Characterization of airborne Ce, Th and Cd in workplace and their co-relation with their concentrations in body fluids and excreta of occupational workers using NAA, ICP-AES and XRF

Measurements of the airborne concentrations of thorium (Th) and Cerium (Ce) and their size characterization were carried out in beach mineral separation and monazite processing plants. Size characterization of airborne dust and elemental concentrations of the dust was also carried out at a Zinc Smelter Unit. Further studies were conducted on elemental distribution of different size fractions of the Airborne Particulate Matter (APM) as also the leaching characteristics of the elements. The levels of Th and Ce in urine samples of occupational workers were discussed in relation to their airborne concentrations and chemical speciation. A limited number of blood samples collected from occupational workers in monazite processing plant were also analysed for Th and Ce content. The results of Thoron (220Rn ) in breath measurements and urine analysis (Th) with respect to two groups of occupational workers with history of chronic exposure to airborne mineral dust and thorium from the mineral separation and chemical processing of monazite at the Mineral Separation Plants (MSP) and Monazite Chemical Processing Plant (MCP) were studied in relation to their exposures. A group of adults of comparable age group from a Natural High Background Radiation Area (NHBRA) were also subjected to the measurements in order to estimate the environmental contribution specific to NHBRA where the MSPs are located. Monitoring of aerosols released during the processing of zinc ore have shown that 85% of the airborne dust released are above 9 μm Mass Median Aerodynamic Diameter (MMAD) at the initial stages. However the MMAD at the down stream processing was about 3 μm. The elemental concentrations and their ratios in the raw material were reflected in the APM at the initial stages. Detailed size characterization studies showed that up to 50% of APM was below 2 μm in some process areas. Elemental concentrations of Cd and Zn exceeded the Threshold Limit Values (TLVs) at some of the locations in this plant and the situation calls for regular monitoring. In the mineral benefeciation plants the Activity Median Aerodynamic Diameter (AMAD) of the particulates ranged from 2.7 to 15 μm with an average of 7 μm., Geometric Standard Deviation (GSD) varied from 2.6 to 4.6. Based on the ICRP dose conversion factors and taking into consideration the equilibrium status of 232Th and 228Th in monazite, a combined Annual Limit of Intake for Th of 534 Bq and corresponding Derived Air Concentration (DAC) of 0.22 Bq/m3 are arrived at for the mineral processing plants. In the plant processing monazite the AMAD of airborne particulates were in the range 2.1 to 9.0 μm (mean 4.5 ± 1.9 μm). The corresponding combined ALI (232Th and 228Th) works out to 385 Bq for unspecified compounds of thorium (DAC 0.16 Bq/m3 The airborne concentrations of Th, Ce, Cd and Zn are compared with the TLVs, ALI and DAC values as applicable to assess the health effects of airborne particulate matter in the industries studied. (author)