Radionuclide Pollution andEnvironmental Fate / Impact

Atomic Structure

Atomic numberbased on number of protons

Atomic massbased 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

14

6CC

12

6

235U 92

238U 92

isotope of a given element - same Z, different A

Atomic Structure and Nuclides

http://ie.lbl.gov/education/isotopes.htmLawrence Berkeley National Laboratory

natural abundance -- percentage of stable isotopes 12C= 98.9 %, 13C = 1.1%

13

6C

Stable isotope -- stable atomic nucleus that does not decay or emit radiationRadioisotope (Radionuclide) -- unstable atomic nucleus that decays spontaneously emitting radiation

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/Z ratio = 1 for Z < 32

N/Z ratio = 1.5 for high Z

Unstable

Unstable

N

Z

Natural Occuring Radionuclides

14C -- generated in stratosphere by cosmic radiation

238U -- in geological material and its many daughter radioisotopes (products of radioactive decay) including 232Th and 222Rn

40K -- in all soils and geomedia

others

Anthropogenic Occuring Radionuclides

Nuclear fission reactions atomic bombs (incl. waste from weapons production) nuclear fission reactor fuel

Americium -241Cesium -137Cobalt-60IodinePlutoniumRadiumRadonStrontiumTechnetiumThoriumTritiumUranium

Biomedical wasteAnthropogenic Occuring Radionuclides

Introduction of Radionuclidesinto Soils and Natural Waters

Extensive above ground testingin US and USSR 1946-1962

Above ground testing by othercountries

Waste generated from weaponsgrade uranium and plutonium production

spent nuclear fuel --- processing to enrich U and Pugenerates large amount of other radionuclide "waste"which has to be "discarded" -- buried? stored?

Weapon production sites

Nuclear Waste Storage / DisposalYucca Mountain, Nevada

Introduction of Radionuclidesinto Soils and Natural Waters

April 26, 1986Nuclear reactor meltdownMassive release of radioactiveparticles to surrounding community and farmland inUkraine

Nuclear reactor meltdowns / accidents

Environmental Impact and Radioactive Decay

Radioisotope radioisotope + radiation

radionuclide1 RN2 + radiation RN3 + radiationRNn + radiation stable isotope + radiation

Environmental impact depends on the type and amount of radiation

Three types of radiation emitted by radioisotopesAlpha ( α) radiationBeta (β) radiationGamma (γ) radiation

222

86Rn

Type of RadioactivityAlpha Radiation

4

2He

218

84Po +

Alpha particleα radiation

Type of RadioactivityBeta Radiation

both types of decay generate "β radiation"

C14

6

14

7N

Negative Beta Decay

0

-1β+ beta is an electron

Zn65

30

65

29N

0

1β+ beta is a positron

(+ charge electron)

Positive Beta Decay

Type of RadioactivityGamma Radiation

Radioactive Decay -- Gamma and Beta

115m

49 In115

49In + γ

gammaradiation

gamma radiation from redistribution of electrical charges in the nucleus

137

55 Cs137

56Ba + γ

gammaradiation

0

-1β+

Radioisotope Decay Chains

238U 206Pb

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 secondor in Curie (Ci); 1 Ci = 3.65 x 1010Bq more common picoCurie (pCi); 1 Bq = 27 pCi

Specific activity = decay rate (dpm)

mass of element / compound (kg)

where dpm = disintegrations (counts) per minute

Specific Activity

Specific activity Radioisotope Half-life

32P 14 days 2.9 x 105 Ci/g131I 8 days 1.2 x 105 Ci/g

238U 4.4 x 109 yr 3.3 x 10-7 Ci/g

232Th 1.4 x 1010 yr 1.1 x 10-7 Ci/g

Specific activity of radioisotopes short t1/2 >> long t1/2

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

Environmental Impact / Health Effects

Danger to biological tissue = radiation type, activityRoentgen Equivalent Man (rem)

Biological Exposure

Environmental Impact / Health Effects

Exposure (rem) Health Effect Time to Onset

70

100

400

1000

2000

vomiting, hair loss

hemorrhage

death

death

death

hrs

2-3 wks

2 months

1-2 wks

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)

Biological Exposure

Normal Exposures

Normal exposure to ionizing radiation << 1 rem/yr or << 1000 mrem/yr

Source Exposure (mrem)

Cosmic rays

Geological

Diagnostic X-Ray

Food

45

60

70

25

Environmental Impact / Health EffectsExposure Pathways

Environmental Impact / Health EffectsTarget Organs

ReactionsDegradation (to other (radio)isotopes)Precipitation Adsorption (soil/colloidal) Bioaccumulation (plants, microbes)

Transport ProcessesVolatilization (radioactive gas)Soil Erosion Soil runoff waterLeaching to groundwater (depends on mobility)

Reaction and Transport Processes Important to Radionuclide Pollution

Environmental Fateof Land Applied Radionuclides

Volatilization

Degradation

Runoff

Soil Soil Adsorption

Precipitation

Bioaccumulation

Leaching

Radionuclide Contaminant

Precipitation, Adsorption Minimize Environmental Impact

Radionuclide behavior -- Actinides

U, Np, Pu, Am

Radionuclide behavior -- Actinides

Very complex speciationvalence states III, IV, V, VI

U (VI): (UO2OH+, UO2(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 pH PuO2CO3

solubility and form greatly affected by redoxsoluble forms absorbed by plants/crops

Long-lived radioisotopes give rise to many daughter radioisotopes

Cesium – 137 137Cs+

Iodine - 131 131I-

Nuclear Reactor Waste & Atomic BombsRadioactive nuclear fisson products

Radionuclide behavior -- Iodine and Cesium

Chemisorption of Potassium in Soils

Chemisorption of K+ By illite (hydrated mica) Clay

Illite + K+ Mica2:1 Silicate Soil SolN “Fixed K”

One Micanot expandable

2:1 clay

+ K+

in solutionK K K K K K

Two illitespartly - expandable

2:1 clay

Chemisorption of K+, Cs+, NH4+

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 (NH4+, Cs+)

They also are “Fixed” or specifically adsorbed by illite

Chemisorption by illiteFate of radioactive Cesium

April 26, 1986Nuclear reactor meltdownMassive release of radioactiveparticles to surrounding community and farmland

Soil Solution K+ or Cs+

Chemisorption of K, Cs by illite

Chemisorption lowersplant uptake

Using Cs chemisorptionfor sediment dating

In 1950’s – Above ground Atomic Bomb Testing

Radioactive Fallout (1-2 years)

illite in soil Traps Cs

Soil / illite with trapped Cs erodes to become lake sediment

137Cs137Cs

Lake

SedimentSoil

Lake Sediment

Layer 3

Layer 2

Layer 1

137Cs Rich Layer (Trapped in illite) Use to Date Layers (date the sediment was deposited, pre-1960)

Radionuclide behavior -- Iodide

I- like Cl-

high mobility, bioavailabilitydrinking water --- thyroid cancer

Natural Occuring Gaseous RadioisotopeRadon

238U 226Ra 222Rn 218Po 208Pb (stable)GAS

Environmental Impact / Health EffectsRadon

222Rn 4

2He

Alpha particleα radiation

218Po +

Concern: Lung cancer from alpha radiation

USEPA limit: >4 pCi/Liter of air in house air remediation requiredNational avg: 1.3 pCi/L for house air

> 4 pCi/L in Basta's house in Columbus

Remediation Required