Lecture 14: Forensic toxicology Flashcards
What is toxicology?
Study of the adverse effects of chemicals (including drugs) on living systems and the means to prevent or ameliorate such effects.
What is forensic toxicology?
The application of the scientific study of poisons/intoxicants to questions raised in judicial proceedings
Workplace for forensic toxicologists
> Police units
Medical facilities
Regulatory bodies
Research institution
Educational institution
Private laboratories
Forensic toxicology: subdisciplines
> Postmortem toxicology (investigation of death)
Behavioural / Human Performance
- Driving under the influence alcohol / drugs
- Drug-facilitated sexual assaults
- Doping Control
Workplace drug testing
Environmental, industrial and public health legislation.
Work for the Police and criminal courts.
Key responsibilities
> Conduct toxicology analysis
Report and document
Consulting and testifying in court
R&D
What are poisons?
Any substance, chemical, physical or biological that is harmful to a biological (living) system.
Most frequent occurrences of poisonings
> Most cases result from social and economic stress or mental disorders.
A minority results from illicit substance abuse.
Substances administered against will e.g. facilitate robbery /sexual abuse (e.g. Rohypnol)
Unintentional / accidental.
Toxicological investigations
> Establish poisoning as cause of death.
Investigate unlawful poisoning by a third party.
Establish the presence of substances that may affect a person’s behaviour/ judgement.
Detect performance enhancing drugs.
Detect non-compliance with for work-place policies etc.
Provide evidence for allowing parental access, if history of drug abuse
Analytical checking of statements
Role of the pathologist
> Perform medico-legal autopsies to establish the cause of death; Issue Death Certificate
Suspicious deaths: attend locus
Estimate time of death
Removal of specimens to assist in the investigation.
Prepare report; precognition; court testimony.
Importance of case notes
> Recent history of patient / deceased
Signs and symptoms on admission / death which may suggest poisoning
Medicaments and other materials found near the patient/body (scene)
- Empty tablet containers etc.
Laboratory investigation result (biomedical and toxicological test)
Post-mortem examinations
Chain of custody
A process that tracks the movement of evidence through its collection, safeguarding, and analysis lifecycle by documenting each person who handled the evidence, the date/time it was collected or transferred, and the purpose for the transfer.
Maintaining chain of custody
> Demonstrate validity of test specimens
Chronological disposition and condition of specimens from the time of collection to time of disposal.
Collection: What specimen is, time and date, by whom, tamper evident tape.
Ensure integrity and security of specimens.
UK Government Legislation: Misuse of Drugs Act (1971)
States that it is an offence to:
> Possess a controlled substance unlawfully.
> Possess a controlled substance with intent to supply.
> Supply or offer to supply a controlled drug (even if it is given away for free).
> Allow a house, flat or office to be used by people taking drugs.
> Serious punishment
- Possession with intent to supply = life imprisonment
> Many also controlled by:
- Medicines Act 1968
- Psychoactive Substance Act 2016
Spectrum of drug use, mis-use and abuse
The 6 main classes of mis-used drugs are :
1. Opiates (morphine, heroin, methadone, dihydrocodeine)
2. Depressants (alcohol, barbiturates)
3. Minor tranquilisers (benzodiazepines, e.g. Diazepam (Valium), Temazepam)
4. Stimulants (cocaine, amphetamines, Ecstasy, ADAM, EVE, ICE)
5. Hallucinogens (LSD, magic mushrooms, mescaline)
6. Others (cannabis, nicotine, volatile solvents)
Types of poisons and poisonings
> Anions: cyanide, fluoride, nitrate, oxolate.
Corrosives: sulphuric acid, sodium hydroxide.
Gases and volatiles: ethanol, products of combustion, solvents.
Metals and metalloids: Iron, lead, arsenic.
Toxins: plant, animal, bacterial, fungi.
Pesticides: organophosphates, herbicides.
Prescription & illicit drugs.
Household chemicals: cleaning products, toiletries, hair products etc.
Exposure to toxicants: acute exposure
Contact with a substance that occurs once for only a short time (up to 14 days)
Exposure to toxicants: Chronic exposure
Contact with a substance that occurs over a long time (more than 1 year)
General symptoms of poisonings
> Neurological: CNS depression, CNS stimulation
- Glasgow coma score.
Respiratory.
Cardiovascular: Dysrythmia, hypotension / hypertension.
Ocular: miosis (constriction), mydriasis (dilation), Nystagmus (“jerky”)
Mouth: Damage, salivation, odour, dysphagia.
GIT : vomiting, diarrhoea
Drugs of abuse
> ‘Any substance used for an alternative purpose than that intended’.
‘Any substance the possession and supply of which is restricted by law’.
Most fall within a few pharmacological groups:
- CNS stimulants, narcotic analgesics, hallucinogens and hypnotics
Most prevalent = plant derived/ semisynthetic
Future - fully synthetic? Fentanyl opioid
Illicit drugs
> Illicit drugs are highly addictive substances
They are illegal to sell, make, and use.
Variable sources: pharmaceutical drugs, plant-based drugs, and synthetic drugs.
Illicit drugs are not used for medical purposes and are illegal to use in these settings.
Most drug misuse deaths are accidental poisonings
> Drug misuse deaths from mental and behavioural disorders (only 5 to 6% ).
- Deaths are due to drug dependence or abuse, but they may involve an acute overdose of drugs similar to an accidental poisoning.
Drug-misuse deaths which are suicides = intentional self-poisoning or poisoning of undetermined intent.
- Rate higher in females (28%, 175 deaths) than males (11%).
- 80% of female drug misuse suicides involve an overdose of an opiate drug (heroin, morphine, tramadol and codeine); some involve drugs such as zopiclone, benzodiazepines and barbiturates.
Toxicological screening techniques
> Aim = confirm and quantify chemical.
Choice depends upon:
- Analytical sensitivity
- Analytical specificity
- Need to know amount present (Qualitative vs. Quantitative)
Various Techniques:
- Immunoassays.
- Spot colour tests – limited specificity, depends upon functional group.
- Thin-layer Chromatography (TLC).
- Gas chromatography (GC) – separates chemicals based on volatility.
- High Performance Liquid Chromatography (HPLC).
- Mass Spectrometry (MS) - identify chemicals based upon their mass – to –charge (m/z) ratio.
Appropriate sample.
Steps to analysis
> Separation of poison and metabolites from biological material
Identification
Confirmation of identity
Quantification/ Concentration
Interpretation
General Schematic of a Toxicological screen
> Choice of sample
Sample preparation
Analysis
Processing data and workflows
Data re-use
