Forensic Toxicology

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Forensic Toxicology?An examination of all aspects of toxicity that may have legal implications.This definition allows us to distinguish this field from other fields such as pharmacology, or occupational toxicology which deals with toxicity of chemicals in the workplace.

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What is a lethal Dose?It is impossible and unwise for a pathologist to comment about lethal doses.Although there is many tables assigning numeric value to lethal doses, the variables in many cases are too great to make these types of predictions.

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What is a lethal Dose? (2)Knowledgeable persons including forensic hobbyist, defense attorneys and so on often bring to light the idea of LD50 LD50 is the idea that is used by pharmacologist and companies in a statistical sense in animal experiments. LD50 = Over a large number of tests, it provides a toxic level at which half the animals will be expected to die.

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Autopsy and PoisoningSuspected poisoning can be the most difficult because:The pathologist will have to base his results on findings that are almost always inconclusive.Debate about the actual cause of death is almost insured at trial.

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Collection of SamplesCare must be taken in procedure because speculation is inherent to the capabilities of the pathologist.The shorter the delay between death and collection of samples the better.Many toxins will be broken down naturally by decay and cellular autolysis.

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Info give to toxicology labsPersonal data of deceased (age, sex, occupation).Brief details of symptomsPost mortem intervalName and number of pathologistList of all samples providedNature of preservatives usedAny delays in transporting of samplesAny special risks associated with samples being handled.In cases of homicide, a proper chain of custody must be observed.

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Areas of Application (3)Postmortem drug testing this is used in death investigations to establish whether or not drugs were the cause or contributing factor in death.Workplace drug testing this consist of evaluation of biofluids, primarily urine and blood from employees or job applicants for drug content.Evaluation of Contraband this is applied when evidence seized is being linked to the illicit drug trade. Police agencies needed labs that could link materials to illegal drug trafficking and manufacture.

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Specimen CollectionBlood the most satisfactory method for obtaining samples is from venous puncture of the femoral vein.An alternate site to collect venous blood is to incise the jugular.this is typically done after the neck has been exposed under the sub-clavicular incision. The correlation between blood concentration and effects of the drug is very high in blood testing.

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Specimen CollectionUrine in pre-employment screening urine is most often used to test for presence of drugs.This is typically because of the types of test that can be run and the cost effectiveness of the testing.One draw back to urine is the correlation between drug concentration in urine and drug effects is usually poor.Urine should also be collected in post mortem investigations since some toxins show in higher levels in urine.At autopsy, a catheter or suprapubic puncture will suffice.

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Specimen CollectionBile this can be useful in cases where morphine and chlorpromazine are suspected toxins.These toxins are concentrated by the liver and excreted into the gall bladder.Direct collection of bile into a bottle is advised because bile is too viscous to be sucked through a needle.

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Specimen CollectionCerebrospinal Fluid not often collected for toxins, but may be needed for microbiological analysis.If needed it should be collected by lumbar or cisternal puncture.Cisternal puncture = Passage of a hollow needle through the posterior anto-occipital membrane into the cerebellomedullary cistern

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Specimen CollectionVitreous Humor sometimes useful in bodies with appreciable post mortem decay.The fluid in the eye resist putrefaction longer than other body fluids.Vitreous can also be used at estimating time of death.Puncture should be made through the sclera with a 5 Gauge needle.

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Specimen CollectionGastric Contents This is typically done in a sudden death in which the deceadant has large quantities of a lethal agent in his stomach.Contents should be emptied into a wide mouth jar.In the case of suicide, large amounts of toxins in the gastric tract may make this point apparent.

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Specimen CollectionVitreous Humor The fluid found in the center of the eye is the vitreous humor. Since this is an isolated area in the body.Vitreous humor is resistant to putrefaction.This is especially handy in a case in which there has been a great deal of decomposition since vitreous humor may be the only fluid still available to test.

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Specimen CollectionBile and Liver the liver filters the blood and is most heavily involved in drug metabolism. Because bile drains from the liver it is often times very rich in certain types of drugs such as opiates.

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Specimen CollectionHair Not common in forensics for a number of reasons.Drugs only present in extremely low concentrations.Controversy between active and passive drug usage arise.The benefit of hair is that its is a good timeline for drug usage since it is only eliminated when hair is cut.

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Drugs of AbuseWorkplace drug testing is primarily concerned with eliminating applicants with drug problems and also explaining dangerous or erratic behavior of current employees. It is important to recall that abusable substances often have legitimate medicinal applications.

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NIDANational Institute on Drug Abuse initiated a program to curb drug use by requiring all federal employees be screened prior to employment.This program specified that screening could cover only the drugs listed belowAmpetamines, opiates, phencyclidine, cocaine, cannabinoids.

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NIDA testing for AmphetamineOpiates and amphetamines are considered to have high abuse potentials and are focused on more in these testing.Both amphetamine and methamphetamine are covered in this testing.Opiates included morphine and codeine.Many labs provide testing for benzodiazepines, barbiturates, and hallucinogens.

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NIDA testing for OpiatesOpiates constitute a large class of drugs distinguished by their ability to cause feelings of euphoria.Morphine, Heroin, Codeine all fall under the umbrella as opiates as do common pain relievers such as loratab, percacet, and many other commonly prescribed pain medicines.Semi-synthetic opiates are those made from modification of morphine or codeine molecules.These include hydromorphiene, OxyContin, and Oxycodone.

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AmphetaminesIn contrast to opiates, these drugs created an excitatory condition characterized by elevated heart rate.They also illicit extreme feelings of euphoria.These drugs have some of the highest incidences of abuse.Ecstasy (MDMA), LSD (lysergic Acid) Crystal Meth ( methamphetamine) all fall under this umbrella.

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CocaineCocaine is a stimulant that resembles amphetamine in its abusive potential.Unlike amphetamine, cocaine is a natural stimulant found in the coca leaf.Cocaine can also be refined further to produce crack cocaine which intensifies its euphoric effects and cost effectiveness.The reason for the increase of potency is because when the drug is smoked, the large surface area of the lungs allots rapid absorption into the body increasing the euphoric feelings.Cocaine is metabolized in the blood to benzoyleganine, and that is what is tested for in labs.

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CannabinoidsMarijuana is a name that applies to parts of the Cannabis sativa plant.Tetrahydrocannabinol (THC) is the major active agent in marijuana.Typically marijuana has a 2-6 percent by volume concentration of THC, Hashish has much higher concentration of THC roughly 12 percent.The average marijuana cigarette contains about 75 mg of THC but it is rapidly absorbed into the blood stream reaching peak concentration around 10 20 minutes after smoking.

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PhencyclidineCommonly known as PCPDeveloped by the Park Davis company and was intended for use as a surgical anesthetic.However it was found to be unsatisfactory because some patients exhibited manic behavior after usage.PCP is measured in blood or urine levels around 25 nanograms per milliliter. Levels of greater than 100 nanograms per milliliter have been related to seizure and some deaths.

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AlcoholsEthanol is beverage alcohol. Low molecular weight alcohols such as methanol and isopropyl may also contribute to human injury.It takes around 90 minutes for the peak level of ethanol to enter the blood.Gas Chromatography is the preferred method for testing alcohol in blood and a proper chain of custody must be observed for criminal cases.

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CyanideHighly toxic substance found in various places throughout nature.Cyanide is dangerous because it binds with ferric ions in cytochrom oxidase, which is an enzyme critical for electron transport.Because it interrupts electron transport it stops the bodies main mechanism for energy production.Most labs can test for cyanide in whole blood and its concentration correlates well with severity of poisoning.Levels higher than 1000 nanograms per mil are associated with stupor and amounts greater than 2500 nanograms per mil are usually fatal.

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Carbon MonoxideSome studies suggest that CO causes more deaths than any other toxin. This is because CO is present in all fires and typically is the cause of death in fire.CO binds to hemoglobin much more tightly than O2 does and decreases our bloods ability to carry oxygen.CO also binds with myoglobin which is also important in electron transport.

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Analytical Methods in Forensic ToxicologyThe methods used in testing of biofluids is important as the types of fluids that are tested.A good working relationship between death investigators and laboratories is essential in success of solving death investigations. Remember, death investigation is a team effort and toxicology is a vital member of the team.

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Screening TestsImmunoassaysFluorescence chemiluminescenceThin Layer ChromatographyUltra-Visible SpectrophotometryGas ChromatographyGas Chromatography-Mass SpectrometryChemical IonizationLiquid Chromatography-Mass SpectrometryColorimetric AssaysAtomic Absorption Specrophotometry (AAS)Neutron Activation Analysis (NAA)Inductively Coupled Mass Spectrometry (ICP-MS)

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Interpreting FindingsWorkplace drug testing is usually conducted for the purpose of answering one of two questionsHistory of drug use for hiring purposes or explanation of erratic behavior of current employee.Table 5.4 page 75 shows cutoff levels for positive specimen levels.

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Interpreting FindingsThe goal of a forensic toxicologist is to confer with the pathologist in determining the cause and manner of death.In simple terms we infer that the death is due to a specific toxin when appropriate quantities of that toxin are found.When other findings conclude cause of death we may specify the toxin as a contributing factor to death.

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