Transcript 10.4 – The Role of the Toxicologists
Toxicologists & Drug Analysis Objectives Describe techniques that forensics toxicologists use to isolate and identify drugs and poisons. Screening Tests Use TLC, GC, Immunoassay Immunoassay – very different Based on specific drug antibody reactions Ability to detect small concentrations Best for detecting marijuana Confirmation Tests GC/MS One step test of unequaled sensitivity and specificity Drug testing not related to criminal matters Drugs in Hair Drugs remain in Bloodstream – 24 hours Urine – 72 hours Tested in Private labs, typical for workplace screenings Hair nourished by blood flowing through capillaries near root Drugs diffuse through capillary walls and become permanently entrapped in hair’s protein structure Drug’s location becomes historical marker for delineating drug intake Heavy Metals Group of poisons Arsenic, Bismuth, Antimony, Mercury, Thallium Reinsch Test Dissolve body fluid or tissue in hydrochloric acid solution then insert copper strip to solution Appearance of silver or dark coating on copper indicates presence of heavy metal Confirm with inorganic analysis Carbon Monoxide One of the most common poisons Primarily absorbed by red blood cells Combines with hemoglobin to form carboxyhemoglobin Not enough hemoglobin left to carry oxygen to tissues Causes asphyxiation 2 Basic Methods for Detection of CO Spectrophotometric – visible spectrum GC – liberates CO from blood Calculate percent saturation Greater than 50-60% = fatal Fatal levels can be lower when in combination with depressants Arson Victim High levels of carbon monoxide in blood indicate that victim breathed in products of fire and was alive when fire began Low levels = dead before fire started Could have been placed there to destroy evidence Significance of findings Interpreting results is the most difficult chore Blood concentration levels can be used to estimate pharmacological effects of drugs Significance of findings Before drawing conclusions, toxicologists must consider other factors – age, physical condition, drug history, tolerance Prolonged use can make an individual less responsive to drug’s effects Additive or synergistic effects provided by interaction of 2 or more drugs Concentration in urine is poor indicator because formed outside circulatory system and drug levels can build up over long periods of time Drug can be found in urine 1-3 days after taken and long after other effects have disappeared Best used to corroborate other findings Drug Recognition experts (DRE) 1970s, LAPD developed and tested clinical and psychophysical examinations that police officers could use to identify and differentiate between types of drug impairment Evolved into national program Standardized methods Not a substitute for toxicology testing 10.7 Questions 1. What is the difference between a screening test and a confirmation test? 2. What are the three screening tests most widely used for forensic toxicology? What is the confirmation test of choice? 3. Which of the following is not classified as a heavy metal? A. Lead B. Arsenic C. Mercury D. Thallium 4. Explain how inhaling carbon monoxide can cause death. 5. Name at least three factors in addition to blood concentration levels that must be considered before drawing conclusions about a subject’s drug induced behaviors. 6. Why is the concentration of a drug present in urine a poor indicator of how extensively an individual’s behavior or state is influenced by the drug?