Introduction to Toxicology

1
Introduction to Toxicology
Larry Johnson Partnership for Environmental
Educationand Rural health (PEER) Texas A M
University
2
Toxicology

• What is toxicology? The study of the effects of
  poisons.
• Poisonous substances are produced by plants,
  animals, or bacteria.
• Phytotoxins
• Zootoxins
• Bacteriotoxins
• Toxicant - the specific poisonous chemical.
• Xenobiotic - man-made substance and/or produced
  by but not normally found in the body.

3
Introduction

• Toxicology is arguably the oldest scientific
  discipline, as the earliest humans had to
  recognize which plants were safe to eat.
• Most exposure of humans to chemicals is via
  naturally occurring compounds consumed from food
  plants.
• Humans are exposed to chemicals both
  inadvertently and deliberately.

4
You Know ?

• 92 of all poisonings happen at home.
• The household products implicated in most
  poisonings are cleaning solutions, fuels,
  medicines, and other materials such as glue and
  cosmetics.
• Certain animals secrete a xenobiotic poison
  called venom, usually injected with a bite or a
  sting, and others animals harbor infectious
  bacteria.
• Some household plants are poisonous to humans and
  animals.

5
History

• 2700 B.C. - Chinese journals plant and
• fish poisons
• 1900-1200
  B.C. - Egyptian documents that had
  directions for collection, preparation,
  and administration of more than 800 medicinal
  and poisonous recipes.
• 800 B.C. - India - Hindu medicine includes
• notes on poisons and antidotes.
• 50-100 A.D. - Greek physicians classified over
• 600 plant, animal, and mineral poisons.

6
History

• 50- 400 A.D. - Romans used poisons for
• executions and assassinations.
• The philosopher, Socrates, was executed
  using hemlock for teaching radical
• ideas to youths.
• Avicenna (A.D. 980-1036) Islamic authority on
  poisons and antidotes.
• 1200 A.D. - Spanish rabbi Maimonides writes
• first-aid book for poisonings,
• Poisons and Their Antidotes

7
History

• Swiss physician Paracelsus (1493-1541) credited
  with being
• the father of modern toxicology.
• All substances are poisons there is none which
  is not a poison. The right dose differentiates a
  poison from a remedy.

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The Dose Makes the Poison
An apparently nontoxic chemical can be toxic at
high doses. (Too much of a good thing can be
bad). Highly toxic chemicals can be life saving
when given in appropriate doses. (Poisons are not
harmful at a sufficiently low dose).
9
Lethal Doses
Source Marczewski, A.E., and Kamrin, M.
Toxicology for the citizen, Retrieved August 17,
2000 from the World Wide Web www.iet.msu.edu/toxc
oncepts/toxconcepts.htm.
10
HistoryItalian physician Ramazzini (1713)
publishedDe Morbis Artificum (Diseases of
Workers)
describing "asthma" in bakers, miners,
farmers, gilders, tinsmiths, glass-workers,
tanners, millers, grain-sifters, stonecutters,
ragmen, runners, riders, porters, and professors.
Ramazzini outlined health hazards of the dusts,
fumes, or gases that such workers inhaled. The
bakers and horse riders described by Ramazzini
would today probably be diagnosed as suffering
from allergen-induced asthma. The lung diseases
suffered by most of the other workers would now
be classified as "pneumoconiosis," a group of
dust-related chronic diseases.
11
History
Spanish physician Orfila (1815)
established toxicology as a distinct scientific
discipline.
12
History

• 20th Century
• Paul Ehrlich developed staining procedures to
  observe cell and tissues and pioneered the
  understanding of how toxicants influence living
  organisms.

13
History
20th Century Rachel Carson - alarmed
public about dangers of pesticides
in the environment.
14
Occupational and Environmental Toxicology

• Environmental toxicants (air
• and water pollutants) are
• substances harmful to the
• environment and to humans.
• Environmental toxicants are both natural and
• man made.
• Public perception that man-made ones are more
  serious than natural ones - Reality both
• are serious.
• 5,000,000 yearly deaths worldwide due
• to bacterial toxicants (Salmonella, E. coli)

15
Occupational and Environmental Toxicology

• Many examples of diseases associated with
  specific occupations were recorded in antiquity,
  but they were not considered serious because the
  health of the workers was not a societal concern.
• - Paracelsus - Miners Disease (1533)
• - Hill Pott (1761 1775)
• - Radium dial painters, aniline dye workers
  (1900)
• - Shoe salesmen (1950s)
• - Industrial chemical workers (1940-present)

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Occupational and Environmental Toxicology

• - Paracelsus - Miners Disease (1533)
  came from inhaling metal vapors,
  foundation for the field of chemotherapy.
• - Hill (1761) linked tobacco (snuff)
  to cancer.
• - Pott (1775) linked scrotal
  cancer
• and soot (benzo(a)pyrene) in
• chimney sweeps.

17
Occupational and Environmental Toxicology

• Radium dial painters,
• aniline dye workers (1900)
• painters licked their brushes
• to pull it to a point.
• Shoe salesmen (1950s)
• shoe-fitting fluoroscopes
• radiation of feet in shoes of children and
  repeated
• exposure for salesmen.

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Occupational and Environmental Toxicology

• Industrial chemical workers
• (1940-present)
• Workers typically are exposed to
• a greater number of carcinogens
• for longer periods of time.
• Occupations with high risk of cancer
• Health care workers, pharmaceutical and
  laboratory workers, refinery workers, rubber
  workers, furniture makers, and pesticide workers.

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Modern Toxicology

• 1961 - Society of Toxicology
• 1970s - EPA, FDA, and NIOSH

20
Toxicology Terms
Toxicity - The adverse effects that a
chemical may produce. Dose
- The amount of a chemical that
gains access to the body.
21
Toxicology Terms
Exposure Contact providing
opportunity of obtaining a
poisonous dose. Hazard
The likelihood that the
toxicity will be expressed.
22
Threshold Effects for Dose
Dose-ResponseRelationships
Is there such a thing as a safe dose??
Agent A
Agent B
Response
NOEL(No Observable Effect Level)
Dose
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Fundamental Rules of Toxicology

• Exposure must first occur for the chemical to
  present a risk.
• The magnitude of risk is proportional to both
  the potency of the chemical and the extent of
  exposure.
• The dose makes the poison (amount of chemical
  at the target site determines toxicity).

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Exposure Concepts

• Different toxic responses may arise from
  different
• Routes of exposure.
• Frequencies of exposure.
• Duration of exposure (acute vs. chronic).

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Routes of Environmental Exposure
Ingestion (water and food) Absorption (through
skin) Injection (bite, puncture, or
cut) Inhalation (air)


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Chemicals, Chemicals Everywhere

• Everything in the environment is made of
  chemicals. Both naturally occurring and
  synthetic substances are chemical in nature.
• People are exposed to chemicals by eating
  or swallowing them,breathing them, or
  absorbing them through the skin or mucosa.
• People can protect themselves by
  blocking these routes of exposure.

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Duration Frequency of Exposure

• Duration and frequency are also important
  components of exposure and contribute to dose.
• Acute exposure - less than 24 hours usually
  entails a single exposure
• Repeated exposures are classified as
• Subacute - repeated for up to 30 days
• Subchronic - repeated for 30-90 days
• Chronic -repeated for over 90 days

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Exposure Concepts

• Exposure to chemicals may come from many sources
• Environmental
• Occupational
• Therapeutic
• Dietary
• Accidental
• Deliberate

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Children Poisons
30
Individual Responses Can Be Different

• The variety of responses among organisms that get
  the same dose of chemical is due to individual
  susceptibility.
• Dose and individual susceptibility play roles in
  all situations involving chemicals, including
  those making medicine and caffeine.

31
Introduction to Xenobiotics

• Recall Foreign chemicals are
  synthesized within the body are termed
  xenobiotics (Gr.Xenos meaning strange)
• Xenobiotics may be naturally occurring chemicals
  produced by plants, microorganisms, or
  animals(including humans).
• Xenobiotics may also be synthetic chemicals
  produced by humans.

Poisons are xenobiotics, but not all xenobiotics
are poisonous.
32
How Does the Body Prevent the Actions of
Xenobiotics ?
1) Redistribution 2) Excretion (primarily
water soluble compounds) - kidney and liver 3)
Metabolism the major mechanism for terminating
xenobiotic activity, and is frequently the single
most important determinant of the duration and
intensity of toxic responses to a xenobiotic. -
LIVER, kidney, lung, GI, and others
Note 1) and 2) are highly dependent upon 3)
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Xenobiotics at Work
TOXICOKINETICS
Xenobiotic
Excretion
34
General Scheme of Xenobiotic Metabolism
Lipophilic Hydrophilic(parent
compound) (metabolite)
Metabolism

1. Decrease biological activity2) Increase
   excretability

Phase I Phase II(oxidative)
(synthetic)
Metabolites
Metabolites
sizeionizationwater solubility Increase
excretability
polarityfunctionality
BioactivationDetoxification
Detoxification
35
How Xenobiotics Cause Toxicity

• Some xenobiotics cause toxicity by disrupting
  normal cell functions
• Bind and damage proteins (structural, enzymes)
• Bind and damage DNA (mutations)
• Bind and damage lipids
• React in the cell with oxygen to form
• free radicals which damage lipid, protein,
• and DNA

36
Types of Toxic Effects

• Death - arsenic, cyanide
• Organ Damage - ozone, lead
• Mutagenesis - UV light
• Carcinogenesis - benzene, asbestos
• Teratogenesis - thalidomide

37
Target Organ Toxicity

• Central Nervous System lead
• Immune System - isocyanates
• Liver - ethanol, acetaminophen
• Respiratory Tract - tobacco smoke,
  asbestos, ozone
• Eye - UV light (sunlight)
• Kidney - metals
• Skin - UV light, gold, nickel
• Reproductive System
• dibromochloropropane

38
Mechanistic Toxicology

• How do chemicals cause their toxic effects?

39
What Do Toxicologists Do?

• Most toxicologists work to develop a mechanistic
  understanding of how chemicals affect living
  systems
• Develop safer chemical products
• Develop safer drugs
• Determine risks for chemical exposures
• Develop treatments for chemical
• exposures
• Teach ( e.g. other toxicologists,
• graduate students, and youth)

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What Do Toxicologists Do?

• Mechanistic toxicologists study how a chemical
• causes toxic effects by investigating its
  absorption,
• distribution, and excretion. They often work in
• academic settings or private industries and
  develop
• antidotes.
• Descriptive toxicologists evaluate the toxicity
  of drugs, foods, and other products. They often
  perform experiments in a pharmaceutical or
  academic setting.
• Clinical toxicologists usually are physicians or
• veterinarians interested in the prevention,
  diagnosis,
• and treatment of poisoning cases. They have
  specialized training in emergency medicine and
  poison management.

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What Do Toxicologists Do?

• Forensic toxicologists study the
  application of toxicology to the law. They
  uses chemical analysis to determine the
  cause and circumstances of death in a
  postmortem investigation.
• Environmental toxicologists study the
• effects of pollutants on organisms,
  populations, ecosystems, and the
  biosphere.
• Regulatory toxicologists use scientific
  data to decide how to protect humans and
  animals from excessive risk. Government
  bureaus such as the FDA and EPA employ this
  type of toxicologist.

?
42
Regulatory Toxicology

• Use data from descriptive and mechanistic
  toxicology to perform risk assessments.
• Concerned with meeting requirements of
• regulatory agencies.
• Industry/government interactions.

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Review

• Toxicology is the science that studies the
  harmful effects of overexposure to drugs,
  environmental contaminants, and naturally
  occurring substances found in food, water, air,
  and soil.
• Main objectives are to establish safe doses and
  determine mechanisms of biologic action of
  chemical substances.
• A career in toxicology involves evaluating the
  harmful effects and mechanisms of action of
  chemicals in people, other animals, and all other
  living things in the environment.
• This work may be carried out in government,
  private industry and consulting firms, or
  universities and other research settings.
• Toxicologists routinely use many sophisticated
  tools to determine how chemicals are harmful.
• (e.g.) computer simulations, computer chips,
  molecular biology, cultured cells, and
  genetically-engineered laboratory animals .

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What Is the Risk?

• People can make some choices about chemical
  exposure however, some exposure is controlled at
  a level other than an individual one. Collective
  groups of people, such as communities and
  governments, seek to control chemical exposure on
  a community or global level.

45
Animals in Research Virtually every medical
achievement of the last century has depended
directly or indirectly on research in
animals. U.S. Public Health Service
46
Summary

• Toxicology is a fascinating science that
• makes biology and chemistry interesting
• and relevant.
• Understanding HOW (i.e. mechanism)
• something produces a toxic effect can lead to
  new ways of preventing or treating
  chemically-related diseases. Animal use in
  research is essential for medical progress.
• Many diseases are the result of an interaction
  between our genetics (individual variability) and
  chemicals in our environment.
• Toxicology provides an interesting and exciting
  way to apply science to important problems of
  social, environmental, and public health
  significance.

47
National Institute of Environmental Health
Sciences
Texas Rural Systemic Initiative
The Center for Environmental and Rural Health
Partnership for Environmental Education and Rural
Health
College of Education, Texas AM University
College of Veterinary Medicine at Texas AM
University
48
Port-Mortem Toxicology
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PM Toxicology

• Following death there can be rapid changes in
  cellular biochemistry as autolysis proceeds, and
  drugs and other poisons may be released from
  their binding sites in tissues and major organs,
  also unabsorbed drug may diffuse from the
  stomach.
• Special care should always be taken in the
  selection of blood and tissue sampling site(s),
  the method of collection of samples, and the
  labelling of sample containers. There is
  substantial published evidence to show that for
  most drugs and poisons, including alcohol, there
  are important differences in their concentration
  in blood according to the time of specimen
  collection after death, choice of sampling site,
  method of sampling and volume of blood collected
  (Pounder and Jones 1990 Pounder 1993).

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PM Toxicology

• It is common to observe tenfold differences in
  the concentration of certain drugs and some
  chemical poisons in post-mortem blood taken from
  different sites. Specimens taken from "central"
  sites e.g. heart tend to give particularly "high"
  values for most analytes. Moreover, certain
  commonly used "peripheral" sites such as
  subclavian, may sometimes give results closer to
  "central" sites such as the heart.
• The most consistent quantitative findings are
  obtained in blood taken from the femoral vein,
  which is the recommended site of specimen
  collection. It is also possible to observe
  differences in the concentration of certain drugs
  obtained from different tissue sampling sites for
  liver and lung.

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PM Toxicology

• Parts of the body extracted and tested for
  toxicology, post-mortem
• Blood and urine
• Bile from the duodenum and/ or liver
• Entire liver in some cases
• Stomach contents and the entire stomach may be
  extracted
• Liquid from the Vitreus Humour (eye)
• Part of the brain and lungs may be extracted and
  tested
• Hair, fingernails, and sometimes bone
• Refer to http//www.toxlab.co.uk/postmort.htm for
  more information about why each element is
  extracted

52
PM Toxicology

• Factors that prevent accurate manner of death due
  to toxins or drugs
• Persons weight and metabolism
• How long the person was dead
• Where sample was extracted from body post mortem
• Differing expert testimonials
• In the case of drugs, deceaseds addiction level
  and tolerance to suspected drug

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Forensic Toxicology
54
Forensic Toxicology

• Definition
• The science of detecting and identifying the
  presence of drugs and poisons in body fluids,
  tissues, and organs.

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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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Role of the Toxicologist

• Must identify one of thousands of drugs and
  poisons
• Must find nanogram to microgram quantities
  dissipated throughout the entire body
• Not always looking for exact chemicals, but
  metabolites of desired chemicals (ex. heroin ?
  morphine within seconds)

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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

58
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

59
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)

60
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

61
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

63
Toxicology Procedures

• 10mL of blood in airtight container
• Add anticoagulant
• Add preservative
• 2 consecutive urine samples
• Some drugs take a while to show up in urine (1-3
  days)
• Vitreous humor
• Hair samples

64
Toxicology Procedures

• Screening-
• quick test to narrow down possibilities
• color tests, TLC, GC, immunoassay
• Confirmation-
• determines exact identity
• GC/Mass Spec

Note TLCthin layer chromatography
65
Color Tests

• Marquis Test
• Turns purple in the presence of Heroin, morphine,
  opium
• Turns orange-brown in presence of Amphetamines
• Scott Test Three solutions (cobalt thiocyanate)
• Blue then pink then back to blue in the presence
  of Cocaine
• Duquenois-Levine
• Test for marijuana turns purple
• Cobalt Acetate/ isopropylamine test
• Barbiburatesturns red-violet
• P-Dimethlyamino-benzaldehyde (p-DMAB)
• LSDturns blue

66
More Analytical Tests

• Microcrystalline Tests Identifies drug by using
  chemicals that reacts to produce characteristic
  crystals
• Chromatography TLC, HPLC and gas separate
  drugs/tentative ID
• Mass Spectrometry chemical fingerprint no two
  drugs fragment the same

67
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

68
Why?

• Think of all the people that you have heard do
  drugs.
• US drug manufacturers produce enough barbiturates
  and tranquilizers each year to give every person
  in the US 40 pills
• (thats about 12 billion pills)
• 18,000 out of 44,000 annual traffic deaths are
  alcohol related and send over 2 million people to
  the hospital

69
Toxicology of Alcohol
70
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

71
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

72
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.

73
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

74
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

75
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

76
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

77
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

78
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

79
Parts of the brain affected by Alcohol

• Alcohol 1st affects the forebrain and moves
  backward
• Last affected is medulla oblongata

80
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

81
Alcohol and the Law

• 1939-1964 intoxicated 0.15 BAC
• 1965 intoxicated 0.10 BAC
• 2003 intoxicated 0.08 BAC

At least we dont live in France, Germany,
Ireland, or Japan (0.05) or especially Sweden
(0.02)!
82
Alcohol and the Law

• Try the drink wheel http//www.intox.com/wheel/dr
  inkwheel.asp

83
Alcohol Detection
84
Field Sobriety Testing

• Two reasons for the field sobriety test
• Used as a preliminary test to ascertain the
  degree of the suspects physical impairment
• To see whether or not an evidential test is
  justified.

85
Field Sobriety Testing Methods

• Field sobriety testing consists of a series of
  psychophysical tests and a preliminary breath
  test (typically done with a handheld fuel cell
  tester)
• These tests are preliminary and nonevidential in
  naturethey only serve to establish probable
  cause requiring a more thorough breath or blood
  test.

86
Field Sobriety Tests

• Horizontal Gaze Nystagmus
• Involuntary eye jerk as eye moves horizontally
• Walk and Turn (divided attention tasks)
• One-Leg Stand

87
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.

88
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.

89
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.

90
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.

91
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.

92
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.

93
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.

94
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