Environmental Engineering FOURTH EDITION

324 ENVIRONMENTAL ENGINEERING

Table 16-6. Yields of DNA Damage Necessary to Kill 63% of

the Cells Exposeda

~ ~ ~ ~~ ~ ~~~

Number of DNA lesions

Agent per damaged cell

Ionizing radiation 1000

UV light 400,000

Hydrogen peroxide 2,600,000

Benzo(a)pyrene 4,5-oxide 100,OOO

Aflatoxin 10,000

=From National Academy of Sciences (1990).

Table 16-7. Average Fatal Somatic Risk from Lifetime Exposure to

1 mSv/yr Low LET Radiation

Year Dose model Effects per lo5 persons

1977

1980

1980

1985

1990

1990

1996

1996

Quadratic

Linear

Quadratic

Linear

Linear-quadratic for males

Linear-quadratic for females

Linear (general public)

Linear (occupational)

75-175

403

169

280

520

600

500

400

the dose-response relationship for ionizing radiation would result in drastic changes
in regulatory standards and limits for radioactive pollutants.
Although we do not know the precise mechanism by which ionizing radiation
produces somatic and genetic effects, we understand that it involves damage to the
DNA of the cell nucleus. Table 16-6 compares DNA damage caused by a variety
of carcinogens. If there is a threshold for effects of ionizing radiation, it would be
related to the high frequency of DNA repair that occurs naturally in human and other
organisms.
Somatic effects include decrease in organ function and carcinogenesis. A variety
of estimates of average fatal somatic risk, using a variety of dose-response models,
have been developed over the years. These estimates are summarized in Table 16-7.
The 1996 estimates given in Table 16-7 are from Publication 60 of the International
Commission on Radiation Protection and are usually used in environmental impact
assessments.
Genetic effects result from radiation damage to chromosomes and have been
demonstrated to be inheritable in animals, but not in the human population. The
human genetic risk is estimated to be between 1 and 45 additional genetic abnormalities