Chapter 13: Forensic Toxicology: Alcohol & Drugs

Forensic Toxicology: Alcohol & Drugs begins by detailing the pharmacokinetics of ethyl alcohol, explaining the metabolic stages of absorption through the gastrointestinal tract, uniform distribution across water-rich body tissues, and elimination via oxidation in the liver and excretion through breath, urine, and perspiration. The text explores the physiological basis of breath testing, utilizing Henry's Law to establish the fixed ratio between alcohol in alveolar deep-lung breath and the pulmonary blood supply. Various instrumentation methodologies are discussed, including infrared light absorption and fuel cell detectors, alongside the necessary protocols to prevent mouth alcohol contamination. The summary covers field sobriety testing, describing psychophysical assessments like horizontal-gaze nystagmus, the walk-and-turn, and the one-leg stand used by law enforcement to estimate impairment. Significant attention is given to the laboratory analysis of blood, emphasizing gas chromatography as the standard for quantification and the critical evidence collection procedures involving nonalcoholic disinfectants, anticoagulants, and preservatives like sodium fluoride to maintain sample stability. Legal standards are reviewed, including the federal 0.08 percent per se blood-alcohol concentration limit, implied consent legislation, and constitutional precedents regarding self-incrimination and warrantless blood searches found in cases such as Schmerber v. California and Missouri v. McNeely. Beyond alcohol, the chapter outlines analytical schemes for isolating acidic and basic drugs using pH extraction, followed by the two-step identification process of screening tests (such as immunoassays) and confirmatory tests (specifically gas chromatography-mass spectrometry). Additional topics include the utility of hair analysis for establishing long-term drug history, the detection of heavy metals like thallium via the Reinsch test, and the measurement of carbon monoxide saturation in blood. Finally, the role of the Drug Recognition Expert (DRE) is explained, highlighting the systematic twelve-step evaluation used to classify drug-induced impairment when alcohol is not the sole factor.