Forensic Toxicology

1
Chapter 12

• Forensic Toxicology

2
Objectives

• Students should gain an understanding of
• The postmortem analysis performed by a
  toxicologist
• The many factors that make postmortem
  toxicological information difficult to interpret
• Alcohols effects on human performance
• The way in which alcohol is absorbed and
  eliminated from the body
• The measurement of blood alcohol concentration
  (BAC)
• Alcohol-related vehicle laws

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Introduction

• Postmortem analysis
• Investigates the presence of drugs, gases,
  metals, and other toxic chemicals in human fluids
  and organs
• Determines their role, if any, in the death
• Human performance toxicology
• Measures the amount of alcohol or drugs in a
  living persons blood or breath
• Estimates their role in modifying human
  performance or behavior

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Postmortem Toxicology (1 of 5)

• Begins with a case history of the deceased
• Includes age, sex, weight, medical history,
  medication before death, autopsy findings, drugs
  available to decedent, and interval between onset
  of symptoms and death
• Includes analyses for poisons as diverse as
  prescription drugs, drugs of abuse, chemical
  products, and gases

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Postmortem Toxicology (2 of 5)

• Collection of postmortem specimens
• All body fluids and organs in which chemicals
  might concentrate are collected during the
  autopsy.
• Specimens should be collected before the body is
  embalmed.
• In cases of decayed bodies, analysis may be done
  on bone marrow, fluid in the eye, or hair.
• Maggots feeding on the corpse have been tested
  for drugs and used as evidence.

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Postmortem Toxicology (3 of 5)

• Analysis of toxicology specimens
• The gastrointestinal tract is often analyzed
  first, followed by urine.
• Analysis focuses on the tissues of organs where
  the concentration of drugs may be the greatest.
• Specimens should be collected as soon as possible
  after death.
• Presumptive testing is performed first to detect
  the presence or absence of drugs.

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Postmortem Toxicology (4 of 5)

• Analysis of toxicology specimens
• A positive immunoassay test leads to a
  confirmation test (usually gas chromatographymass
  spectrometry).
• Each compound gives a characteristic fragment
  spectrum.
• A computer compares the samples spectrum to a
  reference library.
• The toxicologist tests for an inorganic substance
  if the case study suggests poisoning.

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Postmortem Toxicology (5 of 5)

• Interpretation of toxicological information
• The toxicologist must determine how the poison
  entered the body and whether enough poison was
  ingested to cause death.
• The highest concentration of poison is usually
  found where it entered the body.
• Toxicology analysis may be able to estimate when
  the poison was dispensed.

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Human Performance Testing (1 of 3)

• Most common human performance tests are those to
  determine if someone is driving a car under the
  influence of alcohol or drugs
• Amount of alcohol in a persons body is expressed
  as blood alcohol concentration (BAC)
• Studies have shown a direct relationship between
  increased BAC and increased risk of accidents

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Human Performance Testing (2 of 3)

• Field sobriety testing assesses a drivers
  degree of physical impairment
• Interview with officer
• Preliminary examination
• Eye examination
• Divided attention psychophysical tests
• Vital signs exam
• Dark room exam
• Muscle rigidity exam
• Examination for injection site
• Suspects statements
• Opinions of evaluator
• Toxicology exam

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Human Performance Testing (3 of 3)

• BAC levels
• Low BAC alcohol affects cerebral function
• High BAC medullar function is affected
• BAC lt 0.06 sober
• BAC 0.35 coma

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Alcohol and the Law (1 of 2)

• 1939 first drunk driver law passed that used
  BAC as a basis for determining sobriety (Indiana)
  
• 1943 researchers discovered that abstainers were
  more sensitive to alcohol than moderate or heavy
  drinkers
• 1964 Grand Rapids Study
• Established the scientific foundation for per
  se legislation, which triggers sanctions for all
  drivers with a certain BAC
• Validated the Breathalyzers effectiveness and
  accuracy

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Alcohol and the Law (2 of 2)

• Legal limit for first per se laws was 0.15
• Individual states have passed their own laws and
  strengthened DUI penalties
• Citizen-advocacy groups, such as MADD, have
  driven legislation
• 1992 DOT recommended that all states adopt 0.08
  as the legal definition of drunk driving

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Alcohol Metabolism (1 of 3)

• Absorption of alcohol into the body
• Ethyl alcohol is absorbed into the bloodstream
  largely from the stomach and small intestine
• Absorption produces BAC

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Alcohol Metabolism (2 of 3)

• Factors that influence the rate at which alcohol
  enters bloodstream
• Rate of gastric emptying
• Presence of food
• Concentration of alcohol taken in
• Type of beverage
• Rate at which alcohol is consumed

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Alcohol Metabolism (3 of 3)

• Elimination of alcohol by oxidationreduction
  reaction
• During elimination, alcohol is transported to the
  liver, where enzymes catalyze the oxidation of
  the alcohol.
• The end product is sometimes more toxic than the
  chemical being oxidized.
• More than 90 of the ethyl alcohol that enters
  the body is oxidized to acetic acid.

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Measurement of Blood Alcohol Concentration (1 of
2)

• Estimating the BAC from absorption-elimination
  data
• The most obvious way to measure intoxication is
  to record the amount and type of beverage
  consumed.
• Analyses are often performed hours after an
  accident, when metabolic processes have reduced
  the BAC.
• Toxicologists can use rates of absorption and
  elimination to estimate the BAC at the time of
  the accident.

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Measurement of Blood Alcohol Concentration (2 of
2)

• Estimating the amount of alcohol in the
  circulatory system
• Measurement of the concentration of alcohol in
  the persons breath
• Breath sample is easy to collect at the scene
• Direct chemical analysis of a blood sample
• Blood alcohol test is considered more reliable

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Breath Tests for Alcohol (1 of 3)

• Breathalyzer
• Includes two parts
• Instrument that calculates the BAC
• Attached mouthpiece that samples the breath
• Indirectly measures the amount of alcohol in a
  persons breath by measuring the absorption of
  light by potassium dichromate before and after
  its reaction with alcohol
• Must be continually replenished with fresh
  chemical reagents

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Breath Tests for Alcohol (2 of 3)

• Intoxilyzer
• Measures the infrared radiation absorption in a
  specific wavelength to confirm the presence of
  organic chemicals
• Detects only ethyl alcohol
• Requires suspect to blow into a mouthpiece to
  give a sample

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Breath Tests for Alcohol (3 of 3)

• Alcosensor
• The alcohol fuel cell consists of a porous,
  chemically inert layer that is coated on both
  sides with a thin platinum layer.
• Any ethyl alcohol present in the breath samples
  is converted to acetic acid.
• A microprocessor measures the electrical current
  and converts the measured electrical current into
  a BAC.

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Blood Tests for Alcohol (1 of 3)

• Gas chromatograph is the method of choice for
  identifying BAC
• Major drawback is the requirement of a blood
  sample

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Blood Tests for Alcohol (2 of 3)

• Collection and preservation of blood from a
  living person
• Clean the skin with nonalcoholic disinfectant
• Remove blood with a sterile needle
• Add preservative to the sample
• Refrigerate the sample
• Collection of samples from a cadaver
• Collect blood samples from multiple sites or use
  tissue samples other than blood

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Blood Tests for Alcohol (3 of 3)

• Gas chromatography analysis of BAC
• Ethanol has a retention time of 1.9 minutes.
• GC separates ethanol from acetaldehyde and
  acetone, which reach the detector at different
  times than ethanol.
• A calibration curve is constructed that relates
  the area under each peak to the concentration of
  each component in the standard.

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Noninvasive Alcohol Testing

• Limitations of standard techniques
• Require handling of body fluids
• Require a compliant subject
• Can take hours for results or require subject to
  be conscious enough to blow into the instrument
• Touch-based instrument
• Uses near-infrared reflectance spectroscopy to
  measure alcohol on the subjects skin
• Measures alcohol levels in 90 seconds by shining
  a beam of near-IR light on the forearm