READ: Alcohol and Other Toxins

Toxicology of Alcohol

Alcohol Consumption

Alcohol is a colorless liquid that acts as a depressant by suppressing the central nervous system. Within minutes of consumption, alcohol appears in the blood stream and becomes evenly distributed throughout the body. About 20% of the alcohol consumed is absorbed through the stomach and the remaining 80% is absorbed through the small intestine. Once alcohol enters the bloodstream, it is pumped to the lungs and throughout the body. Factors that influence the concentration in the body include the time it takes to consume the drink, the amount of alcohol in the drink, and the number of drinks consumed. Other factors include the age, weight, and gender of the person who is doing the consuming. Interestingly, women metabolize alcohol differently than men. When given the same amount of alcohol, women typically will test with a higher blood alcohol concentration than men. This is due in part to the fact that women have less water in their bodies than men, thus the alcohol is not diluted in the same proportion as in men. Also, women have less response from the alcohol metabolizing enzyme in the stomach known as Alcohol Dehydrogenase, or ADH. Because the enzyme is less effective in women, more alcohol reaches the bloodstream of women after use. It is important to note that these are not simply benign differences between men and women. Because of the difference in alcohol metabolism and decreased efficiency, women are more likely to suffer from alcohol related liver and heart damage!

Alcohol Elimination

 Alcohol is eliminated through two processes: oxidation and excretion. Oxidation, which essentially means that it is combined with oxygen, occurs in the liver by the enzyme ADH. The ADH enzyme turns the alcohol into Acetaldehyde. Acetaldehyde is essentially a poison chemically related to Formaldehyde and can cause damage to your body with repeated exposure. Excretion of alcohol directly occurs in the breath, urine, and sweat. The kidneys convert alcohol to Carbon Dioxide and water. Excretion only accounts for about 2-8% of the alcohol metabolism. The remaining 92+% is metabolised by the body, mainly in the liver.The level of intoxication varies by person due to factors such as body weight, the rate of alcohol absorption, and the time and rate that the alcohol was consumed. This is why some people seem affected in profoundly different ways when drinking the same amount of alcohol.

Testing for Alcohol

Because alcohol is evenly dispersed throughout the body, the amount of alcohol measured in a breath test is directly proportional to the amount of alcohol in the blood stream. Alcohol is excreted, or released from the body without being changed in form, from the lungs through breathing, the pores by sweating, and from the kidneys by urination. This is why alcohol can be smelled on the breath and in the sweat of someone who has recently been drinking it. The body attempts to get rid of it in these ways directly. Alcohol in the blood will pass directly into the alveoli of the lungs where it will be passed out through the mouth and nose as the person breathes. The ratio of alcohol to alveolar breath is approximately 2100 to 1; this is the basis for calculating the Blood Alcohol Content, or BAC. Thus, Breathalyzers, or Breath testers reflect the amount of alcohol that is in the Pulmonary artery at the time of the test. Breath testers use infrared light or fuel cells to measure the concentration of alcohol in the breath and are typically conducted by law enforcement officers in the field. They work by shining an infrared light through the chamber where the breath is captured. As the light passes through the chamber, it will interact with the alcohol and cause the light density to decrease. The decrease in light intensity is proportional to the concentration of alcohol present in the captured breath.

In the Forensic laboratory, toxicologists collect blood, urine, and vitreous humor samples and test them by using gas chromatography. Field sobriety tests are sometimes used in the field by police officers as a type of screening test to either ascertain the level of impairment of the person or to see if further alcohol testing is needed in conjunction with a traffic or legal infraction. Field sobriety tests include various physical tests such as the "walk and turn", "stand on one leg" and "Horizontal Gaze Nystagmus" test. The Horizontal Gaze Nystagmus test is where the eyes will involuntarily jerk as an impaired person looks from one side to the other. When impaired by alcohol, a person has difficulty dividing their attention and maintaining balance; this is the basis for those particular screening tests of sobriety.

Alcohol and the Law

In 1973 a law was adopted by all states that anyone operating a motor vehicle will submit to a test for alcohol intoxication if requested or lose their license. In 2003 every state defined the legal limit of alcohol in the bloodstream to be 0.08 percent for people who are of legal age to drink, which is typically 21 years old. Prior to that, legal limits had been as high as 0.15! See the graph below to see how much more likely a person would be to have an accident with that Blood Alcohol Content or higher! It is important to note that while .08 is the legally accepted level of alcohol in the bloodstream, that it affects each person in different ways. It is also important to note that there are NO acceptable levels of legal alcohol consumption in persons under the age of 21 years of age in the United States.

Georgia Virtual, Forensic Toxicology, CC BY-NC-SA 3.0