US EPA

1422157 

Journal Article 

Occupational radiation exposure associated with milling of Th-U-rich Sn ore in Nigeria 

Oresegun, MO; Babalola, AI 

1990 

Yes 

Health Physics
ISSN: 0017-9078
EISSN: 1538-5159 

NIOSH/00195907 

58 

2 

213-215 

English 

2298578 

An investigation was conducted of radiation exposures associated with milling tin (7440315) ores in Nigeria. The cohort consisted of 53 males employed at two tin ore processing mills in Nigeria. The ores contained significant amounts of thorium (7440291) and uranium (7440611). Gamma radiation levels in the two mills were measured. The mill tailings were analyzed to determine the radionuclides present. Radiation exposures of the workers were monitored for 2 years using thermoluminescent dosimeters. Radiation levels in the mills ranged from 1.1 to 20 microgray per hour (microGy/hr). Radiation levels in the tailing dumps near the mills ranged from 35 to 100microGy/hr. The mill tailings contained thorium-228 (14274829), radium-226 (13982633), and potassium-40 (13966002) having activity concentrations of 1.11802x10(5), 2.1064x10(4), and 5.069x10(3) becquerel per kilogram, respectively. The annual gamma radiation exposures experienced by the mill workers ranged from 0.93 to 39.25 milligray (mGy), mean 9.87mGy. Approximately 50% of the millers were exposed to dose rates below 8.0mGy per year. Approximately 15% of the workers were exposed to doses greater than 0.3 of the maximum permissible dose of 50 millisieverts. The authors conclude that because of the exposures they experience the mill workers should be classified as radiation workers. They experience higher gamma dose rates than workers in other countries. 

DCN-191353; Radiation exposure; Milling industry; Occupational exposure; Gamma radiation; Dosimetry; Radioactive metals; Radioactive isotopes