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

MERCURY 223
2. HEALTH EFFECTS
burning of fossil fuels) activities. Background levels, however, are considerable below harmful levels.
There are a number of possible pathways for exposure to mercury. For a hazardous waste site that contains
mercury that is being released to the environment, pathways that could result in human exposure to
mercury include: (1) eating fish or wild game near the top of the food chain (i.e., larger fish, larger
mammals) that have accumulated mercury in their tissues from living at or near the site; (2) playing on or
in contaminated surface soils; (3) playing with liquid mercury from broken electrical switches,
thermometers, blood pressure monitors etc.; or (4) bringing any liquid mercury or broken mercury device
into the home, where vapors might build up in indoor air. Other potentially harmful exposure pathways
include the excessive use of skin ointments or creams (e.g., skin lightening creams, antiseptic creams) that
contain mercury compounds, the use of mercury fungicides (breathing vapors or contact of the skin with
the fungicide), or the use of liquid mercury in herbal remedies or religious practices, especially if used
indoors. If swallowed, liquid mercury is not very harmful, because it is not easily absorbed into the body
from the gastrointestinal tract. However, small amounts of liquid mercury evaporate at room temperature,
and the inhaled vapors are harmful.
The developing fetus and breast-fed infants are vulnerable to the harmful effects of mercury. The fetus can
be exposed to mercury from the pregnant woman’s body through the placenta, and infants may be exposed
from the nursing woman’s milk. Both inhaled mercury vapors and ingested methylmercury can cross the
placenta. Inorganic mercury, and to a lesser extent elemental mercury and methylmercury, will move into
breast milk. Pregnant women and nursing women need to be extra cautious in their use of consumer
products containing mercury (such as some religious or herbal remedies or skin lightening creams); they
should also pay attention to possible exposures to mercury at work and at home.
The primary pathways of mercury exposure for the general population are from eating fish or marine
mammals that contain methylmercury, or from breathing in or swallowing very small amounts of mercury
that are released from the dental amalgam used for fillings. The relative contribution of mercury from these
two main sources will vary considerably for different individuals, depending upon the amount of fish
consumed, the level of mercury in the fish, the number of amalgam fillings, eating and chewing habits, and
a number of other factors.
Methylmercury levels vary considerably between species and within species of fish (depending on water
conditions and size), so there are wide ranges in estimates of the average exposure levels to mercury in the
general population from consumption of fish. Some researchers estimate that the typical daily exposure to