Forensic Toxicology

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Forensic Toxicology

• Chapter 10

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What is Forensic Toxicology?

• The detection and identification of drugs or
  poisons present in body fluids, tissues and
  organs.

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The Biggest Culprit

• Alcohol is the most abused drug in the West and
  most likely the world.
• 40 of all traffic accidents are alcohol related.
• So the most numbers of samples sent to forensic
  toxicology labs are alcohol related.

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What is Alcohol?

• Organic compound
• Carbon and hydrogen backbone with at least one
  hydroxyl group (OH)
• Many types, depending on the number of carbons
  present
• Humans consume Ethyl Alcohol or Ethanol

• Colorless liquid
• Produced when yeast ferment grain, fruit and
  other vegetation such as potatoes

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Toxicology of Alcohol

• What happens to alcohol once it enters the body?
• Consumption / Ingestion
• Absorption into bloodstream
• It then crosses the blood-brain barrier into
  neurons, affecting the Central Nervous System
  (CNS)
• Elimination
• Oxidation (alcohol is changed to other products)
• Excretion (alcohol is unchanged)

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How do we measure alcohol levels?

• The most obvious measure of intoxication would be
  to see how much an individual has consumed
• This is impossible for a forensic toxicologist
  for several reasons
• He wasnt present (Duh!)
• Persons body weight varies
• Rate of alcohol absorption into bloodstream
  varies

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This is your brain on ethanol

• The Absolute (no pun intended) best way to check
  for intoxication would be to check brain tissue
• This is also impossible for obvious reasons
  unless the person in question is dead.

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The next best thing

• So forensic toxicologists concentrate on blood.
• Blood circulates the consumed alcohol to ALL body
  tissues
• The concentration of alcohol in the blood is
  directly proportional to the concentration of
  alcohol in the brain

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The Route Alcohol Takes

• Mouth ? Esophagus ? Stomach ? Small Intestine ?
  Bloodstream
• Alcohol is absorbed across the lining of the
  small intestine, into the bloodstream (some
  absorption can occur across stomach wall also)
• This happens within minutes of consumption
• The blood concentration levels keep increasing as
  more and more alcohol gets absorbed across S.I.

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The path alcohol follows to your brain, via
bloodstream
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The Rate of Absorption

• Several factors affect the rate of absorption
• The amount of alcohol consumed
• What was the alcohol content (or proof) of the
  beverage?
• The rate at with it was consumed (1 beer over 1
  hour, or 1 beer over 1 minute)
• How much food was in the stomach?

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You need to absorb this material!

• The longer it takes for all the alcohol consumed
  to be absorbed, the lower the peak alcohol
  concentration in the bloodstream.
• Food in stomach hinders/slows absorption

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Empty vs. Full Stomach
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After Absorption

• When all the alcohol is absorbed, its levels will
  be equally distributed in the watery tissues of
  the body (so not in fat, hair, nails, bones,
  etc.).
• If blood is not available (dead body) a
  forensic toxicologist can work with other body
  fluids and tissues Cerebrospinal fluid,
  vitreous humor, or brain

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BAC Blood Alcohol Concentration

• It is usually measured as mass per volume and
  expressed as a percentage.
• For example, a BAC of 0.02 means 0.02 grams of
  alcohol per 100 grams of an individual's blood,
  or 0.2 grams of alcohol per 1000 grams of blood.
• BAC can vary according to the persons tolerance
  and metabolic rate

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Can you tolerate it?

• Tolerance to alcohol varies from one person to
  another, and can be affected by such factors as
  genetics, adaptation to chronic alcohol use, and
  synergistic effects of drugs.

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Metabolism

• The breakdown of chemicals, including alcohol
• The elimination of alcohol from the body depends
  upon the individuals metabolism.

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Elimination by Oxidation

• Nearly all alcohol (95-98) gets oxidized.
• Oxidation Ethanol is oxidized to produce carbon
  dioxide and water
• Oxidation occurs almost entirely in the cells of
  the liver.
• Oxidation of ethanol is performed by an enzyme
  called Alcohol Dehydrogenase in the following
  process.

The Acetic Acid is then oxidized further into CO2
and H2O
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Rate of Ethanol Oxidation

• The rate of elimination via oxidation varies from
  individual to individual, depending upon their
  metabolic rate. Oxidation is also called
  burn-off and it reduces blood-alcohol
  concentrations.
• Absorption must be complete in order for
  burn-off to reduce BAC levels.

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Elimination by Excretion

• The 2 of ethanol that is not eliminated by
  oxidation is excreted through the breath, urine
  and perspiration.
• This excreted alcohol is not changed chemically
  it remains ethanol.

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Breath Dragon (Alveolar breath)

• The amount of alcohol exhaled in the breath is
  directly proportionate to the concentration of
  alcohol in blood.
• When air is exhaled, it contains CO2 and alcohol
• Hence the Breathalyzer Test

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Alveolar Breath
Pulmonary Vein
Pulmonary Artery
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Breathalyzer

• A breathalyzer (or breathalyser) is a device for
  estimating blood alcohol content (BAC) from a
  breath sample.
• Breathalyzer is a brand name and was originally
  made by Smith and Wesson, but now is a generic
  term used for all such devices.
• Measures alcohol found in alveolar breath.

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Wheres the Proof?

• Alcoholic proof is a measure of how much ethanol
  is in an alcoholic beverage, and is approximately
  twice the percentage of alcohol by volume
• The proof number is twice the percentage of the
  alcohol content measured by volume at a
  temperature of 60 F (15.5 C). Therefore "80
  proof" is 40 alcohol by volume, and pure alcohol
  is "200 proof".

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Whats in a drink?
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Legal BAC Levels

• The alcohol level at which a person is considered
  to be legally impaired varies by country.
• In the US the BAC limit is 0.08
• However, drivers of commercial vehicles have a
  limit of 0.04
• Sweden is one of the countries with the lowest
  level of 0.02

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When can you drink legally?

• As of 2007, all U.S. states have a minimum
  purchase age of 21. Unlike the states, Puerto
  Rico, the U.S. Virgin Islands, and Guam have a
  minimum purchase age of 18.
• In Mexico and Canada the drinking age is lower
  than 21, which encourages young people to go to
  these countries if they live near the border.

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The brain of a six-week old baby with Fetal
Alcohol Syndrome
Normal brain of six week old baby
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Field Sobriety Testing

• Horizontal Gaze Nystagmus
• Walk and Turn Test
• One Leg Stand Test

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Horizontal gaze nystagmus
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Horizontal gaze nystagmus

• The officer attempts to estimate the angle at
  which the eye begins to jerk
• "nystagmus" is medical jargon for a distinctive
  eye oscillation
• if this occurs sooner than 45 degrees, it
  theoretically indicates a blood-alcohol
  concentration over .05.
• The smoothness of the eye's tracking the penlight
  (or finger or pencil) is also a factor, as is the
  type of jerking when the eye is as far to the
  side as it can go.

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Walk and Turn
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One leg stand
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Collection and Preservation of Blood Evidence

• Must be drawn aseptically under medically
  accepted conditions
• An anticoagulant such as EDTA or potassium
  oxalate is added to prevent clotting
• A preservative such as sodium fluoride is added
  to prevent bacterial growth
• Stored in refrigerator
• Tested at a lab or medical facility

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Other toxins in blood

• Narcotics (Heroine)
• Non-narcotic substances (Cocaine)
• Carbon Monoxide (CO)
• Heavy metals such as lead, mercury, arsenic, etc.

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ACID vs. BASE Drugs

• Barbiturates and Aspirin (Acetylsalicylic acid)
  are acidic drugs with pHs lower than 7.
• Phencyclidine (PCP), Methadone, Amphetamines and
  Cocaine are basic drugs with pHs higher than 7.

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Carbon Monoxide

• CO is a by product of combustion of organic
  materials (Gas, fires, etc.)
• CO has a greater affinity to hemoglobin than does
  CO2 or O2.
• CO hemoglobin carboxyhemoglobin
• So once it is inhaled an enters the bloodstream,
  it competes with O2 for hemoglobin.
• Too much CO kills death by asphyxiation

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The fate of other drugs in the bloodstream

• Heroin gets converted into morphine once in the
  bloodstream

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THE END