revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY
2.2.1.4 Neurological Effects
2. HEALTH EFFECTS
Metallic Mercury. The central nervous system is probably the most sensitive target organ for metallic
mercury vapor exposure. Nervous system disorders following exposure to metallic mercury vapors are both
consistent and pronounced. Acute-, intermediate-, and chronic-duration exposures elicit similar
neurological effects. Symptoms intensify and may become irreversible as exposure duration and/or
concentration increases. Most occupational studies discuss chronic-duration exposure to a time-weighted
average (TWA) concentration or to a concentration range, thereby preventing the assessment of doseresponse
relationships within the populations studied. However, the average exposure levels for affected
groups are similar in many of these studies.
In humans, several case studies have reported adverse neurological effects following acute inhalation of
high concentrations of mercury vapor. A wide variety of cognitive, personality, sensory, and motor
disturbances have been reported. The most prominent symptoms include tremors (initially affecting the
hands and sometimes spreading to other parts of the body), emotional lability (characterized by irritability,
excessive shyness, confidence loss, and nervousness), insomnia, memory loss, neuromuscular changes
(weakness, muscle atrophy, muscle twitching), headaches, polyneuropathy (paresthesia, stocking-glove
sensory loss, hyperactive tendon reflexes, slowed sensory and motor nerve conduction velocities), and
performance deficits in tests of cognitive function (Adams et al. 1983; Bluhm et al. 1992a; Hallee 1969;
Jaffe et al. 1983; Karpathios et al. 1991; Lilis et al. 1985; McFarland and Reigel 1978; Snodgrass et al.
1981). A few individuals have also noted hearing loss, visual disturbances (visual field defects), and/or
hallucinations (Bluhm et al. 1992a; McFarland and Reigel 1978). In a case study of exposure to a
calculated metallic mercury vapor level of 44 mg/m 3 for