Karen Wetterhahn was a professor of chemistry at Dartmouth College, New Hampshire, who specialised in toxic metal exposure. She died of mercury poisoning at the age of 48 due to accidental exposure to the organic mercury compound dimethylmercury (Hg(CH3)2). Protective gloves in use at the time of the incident provided insufficient protection, and exposure to only a few drops of the chemical absorbed through the gloves proved to be fatal after less than a year.
Wetterhahn was born in Plattsburgh, New York, and had degrees from St. Lawrence University and Columbia University. She joined Dartmouth’s faculty in 1976 and published more than 85 research papers. In 1990, Wetterhahn helped establish Dartmouth College’s Women in Science Project (WISP), which helped to raise the share of women science majors from 13 to 25 percent at Dartmouth College and has become a national model.
Accident and death
On August 14, 1996, Wetterhahn, a specialist in toxic metals, was studying the way mercury ions interact with DNA repair proteins, and she was investigating the toxic properties of another highly toxic heavy metal, cadmium.
Dimethylmercury was a compound used, almost exclusively, as a reference standard for Hg nuclear magnetic resonance (NMR) measurements, a particular type of specialized chemical analysis.
Wetterhahn would recall that she had spilled one or two drops of dimethylmercury from the tip of a pipette onto her latex-gloved hand. Not believing herself in any immediate danger, as she was taking all recommended precautions, she proceeded to clean up the area prior to removing her protective clothing. However, tests later revealed that dimethylmercury can, in fact, rapidly permeate different kinds of latex gloves and enter the skin within about 15 seconds. The exposure was later confirmed by hair testing, which showed a dramatic jump in mercury levels 17 days after the initial accident, peaking at 39 days, followed by a gradual decline.
Approximately three months after the initial accident Wetterhahn began suffering brief episodes of abdominal discomfort and noted a significant weight loss. The more distinctive neurological symptoms of mercury poisoning, including loss of balance and slurred speech, appeared in January 1997, five months after the accident. At this point, tests proved that she was suffering from a debilitating mercury intoxication. Her urinary mercury content had risen to 234 µg per litre; its normal range is from 1 to 5 and the toxic level is > 50 μg/L.
Despite aggressive chelation therapy, her condition rapidly deteriorated. Three weeks after the first neurological symptoms appeared, Wetterhahn lapsed into what appeared to be a vegetative state punctuated by periods of extreme agitation. One of her former students said that “Her husband saw tears rolling down her face. I asked if she was in pain. The doctors said it didn’t appear that her brain could even register pain.” Wetterhahn was removed from life support and died on June 8, 1997, less than a year after her initial exposure.
There had been previous documented cases of death due to dimethylmercury poisoning. In 1865, two English laboratory assistants died several weeks after helping to synthesise dimethylmercury for the first time. In 1972, a 28-year-old chemist in Czechoslovakia had suffered the same symptoms as Wetterhahn after synthesising 6 kg of the compound.
Wetterhahn’s death shocked not only the entire chemistry department at Dartmouth, but also regulatory agencies, as the accidental exposure occurred despite her having taken all required measures known at that time. These included the use of latex gloves, a fume hood, and adherence to standard safety procedures. After Wetterhahn’s mercury poisoning was discovered, her colleagues tested various safety gloves against dimethylmercury and found that the small, apolar molecule diffuses through most of them in seconds, much more quickly than expected. As a result, it is now recommended to wear highly resistant, flexible, plastic-laminate gloves when handling dimethylmercury and other similarly dangerous substances. For increased protection, such thin gloves can be worn under long-cuffed, heavy-duty outer gloves made of, for example, neoprene.
At the time, dimethylmercury was the common calibration standard for Hg NMR spectroscopy because it has certain advantages over the alternatives that exist. As a consequence of Wetterhahn’s accident, safety recommendations have been revised, and the use of dimethylmercury for any purpose has been highly discouraged.
Dartmouth College has since established an award in Wetterhahn’s name to encourage other women to pursue careers in science. Whenever possible, preference in granting the award is given to a woman. The National Institute of Environmental Health Sciences also maintains an annual award, for a graduate student or post-doctoral researcher, in honour of Karen Wetterhahn.