Radioactivity cumulative exposure

A wide variety of monitors have been developed to measure radiation and radioactivity to which personnel may be exposed. Radiation dosimeters are typically carried in pockets by workers and measure cumulative exposure to p radiation, y radiation, and x-rays. A similar device is used to measure exposure to radio-frequency (RF) radiation, especially among workers exposed to communications equipment. A related device can be used to measure exposure to microwaves. 

Information on the excretion of americium after dermal exposure in humans or animals is extremely limited. Some qualitative information is available from an accidental exposure in which a worker received facial wounds from projectile debris and nitric acid during an explosion of a vessel containing 241 Am (McMurray 1983). The subject also inhaled 241Am released to the air as dust and nitric acid aerosols, which was evident from external chest measurements of internal radioactivity thus, excretion estimates reflect combined inhalation, dermal, and wound penetration exposures (Palmer et al. 1983). Measurements of cumulative fecal and urinary excretion of241 Am during the first years after the accident, and periodic measurements made from day 10 to 11 years post accident indicated a fecal urine excretion ratio of approximately 0.2-0.3, although the ratio was approximately 1 on day 3 post accident (Breitenstein and... 

Urinary excretion of radioactivity was measured in human volunteers during and after a 3.5-hour period of dermal exposure to 0.11 or 0.22 g 32P-labeled TOCP (Hodge and Sterner 1943). The specific activity of the test substance was not reported. Radioactivity in urine was measured with a Geiger-Muller counter, but the limits of detection were not reported. Maximum estimated excretion rates, 10 and 43 pg TOCP/hour for the respective dosage levels, were measured within 24 hours of initiation of exposure. Radioactivity was not detected 48 or 72 hours after dosing ceased. Cumulative radioactivity detected in urine accounted for 0.13% and 0.36% of the dermally applied radioactivity. 

Immediately dangerous to life or health (IDLH) conditions pose a threat of severe exposure to contaminants, such as radioactive materials, that are likely to have adverse cumulative or delayed effects on health. Two factors are considered when establishing IDLH concentrations. The worker must be able to escape (1) without loss of life or without suffering permanent health damage within 30 minutes and (2) without severe eye or respiratory irritation or other reactions that could inhibit escape. If the concentration is above the IDLH, only highly reliable breathing apparatus is allowed. 

The purpose of the MCLs for radioactivity (radionuclides) is to limit human exposure. Some waters in contact with radioactive geologic strata (e.g., certain shales) are known to possess radioactivity. Since radioactivity in organisms is cumulative, monitoring should be carried out. 

Because radiation exposure can be cumulative, there are no truly safe levels of exposure to radioactive materials. Radiation does not cause any specific diseases. Symptoms of radiation exposure may be the same as those from exposure to cancer-causing materials. The tolerable limits for exposure to radiation that have been proposed by some scientists are arbitrary. Scientists concur that some radiation damage can be repaired by the human body. Therefore, tolerable limits are considered acceptable risks when the activity benefits outweigh the potential risks. The maximum annual radiation exposure for an individual person in the United States is 0.1 REM. Workers in the nuclear industry have a maximum exposure of 5 REMs per year. An emergency exposure of 25 REMs has been established by The National Institute of Standards and Technology for response personnel. This type of exposure should be attempted under only the most dire circumstances and should occur only once in a lifetime. 

Combinatorial Y and TACE presents an interesting opportunity to assess the cumulative effect of these modalities in effecting tumor kill. Intraarterial infusion of Y in an aerobic environment (non-stasis) could be followed by TACE after the radioactive effect diminishes to sub-therapeutic levels (approximately 2 weeks post Y treatment). TACE administration with cytotoxic tumor exposure in a hypoxic environment would then address any viable (radioresistant) cells that remained. 

Laboratory persoimel work in a potentially extremely hazardous and unforgiving environment. The substances with which they work may be toxic, ffanunable, explosive, carcinogenic, pathogenic, or radioactive, to mention only a few unpleasant possibilities. The hazards may cause an immediate or acute reaction, or the effects may be delayed for several years. A worker may be lulled into a false sense of security because of the seeming safety of a material according to current knowledge, but eventually evidence may develop that continued exposure may cause uneiqiected or cumulative and irreversible effects. 

Immediately dangerous to life or health means conditions that pose an immediate threat to life or health or conditions that pose an immediate threat of severe exposure to contaminants, such as radioactive materials, which are likely to have adverse cumulative or delayed effects on health. 

The dose constraint should be used to ensure that the cumulative effects of all releases of radioactive material to the environment are restricted so that the effective dose due to normal or potential exposures for any member of the public, including populations distant from the radiation source and future generations, is unlikely to exceed any relevant dose limit. 

---