While doing graduate work at the South Dakota State University in 1986, Dr. Mardon was invited to be a member of the 1986-87 Antarctic meteorite expedition for NASA and the National Science Foundation. 170 miles from the South Pole station when his team found hundreds of meteorites. During his sojourn he suffered environmental exposure which damaged his lungs and gave him a permanent cough. He received the U.S. Congressional Antarctic Service Medal for his efforts and risk.On his return to Alberta, he gave lectures on Antarctica at the University of Calgary and the University of Lethbridge. He secured an interview to be a member of the Canadian/Soviet Arctic traverse from northern Siberia to Ellesmere Island in the Canadian Arctic, but failed to get on that expedition.He was a part of the failed meteorite recovery expedition in the Canadian Arctic near Resolute in the Northwest Territories, and wrote a paper on his conversations with locals and what the Inuit thought of meteorites. He was also supposed to join an Argentinian Antarctic expedition in the late 80's, but a fire at the Argentinian Antarctic base caused his membership to be canceled.One of his most significant contributions to astronomical science was a series of articles he wrote on the Anglo-Saxon Chronicle. The Chronicle is a running commentary on different events in England during the medieval period. With the assistance of his father, a medieval scholar, Dr. Mardon found eleven cometary events mentioned in the Chronicle that are not mentioned anywhere else in astronomical literature, as well as two meteor showers recorded in the Chronicle.In 1991, Dr. Mardon was invited to join an expedition to the South Pole sponsored by the Geographical Society of the USSR. He traveled to Moscow and met with some expedition officials, receiving a strange welcome with little information and odd accommodations. He soon found out that he was under suspicion by the authorities and was arrested first by the GRU, then by the KGB. Dr. Mardon was questioned, held for a time, and then forced to wander the streets of Moscow with an escort that could have been a spy or guard as well as a guide. Dr. Mardon finally secured passage back to Canada after a harrowing experience in Moscow, and eventually received an official letter of apology from Moscow.In 1992, Dr. Mardon was diagnosed with schizophrenia. Following his diagnosis, Dr. Mardon began work as an activist for people with mental illnesses. Dr. Mardon has written multiple books on the subject of mental illness, and has been bestowed several honors and awards for his work as a mental health advocate. In 2011 the Canadian Medical Association (CMA) awarded Dr. Mardon the CMA Medal of Honour in recognition of, "[...] personal contributions to the advance of medical research and education." In regards to the awarding of the medal to Dr. Mardon, CMA president Jeff Turnbull said, "Dr. Mardon has worked tirelessly to help Canadians better understand the issues around mental illness. In courageously talking openly about his own experiences, he is truly making a difference in coaxing mental illness out of the shadows in this country."  Dr. Mardon received his most prestigious honor in 2006, when he was awarded the Order of Canada.

Question: What caused the damage to Dr. Mardon's lungs?
Answer: environmental exposure