Occupational exposure uranium

Thorium is commonly found in combination with other actinide elements, with organic and inorganic chemicals, and with acids and bases during occupational exposure. The health effects of occupational exposures to thorium on humans, therefore, cannot necessarily be attributed to thorium. The daughter products of thorium have unique properties that also add to the radiological toxicity of thorium. For further information, see the toxicological profiles on uranium, radon, and radium. 

Occupational and environmental poisoning with metals, metalloids, and metal compounds is a major health problem. Exposure in the workplace is found in many industries, and exposure in the home and elsewhere in the nonoccupational environment is widespread. The classic metal poisons (arsenic, lead, and mercury) continue to be widely used. (Treatment of their toxicities is discussed in Chapter 57.) Occupational exposure and poisoning due to beryllium, cadmium, manganese, and uranium are relatively new occupational problems, which present new and previously unaddressed problems. 

Uranium levels have been measured in tissues from humans, with no occupational exposure where the source of uranium was assumed to be dietary and environmental. 

The biological half-time of uranium dioxide in human lungs (occupational exposure) at German fuel fabrication facilities was estimated to be 109 days. Body burden measurements of uranium taken from 12 people who handled uranium oxides for 5-15 years were used for this determination. Twice a year for 6 years, a urinalysis was conducted on workers exposed to uranium. In vivo lung counting was performed on the last day before and the first day after a holiday period. Levels of uranium in feces were measured during the first 3 days and the last 3 days of a holiday period and the first 3 days after the restart of work. For some employees, the levels of uranium in feces was measured during 3 days one-half year after the holiday period (Schieferdecker et al. 1985). 

Table 2-8 shows the mass equivalents for natural and depleted uranium for radiation levels that caused potential radiological effects in rats exposed once for 100 minutes to airborne 92.8% enriched uranium with an estimated specific activity of 51.6 pCi/g (Morris et al. 1989). These mass equivalent values for natural and depleted uranium for the minimal concentration of radioactivity that is expected to induce potential radiological effects are well above levels that would be expected to be inhaled or ingested. In addition, the mass equivalents for natural and depleted uranium for potential radiological effects are 3,600 and 76,500 times higher, respectively, than the occupational exposure limits (short-term exposure) recommended by the National Institute for Occupational Safety and Health (NIOSH 1997). Therefore, MRLs for uranium based on studies that used enriched uranium are inappropriate. 

PNL. 1981. Occupational exposures to uranium Processes, hazards and regulations. Pacific Northwest Laboratory and Hanford Environmental Health Foundation, PNL-3341 USUR-01 UC-41. 

Stradling GN, Stather JW, Gray SA, et al. 1987. Metabolism of uranium in the rat after inhalation of two industrial forms of ore concentrate The implications for occupational exposure. Hum Toxicol 6 385-394. 

Mixtures of uranium oxides ( yellow cake ) are produced in the processing of uranium ores and can result in occupational exposures in uranium mill workers. Exposure to uranium tetrafluoride and hexafluoride is a potential for workers in the uranium enrichment industry. 

Tab. 26.1-2 Critical effects and occupational exposure limits for thorium, different exposure pathways uranium and decay products for ...

Canadian studies, cumulative occupational exposure to radon and radon daughters were estimated at levels up to about 600 WLMs. A statistically significant excess of mortality due to chronic nephritis and renal sclerosis was also reported in the United States uranium miner cohort, although it is unclear whether this was related to exposure to radon, uranium ore, or other mining conditions or to nonmining factors (Waxweiler et al. 1981). 

The topic came to national attention in late 1984. A nuclear power plant worker was found to be highly radioactive and his exposure was traced back to his home in Pennsylvania, where radon concentrations were as high as one hundred and thirty times the federal occupational exposure standard for underground uranium mines. The home was located on a geological formation, called the Reading Prong, which is in New Jersey, New York, and Pennsylvania. Similarly high levels were found in other homes. " ... 

Uranium enrichment and conversion Yellowcake, UsOg is converted to UF5 and emiched in The enrichment is carried out by the diffusion method or by the centrifugation of UF5. The occupational exposures occur during both conversion and enrichment, but average armual effective doses are rather small. 

The occupational exposure values for the inhalation of uranium have been compiled by the American Conference of Governmental Industrial Hygienists (ACGIH) [14]. These are air concentration exposure limits based on the chemical effects of uranium. In contrast, the International Commission on Radiological Protection (ICRP) has developed the annual limit on intake (ALI) for ingestion and inhalation of uranium compounds based solely on the radiation doses received by tissues and organs of the body [12,15]. Whether the primary concern is the chemical toxicity or radiation dose, the occupational limits take the solubility of the uranium compound into consideration. The occupational limits are summarized in Table 3. It must be emphasized that the air concentration exposure limits are for the typical 8-hr day (see Abbrevi-... 

The uranium concentrations in human tissues and blood were summarized by Fisenne in 1991 [26]. Data from occupational exposure cases and persons from areas having elevated natural radioactivity were excluded from the survey. 

Guidance for the collection of bioassay samples has been summarized by the U.S. National Council on Radiation Protection and Measurements (NCRP) [30]. In most occupational exposure situations, any uranium actually absorbed in the body is rapidly excreted in urine. Therefore, bioassay analyses used to estimate the occupational exposure must be collected as soon as possible and for some time after discovery and control of the exposure conditions. 

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