FORENSIC TOXICOLOGY OF ETHYL ALCOHOL
The analysis of ethyl alcohol provides an excellent illustration of the basic principles of forensic toxicology. There are two independent measuring systems, blood alcohol concentration (BAC) and breath alcohol concentration (BrAC) for alcohol that correlate pretty well with each other. On top of the scientific issues with the measure ment of alcohol, there are a number of social issues that provide another layer of concern for forensic scientists. Operating an automobile (or other conveyance) while under the influence of alcohol has been a serious problem in the United States for many years. An entire body of laws and regulations has been created by the Congress and the 50 state legislatures to deal with this problem. Central to all of these is the notion, unique to alcohol in forensic toxicology, that the degree of sanction or punishment for operating a motor vehicle under the influence of alcohol is tied directly to the concentration of alcohol in the body. This puts an extra burden on the forensic toxicologist who must determine the amount of alcohol in the body, estimate the alcohol concentration at a prior time when drinking was still occurring, determine the effects of the alcohol on that person, and sometimes determine the degree to which alcohol contributed to death. These considerations require a thorough knowledge of all stages of the pharmacokinetics of alcohol; ingestion, absorption, distribution, and elimination. Alcohol is very similar to water in its chemical structure and is soluble in water in all proportions. Because blood and body tissues are largely made up of water, alcohol is easily absorbed, distributes itself rapidly to all parts of the body, and is eliminated easily in urine. For forensic purposes, blood is taken as the reference for alcohol concentrations and measurements of alcohol in other tissues or body fluids refer back to BAC. In blood, alcohol is measured in weight/volume units, specifically the number of grams of alcohol in 100 mL (1 dL) of blood. In breath, a different weight/ volume measure is used. It is the number of grams of alcohol in 210 L of deep, alveolar (lung) air. There is an approximate correlation between BAC and BrAC of 2100:1 ± 300. Some breath testing instruments use 2100:1 conversion to blood alcohol, but some experts believe that the variation in this factor is so large that separate legal limits should be established for BAC and BrAC. In some states there are two parallel sets of regulations that govern drunk-driving behavior. One refers to BAC and the other to BrAC. FORENSIC TOXICOLOGY OF ETHYL ALCOHOL The analysis of ethyl alcohol provides an excellent illustration of the basic principles of forensic toxicology. There are two independent measuring systems, blood alcohol concentration (BAC) and breath alcohol concentration (BrAC) for alcohol that correlate pretty well with each other. On top of the scientific issues with the measure ment of alcohol, there are a number of social issues that provide another layer of concern for forensic scientists. Operating an automobile (or other conveyance) while under the influence of alcohol has been a serious problem in the United States for many years. An entire body of laws and regulations has been created by the Congress and the 50 state legislatures to deal with this problem. Central to all of these is the notion, unique to alcohol in forensic toxicology, that the degree of sanction or punishment for operating a motor vehicle under the influence of alcohol is tied directly to the concentration of alcohol in the body. This puts an extra burden on the forensic toxicologist who must determine the amount of alcohol in the body, estimate the alcohol concentration at a prior time when drinking was still occurring, determine the effects of the alcohol on that person, and sometimes determine the degree to which alcohol contributed to death. These considerations require a thorough knowledge of all stages of the pharmacokinetics of alcohol; ingestion, absorption, distribution, and elimination. Alcohol is very similar to water in its chemical structure and is soluble in water in all proportions. Because blood and body tissues are largely made up of water, alcohol is easily absorbed, distributes itself rapidly to all parts of the body, and is eliminated easily in urine. For forensic purposes, blood is taken as the reference for alcohol concentrations and measurements of alcohol in other tissues or body fluids refer back to BAC. In blood, alcohol is measured in weight/volume units, specifically the number of grams of alcohol in 100 mL (1 dL) of blood. In breath, a different weight/ volume measure is used. It is the number of grams of alcohol in 210 L of deep, alveolar (lung) air. There is an approximate correlation between BAC and BrAC of 2100:1 ± 300. Some breath testing instruments use 2100:1 conversion to blood alcohol, but some experts believe that the variation in this factor is so large that separate legal limits should be established for BAC and BrAC. In some states there are two parallel sets of regulations that govern drunk-driving behavior. One refers to BAC and the other to BrAC.
