Environmental Engineering Reference
In-Depth Information
including Hg. Reptile declines have also been reported
(gibbons et al., 2000).
between the occurrence of amphibian disease in tadpoles
and Hg exposure has been reported (Bank et al., 2007), the
primary mechanisms of this relationship remain unknown.
Byrne et al. (1975) documented Hg levels in a variety of
amphibian species inhabiting sites with varying levels of
Hg contamination in yugoslavia; they reported that
Rana
temporia
from contaminated sites had higher levels of
Hg. Power et al. (1989) and Sparling et al. (2010) provide
extensive reviews of the amphibian toxicologic literature,
and although numerous studies exist on short-term tox-
icity, little is known about Hg exposure and its effects on
amphibians. Kanamadi and Saidapur (1992) reported that
sublethal mercuric chloride exposure inhibited spermato-
genesis in
Rana cyanophlyctis
and studies by Punzo (1993a,
1993b) suggest that Hg, especially from local sources, can
negatively affect the reproductive physiology of amphibi-
ans, including impairment of fertilization, ova maturation,
and postembryonic development, and disruption of neuro-
endocrine regulation. Other amphibian species have also
been studied. chang et al. (1976) evaluated dose-response
effects of MeHg on limb regeneration in
Triturus viridescens
and reported delayed limb regeneration at 8 µg/L MeHg in
water, and death of this species was observed at
.
300 µg/L.
Dial (1976) used
Rana pipiens
embryos at varying stages of
development to study the effects of methylmercuric chlo-
ride (0.5-200 µg/L). concentrations
.
40 µg/L were lethal
to embryos treated at the cleavage stage of development.
Embryos in other stages (blastula, gastrula, and neural-
plate) were exposed for 5 days to concentrations of 5-30
µg/L. At 5 µg/L, tadpoles showed negligible effects; how-
ever 10, 15, or 20 µg/L caused various negative effects,
including exogastrulae, and poor tail development and
poor overall development. Tadpole deaths increased with
exposure time and concentration. At 30 µg/L, tadpole
defects were commonly observed within 24 hours and all
tadpoles died within 3 days (Dial, 1976). Traditional toxi-
cologic profile data for Hg, and other metals in amphibians
and reptiles is reported in Sparling et al. (2010); however,
data on several amphibian and reptile species is either lim-
ited or nonexistent.
Bergeron et al. (2010a, 2010b) described relationships
between Hg, MeHg, and selenium (Se) in three amphibian
species (
Plethodon cinereus, Eurycea bislineata,
and
Bufo ameri-
canus
) along a contamination gradient in Virginia. Mercury
concentrations in amphibians varied and were generally
associated with food habits and habitat selection.
Eurycea
bislineata
had the highest Hg levels, and adults (3.45
6
0.196
µg g
-1
dry mass) had higher concentrations than larvae
(2.48
6
0.171 µg g
-1
dry mass).
Bufo americanus
tadpoles had
higher concentrations (2.13
6
0.60 µg g
-1
dry mass) than
the more terrestrial adults
(0.598
6
0.117 µg g
-1
µg g
-1
dry
mass) and
Plethodon cinereus
(0.583
6
0.178 µg g
-1
dry mass)
had the lowest concentrations. Bergeron et al. (2010a) also
reported a strong correlation between carcass levels of Hg
and blood Hg in
Bufo americanus
) and tail tissue Hg for
amphibians
A variety of terrestrial habitat types, including uplands,
wetlands, riparian areas, and headwater streams and other
surface waters are important to the breeding ecology and
overall life history of herpetofauna. These habitats receive
atmospheric Hg inputs, and some (especially wetlands) may
be important for net MeHg production within watersheds.
Mercury from atmospheric deposition can accumulate in
amphibians and reptiles species inhabiting wetlands and
their associated riparian and upland habitats, and likely
poses a serious threat to the overall population performance
of species with life history characteristics that make them
sensitive to Hg bioaccumulation (Birge et al., 1979; cooke,
1981; Hall and Mulhern, 1984; Bank et al., 2005, 2007).
Stream salamanders are often long-lived as compared
with invertebrates and freshwater fishes (Moyle, 1976).
These organisms are often suitable eco-indicators of envi-
ronmental Hg and MeHg in lotic ecosystems (Bank et al.,
2005). Their high trophic position in headwater streams,
complex life histories, and sensitivity to perturbations make
them reliable indicators of stream and watershed condition
(Welsh and Ollivier, 1998; Rocco and Brooks, 2000; Jung
et al., 2000; Southerland et al., 2004; Bank et al., 2005).
Bank et al. (2005) reported elevated levels of total Hg in
two-lined salamander (
Eurycea bislineata
) larvae (73-97%
MeHg) from streams in Acadia National Park, Maine. These
larvae may serve as an indicator of stream and watershed
Hg and MeHg contaminant levels, since larvae are strictly
aquatic, fairly easy to sample (in comparison to fish), have
low vagility, and have a diet that is comprised of a wide
variety of invertebrate taxa (Petranka, 1984, 1998; Bank
et al., 2005). In terrestrial habitats, red-backed salamanders
(
Plethodon cinereus
), or similar species, may reflect local
atmospheric Hg deposition. In addition, tail clip levels and
regression algorithms may be used as a nonlethal method
to estimate internal tissue mercury exposure (Bergeron et al.,
2010a, 2010b). Unfortunately, no ecotoxicologic studies to
explicitly investigate the possible impacts of Hg or MeHg
have yet been conducted on these widespread species.
Mercury bio-accumulation in bullfrogs (
Rana catesbei-
ana
) and other common
Ranidae
species (chang et al., 1974)
has been investigated across a variety of wetland types in
different geographical regions and in the laboratory (yorio
and Bentley, 1973; Terhivuo et al., 1984; Mudgall and Patil,
1988; Burger and Snodgrass, 1998; gerstenberger and
Pearson, 2002; Loumbourdis and Danscher, 2004; Bank
et al., 2007; Hothem et al., 2008, 2010). The wide distribu-
tion of
Ranidae,
ease of field identification, and apparent
changes in response to local contaminant levels make spe-
cies of this group useful as bioindicators of Hg pollution
in a variety of wetland ecosystem types. Although the link
