Environmental Engineering Reference
In-Depth Information
table 12.3
Exposure Matrix for Mercury Compounds for Humans
Exposure
route
Air
Water
Soil
Food
Products and processes
Inhalation
Elemental
mercury
Some mercury
volatilizes in
showers
Fine, respirable
dusts
Mercury mining, gold
mining, battery
reclamation, dental
amalgams, instrument
manufacture and
breakage, cultural
practices, and
emissions from
incinerators and
coal-fi red power plants
Ingestion
Drinking water
Eating soil
(toddlers)
Eating fi sh
high in
methylmercury
Recreational and
commercial fi sh
Dermal
Dimethylmercury in
laboratory
Injection
Thimerosal in
vaccines: cultural
practices
note: Mercury can be present in environmental media: air, water, soil, and food.
Airborne mercury
deposits on land and water surfaces.
Mercury on land
can wash into waterways.
Mercury in water bodies
can become biomethylated by bacteria in sediment. Mercury can
bio-accumulate and bio-amplify
in the aquatic food chain.
Inhalation
of airborne mercury is a signifi cant route for elemental mercury in both
workplaces and residences.
Ingestion of mercury from soil
is a pathway mainly for toddlers and adults who work with soil.
Foodborne mercury
is present mainly in fi sh.
acceptable, even for consumption every week, while others
may not. Finally, people with occupational exposure to mer-
curial compounds or products may fi nd the risks acceptable
because of their economic gain, while others living nearby
who have no fi nancial interest, may not appreciate air or
water emissions. Determining the risk from mercury in
foods is generally based on epidemiologic studies coupled
with fate and effects of mercury in humans, and the results
of toxicological studies in animals, allowing for uncertain-
ties relating to interspecifi c differences, human variability
and susceptibility, and uncertainties in these measurements.
Methylmercury is one of the few toxicants for which
exposure data are available from either consumption studies
or unintentional poisoning exposures to derive a guideline
intake for methylmercury, based on the most sensitive
stage (the fetus). The consumption of fi sh poses the greatest
risk to the public, making it essential to have accurate
exposure assessments before risk can be evaluated (Hughner
et al., 2008), as well as information on mercury levels in
fi sh (Burger, 2009). For most risk assessments for exposure
to methylmercury, fi sh consumption is the primary path-
way (Boischio and Henshel, 1996; Rice et al., 2000; Burger
and Gochfeld, 2006a), and farm-raised fi sh are not exempt
if they have been fed fi sh meal high in mercury (Dorea,
2009). However, data from China (Zhang et al., 2010)
shows that for some people rice ingestion is the major
source of methylmercury.
In general, agencies often use average or default assump-
tions when computing risk. However, these assumptions
are not suitable for people who consume a lot of fi sh—for
example, Native Americans, subsistence peoples, some rec-
reational fi shers, or for those who eat a lot of fi sh for taste
or health reasons. Sunderland (2007) has reported that per
capita mercury intake rates using FDA mercury data differed
signifi cantly from those calculated based on site-specifi c
mercury data for each area. Thus, site-specifi c informa-
tion on mercury levels in fi sh, site-specifi c information on
Human Health Risk Assessment for Mercury
Exposure Assessment
People are exposed to mercury through multiple path-
ways: air, water, food, cosmetic products, dental amalgams,
cultural practices, and even from the thimerosal preserva-
tive in vaccines (NJDEP, 2001). Exposure assessment for
mercury is a critical phase; it involves examining not only
the routes of exposure, but also the form of the mercury.
Table 12.3 summarizes the exposure pathways for various
forms of mercury in environmental media (air, water, soil,
and food) taken into the body by inhalation, ingestion,
injection, or through the skin.
