Forensic Toxicology

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Forensic Toxicology
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Forensic Toxicology

• The role of the forensic toxicologist is limited
  to matters that pertain to violations of criminal
  law
• Variability in in who conducts toxicology service
  in the U.S.
• Crime lab staff member, government health
  agencies, private lab facilities
• Whatever facility is doing the testing, the
  prevailing popularity of the drug will determine
  the types of cases the toxicologist will see

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Toxicology of Alcohol The fate of alcohol in the
body

• Alcohol is the most readily consumed drug among
  our society
• It use coupled with automobiles have dictated the
  need for reliable indicators of consumption
• Must be on evasive, reliable, meet the demands of
  legal system
• Absorption is highly variable and dependant on a
  number of factors

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The fate of alcohol in the body

• The detection of alcohol, for determining an
  individuals impairment, focuses on the
  concentration of alcohol in the blood
• Blood alcohol levels show a direct relationship
  to the proportion of alcohol in the brain
• Alcohol is readily transferred into the
  circulatory system minutes after it has been
  consumed

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The fate of alcohol in the body

• Factors affecting rate of absorption
• Weight - the higher your weight, the lower your
  Blood Alcohol Content (BAC) will be
• Gender - Men produce more of the enzyme that
  breaks down alcohol
• Food - the more food you eat, especially protein,
  before you drink, the lower your Blood Alcohol
  Content (BAC) will be
• Emotional state - Alcohol is a depressant and
  will enhance your current emotional state. For
  example, if you are upset before you start
  drinking at the end of the night your mood will
  be lower than it was at the beginning of the
  evening
• Drinking Rate - Chugging drinks and doing shots
  results in a large amount of alcohol entering
  your body in a short amount of time. Your body
  cannot process alcohol at a fast pace resulting
  in a higher BAC.

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Elimination of Alcohol from the Body

• Once alcohol begins to circulate in the
  bloodstream the body begins the task of removing
  it, this is done in two ways
• 1) Oxidation The combination of oxygen with
  other substances to produce new products.
• Nearly all alcohol consumed is eventually
  oxidized to carbon dioxide and water
• Takes place in the liver, facilitated by the
  enzyme alcohol dehydrogenase
• Alcohol alcohol dehydrogenase acetaldhyde,
  then to acetic acid

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Elimination of Alcohol from the Body

• The second means by which the remaining alcohol
  is eliminated from the body is
• 2) Excretion Elimination of alcohol from the
  body in unchanged state is excreted in breath
  and urine, also perspiration.
• Alcohol exhaled by the breath is in direct
  proportion to the amount in the blood

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The fate of alcohol in the body

• The fate of alcohol in the body is relatively
  simple
• Absorption into the blood stream,
• Distribution throughout the bodys water,
• And finally elimination by oxidation and excretion

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Alcohol in the Lungs

• It is in the lungs that the respiratory system
  bridges with the circulatory system
• Exchange of Carbon dioxide for oxygen takes
  place, at the Alveoli
• If while this exchange is taken place, alcohol or
  any other volatile substance, happens to be in
  the blood, it too will pass into the alveoli

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Alcohol in the Lungs

• Henrys Law
• When a volatile chemical (alcohol) is dissolved
  in a liquid (blood) and is brought to equilibrium
  with air (alveolar breath) there is a fixed ratio
  between the concentration of the volatile
  compound (alcohol) and in air (alveolar breath)
  and its concentration in the liquid (blood)
• This ratio is a constant for a given temperatures

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Alcohol in the Lungs

• The temperature at which breath leaves the mouth
  is normally 34 degrees Celsius
• At this temperature, experimental evidence has
  shown that the ratio of alcohol in the blood to
  alcohol in alveoli air is approximately
• 2,100 to 1
• 1 ml of blood will contain nearly the same amount
  of alcohol as 2,100 ml of alveoli breath

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Blood and Lungs

• Prior to completion of absorption the blood
  concentration will be greater in the arteries
  than the veins
• Due to diffusion of alcohol into the tissues
• Breath tests reflect measurements in the
  pulmonary arteries
• During absorption phase breath test may be higher
  than the blood test, taken from venous blood of
  arm
• Once absorption is complete blood and breath
  should be of minimal difference

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Infrared Technology

• Since the mid-1980s, infrared (IR) technology has
  been the primary means of breath alcohol testing
  in the United States.
• Current technology uses infrared measurement
  systems that are made more specific for alcohol
  by using several optical filters.
• You determine breath alcohol levels by passing a
  narrow band of IR light, selected for its
  absorption by alcohol, through one side of a
  breath sample chamber.
• By detecting emergent light on the other side,
  you can measure alcohol concentration by using
  the well-known Lambert-Beers law, which defines
  the relationship between concentration and IR
  absorption.
• A major advantage of this technology is its
  ability to make real-time measurements.

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Infrared Technology

• One disadvantage of using IR technology is the
  high cost of achieving specificity and accuracy
  at low breath alcohol concentration levels.
• Also, the IR detector's output is nonlinear with
  respect to alcohol concentration and must be
  corrected by measurement circuits.
• Because of IR technology's expense, mechanical
  components, and other limitations, breath alcohol
  instrumentation manufacturers began a search for
  an alternative.
• One technology, electrochemical cells, also known
  as fuel cells, seemed to offer significant
  advantages.

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Fuel Cell technology

• In the early 1800's a British scientist
  discovered the fuel cell effect.
• He immersed two platinum electrodes in sulfuric
  acid electrolyte and supplied hydrogen at one
  electrode and oxygen at the other.
• The resulting reaction created a current flow
  between the electrodes.
• There was no practical application of fuel cells
  at that time because of high cost and
  technological problems.
• In the 1960s, researchers at the University of
  Vienna demonstrated a fuel cell that was specific
  for alcohol.
• This evolved into the present-day cell used in
  all fuel cell-based breath alcohol measurement
  instruments.

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Fuel Cell Technology

• In its simplest form, the alcohol fuel cell
  consists of a porous, chemically inert layer
  coated on both sides with finely divided platinum
  (called platinum black).
• The manufacturer impregnates the porous layer
  with an acidic electrolyte solution, and applies
  platinum wire electrical connections to the
  platinum black surfaces.

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Fuel Cell Technology

• The manufacturer mounts the entire assembly in a
  plastic case, which also includes a gas inlet
  that allows a breath sample to be introduced.
• Various manufacturers employ numerous proprietary
  nuances in their construction.

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Fuel Cell Technology

• The reaction that takes place in an alcohol fuel
  cell is alcohol oxidation.
• In this chemical reaction a fixed number of 
  electrons are freed per molecule of alcohol.
• The oxidation occurs on the upper surface of the
  fuel cell.

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Fuel Cell Technology

• The freed H ions migrate to the lower surface of
  the cell, where they combine with atmospheric
  oxygen to form water, consuming one electron per
  H ion in the process.
• Thus, the upper surface has an excess of
  electrons, and the lower surface has a
  corresponding deficiency of electrons.

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Fuel Cell Technology

• If you connect the two surfaces electrically, a
  current flows through this external circuit to
  neutralize the charge.
• This current is a direct indication of the amount
  of alcohol consumed by the fuel cell.
• With appropriate signal processing, you can
  display breath alcohol concentrations directly

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The Role of The Toxicologist

• Once the forensic toxicologist ventures outside
  the analysis of alcohols the methods for analysis
  become more complex
• Determining if the victim died from drugs can be
  a daunting task, especially if they have only the
  body and or organs and know external clues
• No symptoms
• Examination of personal effects

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The Role of The Toxicologist

• With out any indicating evidence the toxicologist
  is forced to start with general screening
  procedures in hopes of narrowing the thousand
  possibilities
• Note that the concentration levels once processed
  by the body may vary dramatically from that of
  the non-induced form
• In order to detect these traces a toxicologist
  must understand how the drug metabolizes
• Transforming a chemical in the body to another
  chemical for the purpose of facilitating its
  elimination from the body

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Establishing Toxicity

• Once the obstacle of detecting the drug is
  overcome, the toxicologist must then determine
  the toxicity of the drug
• With a deceased person many tests can be run on
  various organs to determine the precise
  concentrations
• Living subjects are more difficult, due to the
  limited samples (blood and urine)

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Techniques Used in Toxicology

• The three most widely used drug screening tests
  are
• Thin-layer chromatography
• Gas chromatography
• Immunoassay
• Confirmation tests is usually Gas Chromatography
  coupled with Mass Spectrometry

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Immunoassay

• The primary advantage of immunoassay is its
  ability to detect small concentrations of drugs
  in body fluids and organs
• This techniques is based on antigen-antibody
  recognition
• Essentially the drug is coupled with a protein
  carrier and then injected into an animal
• This antigen stimulates antibodies in the animal
• The blood serum recovered from the animal now
  contains antibodies that are specific for the drug

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DRE

• The role of the toxicologist is based on
  knowledge,
• Once the drug is detected determining the effects
  on the body must be done considering a number of
  variables
• Age, tolerance, metabolism
• Multiple drug, synergistic effect
• Before the medical examiner can determine the
  cause of death he or she must rely on the
  interpretation of the toxicologist

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DRE

• Drug Recognition Experts are trained and
  developed for standardization in procedures
• The process is designed so that each individual
  is tested in the same fashion
• It is a twelve step process and evaluates for 7
  categories of drugs
• Central nervous system depressants
• Central nervous system stimulants
• Hallucinogens
• Phencyclidine
• Inhalants
• Narcotic Analgesics
• Cannabis