination of the deposition of thorium in the lung.

Size distribution of airborne particulates in monazite dust

Abstract A six-stage cascade impactor was used to collect airborne dust particulates in the grinding area of a monazite separation plant. The samples were analysed using particle-induced X-ray emission (PIXE) to determine the elemental concentrations, with special attention to thorium and uranium concentrations. The particle size distribution of the samples containing thorium and uranium were determined. The mass median aerodynamic diameter (MMAD) obtained was 1.15 μm for both elements. The activity median aerodynamic diameter (AMAD) was estimated based on the MMAD. The results are compared with ICRP recommendations for derived air concentrations (DAC) for thorium and uranium in restricted areas.

Characterization of environmental exposure to mineral sands by PDMS technique

Abstract The risk to human health due to exposure to aerosols depends on the intake pattern, the mass concentration and the speciation of the elements present in airborne particles. In this work plasma desorption mass spectrometry (PDMS) was used to identify the speciation of metals present in the urine sample of an individual environmentally exposed to mineral sands airborne particles. Aerosol samples were collected at a Brazilian region with high concentration of mineral sands (Buena village), using a six-stage cascade impactor. The mass median aerodynamic diameter (MMAD) determined indicated that the airborne particulate was in the fine fraction of the aerosols. In order to characterize human exposure to mineral sands dust a sample from one inhabitant was analyzed by PDMS. The analysis of the results shows that the inhabitant incorporated metals from mineral sands and suggests that the source of aerosols is the mineral processing plant located at the village.