From HOWDUNNIT: FORENSICS
WHAT IS A POISON?
The terms poison, toxin, and drug are simply different ways of saying the same thing. Though you might think that a poison kills, a toxin harms, and a drug cures, these terms can be used almost interchangeably. The reason is that what can cure can also harm, and what can harm can kill.
Anything and everything can be a poison. The basic definition of a poison is any substance that, if taken in sufficient quantities, causes a harmful or deadly reaction. The key here is the phrase “sufficient quantities.”
The toxicity of any substance depends on how much enters the body and over what time period it does so. For example, you probably know that arsenic is a poison, but did you know that you likely have arsenic in your body right now? If you’re a smoker, you have more than a little bit. Same with mercury and cyanide. These substances are in the environment—you can’t avoid them. But they are in such small quantities that they cause no real harm. However, take enough of any of them and they become deadly.
The same can be said for the medications your doctor gives you to treat medical problems. Consider the heart drug digitalis, which comes from the foxglove plant and has been used for over a hundred years to treat heart failure and many types of abnormal heart rhythms. It is also a deadly poison. Too much can lead to nausea, vomiting, and death from dangerous changes in the rhythm of the heart. It’s ironic that it can treat some abnormal heart rhythms while at the same time can cause other more deadly rhythms. It’s all in the dosage. The right dose is medication; the wrong dose is poison.
Toxicology is a marriage of chemistry and physiology, since it deals with chemical substances (chemistry) and how these substances alter or harm living organisms (physiology), particularly humans.
A forensic toxicologist deals with the legal aspects of toxicology. His job is to find and analyze toxic substances in biological materials taken from both the living and the dead, and to determine the physiological, psychological, and behavioral effects on the individual in question. For example, he might be asked to assess the state of inebriation of an automobile accident victim or to determine if someone died from a poison or if the presence of a drug contributed to the victim’s death. This is often more difficult than it sounds.
When the toxicologist investigates a possible poisoning death, he must answer three basic questions:
Was the death due to a poison?
What was the poison used?
Was the intake of the poison accidental, suicidal, or homicidal?
During his analysis, the modern forensic toxicologist sometimes searches for the poison itself, while other times he searches for the poison’s breakdown products. This brings up the concept of biotransformation, which is the conversion or transformation of a chemical into another chemical by the body. We also call this metabolism and the new product produced a metabolite. This process is simply the body destroying or breaking down chemicals and excreting them from the body. This is why you must take most medications each day. The medication is designed to treat some medical problem, and indeed it may do that. But, to the body, the drug is also a foreign toxin and as such must be metabolized and excreted. So, you have to take another dose day after day to keep the blood level of the medication in the therapeutic level.
The metabolism of a drug or toxin typically deactivates the chemical and prepares it for elimination from the body, usually by way of the kidneys. For example, many chemicals are not soluble in water, which means they aren’t soluble in urine, either. The body gets around this by metabolizing (biotransforming) the chemical in such a way that it becomes a new chemical (metabolite) that is water soluble. The metabolite can then be filtered through the kidney, into the urine, and out of the body.
Most metabolites are inactive in that they possess no biological activity and are inert as far as the body is concerned. Other metabolites are active and may have biological properties that are weaker or stronger than the original compound. They may even behave quite differently from the parent compound. For example, cocaine is metabolized into three metabolites: nor-cocaine, which possesses active properties, and benzoylecgonine and methy-lecgonine, which are inert.
Another example is heroin, which is made from morphine. When heroin is injected into the bloodstream it is immediately converted back into morphine— the chemical that gives the user the “high.”
Since both cocaine and heroin are metabolized to new compounds very quickly, testing for either would be useless. Instead, the toxicologist tests for the presence of cocaine or heroin by searching for their metabolites. Finding them proves that the parent drug was present.
One of the reasons poisoning has been such a popular means for homicide for so many years is that most poisons cause no visible changes in the body, either in the living person or at autopsy. In the days before toxicology labs existed, the poisoner “got away with it” more often than not. After all, if there were no obvious reason for the death, it must have been natural. Since the true cause of death could not be determined, no one could be held responsible.
Of course, some toxins do leave behind visible signs, many of which have been known for years. Corrosive poisons such as acids and lye cause severe damage to the mouth, esophagus, and stomach if they are ingested. Poisonous mushrooms and chlorinated hydrocarbons such a carbon tetra-chloride, which for years was used in many carpet cleaners, may cause fatty degeneration of the liver. Cyanide and carbon monoxide cause a cherry-red appearance to the blood and tissues and lead to pinkish lividity. Metallic poisons such as arsenic, mercury, and lead cause characteristic changes in the gastrointestinal tract and the liver.
But this isn’t the norm. Most poisons work their mischief within the cells of the body and leave behind no visible footprints. This means the ME does not of- ten see visible evidence of toxins at autopsy or on the microscopic slides he pre- pares from the body’s tissues. Instead he collects fluids and tissues from the body and these are analyzed for the presence or absence of toxins by the toxicologist.
Since toxins rarely leave behind visible clues, the ME and the toxicologist must perform specialized tests to reveal their presence. These examinations require various body fluids and tissues, and which ones are used depends on the particular drug in question and the situation under which it is tested. The goal of testing is to establish whether a particular drug is the cause of death, or a contributing factor in the death, or that it played no role at all.
The best places to obtain samples for testing are the locations where the chemicals entered the body, where they concentrate within the body, and along the routes of elimination. This means that blood, stomach contents, and the tissues around injection sites may possess high concentrations of the drug. Analysis of liver, brain, and other tissues may reveal where the drug or its metabolites have accumulated. Finally, urine testing may indicate where the drug and its metabolites are concentrated for final elimination.
During an autopsy, blood, urine, stomach contents, bile, vitreous eye fluid, and tissue samples from the liver, kidneys, muscles, and brain are obtained. If an inhaled toxin is suspected, lung tissue is also taken, and if a chronic heavy metal (arsenic, lead, etc.) poisoning is a consideration, hair samples are taken (the reason is discussed later in this chapter).
It is important that the samples be collected before embalming, since this procedure can interfere with subsequent testing or, as in the case of cyanide, completely destroy the toxin. Also, since embalming fluids may contain methanol and other alcohols, accurate alcohol testing is difficult if not impossible after this procedure.
Let’s look at the most common fluids and tissues obtained by the ME or toxicologist.
BLOOD: Blood is by far the toxicologist’s most useful substance since, with modern toxicological techniques, most drugs and their major metabolites can be found in the blood.
Blood is easily sampled from the living with a simple venipuncture (using a needle to draw blood from a vein, usually in the arm). During an autopsy, blood is typically obtained from several areas. The aorta (the main artery that carries blood out of the heart and to the body), both sides of the heart, and the femoral artery (in the groin area) are common locations. The samples are then placed into glass tubes and sent to the laboratory for testing. If the blood is to be analyzed for volatile chemicals, a sample is placed in a Teflon-lined screw-cap tube. Rubber stoppers should be avoided since they can react with the gases or may also allow them to escape.
The toxicologist not only determines if the toxin is present, but also at- tempts to assess its level in the body. This is important since low levels may be of no consequence, higher doses may have toxic effects and may have contributed to the person’s actions or played a role in his death, and even higher levels may have been the actual cause of death. Blood is most often the best substance for this assessment.
Concentrations of medicines and drugs within the blood correlate well with levels of intoxication as well as with levels that are potentially lethal. Bioavailability is the amount of the drug that is available for biological activity. Since drugs work on the cellular level, bioavailability means the concentration of the drug that reaches the cells of the body. For most chemicals, the blood level correlates with the cellular level.
For example, the level of alcohol in the blood correlates extremely well with a person’s degree of intoxication, and the lethal level of alcohol in the blood is well known. This knowledge means that the ME can use a blood alcohol level to accurately estimate a person’s degree of intoxication in an automobile accident or whether the fraternity boy died from his binge drinking or from some other cause.
Or let’s say that an individual takes a handful of sedative (sleeping) pills in a suicide attempt. In order for the pills to “work” they must be digested, absorbed into the bloodstream, and carried to the cells of the brain, where the concentration of the drug in the brain cells determines the degree of “poison- ing.” And since the amount of the drug in the blood is an accurate reflection of the amount within the brain cells, testing the blood is like testing the cells.
But, if absorption of the pills from the stomach doesn’t occur, the person will have no effect from the drug. The amount of the drug present in the stomach is irrelevant since it is not available to the brain cells. So, a victim found with undigested pills in his stomach and a very low blood level of the drug did not die from a drug overdose and must have died from something else.
URINE: Easily sampled with a cup and a trip to the restroom, urine testing is a staple of workplace drug testing. It is also useful at autopsy, where it is re- moved by way of a needle inserted into the bladder. Because the kidneys are one of the body’s major drug and toxin elimination routes, toxins are often found in greater concentrations in the urine than in the blood. However, one problem is that the correlation between urine concentration and drug effects in the body is often poor at best. All the urine level can tell the ME is that the drug had been in the blood at some earlier time. It can’t tell him if the drug was exerting any effect on the individual at the time of its collection, or in the case of a corpse, the time of death.
Also, estimating blood concentrations from urine concentrations is impossible. The concentration of any drug in the urine depends on how much urine is produced. If the person has ingested a great deal of water, the urine and any chemicals it contains will be more diluted (watered down) than if the person is “dry.” In addition, alcohol and drugs known as diuretics increase urine volume and decrease the urine concentration of any drugs or metabolites present. Many athletes use diuretics in an attempt to mask or dilute performance-enhancing drugs.
STOMACH CONTENTS: The stomach contents are removed from survivors of drug ingestions by way of a gastric tube, which is typically passed through the nose and into the stomach. The contents are then lavaged (washed) from the stomach and tested for the presence of drugs or poisons.
At autopsy, the stomach contents are similarly tested. Obtaining the stomach contents in any case where poison or drug ingestion is suspected is critical. However, as mentioned earlier, the concentration of any drug in the stomach does not correlate with its blood level and thus its effects on the person. It does, however, show that the drug was ingested and in what quantity.
LIVER: The liver is the center of most drug and toxin metabolism. Testing the liver tissue and the bile it produces can often reveal the drug or its metabolites. Many drugs, particularly opiates, tend to concentrate in the liver and the bile, so they can often be found in these tissues when the blood shows no traces. Where the liver might reflect levels of a drug during the hours before death, the bile may indicate what drugs were in the system over the past three to four days. Neither is very accurate, however.
VITREOUS HUMOR: The vitreous humor is the liquid within the eyeball. It is fairly resistance to putrefaction (decay) and in severely decomposed corpses it may be the only remaining fluid. Testing may uncover the presence of certain drugs.
The vitreous humor is an aqueous (water-like) fluid, which means that chemicals that are water soluble will dissolve in it. It also maintains equilibrium with the blood, so that any water-soluble chemical in the blood will also be found in the vitreous. The important thing is that the level in the vitreous lags behind that of the blood by about one to two hours. This means that test- ing the vitreous will reflect the concentration of the toxin in the blood one to two hours earlier.
HAIR: Hair absorbs certain heavy metal (arsenic, lead, and others) toxins and some other drugs. It has the unique ability to give an intoxication timeline for many of these substances. This will be discussed in greater detail later in this chapter.
INSECTS: In cases where the body is severely decomposed and insects have been feeding on the corpse, the maggots can be tested for drugs. And since some insects tend to concentrate certain drugs in their tissues, they may supply information that the drug was at least present in the victim.
TOXICOLOGY AND THE CAUSE AND MANNER OF DEATH
In the remote past, it was very difficult to determine why someone died, and virtually impossible to ascertain whether a poison was involved. Though modern toxicological techniques have changed things greatly, determining that poisoning was the cause of death remains one of the most difficult tasks facing the forensic toxicologist.
The ultimate responsibility for determining the cause and manner of death lies with the ME or the coroner. To do this he will rely on the circumstances of the death, the crime scene reconstruction, the autopsy findings, and the laboratory results, including the toxicology findings.
In cases where a potentially deadly poison is involved, the toxicologist must uncover the toxin, determine its concentration within the victim, and then give his opinion as to whether this level of this drug was likely lethal. To accomplish this he must consider a number of factors.
The lethal level for many drugs is extremely variable from person to per- son. Age, sex, body size and weight, the presence of other drugs or medications, the state of overall health, and the presence of other diseases impact a given person’s tolerance to some drugs.
For example, a frequent and heavy drinker can tolerate much higher blood alcohol levels than could someone who never drank. A heavy drinker might appear completely sober at a level that would render the normal person unconscious.
Similarly, hardcore heroin addicts routinely inject doses of heroin and attain drug blood levels that would kill the average person in a matter of minutes.
In addition, some drugs are more dangerous to individuals with certain medical problems. The use of amphetamines poses a much greater risk for someone with heart disease or high blood pressure than it would for someone in good health. In this circumstance, a blood level of amphetamines that would not harm the average person could prove lethal for a person with these diseases.
So, it’s not straightforward. When the ME attempts to determine the cause of death in the presence of drugs or toxins, he must consider all these factors. In the absence of other possible causes of death, and with the presence of significant levels of a potentially harmful drug, he might conclude the drug was the proximate cause of death or at least a contributing factor.
Remember that the manners of death are natural, accidental, suicidal, homicidal, and the extra classification of undetermined. Drugs and poisons can be the direct cause or at least a contributing factor in any of these.
NATURAL: A person can die of natural causes even if drugs are involved in the mechanism of death. What if a man with significant coronary artery disease (CAD) took an amphetamine or snorted a few lines of cocaine? Coronary artery disease is a very common disease in which the coronary arteries that supply blood to the heart are plugged with cholesterol plaque.
Amphetamines and cocaine are drugs that increase the heart rate and the blood pressure, both of which increase the need for blood supply to the harder working heart muscle. In addition, these drugs can cause the coronary arteries to spasm (squeeze shut), which greatly decreases the blood supply to the heart muscle. Basically, the supply of blood is reduced at a time when the need is increased, so that the person loses both sides of the supply and demand equation. The victim could suffer a heart attack (actual death of a portion of the heart muscle due to lack of adequate blood supply) or a cardiac arrhythmia (a dangerous change in heart rhythm). Either of these could kill the victim. The cause of death would be a heart attack or a cardiac arrhythmia, events that he would be prone to due to his CAD. But, the amphetamine or cocaine would be a contributory factor. This circumstance is common.
When the ME and the toxicologist confront this situation, they must assess the extent of the victim’s heart disease, the amount of the drug in the body, and whether a heart attack actually occurred. If the amount of drug is low and the victim had severely diseased coronary arteries, they might conclude that the death was natural and that the drug was only a minor contributing factor. On the other hand, if his CAD was mild and the level of drug in his body was high, they might favor an accidental drug death.
But, what if the victim intentionally took a large amount of cocaine, or what if the amphetamines were given to him without his knowledge? The manner of death would then be a suicide or a homicide, respectively. The important point is that the autopsy and lab results would be the same in each circumstance. The ME would need to rely on witness statements and the results of the police investigation to sort this out. And even with this information, the picture might simply be too muddy for the ME to determine the manner of death, and it might be classified as undetermined.
ACCIDENTAL: Most accidental poisonings occur at home and often involve children. Curious by nature, children will eat or drink almost anything: prescription drugs, pesticides, household cleaners, paint thinners, weed killers, snail bait, you name it. In adults, accidental poisoning most often occurs because some product is mislabeled, usually because it has been placed in a container other than its original one. This may be in the form of medications dumped into another bottle, some toxic liquid placed in an empty liquor bottle, or the white powders of cyanide or arsenic stored in a container where they could be confused with sugar or salt.
In other situations, the death might be the result of a dosage miscalculation. Addicts often miscalculate the amount of heroin or amphetamine they are taking and die from this error. The fact that street drugs have poor quality control only adds to this problem. How much heroin is actually in the bag the addict just bought? It may be less or many times more than the bag he purchased yesterday. If the latter is the case and he injects the same dose as he did yesterday, he could easily die from an overdose.
Similarly, some people believe that if one dose of a drug is good, then two must be better. This is a dangerous assumption. Digitalis is a common cardiac medication. Sometimes a patient will decide on his own to double his dose. All is well for a couple of weeks, but as the medicine accumulates within his body, he becomes ill and can die.
Another factor in accidental drug deaths is the mixing of drugs. Alcohol taken with a sedative is notorious for causing death. Addicts often mix cocaine with amphetamines, or heroin with tranquilizers, or just about any combination imaginable, often with tragic results.
SUICIDAL: Drugs are a commonly involved in suicides. Sedatives or sleeping
pills, narcotics, alcohol, and carbon monoxide (see Chapter Eight: Asphyxia, “Toxic Gases”) are commonly used. Often the victim takes multiple drugs, basically whatever is in the medicine cabinet. This presents a difficult problem for the toxicologist. He must analyze the stomach contents, blood, urine, and tis- sues, and hopefully determine the level of each drug and assess the contribution of each to the victim’s death. He may find that one particularly toxic drug was present in large amounts and that it was the cause of death. Or he might find that a certain combination of drugs was the cause.
The ME uses these findings in conjunction with information from the au- topsy and from investigating officers to assess the manner of death. The find- ing of multiple drugs in the victim’s system doesn’t necessarily mean that he took them on purpose. It could have been an accidental overdose driven by the need for relief of physical or psychological pain, or someone else could have surreptitiously slipped the drugs into his food or drink, which would be a homicide.
HOMICIDAL: Though homicidal poisoning was common from antiquity to the twentieth century, it is uncommon today.
As with accidental and suicidal poisonings, homicidal poisonings occur most often at home. This means that the killer must possess knowledge of the victim’s habits and have access to his food, drink, and medications. This knowledge is critical in the homicidal administration of a toxin. It is also important in solving the crime. When the toxicologist determines that the victim was poisoned, the police focus on anyone who had access to the victim.