AFRL Study Defines Standards for Low-Level Chemical Agent Exposure

Study results provide an operationally relevant exposure standard.

Results of a 5-year, $40 million effort to study chemical warfare agents will benefit military and civilian personnel alike, helping leaders in both arenas cope with events should a terrorist or combat attack that exposes people to toxic chemical agents occur. Dr. Stephen Channel, an AFRL research veterinarian and toxicologist, is heading the collaborative research effort between AFRL and US Army scientists. Based at the Army's Medical Research Institute of Chemical Defense and the Edgewood Chemical and Biological Center at the Army's Aberdeen Proving Grounds, Maryland, the work is in its final year.

ImageThe likelihood of encountering chemical weapons during Operation DESERT STORM prompted the Department of Defense to increase its emphasis on health protection, a focus which subsequently spurred initiation of a Defense Technology Objective (DTO) under the Defense Threat Reduction Agency. Once established, the DTO provided the impetus to fund and manage the project. According to Dr. Channel, the twofold goal of the collaborative team was to "refine and improve the human risk assessment for a specific agent, and each year give customers an operationally relevant, scientifically defendable exposure standard" for a traditional organophosphate chemical warfare agent (CWA).

Researchers use physiologically based pharmacokinetic (PBPK) modeling to quantifiably predict human response to chemical exposures based on existing laboratory data. By applying a chemical's characteristics to the known physical makeup of humans, researchers can determine—with a high degree of confidence—how humans will react if exposed to that agent. Dr. Channel indicates that "AFRL's role has been [to provide] its expertise in PBPK/dynamic modeling. The technology was largely established at Wright-Patterson Air Force Base, Ohio, almost 20 years ago, and it allows us to more precisely predict a toxic effect in humans when data is based on other animal models."

PBPK models enable predictions regarding how fast a given chemical will flow through body compartments to its final destination. "PBPK is a way of taking a look at the body system and splitting it up into various physiological compartments," Dr. Channel explains. "Our concern is how long it takes and how much [chemical] gets to the target. In the case of organophosphates, that target would be the brain, which shuts down respiration—which, in turn, ultimately kills you. We collect data, and using our knowledge of physiology, we are able to extrapolate it to human exposure scenarios for the purpose of risk assessment," Dr. Channel states. "This is gratifying work. We didn't produce a box or a widget or a mask, but we developed a science that enables us to create these kinds of operational risk management decision tools."

While science-based standards allow warfighters to pursue their mission armed with a better understanding of the risks related to chemical agent exposure (see figure), such standards may also enable civilian emergency officials to prudently determine when to evacuate an area and when evacuees can safely return. Historically, scientists focused CWA research on determining the immediate dangers of human exposure to high concentrations of chemical agents. Although the results of such research efforts aided the design of offensive chemical weapons, this approach led to standards based on a so-called "kill 'em and count 'em toxicology," which provided raw casualty data but low confidence in predicting human response.

Dr. Channel elaborates: "Those were the kind of studies that didn't tell you much about what the consequences were— what happened if the chemicals were used against you. We knew how much we had to put in a bomb or missile or mortar shell to make the enemy quit doing something, but we didn't really understand what happened if it were to be used against us."

Consequently, the current AFRL program focuses on lowlevel exposure, which is defined as the cumulative concentration of chemical exposure over a given time, an exposure without obvious acute medical effects, or both. A person can experience exposure to low-level CWAs if he or she is downwind from (or near) a chemical attack; enters an area that has been attacked; is involved in destroying chemical munitions; or comes into contact with a contaminated, or partially decontaminated, material or surface. AFRL expects the results of this important study to lead to improved designs for chemical detectors and protective equipment.

Mr. John Schutte (Ball Aerospace and Technologies Corporation), of the Air Force Research Laboratory's Human Effectiveness Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at . Reference document HE-H-06-04.