Radionuclide Pollution and Environmental Fate Impact

Radionuclide Pollution and Environmental Fate / Impact

Atomic Structure Atomic number based on number of protons Atomic mass based on number of protons and neutrons Nuclide- any species of atom distinguished by its: • atomic weight • atomic number • energy state

Atomic Structure and Nuclides Z = atomic number = # protons N = number of neutrons A = atomic mass = sum protons + neutrons = Z + N Z identifies element, Z= 6 is Carbon

Atomic Structure and Nuclides isotope of a given element - same Z, different A Stable isotope -- stable atomic nucleus that does not decay or emit radiation Radioisotope (Radionuclide) -- unstable atomic nucleus that decays spontaneously emitting radiation 12 C 6 13 C 6 14 C 6 238 92 U 235 92 U natural abundance -- percentage of stable isotopes 12 C= 98. 9 %, 13 C = 1. 1% http: //ie. lbl. gov/education/isotopes. htm Lawrence Berkeley National Laboratory

When is an isotope unstable (radioactive)? 1. All Nuclei with Z > 84 are Unstable 2. Very stable isotopes have "magic" Z 2, 8, 20, 50, 82 or 126 3. Isotopes are stable in the "zone of stability"

Isotopes and Nuclear Stability Zone of Nuclear Stability N N/Z ratio = 1 for Z < 32 Unstable Z N/Z ratio = 1. 5 for high Z

Natural Occuring Radionuclides 14 C -- generated in stratosphere by cosmic radiation 238 U -- in geological material and its many daughter radioisotopes (products of radioactive decay) including 232 Th and 222 Rn 40 K -- in all soils and geomedia others

Anthropogenic Occuring Radionuclides Nuclear fission reactions atomic bombs (incl. waste from weapons production) nuclear fission reactor fuel Americium -241 Cesium -137 Cobalt-60 Iodine Plutonium Radon Strontium Technetium Thorium Tritium Uranium

Anthropogenic Occuring Radionuclides Biomedical waste

Introduction of Radionuclides into Soils and Natural Waters Extensive above ground testing in US and USSR 1946 -1962 Above ground testing by other countries Waste generated from weapons grade uranium and plutonium production spent nuclear fuel --- processing to enrich U and Pu generates large amount of other radionuclide "waste" which has to be "discarded" -- buried? stored?

Weapon production sites

Nuclear Waste Storage / Disposal Yucca Mountain, Nevada

Introduction of Radionuclides into Soils and Natural Waters Nuclear reactor meltdowns / accidents April 26, 1986 Nuclear reactor meltdown Massive release of radioa particles to surrounding community and farmland Ukraine

Environmental Impact and Radioactive Decay Radioisotope radioisotope + radiation radionuclide 1 RN 2 + radiation RN 3 + radiation RNn + radiation stable isotope + radiation Three types of radiation emitted by radioisotopes Alpha ( α) radiation Beta (β) radiation Gamma (γ) radiation Environmental impact depends on the type and amount of radiation

Type of Radioactivity Alpha Radiation 222 Rn 86 218 Po 84 + 4 He 2 Alpha particle α radiation

Type of Radioactivity Beta Radiation Negative Beta Decay 14 C 6 14 N + 7 0 -1 β beta is an electron β beta is a positron (+ charge electron) Positive Beta Decay 65 Zn 30 65 N + 29 0 1 both types of decay generate "β radiation"

Type of Radioactivity Gamma Radiation 115 m 49 In 115 In 49 + γ gamma radiation from redistribution of electrical charges in the nucleus Radioactive Decay -- Gamma and Beta 137 55 Cs 137 Ba + 56 0 -1 β + γ gamma radiation

Radioisotope Decay Chains 238 U 206 Pb 8 alpha decays and 6 beta decays many radioisotopes generated along the way

Radioisotope Decay Chains

"Amount of Radioactivity" Radioactivity is measured in Becquerel (Bq) = 1 disintegrations (counts) per second or in Curie (Ci); 1 Ci = 3. 65 x 1010 Bq more common pico. Curie (p. Ci); 1 Bq = 27 p. Ci decay rate (dpm) Specific activity = mass of element / compound (kg) where dpm = disintegrations (counts) per minute

Specific Activity Radioisotope Half-life Specific activity 32 P 14 days 2. 9 x 105 Ci/g 131 I 8 days 1. 2 x 105 Ci/g 232 Th 1. 4 x 1010 yr 1. 1 x 10 -7 Ci/g 238 U 4. 4 x 109 yr 3. 3 x 10 -7 Ci/g Specific activity of radioisotopes short t 1/2 >> long t 1/2

Environmental Impact / Health Effects Penetrability of Radiation Alpha radiation Heavy, positive charged, low energy Stopped by a sheet of paper; doesn't penetrate skin Beta radiation Charged, lighter than alpha, higher energy Stopped by aluminum foil Gamma radiation Very high energy low interaction with low density matter (like X-rays)

Environmental Impact / Health Effects Damage to Biological Tissue Damage to tissue from "ionizing radiation" Ionizing radiation -- high energy -- enough to break chemical bonds ("ionize"). Organic biological tissue destroyed by ionizing radiation α, β, γ radiation are ionizing radiation Alpha radiation > Beta radiation, Gamma radiation Danger to biological tissue = radiation type, activity Roentgen Equivalent Man (rem)

Environmental Impact / Health Effects Biological Exposure (rem) 70 Health Effect vomiting, hair loss Time to Onset hrs 100 hemorrhage 2 -3 wks 400 death 2 months 1000 death 1 -2 wks 2000 death hrs Normal exposure to ionizing radiation << 1 rem/yr

RAD vs. REM • The conversion depends on the type of radiation. Rad is the amount of radiation adosorbed by tissue--REM goes further --it is the damage caused by radiation absorbed by tissue. The amount of damage of ionizing radiation to biological tissue is Alpha > gamma = beta. • • for beta & gamma radiation: 1 rad = 1 rem • • for alpha radiation: 1 rad = 10 rem (in the US, 20 rem in Europe) • multiplying rad by 10 accounts for the fact that alpha is more damaging than gamma or beta (10 times worse in the US; the Europeans consider it 20 times worse)

Normal Exposures Biological Exposure Source Exposure (mrem) Cosmic rays 45 Geological 60 Diagnostic X-Ray 70 Food 25 Normal exposure to ionizing radiation << 1 rem/yr or << 1000 mrem/yr

Environmental Impact / Health Effects Exposure Pathways

Environmental Impact / Health Effects Target Organs

Reaction and Transport Processes Important to Radionuclide Pollution Reactions Degradation (to other (radio)isotopes) Precipitation Adsorption (soil/colloidal) Bioaccumulation (plants, microbes) Transport Processes Volatilization (radioactive gas) Soil Erosion Soil runoff water Leaching to groundwater (depends on mobility)

Environmental Fate of Land Applied Radionuclides Volatilizati on Degradation Radionucli de Contamina nt Runoff Soil Adsorption Precipitation Bioaccumulation Leachin g Precipitation, Adsorption Minimize Environmental Impact

Radionuclide behavior -- Actinides U, Np, Pu, Am

Radionuclide behavior -- Actinides Very complex speciation valence states III, IV, V, VI U (VI): (UO 2 OH+, UO 2(OH)2, etc) In general , solubility of lower oxidation state (III) is less than higher oxidation states (V, VI) Some forms adsorb to Fe, Mn oxides precipitate as carbonates at high p. H Pu. O 2 CO 3 solubility and form greatly affected by redox soluble forms absorbed by plants/crops Long-lived radioisotopes give rise to many daughter radioisotopes

Radionuclide behavior -- Iodine and Cesium Nuclear Reactor Waste & Atomic Bombs Radioactive nuclear fisson products Cesium – 137 Cs+ Iodine - 131 I-

Chemisorption of Potassium in Soils Chemisorption of K+ By illite (hydrated mica) Clay Illite + K+ 2: 1 Silicate Soil Sol. N Mica “Fixed K” + K+ in solution Two illites partly - expandable 2: 1 clay KKKKKK One Mica not expandable 2: 1 clay

Chemisorption of K+, Cs+, NH 4+ Illite – Common Soil Material Spec. Ads. Based on Size of K ion K+ Fits Between Layers (like eggs in an egg carton) Other Ions With Same Size (NH 4+, Cs+) They also are “Fixed” or specifically adsorbed by illite

Chemisorption by illite Fate of radioactive Cesium April 26, 1986 Nuclear reactor meltdown Massive release of radioact particles to surrounding community and farmland Soil Solution K+ or Cs+ Chemisorption of K, Cs by illite Chemisorption lowers plant uptake

Using Cs chemisorption for sediment dating In 1950’s – Above ground Atomic Bomb Testing Radioactive Fallout (1 -2 years) 137 Cs illite in soil Traps Cs Lake Sediment Layer 1 Layer 2 Layer 3 Soi l Soil / illite with trapped Cs erodes to become lake Lak sediment 137 Cs e Sedime nt Rich Layer (Trapped in illite) Use to Date Layers (date the sediment was deposited, pre-1960)

Radionuclide behavior -- Iodide I- like Clhigh mobility, bioavailability drinking water --- thyroid cancer

Natural Occuring Gaseous Radioisotope Radon 238 U 226 Ra 222 Rn GAS 218 Po 208 Pb (stable)

Environmental Impact / Health Effects Radon 222 Rn 218 Po + 4 He 2 Alpha particle α radiation Concern: Lung cancer from alpha radiation USEPA limit: >4 p. Ci/Liter of air in house air remediation required National avg: 1. 3 p. Ci/L for house air

> 4 p. Ci/L in Basta's house in Columbus Remediation Required