NEPAL FORENSIC SOCIETY
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JUSTICE BY FORENSIC SCIENCE
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Source: faculty.ncwc.edu/toconnor/425/425lect14FORENSIC TOXICOLOGY Forensic toxicology is essentially a specialty area of analytical chemistry. Toxicology is the science of adverse effects of chemicals on living organisms. In general, a toxicologist detects and identifies foreign chemicals in the body, with a particular emphasis upon toxic or hazardous substances. A descriptive toxicologist performs toxicity tests to evaluate the risk that exposure poses to humans. A mechanistic toxicologist attempts to determine how substances exert deleterious effects on living organisms. A regulatory toxicologist judges whether or not a substance has low enough risk to justify making it available to the public. A toxin is any material exerting a life threatening effect upon a living organism. Poisons are a subgroup of toxins. Toxic materials exist in many forms (gaseous, liquid, solid, animal, mineral, and vegetable), and may be ingested, inhaled, or absorbed through the skin. Poisons generally enter the body in a single massive dose, or accumulate to a massive dose over time. Toxins work in minute quantities or low levels, requiring sensitive analytical instruments for detection. Some toxins have medicinal value, but many produce irreparable damage. Some toxins have antidotes and others do not. Poisons can be combated by prompt treatment, and most organ damage (except for serious CNS injury) may be repairable. Whereas poisons are somewhat easily identifiable by their symptoms, many toxins tend to disguise or mask themselves. Here's a list of the more common poisons and their symptoms:
The true incidence of poisoning in the United States is unknown. Approximately 2 million cases are voluntarily reported to poison control centers each year, and officially, a rather steady figure of about 700 deaths by poisoning is reported each year. Children under age 6 account for the majority of poisonings reported, but adults account for the majority of deaths by poisoning, most of which is intentional rather than accidental. The following tables show a ranking of the most frequently reported poisonings (left) compared to the most frequent deaths by poisoning (right):
Paracelsus (1493-1541) once said "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy." Although society wants the toxicologist to categorize all chemicals as either safe or toxic, this is not possible. It is not easy to distinguish toxic from nontoxic substances. A key principle in toxicology is the dose-response relationship. There is a graded dose-response relationship in individuals, and a quantal dose-response relationship in the population. The quantal dose-response is the more important one, used to determine the median lethal dose (LDm) and judge what percentage of the population is affected by a dose increase. Quantal is a term meaning "all or none", and comes closest to a classification of whether something is safe or toxic. Chemicals are tested for toxicity and the estimation of LDm using at least two (2) animal species by at least two (2) routes of administration. One of these portals or routes of administration is supposed to be the suspected portal for how human beings are exposed. Most animals die within 14 days, and their symptoms are carefully recorded. Subacute exposure is tested for a period of 90 days. Long-term exposure testing takes 6 months to 2 years. Cancer research goes on for the life of the animal, or in the case of the Ames test, to see if reverse mutation occurs to predict carcinogenic effects. Mathematical extrapolation is used to generalize results from animal testing to human risk incidence. A 0.01% risk in the human population represents 25,000 people in a population of 250 million, and to have valid extrapolation at this level, a minimum of 30,000 animals would have to be tested. Humans are generally more vulnerable than animals, so the calculations are inherently conservative. The toxic effects of substances are not side effects. Side effects are defined as non-deleterious, such as dry mouth, for example. Toxic effects are the undesirable results of a direct effect. They occur in a number of ways, most often produced by a dangerous metabolite of the drug which is activated by an enzyme, light, or oxygen reaction in a process known as biotransformation. Toxic reactions often depend on how metabolites are processed by an individual's body, how proteins build up and bind at effector sites in the body. Some metabolites destroy liver cells, others brain tissue, and still others operate at the DNA level. Toxic reactions are classified as one of three (3) reactions:
If the concentration of toxin doesn't reach a critical level, the effects will usually be reversible. Pharmacological reactions, for example, are of this type. In order to sustain permanent brain damage, dosages must be above a standard critical level. Pathological reactions can be repaired if discovered early enough, but most liver damage occurs over a period of few months to a decade. Genotoxic or carcinogenic effects may take 20-40 years before tumors develop. Most of the time, toxic metabolites are activated by enzymatic transformation, but a few are activated by light. This means that exposure of the skin to sunlight produces a photoallergic reaction or phototoxic reaction within 24 hours. It's important to understand that the target organ of toxicity is not the site where toxin accumulates. Lead poisoning, for example, results in an accumulation of lead in bone marrow, but the toxic effect is the creation of lesions on skin and soft tissue. Carcinogenesis is even more complicated, involving the creation of promotor electrophiles which serve to activate or potentiate the growth of latent tumors given some biological trigger or subsequent environmental attack. Different people, of course, have chemical allergies (as well as food allergies), depending upon the serology of their allergen-antigen history. In such people, toxic reactions take different forms. Other people have what are called idosyncratic reactions, which means they have certain unique genetic triggers. Furthermore, people exposed to multiple toxins can have synergistic reactions, which means that two or more toxins interact at the metabolic level to be greater or less than the effects of the individual toxins. QUALIFICATIONS For certification as a toxicologist, an individual must possess a Ph.D. or doctorate in one of the natural sciences. Undergraduate degrees must also be in these areas (biology or chemistry, usually). Grandfather clauses exist in many states for those lacking the requisite degree level, but who have been working six years or more in the field. Certification is bestowed by the American Board of Forensic Toxicology, and the expert may use the title of "Diplomate" which must be renewed every three years. Board-certified toxicologists will never face difficulties qualifying as an expert witness. State crime laboratories may not have a toxicologist on staff, their functions being performed by a criminalist, a biochemist, a forensic biologist, or other technician. Such personnel would normally possess a Bachelor's or Master's degree. A few states have laws which make toxicological examinations admissible by statute without the necessity for testimony by an expert, the purpose of which is to insulate and protect their crime lab technicians. Other states rely upon their Chief Medical Examiner's office, local hospitals, and forensic pathologists or serologists. Professors are usually not "borrowed" from nearby universities as experts as in the case with forensic serology. Toxicology services vary widely from state-to-state. There are about 120 poison control centers in the United States, 34 of these designated as regional centers. They are coordinated and served by the FDA's Poisoning Surveillance and Epidemiology Branch. Many toxicologists work for the FDA (Food and Drug Administration) which is responsible for regulating drugs, medical devices, cosmetics, acceptable daily intake (ADI) of food additives, and enforcing the Delany Amendment, which says that no cancer-producing substance should be added to our diet in any amount. Other agencies where toxicologists are often found include the EPA (Environmental Protection Agency) which is responsible for regulation of pesticides, toxic chemicals, hazardous wastes, and toxic pollutants in water and air. OSHA (Occupational Safety and Health Administration) also uses toxicologists to determine if chemicals in workplace air is below a threshold limit value (TLV). The Consumer Products Safety Commission regulates all products, typically those sold for use in homes, schools, or recreation, not regulated by the FDA or EPA. A forensic toxicologist is normally presented with preserved samples of body fluids, stomach contents, and organ parts. They will have access to the coroner's report which should contain information on various signs and symptoms as well as other postmortem data. The toxicologist needs a through knowledge of how the body alters or metabolizes drugs because few substances leave the body in the same state as they entered. The substances they work with are often derivatives, which is a term meaning a chemical compound which is prepared from a pure compound in order to be more easily detected by the analytical techniques used. They also divide specimens up into acidic and basic fractions for drug extraction from tissue or fluid. Almost all drugs are either acids or bases (on a pH scale from 0 to 14 with closer to 0 being acids and closer to 14 being bases). Acid drugs are easily extracted with a pH solution of less than 7; base drugs are easily extracted with a pH solution of greater than 7. As an example, most of the barbiturate drugs are acid-soluble; most of the amphetamine drugs are base-soluble. After preliminary acid-base procedures are carried out, and the tissue or fluid sample is now a drug sample, examination continues in two steps: (1) screening tests, and (2) confirmation testing. Screening tests allow the processing of many specimens for a wide range of toxins in a short time. Any positive indications from the screening tests must be verified with a confirmation test. The following are some standard laboratory tests for toxin detection: SCREENING TESTS
CONFIRMATION TESTS
Ordinarily, the toxicologist is not required to render an opinion of whether the toxin levels in the body were enough to cause death. A few toxicologists may do so, but they must have had special training in physiology, and this is usually the province of the forensic pathologist, in any event. Often, the defense will call their own medical experts to dispute a cause of death claim. Physicians are the only ones qualified to render opinions on the physiological effects of toxins, and forensic law allows them to provide their testimony in the form of hypotheticals, even though they do not have personal knowledge of the case. Low-level toxin cases usually become a real battle of the experts. Drug overdoses and alcoholic poisonings will provide most of the work for toxicologists, hence a couple of allied subfields may be drawn upon: (1) a field inhabited by what are called Drug Recognition Experts (DRE); and (2) alcohol intoxication measurement (a subject talked about in a previous lecture). Both are sought-after areas of police training. Another related subfield involves carbon monoxide poisoning, which may involve an automobile engineer or fire safety specialist. The Drug Recognition Expertise evolved out of experiments in California with the LAPD during the 1970s in which police officers were trained to identify and recognize certain types of drugs based upon the impairments and physiological symptoms. The examination that such specially trained police officers conduct goes beyond normal Nystagmus testing and more closely resembles the taking of vital signs by a nurse or paramedic, combined with structured interviewing and observation. DRE's opinions are limited by law to identification of a class or family of drugs, not to a specific drug. Standardized checklists and computer programs exist to make this a growing area of modern drug testing. DRUG TESTING The traditional field testing methods run the gambit of color to crystalline tests, and consist of a variety of names, the controversial Nalline test being the most well-known, which presumably indicates recent use of narcotics. Here's a list of some common drugs and specific tests for them:
Opium is a true narcotic, providing an euphoric escape from reality. It is derived from the milky secretions of the poppy bulb before flowering. In raw form, it turns dark brown and stays moist. The most common type of opiates are:
Marijuana is technically a hallucinogen but has been thrown in with narcotics since Reyna v. State 1968. It tends to make a person lethargic rather than euphoric (an effect like alcohol but without the aggression). It's active ingredient is THC (tetrahydrocannabinol) which is contained mostly in the flower tops and to a lesser extent in stems and seeds. One particular species, Cannabis Sativa, as opposed to other species, e.g. Cannabis Indica, Cannabis Ruderalis, tends to contain more THC (Delta-9-THC) as the main cannabinoid, than the other species, if "species" is the right word since Small & Cronquist's (1976) study found only one single species with two subspecies (Sativa & Indica), each divisible into a cultivated and wild variety. Cannibis Indica has a significant amount of THC as well, along with several other cannabinoids. It should be noted that some experts classify Indica as a subspecies of Sativa, thereby frequently missing an accurate description of Indica's chemical profile. The THC content is heavily affected by the sex of the plant, with female plants generating substantially more resin than their male conterparts. Toward this end, during plant growth, males are generally removed before pollination occurs. The average marijuana cigarette contains only 1% THC while hashish (made from ground flower tops) is 10% THC. Other hallucinogens include:
Cocaine is technically a stimulant, but has been thrown in with narcotics since too many cases to remember. It's a natural alkaloid found in coca leaves (C17 H22 CLNO4). For making what is called freebase or crack, it's melting point needs to be lowered, and this is done by releasing the hydrochloride in it (HCL) through mixing it with a sodium substance like baking soda, adding water, letting it cook slowly, and then letting it cool off. The crystal residue or pellets are called "crack" which is a widely abused drug. Other stimulants range from the least powerful (benzedrine and dexedrine) to the most powerful (methamphetamine). Barbiturates are known by the color of their tablets: Nembutal (yellow jackets); Seconal (reds); Tuinal (Christmas trees); and Amytal (blues). Steroids are another group or family of drugs, and the anabolic ones (that promote muscle growth) exist in about 80 different varieties. So-called designer or "rave" drugs are hallucinogens, mostly, which have been chemically altered in some way to as not to be placed on the controlled substances list. However, under emergency measures, the DEA can put anything on the list they want. Such drugs are: MDMA, XTC, Ice, and Nexus. Here's the controlled substances list and some sample penalties for trafficking:
Quite a few interesting defenses exist to a drug charge. With marijuana, for example, one could raise the "species defense" and then the plant would have to be proved to be Cannibus Sativa. With steroids, one could raise the "roid rage" defense, that their behavior was out of control. A basic defense is that the person was not trying to feel good, but feel better, a "medical necessity" defense. It's unconstitutional to make the status of being an addict a crime in itself (Robinson v. California 1962). Drug charges can also be challenged on scientific grounds, as follows:
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