DMM Accident

Chemical & Engineering News May 12, 1997


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 patient s 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 School