Environmental Engineering Reference
In-Depth Information
the system, but also of trends over time. For example, levels
of mercury in bass and the feathers of Great Egrets have
been monitored for many years in the Everglades, show-
ing overall declines, with some regional hot spots requiring
management and restoration (SFWMD, 2007).
For ecosystems, managers often must choose between
prior study and adaptive management, choosing the proper
level of biological organization (individual, populations,
communities, ecosystem), and selecting among short-term
versus long-term goals (Elms, 1997; Wilson and Lantz, 2000).
Is the goal overall individual health and well-being, popula-
tion health and well-being, or community health and well-
being. Risk balancing often involves issues with mitigation
and remediation because of mercury. A balanced risk design
is one where the risks of adverse effects are balanced against
one another such that the total risk is minimized, within a
framework that is transparent to all parties. For example, is
it “better” to remove soil that is contaminated with mercury,
or leave it
in situ
because to remove the soil disrupts the total
ecosystem for little gain in reduction of health effects due to
mercury? Soil characteristics and mercury speciation infl u-
encing bioavailability are also important (Gochfeld, 2003).
Inorganic mercury sequestered as sulphide requires less
interference than more mobile or available species.
Environmental managers often must balance the risks and
benefi ts of actions based on considerations of the exposure
of people and other receptors to mercury through the food
chain. For example, mercury in fi sh in the Savannah River,
coming from the Department of Energy's Savannah River
Site, posed a potential risk to people consuming fi sh from
the river (Burger et al., 1999, 2001a, 2001c). Several risk-man-
agement strategies were considered: (1) Soil and sediment
from Steel Creek could be removed to reduce the source
of the mercury. (2) Other remediation strategies upstream
could be considered, and (3) Consumption advisories could
be promulgated to reach the at-risk populations. The reso-
lution of the issue required obtaining site-specifi c data on
mercury levels and consumption patterns and determin-
ing risk. Then it became a risk-balancing issue: What was
the relationship between remediation (soil removal) and
risk to people versus the ecosystem? Soil removal would
clearly degrade or destroy the existing ecosystem (which
had remained relatively unchanged for over 50 years). This
had to be balanced against the risk to fi sh consumers. After
considerable involvement of a range of stakeholders, includ-
ing state offi cials, regulators, fi shers, and the public, it was
decided that developing a Fish Fact Sheet aimed at the target
audience of fi shers (and consumers) from the Savannah River
would reduce risk to these consumers, while not increasing
the risk to valuable aquatic and riparian ecosystems.
Finally, few studies have attempted to evaluate or rank
the risks to ecosystems from different stressors, chemical as
well as physical disruptions. The EPA has provided a frame-
work for cumulative risk assessment that involves three
phases: (1) planning, scoping, and problem formulation,
(2) analysis, and (3) interpretation and risk characterization
(Callahan and Sexton, 2007; Zartarian and Schultz, 2009).
This is a necessary fi rst step in evaluating multiple stressors
(or multiple chemicals). Evaluating different risks can also
involve a relative risk model to rank and sum individual
risks numerically (Wiegers et al., 1998). Stressor sources and
Risk Balancing
Health professionals, ecologists, managers and the public
must recognize that management of risks involves balanc-
ing both the risks and benefi ts. That is, a person worried
about the risk of mercury from fi sh consumption, will bal-
ance that risk against the health benefi ts of consuming fi sh,
as well as against the risks and benefi ts of eating replace-
ment foods (such as red meat or other protein sources;
Gochfeld and Burger, 2005). Willett (2005) suggested that
the recent decline in fi sh consumption was “probably infl u-
enced” by fears about mercury in fi sh, and concluded that
both risks and benefi ts of fi sh consumption should always
be provided in risk communications.
Another aspect of risk balancing that is important to
consider is the possible effect of other elements on mer-
cury toxicity, or of other foods on mercury toxicity. Both
aspects could be considered in both risk assessment and risk
management. For example, Ralston (2008, 2009) and others
(Cabanero et al., 2007, 2008; Pinheiro et al., 2009, Ralston
and Raymond, 2010), have suggested that selenium reduces
the toxicity of mercury, and thus some reasonable molar
ratio should be used or considered as protective of mercury
toxicity in risk assessment decisions. Selenium-mercury
interaction may reduce the bioavailability or toxicity of
methylmercury, and conversely some mercury toxicity may
be due to impaired selenium-dependent enzyme synthesis
or activity (Ralston et al., 2008). Recent work has included
great variation in the selenium: mercury molar ratios within
a species for both freshwater (Burger, 2011) and marine fi sh
(Burger and Gochfeld, 2011, in press). Such variability makes
it diffi cult to predict how much selenium may be available
to reduce mercury toxicity. While the practical implications
of the modifi cation of mercury toxicity by selenium for risk
assessment and management are unclear at this time, future
work may include such considerations.
A third aspect that bears examination is the rational regu-
lation of environmental hazards, such as mercury, should
enhance the average quality of life for individuals, with
some degree of equity in the distribution of risks and ben-
efi ts (Gilbert, 1984; Bullard, 1990; Holloman and Newman,
2006). This leads to considerations of balancing the risks
among people such that no one group bears the risks, while
another group reaps the benefi ts. This is more likely to be the
case with the siting of plants that expose people to mercury
(e.g. chlor-alkali plants; Ullrich et al., 2007) or downwind of
coal fi red plants (Bradley and Suter, 2002). The question of
environmental equity has moved to the fore, and should be
considered when siting plants or considering the risk from
mercury in fi sh.
