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

MERCURY
2. HEALTH EFFECTS
bronchitis. As these kinds of health effects data become available and methods to assess levels of
significant human exposure improve, these MRLs may be revised.
2.2.1 Inhalation Exposure
Most of the studies on inhalation exposure concern exposure to metallic mercury vapor. For this reason, the
term “metallic mercury” will be used in this section instead of “inorganic mercury.” Other forms of
inorganic mercury do not pose a risk by the inhalation pathway. Inhalation of sufficient levels of metallic
mercury vapor has been associated with systemic toxicity in both humans and animals. The major target
organs of metallic mercury-induced toxicity are the kidneys and the central nervous system. At highexposure
levels, respiratory, cardiovascular, and gastrointestinal effects also occur. Some metallic mercury
vapor may condense (Milne et al. 1970), or in the case of vapors from dental amalgam, may dissolve in
saliva and be ingested (WHO 1991). Condensed droplets are more likely to be ingested than inhaled
(resulting in a lower absorbed dose than would be expected for a given concentration in air). Mercury
vapor concentrations in the general work environment may also be lower than those in the microenvironment
immediately surrounding workers (Bell et al. 1973; Stopford et al. 1978); therefore, estimates
of air mercury values in occupational studies should be carefully evaluated for bias towards a level that may
be lower than actual exposure levels.
No studies were located concerning effect levels following inhalation exposure to inorganic salts of
mercury (e.g., mercuric or mercurous salts, oxides). Also, much of the information located regarding
effects of metallic mercury vapors or volatile organic compounds (VOCs) comes from studies with
significant limitations. Information on inhalation exposure to organic mercury compounds (e.g., alkyl
mercury compounds) in humans is limited to case reports and includes only qualitative data on gastrointestinal,
renal, muscular, and neurological effects. In many cases, it is difficult to determine whether
effects observed in exposed persons were directly attributable to mercury exposure. In addition, a great
deal of the information on effects associated with inhalation exposure to metallic mercury vapor comes
from studies conducted several decades ago, when methods for determining exposure levels were less
precise than current methods.
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