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

MERCURY 124
2. HEALTH EFFECTS
The highest NOAEL values and all reliable LOAEL values for immunological and lymphoreticular effects
in each species and duration category are recorded in Table 2-2 and plotted in Figure 2-2 for inorganic
mercury.
Organic Mercury. No studies were located regarding immunological effects in humans after oral exposure
to organic mercury.
In BALB/c mice administered a diet containing 0.5 mg Hg/kg/day as methylmercury for 12 weeks, the
thymus weight and cell number decreased by 22 and 50%, respectively, compared to the control group
(Ilback 1991). The natural killer cell activity was reduced by 44 and 75% in the spleen and blood,
respectively. However, the lymphoproliferative response in the spleen increased at this dose of mercury.
The LOAEL value for immunological and lymphoreticular effects in mice for intermediate-duration oral
exposure to organic mercury is recorded in Table 2-3 and plotted in Figure 2-3.
2.2.2.4 Neurological Effects
Inorganic Mercury. The oral absorption of metallic mercury is negligible, and even massive doses have
not resulted in neurological effects. The wo case histories identified are unusual in that the dose levels
could be reasonably well quantified. The first case history reported ingestion of 15 mL (204 g) of metallic
mercury by a 17-year-old male storekeeper who swallowed mercury from the pendulum of a clock
(apparently out of curiosity rather than as a suicide attempt). On admission, and 24 hours later, he was
symptom free, and physical examination was normal. The patient complained of no gastrointestinal
symptoms, and was treated with a mild laxative and bed rest. The results of serial daily urine mercury
estimates were normal (all less than 15 µg) and did not suggest significant absorption. The radiological
investigation illustrated a characteristic pattern of finely divided globules of mercury in the gastrointestinal
tract (Wright et al. 1980).
The second and massive incidence of ingestion involved a 42-year-old man who had spent much of his life
(since the age of 13) repairing instruments that contained mercury. He intentionally ingested an estimated
220 mL (or about 3,000 g) while repairing a sphygmomanometer (Lin and Lim 1993). Upon admission, the
patient presented with significantly elevated mercury blood levels (103 µg/L, normal