Transcript forensic science - McEachern High School

FORENSIC SCIENCE
Toxicology
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Review
 Poisons
 Due
Today:
 Over the counter medications lab from
yesterday
 Til Death do us part video organizer
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Forensic File #3
What is the difference between ACUTE and
CHRONIC poisonings?
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Today’s assignments
 Alcohol
notes- from MHS website
 BAC Detection lab- on table 1
 BAC calculations- front table
 Work
on PROJECT!!!!
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Things to know about Alcohol
Ethyl alcohol is a colorless liquid
 Measure of intoxication is based on weight &
absorption
 Toxicology is typically gauged using blood
 Blood-alcohol concentration is directly proportional
to concentration in the brain
 EtOH appears in the blood within minutes of
consumption
 Alcohol enters the bloodstream slowly and becomes
uniformly distributed in watery portions of the body
which is ~ 2/3 of the body volume
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
Elimination of EtOH
Oxidation- the combination of oxygen with other
substances to produce new products.
 95-98% EtOH is oxidized into carbon dioxide and
water
 This process takes place in the liver
 Excretion- elimination of EtOH from body in
unchanged state; EtOH is normally excreted in
breath and urine, but may also be excreted in
sweat
 Exhaled EtOH is directly proportional to
concentration in blood stream
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
Path of alcohol in the body:
Mouth- alcohol enters body
 Stomach: some alcohol gets into the bloodstream in
the stomach, but most goes on to the small intestine
 Small intestine: alcohol enters the bloodstream
through the walls of the small intestine (villi)
 Heart: pumps alcohol throughout the body
 Brain: alcohol reaches the brain
 Liver: alcohol is oxidized by the liver at a rate of
about 0.5 oz per hour
 Alcohol is converted to water, carbon dioxide and
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energy

Movement of EtOH in circulatory system
Artery- blood vessel that carries blood away from
the heart (oxygenated)
 Vein- blood vessel that carries blood towards the
heart (unoxygenated)
 Capillary- tiny blood vessel across whose walls
exchange materials between blood and tissue takes
place; rec’s blood from arts. And carries to vns.
 after ingestion to stomach, ~20% of EtOH is
absorbed thru small intestine’s portal vein.
Remaining EtOH passes into the blood thru walls
of the small intestine
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Movement of EtOH in circulatory system
Once in the blood, it is carried to the liver where
it’s destruction begins.
 The blood is carried to the heart, entering the right
atrium then the right ventricle, this is oxygen poor
 Consequently pumped through the lungs,
replenished with oxygen
 Carbon dioxide and EtOH vapors are exchanged
between blood and breath via alveoli
 Also after emerging from lungs, oxygenated blood
enters left atrium to left ventricle, into arteries to
be moved all over the body

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Testing for EtOH
The breathalyzer was developed in 1954
 Widely used to test motorists suspsected of being
under the influence up until the early 1990’s. This
test measures the alcohol content of alveolar air.
 Recent technology uses IV light absorption. These
instruments operate on the same principle as
spectrophotometers. Fuel cells convert a fuel &
and oxidant into an electrical current; the current
is proportional to the quantity of EtOH in the
breath
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Testing for EtOH
 Field
sobriety tests are normally performed
to ascertain the degrees of a suspect’s
physical impairment & whether or not an
evidential test is justified.
 Psychophysical tests include the walk &
turn, the one leg stand, & the observation of
horizontal nystagmus, which is the
involuntary jerking of the eye as it moves
side to side
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Blood testing
 Gas
chromatography is the most widely
used approach for determining EtOH levels
in blood
 GC is normally used by forensics labs
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Collection & preservation of
blood
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Blood must always be drawn under medically acceptable
conditions by a qualified individual.
Preservation is best ensured when sealed in an airtight
container with an anticoagulant & preservative added.
Anticoagulants- prevent clotting
Preservatives- prevents microorganism growth
Postmortem collection requires extra precautions. EtOH
may be generated by bacterial, therefore blodo should be
collected from a # of sites: heart, femoral artery, cubital
vein, vitreous humor of eye and urine
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What is Henry’s law?
 When
volatile chemical (alcohol) is
dissolved in a liquid (blood) & is brought to
equilibrium with air (alveolar breath), there
is a fixed ratio between the concentration of
the volatile compound (alcohol) in air
(alveolar breath) and its concentration in the
liquid (blood), and this ratio is constant for
a given temperature.
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What is the law regarding
alcohol?
 Blood
toxication level: 0.10
 Refusal to take a test for alcohol
intoxication- must submit to a test or be
subject to lose license for some designated
period
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How do you calculate BAC?
Use consistent formulas- male & female differ in
amount of body water content so you have
different formulas
 For males:

BAC= 0.071 x (volume consumed in oz) x % alcohol
body weight in lbs
 For females:
BAC= 0.085 x (volume consumed in oz) x % alcohol
body weight in lbs.
We typically process out 0.05 per hour after drinking
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