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

MERCURY 163
2.3.1.1 Inhalation Exposure
2. HEALTH EFFECTS
Metallic and Inorganic Mercury. There are limited quantitative data on the absorption of metallic mercury
vapor by humans after inhalation exposure, although it is the most common route of inorganic mercury
uptake. Metallic mercury is highly lipophilic, and absorption of the inhaled vapor, followed by rapid
diffusion across the alveolar membranes of the lungs into the blood, has been reported to be substantial.
Exposure to 0.1–0.2 mg/m3 elemental mercury vapor resulted in approximately 74–80% of inhaled
elemental mercury vapor being retained in human tissues (Hursh et al. 1976; Teisinger and Fiserova-
Bergerova 1965). Indirect evidence of rapid absorption was provided by elevated mercury levels found in
red blood cells, plasma, and excreta of 5 volunteers who inhaled radiolabeled mercury for 14–24 minutes
(Cherian et al. 1978). Elevated blood levels of mercury were also observed in humans following a brief
occupational exposure (3 days) to less than 0.1 mg/m 3 metallic mercury vapor (Barregard et al. 1992).
Recently, Sandborgh-Englund et al. (1998) evaluated the absorption, blood levels, and excretion of mercury
in humans after a single dose of mercury vapor. Nine healthy volunteers (2M, 7F) were exposed to 400 µg
Hg/m3 mercury vapor in air (median 399 µg Hg/m3 ; range, 365–430 µg Hg/m3 ) for 15 minutes. This dose
corresponded to 5.5 nmol Hg/kg body weight. Samples of exhaled air, blood, and urine were collected for
30 days after exposure. The median retention of elemental Hg was 69% of the inhaled dose. During the
first 3 days after exposure 7.5–12% of the absorbed dose was lost by exhalation, with the median half-time
of Hg in expired breath being 2 days. In blood and plasma, a rapid absorption phase of Hg was seen,
followed by a biexponential decline of the curves in both media. A substantial interindividual variation was
observed in the area under the concentration-time curves of Hg in blood and plasma. In plasma, the median
half-time of the second phase was 10 days. About 1.0% of the absorbed Hg was excreted via the urine
during the first 3 days after exposure whereas the estimated amount excreted during the 30 days ranged
from 8 to 40%. In order to evaluate the chronic exposure to mercury from dental amalgam in the general
population, the daily Hg dose from the fillings was estimated based on the plasma Hg levels of subjects
with amalgam fillings and the plasma clearance obtained in this study. The daily dose was estimated to be
from 5 to 9 µg/day in subjects with an average number of amalgam fillings.
There are few reports regarding the respiratory absorption of elemental and inorganic mercury compounds
in animals. Elevated levels of mercury were detected in blood and tissues of pregnant or nursing guinea
pigs after short-term exposure (2–2.5 hours) to metallic mercury vapors (6–10 mg/m 3 ) (Yoshida et al.