lead-radioisotopes and monazite

This paper focuses on a survey of uranium and thorium decay chain radionuclides in food and drinking water from the thorium-rich (monazite-bearing) region of Buena, which is located in the state of Rio de Janeiro, Brazil. The radionuclide concentration values in the food and drinking water from Buena reached values higher than 100-fold the international reference values. The daily intake of radionuclides by the local population is similar to that of another high background radiation area in Brazil, but the intake is higher than that of residents from a normal background radiation area. Approximately 58 % of the food consumed by Buena inhabitants is produced locally. Based on that figure, locally produced food and the dilution of total radionuclides in the diet of residents caused by food importation are both highly relevant to a population's intake of radionuclides. The concentration values for (210)Pb and the radium isotopes in drinking water from Buena are among the highest values to be reported in the literature. (228)Ra is the most important radionuclide ingested with both food and water among the inhabitants of Buena.

Topics: Animals; Brazil; Drinking Water; Food Contamination, Radioactive; Humans; Lead Radioisotopes; Metals, Rare Earth; Radiation Dosage; Radiation Monitoring; Radium; Thorium; Uranium; Water Pollutants, Radioactive

Radiation exposure due to the inhalation of 212Pb has been identified as one of the major hazards encountered in the chemical processing of monazite. Volunteers were exposed to 212Pb in the thorium hydroxide storage facility. Personal air samplers were used to determine the concentration of 212Pb in air. The 212Pb in the chest was measured using a whole body counter and the decay in the chest was followed up for 24 h. From the decay, mean effective half-life for the inhaled 212Pb was estimated as 6.63 +/- 0.23 h. A comparison of the chest burden with the assumed intake indicates that 55-76% of the inhaled 212Pb is deposited in the respiratory system. From the chest monitoring data, it is possible to estimate the working level exposure due to thoron progeny.

Topics: Administration, Inhalation; Adult; Humans; India; Lead Radioisotopes; Metabolic Clearance Rate; Metals, Rare Earth; Occupational Exposure

Estimation of inhaled radiation doses associated with mineral sands processing is commonly performed by gross alpha-counting dust collected on air filters. The technique requires knowledge of the extent of disequilibrium in Th-bearing minerals. The daughters which can be expected to give rise to disequilibrium, viz. 228Ra and 220Rn (also designated thoron in the paper), were investigated in a typical Western Australia monazite. The thoron flux from a dry, "infinitely thick" layer of monazite was found to be 41 Bq m-2 s-1. The depth of monazite from which thoron is exhaled is limited to 40-50 mm, and within the first 10 mm is a linear function of bed thickness. The relative loss within the linear region is approximately 0.02% of the equilibrium concentration and progressively less for layers beyond 10 mm. The sample investigated gave no indication of disequilibrium involving 228Ra. The results indicate that secular equilibrium may be assumed when calculating 232Th daughter concentrations in monazite from the gross alpha activity. More extensive work on monazite samples from a number of sites will be necessary before this can be stated as a general conclusion applicable to all Western Australian monazite deposits.

Topics: Dust; Half-Life; Health Physics; Lead Radioisotopes; Metals, Rare Earth; Minerals; Radiation Monitoring; Radon; Thorium; Western Australia