Occupational
and environmental toxicology of mercury and its compounds.
Tohoku
University School of Medicine, Sendai, Japan.
Mercury exists in various chemical forms. The
important forms from a toxicological viewpoint are the metallic form, also
called the elemental form, the divalent inorganic forms and methylmercury
compounds. Elemental (Hg0) mercury has a high vapor pressure and the vapor
causes a number of cases of poisoning via inhalation. Classical mercury
poisoning is characterized by a triad of signs, namely tremors, erethism and
gingivitis. Mercurial erethism, which is characterized by behavioral and personality
changes such as extreme shyness, excitability, loss of memory, and insomnia are
also observed. Recently, the effects of mercury exposure at levels around 0.05
mg/m3 or lower have been of concern and may include minor renal tubular damage,
increased complaints of tiredness, memory disturbance and other symptoms,
subclinical finger tremor, abnormal EEG by computerized analysis and impaired
performance in neurobehavioral or neuropsychological tests. Abnormal gait,
dysarthria, ataxia, deafness and constriction of the visual field are typical
of the symptoms of methylmercury poisoning observed in Minamata and Iraqi
outbreaks, as well as in occupational methylmercury poisoning cases. Furthermore,
an infant born to a mother with excessive methylmercury consumption showed
various neurological disturbances and delayed development. Since several
populations are believed to be still exposed to methylmercury through the
consumption of fish and sea mammals, neurobehavioral deviations in children of
these populations have recently been investigated.