Forensic Toxicology Study Notes
Introduction to Toxicology
Study of drugs, poisons, toxins, and metabolites. Toxicology is an interdisciplinary science combining biology, chemistry, and medicine to understand how chemicals interact with living systems, encompassing risk assessment and regulatory aspects.
Poison: Harmful substance absorbed, inhaled, or ingested. It is any substance that causes harmful effects when introduced into the body in sufficient quantities, regardless of its origin (synthetic or natural).
Toxin: Natural poisonous substance from living organisms. Examples include snake venom, bacterial toxins (e.g., botulinum toxin), or plant toxins (e.g., ricin).
Toxicologists: Examine effects, establish cause and effect, develop treatments. Their roles include forensic toxicology (investigating deaths), clinical toxicology (treating poisonings), environmental toxicology (assessing impact on ecosystems), and regulatory toxicology (setting safety standards).
Historical Context
Used in ancient hunting and assassination. Early humans used plant and animal venoms for hunting, while civilizations like the Romans and ancient Greeks documented poison use in politics and warfare.
Socrates poisoned with hemlock (399 BCE). This is a classic example of judicial poisoning, highlighting early awareness of toxic substances.
Mithridates VI practiced self-immunization to poison. This practice, known as "Mithridatism," involved ingesting sub-lethal doses of poisons to build up immunity, demonstrating early pharmacological experimentation.
Controlled Substances Act of 1970. This act is significant for regulating psychoactive drugs and establishing drug schedules in the US, impacting forensic toxicology and drug control.
Mechanisms of Toxicity
Absorption: Entry into bloodstream. Chemicals cross biological membranes. Factors influencing absorption include concentration, lipid solubility, and surface area of exposure. Oral absorption occurs in the GI tract, dermal through skin layers, and pulmonary via alveoli.
Distribution: Movement to tissues/organs. Once absorbed, substances are transported via blood and lymph. Distribution depends on blood flow to organs, affinity for tissue components, and binding to plasma proteins. Some substances preferentially accumulate in specific organs (e.g., lead in bone).
Metabolism: Chemical alteration, usually in the liver. Primarily occurs in the liver (hepatic metabolism) but also in kidneys, lungs, and intestines. Involves enzymatic biotransformation (Phase I: oxidation, reduction, hydrolysis; Phase II: conjugation) to make substances more water-soluble for excretion. This can detoxify or activate (bioactivation) a compound.
Excretion: Removal via urine, sweat, etc. Main routes are renal (kidneys filtration in urine), biliary (via bile into feces), and pulmonary (volatile compounds exhaled). Minor routes include sweat, saliva, and breast milk.
Routes of Exposure
Eyes, Nose, Mouth, Lungs, Skin. These are the main portals of entry into the body.
Common routes:
Oral (ingestion): Common for drugs, food contaminants, accidental poisonings. Absorption varies based on GI tract conditions, food presence, and chemical form.
Injection (parenteral): Intravenous (IV), intramuscular (IM), subcutaneous (SC). Bypasses the GI tract, leading to rapid systemic distribution (IV being fastest).
Topical (dermal): Through skin. Absorption depends on skin integrity, lipid solubility, and the vehicle. Relevant for pesticides, cosmetics, and medicinal patches.
Inhalation (respiratory): Via lungs. Rapid absorption due to the large surface area of alveoli and rich blood supply. Important for gases, vapors, aerosols, and airborne particulates.
Toxic Factors
Exposure duration, chemical form, dosage, absorption ability, interactions. These factors determine the severity and nature of toxic effects.
Dose-response relationship: A fundamental concept where "the dose makes the poison." It defines the relationship between the amount of exposure and the severity of effects, often expressed as (lethal dose for 50% of population) or (toxic dose).
Duration of exposure: Acute (single, short-term), subacute (repeated for approximately month), subchronic (repeated for months), and chronic (repeated over life-time). Different durations often cause different effects.
Chemical form/properties: Factors like solubility (lipid vs. water), volatility, particle size, pH, and purity significantly influence how a substance interacts with the body.
Physicochemical interactions: Synergism (combined effect greater than the sum of individual effects), antagonism (combined effect less than the sum), potentiation (one compound enhances the effect of another).
Species, genetics, life stages, gender, health status. Individual biological variations influence susceptibility.
Species differences: Varying metabolic enzymes or target organ sensitivities across species.
Genetic predisposition: Polymorphisms in drug-metabolizing enzymes (e.g., CYP450 genes) can lead to faster or slower metabolism, altering toxicity.
Life stages: Vulnerability varies in fetuses (teratogenesis), infants, children, and elderly due to different metabolic capacities and organ development.
Gender: Hormonal differences or body composition can influence toxicity.
Health status: Pre-existing liver or kidney disease impairs metabolism or excretion, increasing susceptibility.
Classifications of Poisons vs. Venoms
Poison: Absorbed through skin/inhalation (e.g., heavy metals, cyanide, pesticides). Poisons enter the body passively or actively across membranes (ingestion, inhalation, dermal contact).
Venom: Injected via bite or sting (e.g., snakes, spiders, scorpions). Venoms are specifically produced by animals (or sometimes plants) and delivered actively via a wound, bypassing surface barriers. They often contain a complex mixture of enzymes and toxins.
Symptoms of Poisoning
Unexplained recurrent illness, loss of consciousness, or sudden death are red flags. Symptoms are highly variable depending on the substance, dose, and individual.
General indicators: Nausea, vomiting, diarrhea, abdominal pain, altered mental status (confusion, delirium, coma), respiratory distress, cardiac arrhythmias, seizures, skin discoloration.
Diagnostic challenges: Many symptoms mimic common diseases, making diagnosis difficult without a clear history of exposure. Forensic identification is often delayed.
Drug Schedules
Schedule I: No currently accepted medical use; Schedule II-V: Varying medical use and abuse potential. Established by the Controlled Substances Act, this classification dictates how drugs are regulated, prescribed, and researched.
Schedule I: High potential for abuse, no currently accepted medical use (e.g., heroin, LSD, MDMA, cannabis historically).
Schedule II: High potential for abuse, severe psychological or physical dependence, currently accepted medical use (e.g., oxycodone, fentanyl, Adderall, cocaine).
Schedule III: Moderate to low potential for physical dependence, high potential for psychological dependence, currently accepted medical use (e.g., Tylenol with codeine, ketamine, anabolic steroids).
Schedule IV: Low potential for abuse, limited dependence, currently accepted medical use (e.g., benzodiazepines like Xanax, Valium).
Schedule V: Low potential for abuse, limited dependence, currently accepted medical use, often over-the-counter in some preparations (e.g., cough syrups with codeine, Lyrica).
Drug Classifications
Analgesics: Pain relievers (e.g., opioids, NSAIDs). Can cause respiratory depression (opioids), gastrointestinal issues (NSAIDs).
Depressants: Slow down central nervous system (CNS) activity (e.g., alcohol, benzodiazepines, barbiturates). Effects include sedation, decreased coordination, respiratory depression.
Stimulants: Increase CNS activity (e.g., cocaine, amphetamines, caffeine). Effects include increased heart rate, blood pressure, alertness, and paranoia.
Hallucinogens: Alter perception, mood, and thought (e.g., LSD, psilocybin, PCP). Can cause psychosis and flashbacks.
Anesthetics: Induce partial or complete loss of sensation; general anesthetics induce loss of consciousness (e.g., propofol, nitrous oxide). Risks include respiratory depression and cardiovascular effects.
Steroids: Both anabolic (muscle building) and corticosteroids (anti-inflammatory). Abuse of anabolic steroids can lead to liver damage, cardiovascular issues, and mood swings.
Naloxone (Narcan)
Opioid receptor antagonist used for overdose treatment. It rapidly reverses the effects of opioid overdose by competing with opioids for binding to opioid receptors, particularly mu-opioid receptors.
Administered intravenously, intramuscularly, or intranasally. Its life-saving role and increasing availability for first responders and laypersons are crucial. The rapid onset of action is important in emergencies, and multiple doses may be required due to a shorter half-life compared to some opioids.
Blood Alcohol Concentration (BAC)
Calculated based on alcohol consumed and body weight. BAC is the percentage of alcohol in the bloodstream. Factors influencing BAC include sex, age, metabolism rate, medications, and food consumption.
Legal BAC limit: for operating vehicles in most US states for driving under the influence (DUI).
Effects at different BAC levels:
: Mild euphoria, relaxation, slight coordination impairment.
: Impaired judgment, reduced coordination, exaggerated behavior.
: Significant impairment in motor skills, reaction time, judgment.
: Slurred speech, slowed thinking.
: Nausea, vomiting, severe CNS depression, confusion.
and above: Potentially fatal due to respiratory arrest.
Cannabis and Cannabinoids
CBD (cannabidiol) vs. THC (tetrahydrocannabinol). Both are cannabinoids found in the cannabis plant.
THC: The primary psychoactive compound responsible for the "high" associated with cannabis. It acts primarily on receptors in the brain.
CBD: Non-psychoactive and is being studied for its potential therapeutic benefits, including anti-inflammatory, anxiolytic, and anticonvulsant properties. It interacts with various receptors but poorly with and directly.
Psychoactive effects and therapeutic use. Cannabis can cause altered perception, relaxation, impaired memory, and motor skills. Therapeutically, it's used for chronic pain, nausea (chemotherapy), spasticity (MS), and certain seizure disorders, though legality varies.
Inhalants and Their Risks
Solvents and gases, risk of brain damage and death. A diverse group of volatile substances whose fumes are inhaled to achieve a mind-altering effect.
Types: Industrial solvents (toluene, acetone), fuels (gasoline, propane), aerosols (hairspray, spray paint), nitrites (poppers), anesthetic gases (nitrous oxide).
Risks:
Sudden Sniffing Death Syndrome: Caused by cardiac arrhythmia, especially with fluorinated hydrocarbons (aerosols).
Brain damage: Chronic use can lead to irreversible neurological damage, cognitive impairment, and demyelination.
Organ damage: Liver, kidney, heart, and bone marrow damage.
Asphyxiation: Displacement of oxygen in the lungs.
Testing and Evidence Collection
Evidence must be properly documented and analyzed for drugs/chemicals post-exposure. This is crucial in forensic and clinical toxicology.
Collection: Proper chain of custody is essential to maintain the integrity and admissibility of evidence. Blood, urine, hair, tissue samples, gastric contents, and even environmental samples are collected.
Analysis: Techniques include:
Screening tests: Immunoassays (ELISA, EMIT) to detect classes of substances.
Confirmatory tests: Gas Chromatography-Mass Spectrometry (GC-MS), Liquid Chromatography-Mass Spectrometry (LC-MS) for specific identification and quantification. These methods separate and identify individual compounds, providing definitive results.
Interpretation: Involves understanding pharmacokinetics, pharmacodynamics, and potential interferences to correlate findings with observed effects.