Forensic toxicology

DEFINITION: Application of the knowledge of poisons to the identification of cases of homicide, suicide, accidents, and drug abuse for legal purposes.

SIGNIFICANCE: Forensic toxicologists provide information for law-enforcement investigators by determining the substances involved in deaths caused by poisoning, whether accidental, homicidal, or suicidal. Toxicologists also determine the amounts of toxic substances present in poisoning cases, thus helping investigators to distinguish cases of accidental poisoning from cases of intentional homicidal poisoning.

Forensic toxicology plays the important role of linking specific chemicals with homicides, suicides, and alcohol- and drug-related deaths. Most homicidal and suicidal poisonings involve single, large doses of toxic substances (accidental and suicidal poisoning deaths include accidental and intentional deaths caused by drug abuse). Many job-related poisonings, in contrast, result from chronic exposure to low concentrations of poisons; in such cases, those exposed may have no apparent symptoms for a long time after exposure begins. In cases of suspected poisoning, forensic toxicologists use chemical and biological techniques to analyze samples of the bodily fluids and tissues of victims for the presence of poisons.

According to a 2021 report from the National Forensic Laboratory Information System (NFLIS), toxicology laboratories in the United States handled more than 28 million cases during 2019. The NFLIS reported that 204 out of 281 laboratories responded to the organization’s survey.

Poisons

Poisons are substances that, when introduced into the body, cause disturbances of normal body functions, injury, disease, or death. Chemical poisons are grouped as supertoxic (this group includes botulinum toxin), extremely toxic (this group includes the most toxic dioxin, known as TCDD), highly toxic (this group includes nicotine), and moderately toxic (this group includes alcohol). Poisons can enter the body through ingestion of contaminated foods or liquids, through inhalation, or through contact with skin and eyes. Knowledge of the route of entry of a poison into the body can help forensic scientists to determine when an individual was poisoned. The dosage (dose multiplied by the duration of intake) of the poison determines the poisoning.

Certain poisons can be more toxic to particular persons because of specific genetic and physiological traits, including weight, health, gender, and developmental maturity. Conditions surrounding the victim, such as activity, crowding, and environment (temperature, humidity, barometric pressure), can also affect the manifestation of poisoning. After entering the body, any poison is diluted by water in the blood and body tissues.

Signs and Symptoms of Poisoning

The analytical chemistry techniques used in forensic laboratories can detect minute amounts of chemical poisons and their alteration products in postmortem materials when there is a suspicion that chemicals have played a role in murders, suicides, or accidents (traffic and workplace). Forensic toxicologists must have extensive knowledge of deadly and slow-acting poisons—their chemistry and their biological actions—and expertise in identifying the signs and symptoms of poisoning caused by specific substances. Such practitioners have broad educational backgrounds in biology, chemistry, and psychology. The responsibility for establishing cause of death in a given case rests with the medical examiner, coroner, or pathologist, but success in arriving at the correct conclusion depends on the combined expertise of the pathologist and the toxicologist. The cause of death cannot be proved without a toxicological analysis, which establishes and confirms the presence or absence of specific poisons in the biological specimens of the deceased.

The suspicion of poisoning or intoxication of the victim is based on the signs and symptoms observed and recorded. Knowledge of the common symptoms of particular kinds of poisoning enables forensic toxicologists to test for specific poisons; in some cases, this knowledge can be helpful in protecting the lives of victims by pointing to correct treatment.

The signs and symptoms of poisoning are identical whether the exposure to the poison is accidental, suicidal, or homicidal. Investigating police officers at death scenes where poisoning is suspected ascertain whether the victims vomited and whether the victims suffered convulsions, diarrhea, or paralysis before they died. Along with this information, they also record any information available from witnesses regarding the victims’ breathing, pupil size, skin color, and difficulty in swallowing before death. The investigating officers then attempt to compile detailed histories of the victims’ activities during the three days preceding their deaths. These histories include information on any medications taken by the victims and the sources of those medications and on any meals eaten by the victims and when and where they were eaten. Medical histories of the victims are also investigated.

Chronic or even acute nonfatal exposures to poisons can cause some observable symptoms. Early warning signs of poisoning include headache, nausea, dizziness, discomfort in the epigastric region, gastrointestinal upset, and excessive fatigue. These symptoms occur without fever after the entry of the poison into the body and usually disappear with the cessation of exposure to the poison.

Homicides, Suicides, and Accidental Poisonings

In cases of poisoning in which homicide is suspected, crime scene investigators collect physical evidence in the same manner they would if the cases were clearly homicides. Sometimes, deaths involving poisonings can be confusing because of the synergistic interaction of several poisons; for example, the ingestion of alcohol with amphetamines can be fatal. Identifying the signs of poisoning enables forensic toxicologists to decide what specimens to collect from bodies (tissues, fluids, organs) and what laboratory tests to run on those specimens.

In the United States, poisons are involved in 26 percent of suicidal deaths, and law-enforcement investigators must be aware of the signs of the use of poisons in such deaths. About 75 percent of those who commit suicide using poisons take some form of barbiturates, 17 percent poison themselves with carbon monoxide from automobile exhaust, and the rest use various other kinds of poisons, such as arsenic or strychnine. Alcoholics and drug abusers are more susceptible to suicide than are persons who do not abuse such substances. In cases of suicide, investigators examine the scenes for suicide notes and interview any witnesses as well as all persons who were close to the deceased.

Poisons are involved in only 3 percent of accidental deaths in the United States. Of these deaths, 20 percent are connected with barbiturates and 20 percent with opiates. The victims of some 65 percent of accidental poisonings in the United States are children under the age of six; another 21 percent are children between the ages of seven and fifteen; the remainder are adults. Oral medications, especially painkillers, account for 90 percent of accidental poisoning deaths. The rest are caused by cleaning and polishing agents, turpentine, petroleum products, pesticides, and plants.

Specimen Collection and Initial Testing

In cases of suspicious deaths, pathologists collect at autopsy the specimens that will be subjected to toxicological analysis. In general, the specimens collected from a body for this purpose include urine, blood, stomach and intestinal contents, bile, bone, fat, tissues of the brain and liver, and one whole kidney. When such specimens cannot be collected—for example, when a body has been badly burned or only skeletal remains are available—bone marrow, hair, muscle, or vitreous humor may provide specimens for toxicologists to analyze for the presence of poisons. In cases of severely decomposed bodies, maggots (which feed on dead flesh) found on the corpses may be collected for analysis. In every case, the collection, handling, and storage of the specimens and their transportation to the forensic toxicology lab are thoroughly documented for court presentation, as are the toxicologist’s analysis and the resultant reports.

At the forensic toxicology lab, the analytical toxicologist carefully chooses the test methods to apply to the specimens and conducts repeated procedures to ensure maximum accuracy. The analysis of specimens takes into account the chemical changes that take place during the decomposition of the cadaver. The tests selected to determine the presence of causative chemicals in specimens depend on the suspected agent. For example, when substance abuse is suspected, urine samples are analyzed. The initial screening tests include common tests (such as tests of urine color and pH) and immunoassays conducted using high-speed, large-throughput analyzers for drugs and their metabolites in urine.

Chemical Analysis of Specimens

Forensic toxicologists use sophisticated techniques and equipment to detect the presence of minute amounts of chemicals and their metabolites in the specimens they examine. These techniques and equipment are capable of analyzing specimens for the presence of such diverse poisons as prescription drugs (including analgesics, antidepressants, hypnotics, and tranquilizers), drugs of abuse (such as hallucinogens, antidepressants, narcotics, and stimulants), and many different commercial products (including antifreeze, pesticides, and radioactive substances).

The qualitative and quantitative techniques that forensic toxicologists use include various chromatographic methods—such as column, thin-layer, gas, and liquid chromatography—as well as spectrophotometry and spectrometry. Final identification of the chemical structure of a substance is made using gas chromatography coupled with mass spectrometry (GC-MS) and liquid chromatography with mass spectrometry (LC-MS). The interpretation of the results of an analysis takes into consideration the case history, the site of the specimen collection, and postmortem changes.

Forensic Testing for Drugs of Abuse

In the United States, many categories of employers subject employees to mandatory urine testing to screen for the presence of illicit substances; these include federal and state agencies, the military, public utilities, employers related to the criminal justice system, and employers in the transportation and nuclear industries. Two national agencies regulate the laboratories that are involved in drug urine testing: the Substance Abuse and Mental Health Services Administration (part of the US Department of Health and Human Services), which has established mandatory guidelines for workplace drug testing; and the College of American Pathologists, which has established the Forensic Urine Drug Testing Accreditation Program. Specific regulations are in place for every step of the process, from specimen collection through the reporting of the analysis results.

Urine testing is performed for a limited number of drugs (marijuana metabolites, cocaine metabolites, morphine and codeine opiates, phencyclidine, and amphetamines and methamphetamine). Initial screening analysis uses immunoassays on high-speed, large-throughput analyzers. Positive samples are then processed through GC-MS for confirmation of the drug structure.

In cases of fatal accidents—motor vehicle accidents, workplace accidents, and others—high concentrations of alcohol, drugs, or both are often found in the bodies of the persons involved. Toxicological analyses for alcohol and other drugs are performed on breath, blood, and other specimens taken from persons suspected of driving under the influence. Cocaine, benzodiazepines, marijuana, and phencycladine (PCP) are the drugs most commonly related to traffic accidents. The analytical methods used by forensic toxicologists can detect minute concentrations of these drugs.

Bibliography

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Hayes, A. Wallace, ed. Principles and Methods of Toxicology. 5th ed. Philadelphia: Taylor, 2007. Print.

Klaassen, Curtis D., ed. Casarett and Doull’s Toxicology: The Basic Science of Poisons. 7th ed. New York: McGraw, 2007. Print.

Levine, Barry, ed. Principles of Forensic Toxicology. 2nd ed., rev. Washington, DC: Amer. Assn. for Clinical Chemistry, 2006. Print.

Marrs, Timothy C., Robert L. Maynard, and Frederick R. Sidell, eds. Chemical Warfare Agents: Toxicology and Treatment. 2nd ed. Hoboken: Wiley, 2007. Print.

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Trestrail, John Harris, III. Criminal Poisoning: Investigational Guide for Law Enforcement, Toxicologists, Forensic Scientists, and Attorneys. 2nd ed. Totowa: Humana, 2007. Print.

“2021 Toxicology Laboratory Survey Report.” National Forensic Laboratory Information System, August 2022, www.nflis.deadiversion.usdoj.gov/nflisdata/docs/NFLIS‗2021ToxicologyLabSurvey.pdf. Accessed 14 Aug. 2024.