Info

takes into account fatal and nonfatal cancers, severe hereditary effects, and loss of relative length of life.

The ICRP occupational guideline for radiation protection (1990) limit the dosage received to an average of 20 mSv (2 rem) per year over five years, with a maximum of 100 mSv in any one year. A dosage of 20 mSv with a fatal cancer occupational risk factor of 4% per sievert corresponds to an 8 x 10~4 risk. The NCRP (1993) has defined a negligible individual dose (NID) below which efforts to reduce radiation exposure further are unwarranted. The NID was selected to be 0.01 mSv (1 mrem) per year. This corresponds to 5 x 10-7 added risk of fatal cancer per year.

Acute effects in humans are found at higher dosages. The 30-day LD50 for whole-body radiation depends on individual factors and the level of medical support provided, but is considered to be about 4 to 7 Gy (400 to 700 rad). At such levels the first symptoms include nausea and vomiting within about a week. After two weeks sore throat and loss of appetite occurs, followed by diarrhea, emaciation, and death. Suppression of the immune system can result in infections that contribute to death rates. Exposure can cause skin lesions, damage to leukocytes and lymphatic tissue, and ultimately the complete elimination of antibody production. Bone marrow depression is observed at about 2 Gy, and changes in blood counts result at exposures from 0.14 to 0.50 Gy.

In organisms other than humans, the genotoxicity has been shown to be strongly related to the amount of haploid DNA in the organism (Figure 21.5). This relationship seems to be reflected in the lethal toxicity of radiation to various groups shown in Table 21.17.

The fate and transport of radionuclides is as varied as their chemical composition. Radon, an ideal gas, is fairly soluble in water. Some of its daughters, however, are solids that attach to particles in the air that in turn may be deposited in the lungs (see Figure 21.4). Many of the metal radionuclides released by nuclear power plants have been found to be strongly adsorbed by sediments. The concentration of plutonium in aquatic organisms has been found not to exceed the concentration found in associated sediments. It has also been found to decrease with trophic level.

Figure 21.5 Relation between forward mutation rate per locus per rad and the DNA content per haploid genome. The line is a regression line. The point for humans is estimated from the DNA content.

DNA per haploid genome

Figure 21.5 Relation between forward mutation rate per locus per rad and the DNA content per haploid genome. The line is a regression line. The point for humans is estimated from the DNA content.

TABLE 21.17 Lethal Dosage of Radiation for Adult Organisms of Several Groups

Group

Lethal Dose (krad)

Toxic Measurementa

Bacteria

Was this article helpful?

0 0
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment