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Chapter 12

CRIM 355 Chapter 12: Forensic Toxicology

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Simon Fraser University
CRIM 355
Gail Anderson

CHAPTER 12: FORENSIC T OXICOLOGY  Toxicologists detect and identify drugs + poisons in body fluids, tissues, organs  Forensic toxicologists’ role is limited to matters that pertain to violations of criminal law  Handles numerous requests relating to the determination of the presence of alcohol in the body  Assist in establishing the true cause of death  Basis for intoxicated behavior  Clue to clinical history when subject is unable/unwilling to do so  Assist in establishing the truth of statements  Need to know how a drug metabolizes itself in the body  Assess substance toxicity  Working with minimal amount of evidence/drugs ALCOHOL  Central nervous system (CNS) suppressor  Low doses = inhibit mental processes of judgment, memory and concentration, expansive, overconfident  Moderate doses = effects coordination, inhibits though processes, speech patterns, slows reaction times  High doses = highly irritable, emotional, angry, may cry easily TOXOCOLOGY OF ALCOHOL  Primary objective of forensic toxicology: to detect and isolate drugs in the body so that their influence on human behavior can be determined  Pioneered the development of instruments that measure the presence and concentration of alcohol in individuals suspected of driving while under its influence Metabolism of alcohol  Metabolism = transformation of a chemical in the body to another chemical to facilitate its elimination from the body  Chemicals that enter the body are broken down by chemicals within the body and transformed into other chemicals that are easier to eliminate  Three basic steps: absorption, distribution, elimination ABSORPTION AND DISTRIBUTION  Alcohol (ethyl alcohol) = colourless liquid diluted with water and consumed as beverage  Appears in blood within minutes after it has been consumed and slowly increases in concentration while it’s being absorbed from the stomach + small intestine into the bloodstream  Absorption = passage of alcohol across the wall of the stomach and small intestine into the bloodstream  Alcohol slowly enter the body’s bloodstream and is carried to all parts of the body  Post-absorption: alcohol concentration slowly decreases until it reaches zero  The rate alcohol is absorbed into the bloodstream is determined by several factors: total time taken to consume the drink, alcohol content of the beverage, amount consumed, quantity + type of food present in the stomach  Oxidation = combination of oxygen with other substances to produce new products  Takes place almost entirely in the liver: in the presence of enzyme alcohol dehydrogenase, alcohol is converted into acetaldehyde and then to acetic acid -> finally oxidized to become carbon dioxide and water  Level of alcohol dehydrogenase varies with gender, age and ancestry  Excretion = elimination of alcohol from the body in an unchanged state  Alcohol is normally excreted in breath and urine and perspiration  The amount of alcohol exhaled in the breath is in direct proportion to the concentration of alcohol in the blood  Fate of alcohol in the body:  Absorption into the bloodstream -> distribution throughout the body’s water -> elimination by oxidation and excretion  The elimination/burn-off rate of alcohol varies in different individuals  0.015 % weight per volume per hour is the average rate after absorption process is complete  Average varies by as much as 30% among individuals BLOOD-ALCOHOL CONCENTRATION  Directly proportional to the concentration of blood in the brain  Alcohol becomes concentrated evenly throughout the watery portions of the body  If blood is not available, then a medical examiner can select a water-rich organ/fluid to estimate the body’s equivalent alcohol level TESTING FOR INTOXICATION Breath testing for alcohol  Breath tester = device for collecting and measuring the alcohol content of alveolar breath
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