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Chemical Safety Hazard Alert - Handling Methyl Mercury
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Title: Handling Dimethylmercury
Source: C&EN
Date: May 12, 1997
Author: Michael B. Blayney, Environmental Health & Safety, Dartmouth College
John S. Winn, Department of Chemistry, Dartmouth College David W.
Nierenberg, Departments of Medicine and Pharmacology/Toxicology, Dartmouth
Medical School
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 circumstance and events
described here. Testing of the type of gloves worn by the patient supports
the hypothesis that dimethylmercury rapidly penetrated them, resulting in
trans-dermal 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 that 0.2 mL of liquid (density 3 g per mL). The
possibility of inhalation exposure (the vapor pressure at 20 OC is 50 torr
[J. Inorg. Nucl. Chem., 20, 340 (1961)]) 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 15-cm 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 (difficult 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 L-80 times the usual toxic
threshold (50 up 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 repeat 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.
Last Modified: February 1, 2008
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