Download Forensic Toxicology

Forensic Toxicology
Harrison
Role of Forensic Toxicology
• Forensic toxicologists detect & identify
drugs & poisons in body fluids, tissues, &
organs in matters that pertain to violations
of criminal laws.
• Ethyl alcohol is the most heavily abused
drug in Western countries.
Ethyl Alcohol
• All evidence shows ethyl alcohol (which is
legal if over 21) is the most heavily abused
drug, causing 40% of all traffic deaths in
the US.
• Nearly 17,500 fatalities/year are alcohol
related & over 2 million injuries requiring
hospital care.
Toxicology
• Detect and isolate drugs in the body to
determine their influence on human
behavior.
• Knowing how the body metabolizes
alcohol is key to understanding its effects.
• Knowledge made development of
instruments to measure presence &
concentration of alcohol.
Metabolism of Alcohol
• Metabolism- body breaks down one
chemical into chemicals that are easier for
it to eliminate.
• Three basic steps:
• 1.Absorption
• 2.distribution
• 3.elimination
Metabolism of Alcohol
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Step 1 Absorption
• Consumed as a colorless liquid in a
mixture
• Appears in blood w/in minutes
• Increases in concentration as it is
absorbed by stomach & sm. intestines into
bloodstream
• Absorption to the blood allows the alcohol
to be carried to all parts of the body
Distribution
• The body is 2/3 water and the alcohol gets distributed
evenly through the bodies liquid parts.
• The timeframe for rate of absorption/distribution:
• Total time taken to consume
• Amount consumed
• Quantity & type of food present in stomach
• Size of individual consuming total volume of liquid
present in the body)
Elimination
• As the alcohol is circulated by bloodstream, the
body begins to eliminate it by two processes,
oxidation & excretion.
• 95-98% is oxidized to CO2 & H2O starting in the liver
• In the presence of enzyme alcohol dehydrogenase
it is converted into acetaldehyde and then to acetic
acid which is broken down throughout the body to
CO2 & H2O
• Remaining 2-5% is excreted unchanged in the
breath, urine & perspiration (in proportion to level in
blood stream)
“Burn-off” rate of alcohol
• Postabsorption varies by individual
•
the average (which can vary by 30%):
• .015% w/v (weight per volume) per hour upon
completed absorption
BAC- blood alcohol Concentration
• Best way to determine- remove a portion
of the brain & analyze for alcohol content
• (problematic for the living)
• Blood alcohol levels are the legally
accepted standard for measurement in the
living. (postmortem- brain, cerebrospinal
fluid, or vitreous humor is tested)
Taking Measurements
• Measure concentration in Blood test
• Measure alcohol content in breath
Henry’s Law is applied:
• When a volatile chemical is dissolved in a
liquid & is brought to equilibrium with air, there
is a fixed ratio between the concentration of
the volatile compound in air & its concentration
in the liquid & this ratio is constant for a given
temperature.
• Breathe leaves the mouth at an ave. of 34°C,
the ratio of alcohol in the blood; to alcohol in
the aveolar air is approximately 2,100 to 1.
(1 ml of blood same amt. alcohol as 2,100ml of breath)
Testing for Intoxication
• Hundreds of thousands of motorists tested
annually.
• Breathe testing, quick- convenient &
reliable
• (early in absorption process- breathe test
will show higher levels than blood tests;
but match effects on the brain)
Breathalyzer
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Developed in 1954 by R.F. Borkenstein
modified over years- basic principles still apply.
Breathalyzer replaced chemical free devises:
Infrared & fuel-cell-based devices controlled by
microprocessors.
Process:
Start with field sobriety test
Nothing taken orally for 15 min. prior to test.
Take two test samples minutes apart
Field Sobriety test
• Used to determine an individuals physical
impairment & to justify further testing
• Series of psychophysical tests:
• Horizontal-gaze nystagmus (follow pen light w/
eyes)
• walk & turn
• One-leg stand
Higher BAC:Higher physical impairment
• .10% BAC = eye jerk before eye has moved 45°
• Other drugs can trigger this effect, phencyclidine,
barbituates, & other depressants)
• Walk/turn & one-leg stand are divided attention
tasks. Requiring ability to understand & carry
out more than 2 instructions: this ability is
affected by blood-alcohol levels.
Blood Analysis
• Forensic toxicologists
must devise an
analytical scheme to
detect, isolate, & identify
toxic drug substances
extracted from biological
fluid, tissues, and
organs.
• A screening test gives quick insight into
the likelihood that a specimen contains a
drug substance.
• Positive results arising from a screening
test are tentative at best and must be
verified with a confirmation test.
• The most widely used screening tests are thinlayer chromatography, gas chromatography,
and immunoassay.
• Gas chromotography/mass spectrometry is
generally accepted as the confirmation test of
choice.
• Once a drug is extracted & identified, a
toxicologist may be required to judge the
drug’s effect on an individual’s natural
performance or physical state.
• This is different depending on whether the
individual is a live or deceased.
• Field sobriety results come into play for
the living. (much easier to use in court
since video camera’s were added to police
vehicles)
• Deceased, requires the ME to determine
cause of death, for this the ME and
toxicologist work together.
Alcohol Intoxication vs Drug Induced Intoxication
• Alcohol intoxication is widely recognized, police
are highly trained for & the courts are
accustomed to the effects.
• Drug Induced Intoxication is harder to recognize.
In the 1970s they developed & tested a series of
clinical & psychophysical examinations that a
trained police officer could use. The program is
now used nationwide to train drug recognition
experts (DRE); a 3-5 month training program is
required to certify.
Texas Laws
• The Legal Limit. The legal limit for
intoxication in Texas is .08 blood alcohol
concentration (BAC). However, drivers can
be stopped and cited for impaired driving
due to alcohol or other drugs regardless of
BAC. Texas also has a zero tolerance law.
For anyone under 21, it is illegal to drive
with any detectable amount of alcohol.
How Much is Too Much?
• Impairment begins with the first drink.
Gender, body weight, the number of drinks
consumed and the amount of food in one’s
stomach affect the body’s ability to handle
alcohol. Women, younger people and
smaller people, whether male or female,
often have lower tolerances.
What Happens If You're
Stopped.
• If a law enforcement officer asks you to
take a blood or breath test to measure
how much alcohol is in your system, you
should comply. If you refuse, you are
subject to an automatic 180-day driver’s
license suspension. Punishment for DWI
varies depending on the number of times
you've been convicted.
First Offense:
• up to a $2,000 fine
• 72 hours to 180 days in jail
• driver’s license suspension: 90 days to 1
year
Second Offense:
• up to a $4,000 fine
• 30 days to 1 year in jail
• driver’s license suspension: 180 days to 2
years
Third Offense:
• up to a $10,000 fine
• 2 to 10 years in penitentiary
• driver’s license suspension: 180 days to 2
years
Underage Drinking
• If you’re under 21, here’s what happens the first time
you are found in possession of alcohol.
Any amount of beer, wine or liquor will trigger the
penalties.
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30-day driver’s license suspension
up to a $500 fine
8 to 12 hours of community service
mandatory attendance in alcohol-awareness classes
A second or third offense can lead to suspension of your
driver’s license for 90 to 180 days. If you’re 17 or older, you
also can be fined as much as $2,000 and go to jail for up to
180 days for a third offense.
If you’re under 21, here’s what happens the
first time you are stopped for drinking and
driving.
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60-day driver’s license suspension
up to a $500 fine
20 to 40 hours of community service
mandatory attendance in alcohol-awareness
classes
Get caught drinking and driving a second or third time,
and the penalties increase, including suspension of
your driver’s license for up to 180 days. That’s
called zero tolerance. It means “zero” alcohol. And
that’s the law in Texas.
If you’re 17 and over, here’s what happens if
you’re stopped for drinking and driving with a
blood alcohol concentration of .08 or greater.
• Some people, particularly teenagers, can
reach a .08 BAC with two or three beers
an hour.
• up to a $2,000 fine
• 72 hours to 180 days in jail
• driver’s license suspension of 90 days to
one year