Download Chapter 12 Forensic Toxicology

Chapter 12
Forensic Toxicology
Introduction
 Forensic toxicologists - detecting and identifying the
presence of drugs and poisons in body fluids, tissues,
and organs.
 Forensic toxicologists work in crime laboratories,
medical examiners’ offices, hospital laboratories, and
health facilities
Toxicology of Alcohol
 A major branch of forensic toxicology deals with the
measurement of alcohol in the body for matters that pertain
to violations of criminal law.
 The analysis of alcohol exemplifies the primary objective of
forensic toxicology—the detection and isolation of drugs in
the body for the purpose of determining their influence on
human behavior.
 Alcohol or ethyl alcohol
 40% of all traffic deaths (~17,500 traffic deaths) each year are
attributed to alcohol
 affects the central nervous system
◊ Blood alcohol concentration has been shown to be directly
proportional to the concentration of alcohol in the brain.
Alcohol’s Fate in the Human Body
 Absorption
 Distribution
 Elimination
Alcohol Absorption
 Alcohol
 Absorbs from the stomach and the small intestine into
the bloodstream.
 On an empty to modestly full stomach, alcohol is
absorbed entirely into the blood stream 30-90 minutes
 On a full stomach, the absorption time can be as long
as 2-4 hours
 The type of beverage also affects absorption time: beer
vs 80 proof alcohol.
 The longer the time for complete absorption to occur,
the lower will be the peak alcohol in the blood for a
given number of drinks.
Alcohol Distribution
 When absorption is complete, alcohol becomes
uniformly distributed between all the watery portions of
the body which is about two-thirds of body volume.
 In decedents, if blood is not available other watery
portions of the body; e.g., brain, cerebrospinal fluid, or
vitreous humor, can be used to determine alcohol
levels.
Alcohol Elimination
 Elimination of alcohol throughout the body is
accomplished through oxidation and excretion.
 Oxidation takes place almost entirely in the liver, where
the enzyme alcohol dehydrogenase converts alcohol to
acetic acid and then into carbon dioxide and water.
Alcohol Elimination
 About five percent of the alcohol is excreted unchanged
in the breath, urine, and perspiration.
 Blood alcohol concentration is defined as percent weight
per volume. Hence, 0.10% is equivalent to 0.10 grams
per 100 milliliters of blood.
 The elimination or “burn-off” rate of alcohol varies, but
0.015%/hr. seems to be a reasonable average.
 Hence, if your blood level of alcohol is 0.10%, it takes
about 6.5 hours for you to come down to zero.
Blood Alcohol Concentration (BAC)
Blood Alcohol Concentration (BAC)
 The analyst will measure the quantity of alcohol present
in the blood system or measure the alcohol content in
the breath.
 The amount of alcohol exhaled in the breath is in direct
proportion to the blood concentration and is directly
proportional to alcohol in the brain.
 Blood-alcohol concentration of 0.08 percent, or 0.08
grams of alcohol per 100 milliliters of blood. Another
way of expressing this is 80 mg/dL.
Simplified diagram of the human circulatory system. Dark vessels
.
contain oxygenated blood; light vessels contain deoxygenated blood
Gas exchange in the lungs. Blood flows from the pulmonary artery into vessels
that lie close to the walls of the alveoli sacs. Here the blood gives up its carbon
dioxide and absorbs oxygen. The oxygenated blood leaves the lungs via the
pulmonary vein and returns to the heart.
The respiratory system. The trachea connects the nose and mouth to the
bronchial tubes. The bronchial tubes divide into numerous branches that
terminate in the alveoli sacs in the lungs.
Breath Testers
 Breath testers operate at
34°C (93.2°F), the ratio of
alcohol in the blood to alcohol
in alveolar breath is
approximately 2,100 to 1.
 1 milliliter of blood contains
nearly the same amount of
alcohol as 2,100 milliliters of
alveolar breath.
 an individual’s breath as it
flows through a chamber in
the breath tester and is
exposed to infrared radiation.
An infrared breath-testing instrument—the
Data Master DMT. Courtesy Intoximeters,
Inc., St. Louis, MO, www.intox.com
A subject blowing into the DMT breath tester.
Courtesy Intoximeters, Inc., St. Louis, MO, www.intox.com
Schematic diagram of an infrared
breath-testing instrument.
Schematic diagram of an infrared
breath-testing instrument.
Schematic diagram of an infrared
breath-testing instrument.
Schematic diagram of an infrared
breath-testing instrument.
Schematic diagram of an infrared
breath-testing instrument.