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Health Effects of Radiation. What Radiation Affects. Directly or indirectly, radiation affects the DNA in cells DNA controls the cell’s function and ability to reproduce. Possible Effects. Destroy the DNA Kill the cell Damage the DNA; cell can: Repair itself (most likely)
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What Radiation Affects • Directly or indirectly, radiation affects the DNA in cells • DNA controls the cell’s function and ability to reproduce
Possible Effects • Destroy the DNA • Kill the cell • Damage the DNA; cell can: • Repair itself (most likely) • Not function or function improperly • Undergo uncontrolled division (cancer)
Cell Sensitivity • Cells most affected: • Rapidly dividing cells: • (small intestines, bone marrow, hair, fetus) • Cells least affected: • Slowly dividing cells: • (brain, nerves)
Category of Effects • Acute Somatic • Immediate effects to the organism receiving the dose • Delayed Somatic • Effects that appear years later to organism receiving the dose • Genetic • Effects that appear in offspring
Units of Dose • Dose measured as energy absorbed per mass • Units of Gray (Gy) or rad (= 0.01 Gy) • Dose equivalent accounts for different effect of different radiations • Units of Sieverts (Sv) or rem (= 0.01 Sv) • Dose measured equated to dose equivalent • 1 rad roughly equals 1 rem
Dose • Average US annual radiation dose from soil, cosmic, and internal radiation • 0.001 Sv = 1 mSv (0.1 rem = 100 mrem • Maximum allowed annual dose for a nuclear worker • 0.5 Sv = 50 mSv (5 rem)
Acute Somatic Effects • <250 mSv (25 rem) • No detectable effects • 250 - 1,000 mSv (25 - 100 rem) • Reduced red & white blood cell count • 1,000 - 3,000 mSv (100 - 300 rem) • Nausea, vomiting, may not be able to fight infection
More Acute Somatic • 3,000 - 6,000 mSv (300 - 600 rem) • More severe nausea and vomiting, hemorrhaging, diarrhea, loss of hair, cannot fight infections, sterility. At 4,500 mSv, about half exposed will die within 30 days, others will survive. • >6,000 mSv (600 rem) • Same as above plus central nervous system impairment. Death within 30 days.
Delayed Somatic Effects • 1. Cancer: solid tumors • Increased risk • 2. Cancer: leukemia • Increased risk • 3. Degenerative effects • Life shortening (not sure)
More Delayed Somatic Effects • 4. Cataracts • 2,000 mSv single dose threshold • 5. Birth defects (fetus exposed) • Effects depend on time of gestation • 6. Sterility • 2,000 mSv temporary - male • 8,000 mSv permanent - male
Cancer Risks • Radiation dose above 10 rem produces a small increased risk. • Radiation dose does not produce cancer in every exposed person • Latency period: • Solid tumors: 10 - 20 years • Leukemia: 2 - 4 years
Cancer Risks • Normal cancer incidence: • About 55% of US citizens get cancer • Normal mortality: • About 25% of US citizens die from cancer
Most Common Cancers • High spontaneous incidence: • Breast, lung, skin, prostate, cervix, acute myelogenous leukemia • Moderate spontaneous incidence: • Kidney & bladder, ovary, pancreas • Low spontaneous incidence: • Thyroid, liver, brain, testis, bone, chronic lymphocytic leukemia
Radiation Induced Cancers • High sensitivity to radiation: • Breast, thyroid, kidney & bladder, ovary, acute myelogenous leukemia • Moderate sensitivity to radiation: • Lung, liver • Low sensitivity to radiation: • Brain, bone, skin, prostate, cervix
Radiation Induced Cancers (continued) • Not observed to be initiated by radiation: • Pancreas, testis, chronic lymphocytic leukemia
Low Dose Risk • Data are good for risks from high doses of radiation (>100 mSv) • At lower doses, the effects are masked by natural high incidence • Extrapolate from high dose effects to low dose effects
Supralinear Extrapolation • Some critics claim that the risk per dose is higher at low dose that at high dose • This would mean that natural background is more harmful than high dose medical exposures
Threshold • Some effects do have a threshold dose for the effect to appear • Sterility, cataracts • Cancer does not seem to have a threshold, but this is not known for sure
Linear-Quadratic • Leukemia seems to obey this extrapolation
Linear - No Threshold • If we can’t see the effects, are they really there? • If yes: the smallest dose may increase risk • If no: there is some level below which there is no effect • Controversy among radiation scientists
Cancer Risks • Increased risk of cancer mortality from 1 mSv of radiation (average annual background): • Solid tumor cancer risk is about one chance out of 25,000 (1:25,000) • Leukemia risk is about one chance out of 125,000 (1: 125,000) • Total risk is about one chance out of 20,000 (1: 20,000)
Comparative Risks • “Normal” risks we face: • Smoking (lifetime): 1:4 • Police officer: 1:2500 • Agriculture industry (per year): 1:2600 • Vehicle accident (per year): 1:6000 • Falls (per year): 1:20,000 • Home fire (per year): 1:50,000 • Airplane crash (one trip): 1: 1,000,000
What is Safe? • Driving a car is “safe” • (1:6,000) • Living at home is “safe” • (Falls: 1:20,000, Fires: 1:50,000, Poisoning: 1:40,000; total: 1:10,000) • Radiation (1 mSv) is safe • (1:20,000)
