Environmental Engineering Reference
In-Depth Information
can partially be removed by selecting indicators that can be
used to assess both human and ecologic health (DiGuillio
and Monosson, 1996; Burger and Gochfeld, 2001, 2004a;
Suter et al., 2003). Further, the ecologic risk caused by reme-
diation to protect human health is a concern, since some-
times soil removal or other physically disruptive activities
destroy functioning ecosystems with very little improve-
ment in human health (Burger, 1999, 2007).
Eisler, 2003; Loredo et al., 2003; Mueezzinoglu, 2003;
Goldblum et al., 2006). In some artisinal gold mining areas,
elemental mercury is mixed with gravel to amalgamate
gold dust. This is followed by heating the resultant pel-
lets to drive off the gaseous mercury, leaving behind gold.
This heated elemental mercury can pose a signifi cant direct
human health risk, including from mercury vapor (Beate
et al., 2010). This occurs during both the initial handling of
the mercury and the heating of the amalgam pellets. Much of
this gold extraction involves alluvial deposits in streams and
rivers. Some of the mercury that escapes from this process
reaches the aquatic sediments, where it becomes biomethyl-
ated, which renders it accessible for bio-amplifi cation up the
food chain as methylmercury (Marins et al., 2000; Castilhos
et al., 2006; Swain et al., 2007; Paruchuri et al., 2010). Incom-
plete information regarding the various chemical forms of
mercury exposure, and the need to target the information
provided to gold mining and subsistence communities,
prevents the development of consistent public health poli-
cies (Dorea, 2010). Exposure to elemental mercury can also
occur during building demolition from mercury-bearing
fl uorescent and high-intensity discharge lamps (Sheridan
et al., 2000), from dental fi llings (Fung and Molvar, 1992), and
from cultural practices (Wendroff, 1995; Riley et al., 2001).
Methylmercury affects neurobehavioral development,
and causes defi cits in cognitive function, as well as nephro-
logic, immunologic, cardiac, motor, reproductive, and even
genetic effects (ATSDR, 1999; NRC, 2000a). However, the
analytical procedures for measuring methylmercury are
more costly and complex than the analysis of total mer-
cury, hence total mercury is usually measured. Thus, it has
been necessary to develop conversion factors for fi sh. On
average, across a variety of fi sh species and studies, about
90% of the mercury in edible fi sh muscle is methylmercury
(Bloom, 1991; Lansens et al. 1991; Jewett et al. 2003). Such
conversion factors, which require testing in different kinds
of fi sh and under different conditions, allow laboratories to
measure total mercury as a surrogate for methylmercury.
However, some agencies simply assume that all the mea-
sured mercury is methylmercury (JECFA, 2006).
Assessment End Points and Measurement
End Points
For most risk evaluations or assessments for mercury, the
quality that stakeholders wish to understand cannot be eas-
ily measured. That is, managers, regulators, public policy
makers and the public may be interested in whether the
quality of a particular ecosystem is increasing or decreasing
and whether mercury is contributing to the decline of the
ecosystem or the populations within these ecosystem (the
assessment end points). Overall ecosystem health, however,
cannot be easily measured. Instead, we defi ne measurement
end points, which provide information about the overall
assessment end points. Assessment end points are the val-
ued properties of the environment (or of individual spe-
cies) that are susceptible to the stressors of concern, such as
mercury. It is the measurement end point (or metric) that
can be quantifi ed over some temporal and spatial scale and
that can be used by managers and public policy makers.
Measurement end points usually involve indicator species
(Burger and Gochfeld, 2001; Suter, 2001). For example, one
might measure mercury concentrations in the muscle of
bass (
Micropterus salmoides
). In this case, bass are the indica-
tors and mercury concentration in muscle is the measure-
ment end point. Managers then use the measurement end
point as an indication of the overall health of bass popu-
lations. Ecologists can use this measurement end point as
an indicator of possible harm to organisms higher on the
food chain that consume the bass (such as egrets [
Egretta
species], alligators [
Alligator mississippiensis
], and panthers
[
Puma concolor
]), and human health professionals can use
the same measurement end point as an indicator of poten-
tial risk to human consumers of this fi sh (see Bioindicators).
Acceptable Risk for Mercury
Ultimately, the question facing health professionals, ecolo-
gists, regulators, and the general public is: What risk from
mercury is acceptable? It is a common goal of both HRA and
ERA to identify whether a particular exposure scenario or
toxicant level will lead to unacceptably high consequences,
but whether this risk is “acceptable” to society. This is clearly
a public policy, not at scientifi c, decision. The decision about
acceptability is fraught with diffi culties, since even within
humans there is great variation is what risks are considered
acceptable. Some people may accept the risks of riding motor-
cycles, bungee-jumping, and skydiving, while others may
fi nd them unacceptable. Similarly, some people may con-
sider the risks of eating fi sh with mercury levels of 0.5 ppm
Mercury, Methylmercury, and Their Effects
For mercury, the risk from elemental, inorganic (mainly
divalent mercuric compounds), and organic (methylmer-
cury) forms needs to be considered separately (Schoeny,
1996). For biota, including humans, ingestion of methyl-
mercury provides the greatest risk. Inorganic mercury poses
a problem mainly for workers. Elemental mercury poses
a problem through both occupational and community/
residential inhalation exposure near gold mines and
mercury-processing plants, as well as spills from mercury-
containing instruments and devices (Hylander et al., 1994;
USEPA, 1997; ATSDR, 1999; Ehrlich, 2001; NJDEP, 2001;
