Radiation: Unseen, Growing, but
Most Worry is Focused on the
Wrong Thing
PM 529
Week Ten, Apr 1, 2015
Radiation Exposures of Concern
Radon from basement soils
X-rays from medical tests
Solar ultraviolet radiation
Any more?
Scott Fruin
Preventive Medicine
Radiation: Propagation of Energy
through Space
Can be waves or particles
Unlike other pollutants, exposure can occur without
physical contact with source
Key health consideration is whether enough energy
to dislodge electrons (ionize) molecules.
If yes, ionizing radiation can damage DNA
If no, non-ionizing typically only causes thermal effects
(Electromagnetic fields are not radiation! No direct
transfer of energy)
Electromagnetic Spectrum
Ionizing vs Non-ionizing Radiation
Ionizing: high energy (high frequency, short
wave length)
X-ray, gamma ray, alpha or beta particles
Non-ionizing: lower energy
Microwaves, radiowaves
Ultraviolet (UV) is on the threshold
Ionizing fraction ionizes air and is mostly blocked by
atmosphere and ozone layer (UVC)
Transmitted fraction is relatively high energy and
capable of skin damage though not ionizing
Another View of
the
Electromagnetic
Spectrum
from NIH, 2002, EMF
IONIZING
Assessing (Ionizing) Radiation
Risk
Assumption is a linear dose-response with no
threshold,
Since DNA does undergo repair, this assumption is
probably conservative, but at low doses, cancer risk
increases are very difficult to ascertain against a
background cancer rate of ~40%
Naturally Occurring Ionizing Radiation:
Radioactive Decay of Less Stable Isotopes
Isotopes have same
number of protons and
electrons, so similar
chemical properties, but
different masses
Number of
neutrons
Stable nucleus depends
on fairly precise p:n ratio,
small surplus of neutrons
Deviation from stable ratio
strongly affects decay rate
Short half-life (y axis on
right) indicates lower stability
(time for half of atoms to
decay)
Units of Radiation
Three types:
Number of protons
Units of Measurement:
Decay Rate
How many atoms decay per unit time
Decays per time (for radioactive decay)
Energy per unit area
Biologically effective dose (takes tissue differences into
account)
Becquerel (Bq) is one decay per second
Older unit, the Curie (Ci) is based on gram of
radium, 3.7 x 1010 Bq
Radon action level: 4 pCi/liter (4x10-9 Ci/L), ~150
Bq/m3 or 150 decays per second per m3quite
a bit of activity!
Decay Product Differences
Alpha decay: two protons and two
neutrons (basically a high velocity
He ion) from heavier elements
Low penetration into matter due to high
charge to mass ratio (e.g., stopped by
skin or even a few cm of air)
When ingested, destructive due to high
energy (e.g., radon breakdown in
lungs)
Units of Measurement:
Absorbed Dose of Energy
Measure of energy transfer per amount of
tissue impacted
Gray (Gy)
1 joule of energy deposited in 1 kilogram of mass.
Rad "radiation absorbed dose"
1 Gy = 100 rad
Beta decay: high speed electron,
medium penetration ability
Any surplus energy can form
gamma waves (high E photon)
Risk also Depends on Receiving
Tissue
Biggest concern is damage to DNA; unrepaired
DNA is a mutation.
Rapidly-developing or dividing cells more prone to
permanent damage
Less time to repair damaged DNA before replication
Time in womb especially sensitive during organogenesis,
followed by times of rapid growth in childhood and
adolescence
Units of Measurement:
Biologically-Effective Dose
Measured in Sieverts
(Sv),
Neutron, proton and alpha
radiation cause 5-20 times
more damage (Q Factor)
than the same amount of
the absorbed dose of beta
or gamma radiation.
(Particles are more
effective at producing
damage than waves due to
smaller area of impact)
Biological Effectiveness
Factor by Radiation Type
Type of Radiation
Q Factor
Alpha particles
20
Beta particles
Gamma radiation
Protons, fast neutrons
10
Slow (thermal) neutrons
Population Exposure to Ionizing Radiation
Population Radiation Doses
US general population
3-4 mSv every year whole body equivalent dose
(higher now?)
Avg contribution:
(Nat Council on Radiation Protection)
Focus of
exposure
reduction
should be:
1. Radon
2. Medical
3. UV
4. All
others
Radon 2.0 mSv
Cosmic radiation 0.3 mSv
Internal (food or water ingestion) 0.4 mSv
X-rays 0.4 mSv
Cigarettes ~15 mSv per year!
CAT scan ~50 mSv
Sources of Exposure
Growth in Ionizing Medical
Radiation Exposure, 1980 to 2006
(Mettler et al., 2009, Radiology)
Most ionizing exposure is naturally-occurring
Radon accounts for ~half of population exposure
Cosmic radiation significant (gamma radiation
[photons]; most absorbed by atmosphere, so higher
at higher altitudes)
1980
2006
Most man-made ionizing exposure is medical
and increasingly unnecessary (e.g, CAT scans)
Medical Procedures: A Growing
Concern
X-rays equal to 2-3 days of natural background
CAT scans
Hundreds of times higher dose; multiple years of
background exposure
Over-use from efforts to recoup high machine costs
Radon: 55% of Population
Exposure to Ionizing Radiation
Leading cause of lung cancer for nonsmokers
Source is naturally-occurring
radon gas from soil as a 238U
break-down product (radium).
Radium gives off an alpha
particle, turns to radon gas
Radon itself has little effect, but
produces a short-lived particle
that lodges in lungs and
produces alpha decay
Radon and Cancer Risk
Radon: Prevention
Health effects: large increases in lung cancer risk
for both smokers and non-smokers
Source is high uranium content soil. Varies by region
(next slide), but estd 1 of 15 homes above action
level (next slide)
Recommended action level 4 pCi/L
2% of Europes cancer deaths; strong interaction with
smoking (Darby et al., 2004)
12% of US lung cancer deaths, 15,000 22,000
Outdoor levels 0.4
Testing is cheap, easy and accurate
Especially important for anyone with a basement or
anyone living in area of high soil U
Mitigation
Can reduce radon by re-routing air in contact with soils to
prevent entering home (vents and fans), along with sealing
basement cracks and/or increasing home ventilation
Radon by County (Avg Only)
U in Soils
Yellow < 2 pCi/L; Red > 4, the action level
Radon: CA
Cosmic Radiation: 8-24%
West LA County is red,
Eastern LA County is
orange
Earth protected from cosmic particles by magnetic
field, atmosphere
My house (Pasadena):
1.3 pCi / L, the avg
indoor level
At jet altitudes can be up to two orders of
magnitude higher ; airline crew guidelines are 20
mSv per year, while most people on ground get 2-4
mSv per year
~ Two-fold increase from sea level to mountains
Can vary strongly with solar activity
Radiation Protection
Shielding depends on type of radiation
Distancewave intensity or emitted
particles per area fall off with cube of
distance
Timelonger time allows cellular
damage repair
UV Radiation: Three Types
UVA
320-400 nm. It passes through the Earth's
ozone layer. Can cause early aging of the
skin.
UV Radiation: Non-ionizing, but
Still a Skin Cancer Concern
Strongly varies by latitude, season, time of day
Risk also varies by skin pigment
Some UV essential for vitamin D production, esp. at
extreme latitudes
Inverse relationship between UVR and
latitude
UVB
280-320nm. The ozone layer absorbs most
of the sun's UVB. It does not go as deeply
into the skin as UVA does, but can cause
sunburn. Large doses increase risk of skin
cancer and possibly cataracts.
UVC
< 280 nm. Is completely absorbed by the
Earth's ozone layer. Implications for the
ozone hole
Seasonal Differences:
LA max UV Index
from www.city-data.com
Radiation Exposure Assessment
Naturally occurring:
Radon: home concentrations work well, but can vary by
floor or room due to differences in air exchange rates
Can use regional surrogates if not measured
Water: also from radon (slightly soluble in water);
Cosmic radiation: varies primarily with altitude
UV: very behavior dependent (time outdoors, time of day).
Man-made
Medical procedures: can be tabulated; may be dominated
by CAT scans or other radiographic procedures
Smoking an important source of exposure
Workplace: radiation badges (miners, flight crews,
etc)
Non-Ionizing Radiation
Not enough E to break chemical bonds, but
can be enough energy to excite molecules
(heat), cause burns, etc.
Overall, some evidence (but inconclusive) of
possible effects on immune system,
developmental disturbances, neurobehavioral
abnormalities, cell proliferation
Inter-individual sensitivities may show large range
Exposures increasing over time and effects may
take decades to show up
Microwaves, Radiowaves
Long waves, 0.1 mm to football field; 3 kHz
to 300 GHz (7 orders of magnitude)
Includes cell phones, other
telecommunications
Large studies to date are inconclusive, likely a
combination of small effect and exposure
assessment error
Exposures increasing in recent decades;
probably worthy of no-regrets avoidance
How fast do you have to run to escape a lion?
A Larger Concern:
Extremely Low Frequency (ELF)
Magnetic Fields
Frequencies below 300 Hz, often 60 Hz
Almost all exposure is man-made
Technically not radiation since energy is not
being propagated
Induction of small electrical currents in the
conductive parts of the body: cell membranes,
nerves, retina, etc.
Some evidence for increased risk of childhood
leukemia; also, effects on ion transport, melatonin
secretion, and tumor promotion
ELF EMFs: Health Effects
Most prominent health risk is childhood
leukemia above 4 mG
Magnetic fields implicated, not electrical
One worry is recall bias in case control studies
Animal and occupational studies inconclusive
Static fields do not appear to be of concern at
typical levels
Magnetic vs Electrical Fields
SOURCE
Magnetic Fields
Electrical Fields
Flowing current
High voltage
HEALTH EFFECTS Possible
increased risk of
childhood
leukemia
SHIELDING
DIFFICULT:
Expensive metal
alloys
Little evidence
EASY: Any
conductive
shields or frame
Avoid MRIs?
Field strengths are very high
The combination of high static, gradient, and ELF
MF and high RF fields have been virtually
unstudied; each separately has detectable but small
biological effects
Yes, unless medically necessary
Magnetic Resonance Imaging (MRIs)
First medical use 1980
MRI typically 20 min @ 1.5 T (15 x 106 mG)
Combination of strong static, gradient, and 1001000Hz magnetic fields as well as RF fields of 10400 MHz.
High static and gradient fields show many biological
effects but conclusions uncertain
Almost no research on the combined exposure
Some evidence for chromosome damage
(increased micronuclei) from MRI magnetic fields,
though reversed within 48 hours (Simi, S. et al., Mutat. Res.
Fundam. Mol. Mech. Mutagen. 2008 )
Conclusions
Few environmental risks show the range of energy /
toxicity / uncertainty as radiation (>1010)
Worry should be concerned with energy level, but usually
is not
Most envl exposures of concern are decreasing; this not
the case for radiation and EMF
Medical exposure to ionizing radiation is an important PH
problem
ELF EMF possibly a cause for concern
The good news: most of ionizing radiation exposure
is avoidable:
E.g., radon, unnecessary medical X-rays, UV, etc.
