Environmental Engineering Reference
In-Depth Information
cHaP ter 11
ecotoxicology of mercury in fish and Wildlife
recent advances
anton m . sc HeuHam m er , n i l adr i Basu, david c. e vers,
gary H . Heinz , mar k B . sandHeinr ic H , and m ic Hael s. Ban k
of MeHg (skeletal muscle typically greater than 5 µg g
-1
wet weight) derived from point-source industrial pollu-
tion (see reviews by Wiener and Spry, 1996; Wiener et al.,
2003). Although point sources of environmental Hg con-
tamination are still of concern in some locations, increas-
ing emphasis is being placed on Hg-sensitive habitats,
such as low-alkalinity lakes and flooded impoundments,
where a major proportion of the annual Hg load derives
from atmospheric deposition, and where physical and
chemical conditions facilitate methylation and incorpora-
tion of MeHg into the food chain. In these systems, the
long-term effects of lower, but substantive, concentrations
of MeHg are of greatest interest. A survey of Hg (primarily
MeHg) concentrations in freshwater fish of northeast North
America reported that mean Hg concentrations in fillets of
standard-length fish of 13 species ranged from 0.19 µg g
-1
(white sucker,
Catostomus commersoni
) to 0.98 µg g
-1
wet
weight (muskellunge,
Esox masquinongy;
Kamman et al.,
2005). Mercury concentrations of about 0.06-2.5 µg g
-1
dry
weight (0.02-0.63 µg g
-1
wet weight) in zooplankton, ben-
thic invertebrates, and small fish that serve as prey for fish
in low-alkalinity lakes and newly flood reservoirs are not
atypical (Hammerschmidt et al., 2002).
Laboratory and field studies provide convincing evidence
that environmentally relevant concentrations of MeHg in
fish tissues, and in their diets, cause oxidative stress through
the formation of reactive oxygen species (ROS). Both enzy-
matic and nonenzymatic antioxidants, such as superoxide
dismutase (SOD), glutathione, and compounds associated
with glutathione metabolism, are important in regulating
free radicals in cells (Hayes and McLellan, 1999; Valavanidis
et al., 2006). Unregulated ROS may cause tissue damage,
including lipid peroxidation, resulting in biochemical and
structural changes in various tissues of diverse species of
aquatic organisms (Livingstone, 2001). These biochemi-
cal changes may serve as biomarkers of oxidative stress
EffEcts of MEthylMErcury in fish
MErcury in AMphibiAns And rEptilEs
amphibians
reptiles
EffEcts of MEthylMErcury in Wild birds And MAMMAls
effects on neurochemistry
reproductive effects in Birds (egg-injection studies)
reproductive effects in Birds (field-Based studies)
mercury-selenium relationships
conclusions
The toxic effects of mercury (Hg) in fish and wildlife have
been extensively reviewed (e.g., Scheuhammer, 1987; Heinz,
1996; Thompson, 1996; Wiener and Spry, 1996; Wiener et al.,
2003; Scheuhammer et al., 2007). However, some research on
the subtle effects of methylmercury (MeHg) on brain chemis-
try, hormones, and reproductive success and the implications
for population-level effects in certain at-risk species, such as
the common loon (
Gavia immer
) have not been reviewed pre-
viously. A number of the newer studies demonstrate that cur-
rent levels of environmental MeHg exposure are sufficient to
cause significant biological impairment, both in individuals
and in whole populations, in some ecosystems. In addition,
there has historically been a lack of published research or
critical review on the accumulation and toxicity of Hg in
amphibians and reptiles. Here, we review recent findings on
the ecotoxicology of Hg (primarily MeHg) in fish and wildlife
(herptiles, birds, and mammals).
Effects of Methylmercury in fish
Early toxicologic studies of MeHg exposure in fish exam-
ined survival and growth of different saltwater and fresh-
water species with relatively high tissue concentrations
