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|U. S. Department of Labor
Occupational Safety and Health Administration
Directorate of Science, Technology and Medicine
Office of Science and Technology Assessment
OSHA Safety Hazard Information Bulletin on Dimethylmercury
February 15, 1991
The Boston Regional Office has brought to our attention the extreme toxicity of an organometallic chemical, dimethylmercury following the investigation of a fatal chemical exposure to a researcher. The death of a chemistry professor in June 1997 was apparently due to a single exposure to dimethylmercury.
Dimethylmercury belongs to a class of organic mercury compounds known as alkyl mercuries. It is used primarily in research. It is a colorless liquid described as having a weak, sweet odor. Dimethylmercury is readily absorbed through the skin. A severely toxic dose requires the absorption of less than 0.1mL.2 Many materials, including several plastics and rubber compounds, have also been shown to be permeable to this chemical. It is highly reactive and flammable. Because of its high vapor pressure (50-82 mm Hg at 20°C), the inhalation route of entry is also significant.
The exposure occurred when, during a transfer to another container, one to several drops of dimethylmercury were spilled on the back of the researcher's gloved left hand. The transfer was conducted under a fume hood and the researcher was wearing disposable latex gloves. Five months later the researcher experienced progressive difficulty characterized by numbness and tingling in both lower extremities, along with difficulty in vision, walking, speaking, and hearing. When informed that her symptoms were due to mercury poisoning, the spill incident was recalled and she indicated that she had removed the gloves promptly and did not think any more about the incident. As a result, no medical monitoring or other follow-up was done until the diagnosis five months after the exposure.
Full diagnostic evaluation identified organometallic toxicity as a result of exposure to dimethylmercury as the cause. Hair analysis for mercury was consistent with a single or short exposure, such as the reported spill, and peaked at 54 days post exposure followed by subsequent slow decline in mercury levels. Mercury levels in hair are reflective of blood mercury levels at the time the hair was formed. Therefore, analysis of the levels versus time (hair length where sample was taken) can give a history of mercury exposure prior to when the problem was recognized. The mercury level in the urine was 234 µg/L; blood mercury level was 4,000 µg/L five months after the exposure (background levels in unexposed populations are 4-5 µg/L and 1-8 µg/L respectively). Despite aggressive chelation treatment, the patient went into a coma and died 10 months after exposure. Diagnosis at the time of death was encephalopathy as a result of mercury intoxication. The gloves used in this incident were disposable latex examination gloves and subsequent permeation testing of the gloves by a certified, independent testing laboratory indicated that the chemical permeates latex, PVC, and neoprene almost instantaneously.
In keeping with other reported cases, the delayed onset of symptoms is not completely understood, although the intense lipophilia of the compound may play a role. Estimates regarding the amount of exposure ranged from "one to several drops".
As a result of this lethal incident of dimethylmercury exposure, the following recommendations are made regarding the use of dimethylmercury:
* Individuals should consider the use of less hazardous substances unless dimethylmercury is specifically required. For example, a major use of dimethylmercury is to calibrate certain research equipment such as Nuclear Magnetic Resonance (NMR). Inorganic mercury salts reportedly can be substituted for most of these operations.3
* Employees must wear impervious gloves, a face shield a minimum of 8 inches in length, and work under a hood when handling this chemical. Latex, neoprene and butyl gloves do not provide suitable protection for direct contact with dimethylmercury (dimethylmercury migrates through plastics and rubber). Permeability tests have shown that Silver Shield laminate gloves are impermeable to dimethylmercury for at least 4 hours. The Silver Shield glove should be worn under an outer glove that would be resistant to abrasion and tears. The vial containing the dimethylmercury should be clamped and the contents drawn up by means of a glass syringe and cannula. Gloves should be removed and disposed of in a manner that precludes re-entry of this material back into the workplace and in accordance with the requirements of the State Hazardous Waste Regulatory Authority. All gloves that may have been in contact with dimethylmercury should be considered contaminated and not reused.
* Employees using organometallic compounds such as dimethylmercury must be trained and aware of the toxic properties of these materials. MSDSs must be read with the understanding that they may not provide adequate guidance on glove selection.
* Individuals should use precautions similar to those described in the "Prudent Practices in the Laboratory"4. Additional information on this case can be found in Chemical and Engineering News5.
* All spills of this material or even suspected contact must be reported immediately to the employer and medical attention sought as soon as possible. Because of the high vapor pressure, dimethyl mercury evaporates rapidly and nearby workers could be quickly exposed to levels above the PEL of 0.01mg/cu.m.6
* Emergency showers and eyewash facilities must be provided within the immediate work area for emergency use particularly to deal with eye or skin contact. Soap must also be available.
* Medical surveillance consisting of periodic blood and urine testing of all individuals who work with this chemical on a routine or frequent basis should be provided by a physician experienced in occupational medicine.
This tragedy highlights the need for research laboratories to develop a protective chemical hygiene plan which includes adequate guidance on the appropriate selection of personal protective equipment and engineering controls. Highly placed or very well qualified researchers should not be assumed to have adequate health and safety information. Research facilities should recognize that the nature of their work leads to diverse and often severe health hazards, and occupational health and safety must be proportionately pro-active.
This document should be distributed to all laboratories and trade organizations that either use or distribute NMR scanners.
1 The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood health hazards, inadequacies of materials, devices, techniques, and safety engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports and concerns expressed by safety and health professionals, employers, and the public. Information is complied based on a thorough evaluation of available facts, literature and in coordination with appropriate parties. HIBs do not necessarily reflect OSHA policy. [Back to Text]
2 Blayney MB, JS Winn, and DW Nierenberg. "Letters; Chemical Safety - Handling Dimethylmercury" Chemical and Engineering News (1997, May 12): 7. [Back to Text]
3 Zachs R. Scientific American 277:20(1997, September). [Back to Text]
4 Prudent Practices in the Laboratory, Sections 5C; 5D; Nat. Acad. Press 1995. [Back to Text]
5 Blayney MB, et al, op.cit. [Back to Text]
6 Toriba TY, TW Clarkson, and DW Nierenberg. "Letters: More on working with dimethylmercury" Chemical and Engineering News (1997, June 16): 6. [Back to Text]