Physical Agents Environmental and Occupational Health 1 Model for Physical Agents Physical Agents in Environmental and Occupational Health Source Energy Person Thomas E. Bernard [email protected] (813) 974-6629 Type and quantity of personal.health.usf.edu/tbernard energy affect health risk College of Public Health Some Types Quantity Radiation Total Amount of Energy Absorbed (Work) Ionizing What does it take to raise water temperature? Nonionizing Joules Noise Rate of Absorption (Power) Thermal: Heat and Cold How fast does the temperature rise? Vibration Watts (J/s) Plus Normalized to Surface Area (W/m2, mW/cm2) Electricity Impact and Shock Waves Frame of Reference Pressure (Diving and Altitude) Basal Metabolic Rate is 6 mW/cm2 College of Public Health College of Public Health Bernard Watt-O-Meter The BWOM does not exist in this reality; it may violate known physical laws and grossly simplifies others. Ionizing Radiation But perhaps it will give you some perspective. If you care to know how I came up with a number, ask. College of Public Health © 2008 Thomas E. Bernard Physical Agents Environmental and Occupational Health 2 Q1 Q2 Who discovered X-rays? Hint: First What disease is most associated with low-level exposures to ionizing radiation? Hint: By 1940s, example was radiograph of wife’s hand. incidence among physicians, especially radiologists, was higher than general population. a. Becquerel b. Curie a. leukemia b. lung cancer c. Roentgen c. schizophrenia d. Seivert d. tuberculosis e. Zen e. xeroderma pigmentosum College of Public Health College of Public Health What happened 113 years Q3 ago? Among consumer products, what is the In October 1895, Wilhelm Roentgen greatest source of ionizing radiation exposure? Discovered X-rays a. Cigarettes Packets of Energy Called Photons b. Gas stoves = 12 eV to 108 eV c. Old luminous watch dials (pre-60s) Can Ionize Atoms d. Smoke detectors e. Televisions College of Public Health College of Public Health 1845-1923 Results of Ionization Biological Effects Break DNA -- Direct Hit Determinants of Biological Effects Rate of absorption Total dose Tissue exposed Create Free Radicals and Peroxide Individual variations Results on Cell Viability Classes of Effects Acute somatic effects (acute radiation sickness) No Effect Delayed somatic effects (leukemia, cancers) Cell Dies Genetic effects (birth defects) Takes a Step on Carcinogenic Pathway College of Public Health College of Public Health © 2008 Thomas E. Bernard Physical Agents Environmental and Occupational Health 3 Energy Levels Types 2 LD50 = 0.3 mW/cm Electromagnetic Radiation / Photons X-rays One Time = 0.01 mW/cm2 Gamma Rays Occupational = 0.00000003 mW/cm2 over 1 yr Particle Radiation Public = 0.0000000008 mW/cm2 over 1 yr Alpha Beta 70 kg person; gamma / x-ray only Neutron College of Public Health College of Public Health Chemical Elements Nuclear Radiation Element Nature Seeks Stability Defined by Atomic Number Atomic Number Equals Number of Protons Radioisotopes Instability occurs when the right blend is not Isotopes present Same Element Nature attempts to create the right blend by Different Numbers of Neutrons radioactive decay. 1 12 H 2 C 14 1 H 3 6 C Nuclear Radiation is Result 1 H 6 College of Public Health 1 College of Public Health Types of Nuclear Radiation Types of Nuclear Radiation Alpha Particles Alpha Particles Helium nucleus (2 protons + 2 neutrons) {e–} Positive charge ((2)+2) Beta Particles Dissipate energy quickly Electron (neutron to proton) Travel short distances Negative charge (-1) Stopped by sheet of paper / skin Loss energy over short distance Stopped by aluminum foil / skin (deeper) 4+2 { 2He } College of Public Health College of Public Health © 2008 Thomas E. Bernard Physical Agents Environmental and Occupational Health 4 Decay Series Types of Nuclear Radiation 238 U – Alpha Particles 92 {e } 234 Beta Particles 90Th 234 91Pa 234 GRGamma Rays 4+2 92U { 2He } Excess energy dissipation from nucleus 234 92U Photons with high energy 230 Travel great distances 90Th Ra226 Give up energy slowly 88 Stopped by lead, concrete 222 86Rn ... College of Public Health College of Public Health Q4 Measurement Units What distinguishes the energy paths associated with Activity (Ci / Beq) alpha and gamma radiation? a. Gamma radiation is readily stopped. Radiation Absorbed Dose (rad / Gray) b. Alpha radiation passes through lead more rad Equivalent - Man (rem / Sievert) easily than gamma radiation. Relative Biological Effectiveness (RBE) Gamma has least effect (RBE = 1) c. An alpha radiation source is a problem only when it is in the body while a gamma source can be a Alpha has greatest effect (RBE = 20) problem inside or outside. Beta tends to be closer to Gamma (RBE = 1 to 5) rem = RBE x rad Sv = RBE x Gr College of Public Health College of Public Health Half-Life Q5 Time to reduce activity by 1/2 For the same amount of potential damage (risk) to a particular organ, 1 2 A. alpha particles cannot cause any problems, but beta 3 particles can. B. the amount of energy deposited in the organ is the same, no matter what the type of radiation is. C. gamma rays require more total energy than alpha 4 half-lives is a 95% reduction. particles. Short half-life is related to high activity. College of Public Health College of Public Health © 2008 Thomas E. Bernard Physical Agents Environmental and Occupational Health 5 Radiation Threat Radon Major Natural Source Sources Uranium-238 Natural 55% Artificial (solids) Hazards External (long distances) (gas) . Gamma rays Radon-222 . X-rays Internal (short distances) (solids) . Alpha . Beta and Particles: Internal Hazard • Lungs: inhaled Lead-206 • Stomach and intestines: ingested College of Public Health College of Public Health Medical X-rays and Nuclear Medicine Other Natural Sources Artificial Sources Internal: 11% 15% Cosmic: 8% 27% Terrestrial: 8% Humans may enhance exposure to natural sources. College of Public Health College of Public Health Commercial Power Other Artificial Sources Generation Consumer Products: 3% Nuclear Fuel Cycle: 0.1% Mining and Milling 3.4% Enrichment and Fuel Fabrication Occupational: 0. 3% . Japan Incident Power Generation Nuclear Fuel Cycle: 0.1% . Routine and Catastrophic Releases . Three Mile Island . Chernobyl Waste Disposal College of Public Health College of Public Health © 2008 Thomas E. Bernard Physical Agents Environmental and Occupational Health 6 Waste Disposal Q6 High-Level Wastes What is the role of public health professionals in trying Nuclear Waste Policy Act (1982) to influence individual decisions concerning ionizing . Federal Responsibility radiation? . Permanent: Yucca Mountain (Open in 20??) . TMitdRtiblStTemporary: Monitored Retrievable Storage A. IitIgnore it Military (weapons) Waste: New Mexico Low-Level Wastes B. Prudent avoidance Low-Level Waste Policy Act (1980) . State Responsibility C. As low as reasonably achievable (ALARA) . Groups of States form Compacts Siting Problems D. Education on risks and actions College of Public Health College of Public Health Questions? College of Public Health © 2008 Thomas E. Bernard.