Forensic Toxicology O’Connor

Role of Forensic Toxicology Forensic toxicologists detect & identify drugs & poisons in body fluids, tissues, & organs in matters that pertain to violations of criminal laws. Ethyl alcohol is the most heavily abused drug in Western countries.

Ethyl Alcohol All evidence shows ethyl alcohol (which is legal if over 21) is the most heavily abused drug, causing 40% of all traffic deaths in the US. Nearly 17,500 fatalities/year are alcohol related & over 2 million injuries requiring hospital care.

Toxicology Detect and isolate drugs in the body to determine their influence on human behavior. Knowing how the body metabolizes alcohol is key to understanding its effects. Knowledge made development of instruments to measure presence & concentration of alcohol.

Metabolism of Alcohol Metabolism- body breaks down one chemical into chemicals that are easier for it to eliminate. Three basic steps : 1.Absorption 2.distribution 3.elimination

Metabolism of Alcohol Step 1 Absorption Consumed as a colorless liquid in a mixture Appears in blood w/in minutes Increases in concentration as it is absorbed by stomach & sm. intestines into bloodstream Absorption to the blood allows the alcohol to be carried to all parts of the body

Distribution The body is 2/3 water and the alcohol gets distributed evenly through the bodies liquid parts. The timeframe for rate of absorption/distribution: Total time taken to consume Amount consumed Quantity & type of food present in stomach Size of individual consuming total volume of liquid present in the body)

Elimination As the alcohol is circulated by bloodstream, the body begins to eliminate it by two processes, oxidation & excretion % is oxidized to CO 2 & H 2 O starting in the liver In the presence of enzyme alcohol dehydrogenase it is converted into acetaldehyde and then to acetic acid which is broken down throughout the body to CO 2 & H 2 O Remaining 2-5% is excreted unchanged in the breath, urine & perspiration (in proportion to level in blood stream)

“Burn-off” rate of alcohol Postabsorption varies by individual the average (which can vary by 30%):.015% w/v ( weight per volume ) per hour upon completed absorption

BAC- blood alcohol Concentration Best way to determine- remove a portion of the brain & analyze for alcohol content (problematic for the living) Blood alcohol levels are the legally accepted standard for measurement in the living. (postmortem- brain, cerebrospinal fluid, or vitreous humor is tested)

Taking Measurements Measure concentration in Blood test Measure alcohol content in breath

Henry’s Law is applied: When a volatile chemical is dissolved in a liquid & is brought to equilibrium with air, there is a fixed ratio between the concentration of the volatile compound in air & its concentration in the liquid & this ratio is constant for a given temperature. Breathe leaves the mouth at an ave. of 34°C, the ratio of alcohol in the blood; to alcohol in the aveolar air is approximately 2,100 to 1. (1 ml of blood same amt. alcohol as 2,100ml of breath)

Testing for Intoxication Hundreds of thousands of motorists tested annually. Breathe testing, quick- convenient & reliable (early in absorption process- breathe test will show higher levels than blood tests; but match effects on the brain)

Breathalyzer Developed in 1954 by R.F. Borkenstein modified over years- basic principles still apply. Breathalyzer replaced chemical free devises: Infrared & fuel-cell-based devices controlled by microprocessors. Process: Start with field sobriety test Nothing taken orally for 15 min. prior to test. Take two test samples minutes apart

Field Sobriety test Used to determine an individuals physical impairment & to justify further testing Series of psychophysical tests: Horizontal-gaze nystagmus ( follow pen light w/ eyes) walk & turn One-leg stand

Higher BAC:Higher physical impairment.10% BAC = eye jerk before eye has moved 45° Other drugs can trigger this effect, phencyclidine, barbituates, & other depressants) Walk/turn & one-leg stand are divided attention tasks. Requiring ability to understand & carry out more than 2 instructions: this ability is affected by blood-alcohol levels.

Blood Analysis Forensic toxicologists must devise an analytical scheme to detect, isolate, & identify toxic drug substances extracted from biological fluid, tissues, and organs.

A screening test gives quick insight into the likelihood that a specimen contains a drug substance. Positive results arising from a screening test are tentative at best and must be verified with a confirmation test.

The most widely used screening tests are thin- layer chromatography, gas chromatography, and immunoassay. Gas chromotography/mass spectrometry is generally accepted as the confirmation test of choice.

Once a drug is extracted & identified, a toxicologist may be required to judge the drug’s effect on an individual’s natural performance or physical state. This is different depending on whether the individual is a live or deceased.

Field sobriety results come into play for the living. (much easier to use in court since video camera’s were added to police vehicles) Deceased, requires the ME to determine cause of death, for this the ME and toxicologist work together.

Alcohol Intoxication vs Drug Induced Intoxication Alcohol intoxication is widely recognized, police are highly trained for & the courts are accustomed to the effects. Drug Induced Intoxication is harder to recognize. In the 1970s they developed & tested a series of clinical & psychophysical examinations that a trained police officer could use. The program is now used nationwide to train drug recognition experts (DRE); a 3-5 month training program is required to certify.