Source: Chemical &
Engineering News May 12, 1997
news story, Lyme, NH paper)
CHEMICAL SAFETY - Handling dimethylmercury
We report a case of severe mercury toxicity resulting from a single exposure to
dimethylmercury. Review of research notes interviews, hair analysis, and statements made
by the patient established the circumstances and events described here. Testing of the
type of gloves worn by the patient supports the hypothesis that dimethylmercury rapidly
penetrated them, resulting in transdermal exposure.
It appears that there was only one acute exposure to dimethylmercury. The patient
recounted spilling one or several drops (estimated to total 0.1 to 0.5 ml) on disposable
latex gloves during a transfer procedure in a fume hood while preparing a mercury nuclear
magnetic resonance (Hg NMR) standard.
A severely toxic dose of 100 to 200 mg of mercury absorbed requires absorption of less
than 0.1 ml of liquid (density 3 g per ml.). The possibility of inhalation exposure (the
vapor pressure at 20C is 50 torr is considered highly unlikely given the brief time the
material was handled, the use of the fume hood, and the high concentration in the
patient's body. A profile of the mercury content along a 15cm length of the patients hair
revealed what was probably a single, large exposure to mercury in mid-August 1996, in
accord with a review of research notes and interviews with colleagues.
Approximately THREE MONTHS later, the patient experienced episodes of nausea and
vomiting spaced weeks apart. Approximately five months after exposure, the patient noted
the onset of ataxia (difficulty with balance), dysarthria (slurred speech), loss of
vision, and loss of hearing.
Medical evaluation at this time revealed a whole blood mercury concentration of 4,000
,ug per L80 times the usual toxic threshold (50 ,ug per L) and markedly above the normal
range (<10 ,ug per L). The patient's symptoms progressed rapidly over approximately
three weeks to cognitive deficits and coma. Chelation increased the rate of elimination of
mercury from the body, but without clinical improvement. Whole blood and urine testing of
family members and laboratory coworkers revealed no other abnormal mercury levels.
Air samples from the patient's laboratory, office, and home revealed detectable levels
of mercury only near the sealed mercury waste can in the laboratory hood. Permeation tests
done by an independent testing laboratory found that dimethylmercury penetrates disposable
latex gloves in 15 seconds or less, and perhaps instantaneously.
Individuals working with alkyl mercury compounds should employ cautions similar to
those described in 'prudent Practices in the Laboratory" (National Research Council,
1995) for highly toxic substances. A highly resistant laminate glove (Silver Shield or 4H)
should be worn under a pair of long cuffed, unsupported neoprene, nitrile, or similar
heavy-duty gloves. Latex or PVC gloves have an important role in many laboratory
activities, but they are not suitable for significant, direct contact with aggressive or
highly toxic chemicals.
Medical surveillance measuring mercury concentrations in whole blood or urine
should be considered for repeated or extended use of alkyl mercury compounds.
In all: cases, :the potential hazards associated with dimethylmercury and related alkyl
mercury compounds must not be underestimated. All laboratories working with such compounds
are strongly encouraged to conduct an assessment of existing work practices and
precautions. We urge the Hg NMR community to consider a safer standard compound.
Michael B. Blayney Environmental Health & Safety Dartmouth College
John S. Wiinn Department of Chemistry Dartmouth College
David W. Nierenberg Departments of Medicine and Pharmacology/Toxicology Dartmouth Medical