A toxicologist is a person who studies poisons. As NASA's Chief Toxicologist, I am responsible for studying chemicals that could harm people in spaceflight and on the ground as well.

In the Shuttle/Mir program, my primary concerns include airborne contaminants that have accumulated in the Mir over years of operation and the risk of release of chemicals from Shuttle/Mir experiments, operating systems, or overheated electronic circuits.

It is my responsibility to set astronaut exposure limits for potentially harmful airborne pollutants. The National Research Council's Committee on Toxicology reviews all exposure limits set by my toxicology group at Johnson Space Center (JSC). One challenge I face right now is how to reconcile NASA exposure limits with Russian exposure limits, which are often much stricter than NASA's.

In cooperation with Russian experts, my group also collects air samples from the Mir and the shuttle to determine crew members' exposure to pollutants. Air samples are brought back to JSC, where we analyze them by gas chromatography and mass spectrometry. The Russians conduct their own analyses as well. We are working on methods to analyze air pollutants aboard the shuttle (and possibly Mir), and we hope to fly a prototype analyzer as early as STS-81, a shuttle mission scheduled for launch in December.

When I was very young I wanted to be an astronomer, but the practical limitations of that career led me to pursue medical sciences instead. I have advanced degrees in analytical chemistry and experimental pathology, which are both cornerstones of toxicology. After spending many years in graduate schools I made the natural choice of toxicology as a way to earn a living.

I found inhalation toxicology particularly interesting because of the challenge of exposing test animals in well-defined ways. In the early 1980s I began working for the U.S. Army on the toxicology of chemical warfare agents. In the late '80s I came to NASA to be technical lead for the agency's toxicology program.

The best preparation for this kind of job is to develop an analytical or scientific approach to problem solving, rather than simply acquiring a specific body of knowledge in school.

The best part of my job is working with other scientists to develop scientific reports. I enjoy the lively discussions with my colleagues, the data analysis, and finally the day when the work is published. What I dislike about my job is having to prepare program budgets when total funding levels are not clear and everyone is fighting over money.

I am a person who likes to run fast, grow flowers, fish with my kids, hear a good sermon and give hugs. People probably think I am crazy to run like I do in the hot, humid climate of Houston....

My teacher in the fifth and sixth grades greatly spurred my interest in science by showing his own interest in science and spending many hours after school helping us build electronic devices, learn codes and so on. And I recall a specific experience that began my lifelong interest in astronomy. When I was eight years old, a neighbor set up a Newtonian reflector in his front yard to observe Saturn. Its eyepiece was far off the ground so it was awkward for me to see into it. But somehow I did, and the beauty of the ringed planet, magnified perhaps 200 times, was something I'll never forget.

I grew up in Wichita, Kanas and lived there for about 20 years. (My parents still live in Wichita, which is now a city of 300,000 people.) In my home town people could see stars at night and had telescopes; hence, my early interest in astronomy.

I now live in Clear Lake City, near JSC. I have been married for almost 20 years. My wife Donna and I have three children who keep us busy. Alex, age 13, excels at the euphonium in the school band. Laura, age 11, is an excellent swimmer. And Austen, age 4, enjoys fishing and cap guns (he is our only native Texan). Since the deaths last year of our dog Buffy, who lived with us for 14 years, and our hamster Spike, we are left with only one pet, a rabbit named "Frisky." Frisky likes to eat too much to be very frisky....

I hope to work at NASA at least until the International Space Station (ISS) is nearly complete. Much of the work we are now doing on real-time air pollutant analyzers will be used on the ISS, and I look forward to using the tools my group has created to manage air quality. This effort represents a new era in spacecraft air-quality measurement.

If I stay with NASA any longer, it will be because the agency has a clear mandate to put a sustained human presence on the Moon and lay the foundations for human exploration of Mars. If I leave NASA, I would like to begin another career outside the field of toxicology, perhaps teaching science to high school students, teaching astronomy in a small college, or running a hardware store.

A goal I have today is that some day I would like to discover a comet.