Karen Wetterhahn was pipetting a small amount of dimethylmercury under a fume hood in her lab at Dartmouth College when she accidentally spilled a drop or two of the colorless liquid on her latex glove. The chemistry professor and toxic metals expert immediately followed safety protocol, washing her hands and cleaning her tools, but the damage was already done, even though she didn't know it. It was August 14, 1996. By June of the next year, the mother of two was dead.

Scientists would later learn that Wetterhahn’s latex gloves offered no protection from the dimethylmercury, an especially dangerous organic mercury compound. Although a few other people had died from dimethylmercury poisoning before, including English lab workers in 1865 and a Czech chemist in 1972, no one understood how dangerous the substance really was. Wetterhahn’s death would change that, and usher in new safety standards for one of the most toxic substances known to humans.

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Born in 1948 in Plattsburgh, upstate New York, Wetterhahn loved science. After graduating from St. Lawrence University in 1970, she earned her doctorate at Columbia University, then spent a year working at Columbia’s Institute of Cancer Research for the National Institutes of Health before joining the Dartmouth faculty in 1976.

As Dartmouth’s first female chemistry professor, Wetterhahn mentored students and co-founded the college’s Women in Science Project, which encourages female undergraduates in science majors. She served as an academic dean, and in 1995, with a $7 million grant from the National Institute of Environmental Health Sciences, started Dartmouth’s Toxic Metals Research Program to investigate the effects of common metal contaminants on human health.

Wetterhahn also made a name for herself outside Dartmouth, especially through her investigations into how our cells metabolize chromium and how the metal can cause cancer. She served as an officer of the American Association for Cancer Research, and wrote over 80 research papers for scientific journals. While she wasn’t working, the professor spent time with her husband Leon, their son Ashley, and daughter Charlotte.

In November 1996, Wetterhahn began vomiting and feeling nauseous. Over the next couple of months, her condition worsened; her speech was slurred, she had trouble seeing and hearing, and she was regularly falling down.

At first, doctors in the emergency room didn’t know what was wrong. After a series of spinal taps and CT scans, doctors told Wetterhahn her symptoms were consistent with mercury poisoning. One of them asked her husband if she had any enemies who might have poisoned her; Wetterhahn told them about the dimethylmercury spill in her office. She was diagnosed with mercury poisoning in late January 1997 and soon after began chelation therapy, ingesting medication that would bind to the toxic chemical and help it pass through her body.

In the late 1990s, although scientists knew about the dangers of mercury and some of its compounds, the danger of dimethylmercury was little understood. The compound was employed exclusively for research: Scientists used it as a reference standard for nuclear magnetic resonance (NMR) spectroscopy, a process that allows scientists to study the effects of toxins in human cells. As a liquid, dimethylmercury made an ideal reference standard, because scientists could use it in its pure form without diluting it in a solution and potentially altering its properties. When she spilled the drop of dimethylmercury on her glove, Wetterhahn was measuring its NRM so she could get a baseline to study the effects of other toxic metal compounds.

While Wetterhahn was fighting for her life, her colleagues at Dartmouth (as well as scientists around the world) read scientific papers about mercury, hoping to discover a way to help her. They also tested her hair, clothing, car, students, family, and hospital room to make sure that no one else had been exposed to dimethylmercury.

Sadly, the level of mercury in Wetterhahn’s blood was too high—800 times the normal level—for doctors to save her. She went into a coma in February, and died on June 8, 1997.

According to Dr. David Nierenberg, a member of the toxicology team that treated Wetterhahn, one of her last wishes was for scientists and physicians to investigate dimethylmercury so that other researchers wouldn’t be sickened as she had been.

“She really, really cared that the message get out to other scientists and doctors that poisoning with mercury is possible and we need to do everything possible to prevent it,” he told The New York Times.

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Wetterhahn did not die in vain. Her death changed the kinds of precautions scientists at Dartmouth and around the world take when working with toxic substances.

Shortly before she died, her colleagues initiated research that showed dimethylmercury races through latex gloves almost instantly [PDF]. They then published an article [PDF] warning scientists about her fate and urging them to wear two pairs of gloves, including heavier laminate gloves, when working with toxic chemicals.

That same year, the Occupational Safety and Health Administration fined Dartmouth for failing to adequately train staff on the limits of disposable gloves, and published a bulletin about Wetterhahn’s death, instructing scientists about the precautions they should take in the lab—wearing impervious gloves and a face shield, immediately reporting spills, getting periodic blood and urine testing when regularly working with dimethylmercury, and substituting less-hazardous substances when possible. All of this has made scientists more cautious when it comes to using simple latex gloves around toxic materials.

Her death also raised the alarm about the long time frame that can elapse between exposure and manifestations of mercury poisoning—Wetterhahn had largely forgotten the incident by the time her symptoms began to occur. Conventional toxicological wisdom had assumed that large doses of mercury would produce poisoning symptoms sooner than small doses, but Wetterhahn's death proved otherwise. In 2002, her case was one of three reviewed in an article in Environmental Health Perspectives [PDF], which noted that “low-level exposures are more likely than high-level exposures to show evidence of adverse effects or, at least, to show them more rapidly.” In other words, the stealth of high-dose mercury poisonings makes them even more dangerous.

But stepped-up safety standards aren’t the only way Wetterhahn has been remembered. Dartmouth has honored her legacy by naming chemistry fellowships, faculty awards, and an annual science symposium after her. The National Institute of Environmental Health Sciences also established the Karen Wetterhahn Memorial Award, for graduate students and post-doctoral researchers who demonstrate “the qualities of scientific excellence exhibited by Dr. Wetterhahn.”

"The accident was a wake‐up call," Ed Dudek, a post‐doctoral fellow working in Wetterhahn’s chromium group, told Dartmouth Alumni Magazine. "We’re now extremely aware of everything we’re doing.”