Studies on dentist have suggested adverse effects at air concentrations lower than
50mg Hg /m3
. Average air concentrations as low as 14 mg Hg/m3, were associated with
decreased performance on psychomotor tests. Changes in the mood and behavior have
also been noted, such as emotional liability, somatosensory irritation, and alterations in
mood scores. The major toxic effects of methyl mercury are on the central nervous
system. Paresthesia, numbness or a “pins and needles” sensation is the first symptom to
appear at the lowest dose. This may progress to cerebellar ataxia, dysarthria, constriction
of the visual fields, and loss of hearing.