Forensic Toxicology Introduction PDF

Forensic Toxicology Introduction Forensic toxicologists are charged with the responsibity for detecting and identifying the presence of drugs and poisons in body flluids, tissues, and organs Forensic toxicologists not only work in crime laboratories and medical examiners officers but may also reach...

Forensic Toxicology Introduction Forensic toxicologists are charged with the responsibity for detecting and identifying the presence of drugs and poisons in body flluids, tissues, and organs Forensic toxicologists not only work in crime laboratories and medical examiners officers but may also reach into hospital laboratories and health facilities to identify a drug overdose or monitor the intake of drugs 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 exemplfies the primary objective and isolation of drugs in the body for the purpose of determining their infleue on human behavior Alcohol, or ethyl alcohol is a colorless liquid normally diluted with water and consumed as a beverage Alcohol is the most heavily abused legal drug in Western countries. About 17,000 traffic deaths each year are attrubuted to alcohol intoxication Like any depressant, alcohol prinipally affects the central nerous system, particularly the brain Blood alcohol concentration has been shown to be directly proportional to the concentration of alcohol in the brain Alcohols Fate in the Human Body Absorption Distribution Elimination Alcohol Absorption Alcohol appears in the blood within muinutes after it has been taken by mouth and slowly increases in cocnertaion while it is being absorbed from the stomach and the small intestine into the bloodstream When all the alcohol has been absorbed a maximum alcohol level is reached in the blodd, and the post absorption or elimination period begins For an average human drinking on an empty to modestly full stomach, alcohol is absorbed entirly into the blood stream 30-90 minutues after the completion of drinking, When drinking on a full stomach the absorption time can be as long as 2-4 hours The type of beverage also affects absorption time. For example, beer is absorbed more slowly than 80 proof alcohol because of the carbohdrates in beer The longer the time for complete absorption to occur, the lower will be the peak alcohol in the blood for a given numbere of drinks Alcohol Distrbution 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 About five percent of the alcohol excreted uncahnged in the breath, urine and perspiration Blood alcohol cocnertration 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 Concentraion (BAC) The extent to which an individual may be under the influence of alcohol is usually determined by either measuring the quantity of alcohol present in the blood system or by measuring the alcohol content in the breath Experimental evidence has verified that the amount of alcohol ehaled in the breath is in direct proportion to the blood cocnentration and is direrly proportional to alcohol in the brain The current legal measure of drunk driving in the United Stated is a blood-alcohol cocnertraion of 0.08 percent, or 0.08 grams of alcohol per 100 milliters of blood. Another way of expressing this is 80mg/dl Alcohol and the Circulatory System Humans have a closed cirucalory system consisting of a heart, arteries, veins and capillaries Alcohol is absorbed from the stomach and small intestines into the blood stream Alcohol is carried to the liver where the process of its destruction starts Blood, carrying alcohol, moves to the heart and is pumped to the lungs Humans have a closed circulatory system consisting of a heart, arteries, veins and capillaries In the lungs, the respiratory system bridges with the circulatory system. A rapid exchange takes place between fresh air in the lungs alvel=oli sacs and spent blood in the capilaries surrounding the sacs. If alcohol is present in the blood, it participates in this exxchange As one exhales carbon dioxide and alcohol leave the blood and oxygen enters the blood in the air sacs known as alveoli. Its in the alveoli sacs that alcohol is in equilibrium with the blood After leaving the lungs, the oxyenated blood returns to the heart where it is pumped to all parts of the body through arteries only to eventually return to the heart through blood veins completing the circuatory proces. Breath Testers The temperature at which the breath leaves the mouth is normally 34 degrees celsius Breath testers operate on the fact that at 34 degrees celsius the ratio of alcohol in the blood to alcohol in alveolar breath is approcimately 2100 to 1 In other words, 1 militler of blood contains nearly the same amount of alcohol as 2100 militlers of alvelar breath Breath testers that operate on the pricnople of infrared light absorption are becoming increasingly popular within the law enforcement community Many types of breath testers are designed to analyze an indovuidals breath as it flows trough a chamber in the breath tester and is exposed to infrared radiation Its the degree of the interaction of the infrared light with alcohol in the breath chamber that allows the instrument to measure a blood alcohol cocnertaion in breath Some breath testing devices also use fuel cells which converts alcohol to an electrical current Field Testing Law enforcement officers typically use field sobriety tests to estimate a motorists degree of physical impairment by alcohol and whether or not 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 A portable, handheld, roadside breath tester may be sussed to determine a preliminary breath-alcohol content. These testers use fuel-cell detectors are not admissible in court proceedings as proof of intoxication Testing Blood for Alcohol Content Gas chromatogrpahy offers the toxicoligst the most widely used approach for determining alcohol levels in blood in forensic labs Hosptial or clinical labs normally use autoanalyzers to measure alcohol content. These instruments measure the conversion of alcohol to acetaldehyde by alchol dehydrogenase. The determination is made as a serum alcohol level Serum alcohol is normally converted to a blood- alchol concetraiton by divding by the factor 1.16. Thus 250 mg/dl is equivalent to 215mg/dl of 0.215% Collection and Preservation of Blood Blood must always be drawn under medically accepted conditions by a qualified individual It is important that a nonalcohlic disinfectant such as betadine be applied before the suspecfcts skin is penetrated with a sterile needle or lancet Once blood is removed from an indivual its preservation is be ensured when it is sealed in an airtight container after an anticoagulant and a preservative have been added and stored in a refrigerator Failure to properly preserve blood removec from living indivuals may resukt in a decline of the blood alcohol level In decedents alcholo maybe produced during composition creating an elevated blood alcohol level Alcohol and the Law All 50 states have established per se laws, meaning that any individual at a defined blood alcohol concentration (normally 0.08%) shall be deemed to be intoxicated. At 0.08% a driver if four times likely to become involved in an accident. At 0.15% the chances rise to 25 times. To prevent a person’s refusal to take a test for alcohol consumption, all the states have adopted an “implied consent” law. This law states that the operation of a motor vehicle on a public highway must either consent to a test for alcohol intoxication, if requested, or lose his or her license for some designated period. In Schmerber v. California (1966), the Supreme Court ruled that the taking of blood samples was not protected by the fifth amendment. In a 2013 decision the Supreme Court in Misssouri v. McNeely ruled that police should obtain a search warrant prior to the drawing of a person’s blood for alcohol testing Role of the Foresenic Toxicologist Beyond the analysis of alcohol, the toxicologist is confronted with a maze of drugs and poisons. The toxicologist is originally presented with body fluids and/or organs and is normally requested to examine them for the presence of drugs and poisons. Without supportive evidence, such as the victim’s symptoms, a postmortem pathological examination, or an examination of the victim’s personal effects, the toxicologist is forced to use general screening procedures with the hope of narrowing thousands of possibilities to one. In addition, the toxicologist is not dealing with drugs at the concentration levels found in powders and pills, having been dissipated and distributed throughout the body. Furthermore, the body is an active chemistry laboratory as few substances enter and completely leave the body in the same chemical state. Many drugs are chemically changed or are metabolized in the body to different chemical substances. Last, when and if the toxicologist has surmounted all of these obstacles, he or she must be prepared to assess the toxicity of the drug or poison. The Analytical SchemeThe Analytical Scheme The strategy used for identifying abused drugs entails a two-step Approach: screening Confirmation The Screening Step A screening test is normally employed to provide the analyst with quick insight into the likelihood that a specimen contains a drug substance Positive results arising from a screening test are considered to be tentative at best and must be verified with a confirmation test The most widely used screening tests are gas chroamtogrpahy and immunoassay The Confirmation Step Gas chromatogrpahy/mass spectrometry is genera;ly accepted as the confirmation test of choice The GC separates the sample into its components while the MS represtns a unique “fingerprint” pattern that can be used for identification Typically for a living person, its the blood that is test for drug content; however urine drug testing for drugs is becoming common for job and employees in the work place The Significance of Toxicolgiical Findings Once the drug is extracted and identified the toxiolgoist may be required to provide an opinion on the drugs effect on an indivuals natural performance or physical state For many drugs blood concernttation levels are readily determined and can be used to estimate the pharmacological effwecs of the drug on the individual The concertation of a drug in urine is a poor indiaator of how extensively an individuals behaviour or state is inflecned by the drug Before drawing conclusion about drug0induced behaviour the analyst must consider other factors including age, health and tolerance Often when dealing with a living person, the toxicologust has the added benefit pf knowing what a police officer may have observed about an indivffuals behaviour and motor skills Detecting Drugs in Hair Drugs present in blood diffuse through the capilarary walls into the base of the hair and become permanently entrapped in the hairs hardening protein structure As the hair continues to grow, the drugs location on the hair shaft becomes a historical marker for delineating drug intake Given that the average human head hair grows at the rate of 1 centimeter per month, analyzing segments of hair for drug content may define the timeline for drug use The chronology of frug intake may be distorted by drugs penetrating the hairs surface as a sreust of enviromental exposure, or drugs may eneter the hairs surface through sweat Non Drug Poisons Heavy metals such as arsenic,, bismuth, antimony, mercury and thallium are only occasiaonylly encountered because severe environmental protection regulations restrict their availability to the general public To screen for many of these metals, the suspect body fluid is dissolved in a hydrocholor solution and a coppers strip is inserted into the solution. The presence of a sivery or dark coating on the copper indicated the presence of a heavy metal Carbon monoxide is one of the most common poisons encountered in a forensic laboratory To measure the concentration of carbon monoxide in the blood, spectrophtoometric methods determine the amount of ccarboxyhemoglobin relative to oxyhemoglobin or total hemoglobin; or a volume of blood can be treated with a reafent to liberate the carbon monoxide which is then measured by gas chromatography The Drug Recognition Expert (DRE) Program During the 1970s the Los Angles Police department developed clinical and psychological exaniantions that a trained police officer could use to idetnnify and differentiate between types of drug impairment This program has evolved into a national program to train police as drug recognition experts Normally a three-to five month training program is required to certify an officer as a drug recognition expert (DRE) The DRE program incorporates standardized methods; eg blood pressure, pulse, pupil size, for examining suspsects to determine whether they have taken one or more drugs The DRE To ensure that each subject has been tested in a rountien fashion, each DRE must complete a standard Drug Infleunce Evaluation form The DRE program usually cannot determine which specific drug was ingested Hence, it is production of reliable data from both the DRE and the forensic toxicologist that is required to prove drug intoxication