Professor Karen Wetterhahn knew firsthand how dangerous heavy metals could be. Her research involved determining the biologic toxicity of heavy metals. The chemical she was working with on August 14, 1996, was particularly dangerous. Dimethylmercury, used as a reference standard, is lethal at about 400 mg, a few drops. This classifies it as “supertoxic”. When she spilled a few drops on her gloved hand, she assumed the precautions she had taken (the use of disposable latex gloves and a ventilated hood) were adequate. She was incorrect, but would not know it for quite a while.
It took 149 days before Professor Wetterhahn began to exhibit neurological symptoms, 154 days before she sought care, and 168 days before chelation therapy began. Chelation therapy involves the use of agents that form chemical bonds with metal ions to form a water-soluble complex, allowing the heavy metal to be excreted from the body. However, according to a report on Professor Wetterhahn’s death in the New England Journal of Medicine (NEJM), chelation treatment delayed after exposure “is of little or no clinical benefit”.
Professor Wetterhahn became unresponsive on February 12, 1997 and died on June 8. As a result of her poisoning, more research has been done to better determine the causes that led to her death, as well as determining actions that can reduce the risk of more deaths from mercury poisoning. We can look at these causes in a Cause Map, or visual root cause analysis.
The death of Professor Wetterhahn was due to accidental dimethylmercury poisoning, which is lethal in just a few drops, and ineffective chelation therapy (which may have been able to reduce the impact had it been administered immediately after exposure). Due to the latency of neurological symptoms and the belief that protections taken while working with dimethylmercury were adequate, this did not occur.
Based on later research and testing, it was determined that Professor Wetterhahn was exposed through her skin when she dropped a few drops of dimethylmercury on her glove. The disposable latex gloves she was wearing were later found to result in permeation to the skin in a matter of seconds. The Material Safety Data Sheet (MSDS), which defines necessary personal protection for working with various chemicals, specified only “wear appropriate chemical-resistant gloves”. The use of a plastic-laminate chemically-resistant glove was found to result in no permeation after four hours and should be used rather than disposable latex while working with this chemical.
It is also possible that mercury exposure occurred via inhalation. Although Professor Wetterhahn was using a ventilated hood, dimethylmercury is extremely volatile and could have created an inhalation hazard when it was spilled.
Many organizations would be tempted to identify the spill of the dimethylmercury as the root cause and end the investigation there. However, basing personnel safety solely on attempting to prevent spills does not provide adequate protection. In this case, the risks of using dimethylmercury were found to be so high that an alternative is recommended unless absolutely necessary. If the use of the supertoxic compound is found to be essential, very specific personal protection equipment is called for as well as seeking treatment immediately after possible exposure.
In the NEJM report, the authors state “Before she lapsed into a vegetative state, the patient requested that her case be presented to the general medical community, to scientists working with mercury, and to toxicologists, in the hope of improving the recognition, treatment, and prevention of future cases of mercury poisoning.” By examining all the causes and possible solutions, it is hoped that all chemical work can be made safer, in honor of Professor Wetterhahn.
To view the Outline, Cause Map and timeline of this issue, please click on “Download PDF” above.