Forensic Toxicology

1. Forensic Toxicology Forensic Science K. Davis

2. Toxicology • Toxicologists detect and identify the presence of drugs and poisons in body fluids, tissues, and organs.

3. Alcohol • The most heavily abused drug in Western countries. • Consumed as a liquid • Depressant • Alcohol appears in the blood within minutes after it has been taken by mouth. It slowly increases in concentration while it is being absorbed from the stomach and the small intestine into the bloodstream.

4. Toxicology of Alcohol • Absorption: passage alcohol across wall of stomach & small intestine into blood stream • Absorbed in surface areas of forebrain, then central and rear portions of brain • Blood concentration is directly proportional to alcohol levels in brain. • Factors that affect intoxication levels: • amount consumed • body weight • rate of alcohol absorption

5. Rate of absorption determined by: Total time to consume drink Alcohol content of beverage Amount consumed Quantity & type of food present in stomach (Sometimes it is difficult to predict)

6. Absorption Phase • Alcohol slowly enters body’s bloodstream and is carried to all parts of body. • After absorption, alcohol is distributed throughout watery portions of body. • Under normal conditions, this takes ≈ 30 -90 minutes.

7. Movement of alcohol through system http://www.dnatube.com/video/4871/Drug-Metabolism • Mouth → esophagus → stomach → small intestine → bloodstream → liver → heart → lungs → alveoli → bronchioles → expelled into air • Esophagus –> stomach : 20 % absorbed into blood • Small intestine : remainder absorbed into blood • If blood is not available, the medical examiner can use cerebrospinal fluid, vitreous humor, and brain tissue to determine the body’s alcoholic content to a reasonable degree of accuracy.

8. Alcohol in Circulatory System • Can measure the extent an individual is under the influence by measuring quantity of alcohol present in blood • Direct chemical analysis of blood • Measure alcohol content of breath

9. Circulatory system • Humans have a closed system of heart, arteries, capillaries, & veins • artery : blood away from heart • vein : blood toward heart • capillary : tiny blood vessel that interconnects arteries & veins

11. Post- absorption Phase • • When all the alcohol has been absorbed, a maximum alcohol level is reached in the blood, and the post-absorption period begins. • During post-absorption, the alcohol concentration slowly decreases until a zero level is reached.

12. Elimination • The elimination or “burn off” rate of alcohol averages 0.015 % w/v per hour. • Elimination of alcohol throughout the body is accomplished through oxidation and excretion. • Oxidation: combination of oxygen with other substances to produce new products; takes place almost entirely in the liver • Excretion: elimination of alcohol from body in an unchanged state; takes place in the breath, urine, & perspiration

13. Metabolism • Metabolism is the process by which the body changes one chemical to another in order to facilitate its elimination from the body. • Because of metabolism, few substances enter and completely leave the body in the same chemical state. • Thus, the forensic toxicologist must thoroughly understand how the body alters or metabolizes the chemical structure of a drug in order to detect the presence of that drug.

14. Heroin Metabolism • Upon entering the bloodstream, heroin is almost immediately metabolized into morphine. • Therefore, heroin is NOT typically found in blood or urine.

15. Carbon Monoxide • Carbon monoxide is toxic because it combines with hemoglobin to form carboxyhemoglobin. • Carbon monoxide can increase in a victim’s blood after a fire.

16. Henry’s Law • When a volatile chemical (alcohol) is dissolved in a liquid (blood), & it is brought to equilibrium with air (alveolar breath), there is a fixed ratio between the concentration of the volatile compound in air & its concentration in the liquid. • This is a direct relationship between the amount of alcohol in the blood and alveolar breath. • This ratio is constant for a given temperature (34 degrees C).

17. Henry’s Law Applied • Evidence shows that the ratio of alcohol (in blood) to alcohol (in alveolar air) is ≈ 2100:1. • Blood alcohol concentration is higher in the arteries than it is in the veins until absorption is complete. • Once absorption is complete, no difference should be seen between blood and breath test. • A breath test reflects the alcohol concentration in the pulmonary artery.

18. Breath Tests • Many breath testers capture a set volume of breath and expose it to infrared light. • The instrument measures blood-alcohol concentration in breath by measuring the degree of the interaction of the light with alcohol in the captured breath sample. • Breath-testing devices operate on the principle that the ratio between the concentration of alcohol in deep-lung or alveolar breath and its concentration in blood is fixed.

19. Breath Analysis “The Breathalyzer” • Developed in 1954 by police captain • Blow into mouthpiece • Collects about 52.5 ml • Designed to measure alcohol concentration present in 1/40 milliliter of blood

20. “The Breathalyzer” (cont.) • Basically is a spectrophotometer • Indirectly determines the quantity of alcohol consumed by measuring the absorption of light by potassium dichromate before and after its reaction to alcohol.

21. Intoxilyzer • Infrared light absorption techniques • Operates same as spectrophotometers • Still tests alcohol concentration in breath

22. Field Sobriety Testing • Law enforcement officers use field sobriety tests to estimate a motorist’s degree of physical impairment by alcohol and to determine whether an evidential test for alcohol is justified. • The horizontal gaze nystagmus test, walk and turn, and the one-leg stand are all considered reliable and effective psychophysical tests for alcohol impairment.

23. Walk & Turn and One Leg Tests • A divided-attention task tests a subject’s ability to comprehend and execute two or more simple instructions at one time. • The walk and turn test requires the suspect to walk a straight line, touching heel to toe for nine steps, then turn around on the line and repeat the process. • The one-leg stand requires the suspect to stand on one foot while holding the other foot several inches off the ground for 30 seconds and simultaneously counting out loud.

24. Horizontal Gaze Nystagmus Test • Horizontal gaze nystagmus is an involuntary jerking of the eye as it moves to the side. The subject is asked to follow an object with his or her eye as far to the side as the eye can go. The higher a person’s blood-alcohol concentration, the less the eye has to move toward the side before jerking or nystagmus begins.

25. Hair Testing • Often done for work drug screens • Analyzing segments of hair for drug content may define the timeline for drug use, dating it back over a period of days, weeks, or months.

26. Analysis of Blood for Alcohol • Screening test - quick insight into the likelihood a specimen contains a drug • TLC (thin-layer chromatography) • Immunoassay • GC (gas chromatography)- most widely used approach for determining blood alcohol levels in a forensic laboratory • Positive results from a screening test are considered tentative at best and must be verified with a confirmation test.

27. Analysis of Blood for Alcohol • Confirmation tests are required after a positive screening test to ensure that the positive result was not caused by a substance with a chemical structure similar to that of an illegal drug. • GCMS (Gas chromatography/mass spectrometry) - generally accepted as the confirmation test of choice because it separates and then identifies the drugs.

28. Collection & Preservation of Blood • Must be drawn under medically accepted conditions by qualified individual • Use sterile needles or lancets, non-alcoholic disinfectant • Sealed in airtight container after anti-coagulant & preservative are added • anti-coagulant: substance that prevents coagulation or clotting of blood • preservative: substance that stops the growth of micro-organisms in blood • Refrigerated

29. Blood is drawn from a living suspect involved in an automobile accident. • If the specimen is kept unrefrigerated and at a moderately warm temperature, the alcohol concentration can be expected to decrease with time.

30. Forensic Toxicologists • The forensic toxicologist often has no clue as to which drug or drugs may be present. • Also, by the time a drug specimen reaches the toxicology laboratory, it has been dissipated and distributed throughout the body, so the toxicologist must work with very small amounts of drugs.

31. Forensic Toxicologists • These small amounts must be carefully extracted from the body before they can be analyzed. • The forensic toxicologist must devise an analytical scheme to detect, isolate, and specifically identify toxic drug substances extracted from biological fluids, tissues, and organs.

32. Collection of Post-mortem Samples • It is best to collect a number of blood samples from different body sites because ethyl alcohol may be generated in a deceased individual as a result of bacterial action. • Several samples taken from different sites can then be compared to each other. • If the results for all blood samples are similar, the blood-alcohol levels can safely be attributed to alcohol consumption.

33. Drug Recognition Expert (DRE) • Once a drug is extracted and identified, a toxicologist may be required to determine the drug’s effect on an individual’s natural performance or physical state. • The drug recognition expert (DRE) program uses standardized methods to examine automobile drivers who are suspected of being under the influence of drugs. • Because the DRE program usually cannot determine which specific drug was ingested, reliable data from a forensic toxicologist is also required to prove drug intoxication.

34. Alcohol and The Law • Most states have limit of 0.08% BAC • The DOT set the maximum allowable BAC for commercial truck & bus drivers at .04% • Increased driving risk in relation to BAC • Sweden has the lowest BAC in determining legal impairment level.

35. Constitutionality of BAC (w/o consent) • Implied Consent- anyone operating a motor vehicle has already given “consent” to a test for alcohol intoxication • Schumber vs. California • Court requires submission of physical evidence. • No warrant needed because it was an “emergency situation”.

36. Acids & Bases • pH < 7 is acidic • pH = 7 is neutral • pH > 7 is basic • Acidic drug: aspirin • Basic drug: amphetamine

37. Why is knowledge of an individual’s history of drug use important in evaluating drug concentrations found by a toxicologist? • Knowledge of an individual’s history of drug use is important in evaluating drug concentrations found by the toxicologist because factors such as age, physical condition, and tolerance of the drug user can affect an individual’s response to a drug’s effects. • For example, long-term users of a drug may be able to tolerate blood-drug concentrations that would normally be fatal to the casual drug user.

38. A body is found at a fire scene but investigators are not sure whether the victim was alive when the fire began. • How can measuring the level of carbon monoxide in the victim’s blood help determine this? • The presence of high levels of carbon monoxide in the blood would prove that the victim breathed the combustion products of the fire and was therefore alive when the fire began. • Low levels of carbon monoxide would suggest that the victim was dead before the fire started.