Climate-Driven Alterations in the Mercury Cycle: Implications for Wildlife Managers Through a One Health Lens

Abstract

Mercury (Hg) is a naturally occurring element, but atmospheric Hg has increased due to human activities since the industrial revolution. When deposited in aquatic environments, atmospheric Hg can be converted to methyl mercury (MeHg), which bioaccumulates in ecosystems and can cause neurologic and endocrine disruption in high quantities. While higher atmospheric Hg levels do not always translate to higher contamination in wildlife, museum specimens over the past 2 centuries have documented an increase in species that feed at higher trophic levels. Increased exposure to pollutants presents an additional threat to fish and wildlife populations already facing habitat loss or degradation due to global change. Additionally, Hg cycling and bioaccumulation are primarily driven by geophysical, ecological, and biogeochemical processes in the environment, all of which may be modulated by climate change. In this review, we begin by describing where, when, and how the Hg cycle may be altered by climate change and how this may impact wildlife exposure to MeHg. Next, we summarize the already observed physiological effects of increased MeHg exposure to wildlife and identify future climate change vulnerabilities. We illustrate the implications for wildlife managers through a case study and conclude by suggesting key areas for management action to mitigate harmful effects and conserve wildlife and habitats amid global change.

Full text

Academic Editor: Fei Jiang
Received: 6 March 2025
Revised: 5 April 2025
Accepted: 10 April 2025
Published: 14 April 2025
Citation: Wilkening, J.L.; Kurthen,
A.L.; Guilbeau, K.; Libera, D.A.;
Nelson, S.J.; Ming, J. Climate-Driven
Alterations in the Mercury Cycle:
Implications for Wildlife Managers
Through a One Health Lens. Land 2025,
14, 856. https://doi.org/10.3390/
land14040856
Copyright: © 2025 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/
licenses/by/4.0/).
Review
Climate-Driven Alterations in the Mercury Cycle: Implications
for Wildlife Managers Through a One Health Lens
Jennifer L. Wilkening 1,* , Angelika L. Kurthen 1,2, Kelly Guilbeau 3, Dominic A. Libera 1, Sarah J. Nelson 4
and Jaron Ming 1
1Natural Resource Program Center, National Wildlife Refuge System, U.S. Fish and Wildlife Service,
Fort Collins, CO 80525, USA; kurthena@oregonstate.edu (A.L.K.); dominic_libera@fws.gov (D.A.L.);
jaron_ming@fws.gov (J.M.)
2Department of Integrative Biology, Oregon State University, Corvallis, OR 97333, USA
3Science Applications, U.S. Fish and Wildlife Service, Lafayette, LA 70517, USA; kelly_guilbeau@fws.gov
4Appalachian Mountain Club, Gorham, NH 03581, USA; snelson@outdoors.org
*Correspondence: jennifer_wilkening@fws.gov
Abstract: Mercury (Hg) is a naturally occurring element, but atmospheric Hg has increased
due to human activities since the industrial revolution. When deposited in aquatic environ-
ments, atmospheric Hg can be converted to methyl mercury (MeHg), which bioaccumulates
in ecosystems and can cause neurologic and endocrine disruption in high quantities. While
higher atmospheric Hg levels do not always translate to higher contamination in wildlife,
museum specimens over the past 2 centuries have documented an increase in species
that feed at higher trophic levels. Increased exposure to pollutants presents an additional
threat to fish and wildlife populations already facing habitat loss or degradation due to
global change. Additionally, Hg cycling and bioaccumulation are primarily driven by
geophysical, ecological, and biogeochemical processes in the environment, all of which
may be modulated by climate change. In this review, we begin by describing where, when,
and how the Hg cycle may be altered by climate change and how this may impact wildlife
exposure to MeHg. Next, we summarize the already observed physiological effects of
increased MeHg exposure to wildlife and identify future climate change vulnerabilities.
We illustrate the implications for wildlife managers through a case study and conclude
by suggesting key areas for management action to mitigate harmful effects and conserve
wildlife and habitats amid global change.
Keywords: global change; pollutants; synergistic stressors; national wildlife refuge; climate
change vulnerability; one health; changing hydrology
1. Introduction
Mercury (Hg) is an element naturally found in the environment, which is released into
the atmosphere through processes like volcanic activity, forest fires, and rock weathering.
However, since the industrial revolution in the 1890s, there has been a rise in Hg levels
in the geologic record as human activities began releasing large quantities of elemental
mercury Hg
0
into the atmosphere [
1
]. Although increases in atmospheric mercury do not
necessarily equate to high mercury contamination of wildlife, museum specimens show a
similar increase in methylmercury (MeHg) burden for piscivorous birds and polar bears
(Ursus maritimus) over the last 120 years [
2
,
3
]. MeHg, the more toxic bioavailable form
of mercury, bioaccumulates in organisms, leading to detrimental effects on neurological
and endocrine systems [
4
]. Significant increases in MeHg within these predators during
Land 2025,14, 856 https://doi.org/10.3390/land14040856

Land 2025,14, 856 2 of 22
the post-1940s and post-1990s time periods coincide with periods of high anthropogenic
Hg
0
emissions, linking increased emissions to the increased bioaccumulation of MeHg in
wildlife [
2
]. Gaseous elemental mercury (Hg
0
; GEM), gaseous oxidized mercury (HgII),
and particulate mercury (PHg) are deposited on the landscape via precipitation and dust
particles, which are then integrated into the environment (Figure 1). In the simplest of
terms, deposited Hg can undergo four main pathways: (1) it may be methylated and
converted to its more toxic form (MeHg) by bacteria in aquatic environments, (2) it may be
stored long term in deep reservoirs such as ocean sediments or soils, (3) it may be stored
temporarily by accumulating in surface environments such as vegetation, the upper soil
layer, or surface waters, (4) it may be volatilized and returned to the atmosphere [
4
,
5
].
The fate of deposited Hg depends on environmental factors like temperature, chemical
conditions, and biological activity.
Land 2025, 14, x FOR PEER REVIEW 2 of 23
neurological and endocrine systems [4]. Significant increases in MeHg within these pred-
ators during the post-1940s and post-1990s time periods coincide with periods of high
anthropogenic Hg0 emissions, linking increased emissions to the increased bioaccumula-
tion of MeHg in wildlife [2]. Gaseous elemental mercury (Hg0; GEM), gaseous oxidized
mercury (HgII), and particulate mercury (PHg) are deposited on the landscape via pre-
cipitation and dust particles, which are then integrated into the environment (Figure 1).
In the simplest of terms, deposited Hg can undergo four main pathways: (1) it may be
methylated and converted to its more toxic form (MeHg) by bacteria in aquatic environ-
ments, (2) it may be stored long term in deep reservoirs such as ocean sediments or soils,
(3) it may be stored temporarily by accumulating in surface environments such as vege-
tation, the upper soil layer, or surface waters, (4) it may be volatilized and returned to the
atmosphere [4,5]. The fate of deposited Hg depends on environmental factors like tem-
perature, chemical conditions, and biological activity.
Figure 1. The biogeochemical mercury (Hg) cycle. Arrows denote Hg fluxes. All fluxes will be im-
pacted by climate change, represented by the globe and thermometer icons, as described in this
review. Original figure from U.S. National Park Service.
There is a long history of studying the human health impacts of Hg exposure, with
the first documented account appearing in patient records at Saint Bartholomew’s Hospi-
tal in 1865 [6]. Since then, global public health and medical communities have pinpointed
the common source of human exposure as the consumption of aquatic species in which
bioaccumulation of toxicity had occurred [7]. Effects vary by individual but may include
severe neurologic, cardiovascular, and reproductive issues upon exposure [8–10]. Similar
effects have been observed in wildlife, including neurological issues (e.g., visual impair-
ment), physiological impacts (e.g., inhibited growth), behavioral changes (e.g., lethargy),
and decreased reproductive success [11,12]. While convincing evidence indicates that
wildlife exposure to Hg has increased since the Industrial Revolution [13–15], trends in
MeHg accumulation vary, with concentrations rising in populations in some geographic
areas while remaining stable or declining in others. The toxicological impacts of Hg to
wildlife health have been summarized for several taxa (e.g., birds, fish, and mammals),
but questions remain about the complexities of the mercury cycle and the diverse methods
Figure 1. The biogeochemical mercury (Hg) cycle. Arrows denote Hg fluxes. All fluxes will be
impacted by climate change, represented by the globe and thermometer icons, as described in this
review. Original figure from U.S. National Park Service.
There is a long history of studying the human health impacts of Hg exposure, with
the first documented account appearing in patient records at Saint Bartholomew’s Hospital
in 1865 [
6
]. Since then, global public health and medical communities have pinpointed
the common source of human exposure as the consumption of aquatic species in which
bioaccumulation of toxicity had occurred [
7
]. Effects vary by individual but may include
severe neurologic, cardiovascular, and reproductive issues upon exposure [
8
–
10
]. Similar
effects have been observed in wildlife, including neurological issues (e.g., visual impair-
ment), physiological impacts (e.g., inhibited growth), behavioral changes (e.g., lethargy),
and decreased reproductive success [
11
,
12
]. While convincing evidence indicates that
wildlife exposure to Hg has increased since the Industrial Revolution [
13
–
15
], trends in
MeHg accumulation vary, with concentrations rising in populations in some geographic
areas while remaining stable or declining in others. The toxicological impacts of Hg to
wildlife health have been summarized for several taxa (e.g., birds, fish, and mammals),
but questions remain about the complexities of the mercury cycle and the diverse methods
used to measure trends. When viewing this widespread challenge through the lens of the

Land 2025,14, 856 3 of 22
interdisciplinary practice of One Health, addressing MeHg accumulation and exposure
becomes not only a human health concern but an environmental and wildlife health concern
as well.
Although international efforts, such as the Minamata Convention on Mercury, have
been implemented to reduce Hg emissions, legacy emissions and delays in the response
of global Hg reservoirs to atmospheric inputs continue to pose challenges [
16
,
17
]. Even if
Hg emissions remain constant, atmospheric and ocean surface Hg concentrations are still
expected to increase, as new emissions will accumulate in these reservoirs faster than they
can be transferred to deep ocean storage for long-term sequestration [
18
]. Global Hg levels,
particularly in surface reservoirs, are influenced by both climate change and anthropogenic
activities [19].
The 5th National Climate Assessment (NCA5) provides a snapshot of how climatic
shifts have impacted ten distinct regions of the United States and its territories [
20
]. While
each region presents unique challenges and opportunities, there are commonalities across
regions, such as compounding extreme events, impacts on social and economic systems,
and disproportionate effects on vulnerable communities. Seven regional chapters include a
key message related to ecological composition or shifts in biodiversity, while five of the
regional chapters include a key message connected to the quality or quantity of water
resources. Of note, there are no mentions of MeHg within the NCA5, although Hg is
mentioned in two places: the Midwest chapter in reference to fish consumption and toxic
chemicals (see Table 24.1 in [
21
], as well in a reference citation within the Southern Great
Plains chapter regarding dispersal of mercury-contaminated sediment during Hurricane
Harvey [
22
]). Table 1shows the occurrence of the following mercury-related effects in each
of the regional chapters of the NCA5.
Table 1. References to identified effects of changes to mercury (Hg) cycling throughout the regional
chapters of the Fifth National Climate Assessment. An X within a cell shows that the topic concept
appears within the chapter’s text.
Northeast
Southeast
Caribbean
Midwest
Northern Great Plains
Southern Great Plains
Northwest
Southwest
Alaska
Hawaii and US-Affiliated
Pacific Islands
Effects of increasing global temperatures
Increases in ocean temperatures X X X X X X
Increases in land temperatures X X X X X X X X X X
Increased cryosphere melting X X X
Increases in temperatures in freshwater systems X X X X X
Changing climate oscillations X X X X X X
Sea level rise X X X X X X X X
Increase in heavy precipitation and storms X X X X X X X X X X
Effects of increasing drought conditions Increase in wildfire intensity X X X X X X X X
Drying of freshwater systems X X X X X X X X X
Other co-factors influencing
mercury in wildlife
Human land use change X X X X X
Overfishing X X X X
Other pollutants X X X X X X
Climate change is also predicted to impact many pathways through which Hg is re-
leased, taken up, and moved worldwide [
4
]. Hg cycling and bioaccumulation are primarily
driven by geophysical, ecological, and biogeochemical processes in the environment, all of

Land 2025,14, 856 4 of 22
which may be modulated by hydrological or ecological disturbances. For example, climate
change may influence Hg cycling and environmental risk via altered wind currents and
warmer temperatures affecting patterns of Hg deposition and oxidation; changes in the
timing, frequency, type, and amount of precipitation; and altered frequency and intensity
of wildfires or melting of permafrost, which may result in increased Hg. Climate change is
a global driver that has both direct and indirect effects on the four ecological mechanisms
associated with local MeHg bioaccumulation, which are (1) primary productivity, (2) habitat
use, (3) bioenergetics, and (4) food web structure [
23
]. All of these can be directly influenced
by climate change through the alteration of the physical environment and indirectly via
the human response, such as adaptation in land use [
23
] or changes in water storage or
conveyance [
24
–
26
]. The broader ecological consequences may vary, resulting in both
beneficial and harmful outcomes, yet their precise influence on fish, wildlife, and their
habitats is not well understood.
In this review, we first explore the spatial, temporal, and mechanistic alterations of the
Hg cycle driven by climate change and their implications for wildlife Hg exposure. Next,
we summarize the documented physiological effects of increased Hg exposure to wildlife
and highlight future vulnerabilities associated with climate change. We then highlight
the implications for wildlife managers using the United States National Wildlife Refuge
System as a case study. We conclude by suggesting key strategies for wildlife managers
to mitigate Hg exposure and its harmful effects, supporting wildlife conservation amid
shifting climate conditions and evolving environmental contamination patterns.
2. Materials and Methods
The last review paper on the interaction between MeHg and wildlife was published
in 2020 [
27
]. Since then, there have been continued publications on mercury exposure
in wildlife, and we wanted to expand the assessment to consider climate change more
explicitly. While neither a meta-analysis nor a systematic review, we started our literature
review process by conducting a Boolean search in Web of Science, a commonly used
database with access to 22,000 journals, to understand the current issues at the nexus of
these topics and construct the manuscript outline. Specifically, we used the query “climate
change” AND “mercury” AND “wildlife” and chose to limit the publication years from
2020, the year of the last major review paper in the field, to 2024, the year this manuscript
was written, to capture the most updated literature. One benefit of the Web of Science
is the compilation of search results, including authors, abstracts, keywords, and links to
the publications so they can be further reviewed. We read through each of the 96 papers
that were listed with all three keywords. Some papers were incorrectly labeled or had
misleading keywords (for example, a study about climate change and wildlife included
“mercury” as a keyword, even though the only mention of mercury was in regard to a
mercury thermometer). Some papers were topical but were more focused on describing new
methods of measuring mercury in wildlife or developing a new model to predict mercury
burdens. Other papers quantified the mercury burden of species, but not specifically how
that mercury burden or exposure might be altered in the context of climate change.
Based on our reading and the current published literature, we developed the structure
of the review paper and the specific focus on implications for wildlife managers. After
choosing the topics we wanted to cover in the literature review, we proceeded to flesh out
each section without limiting the articles cited to the Boolean results mentioned earlier.
In the end, only 38 of the 96 papers from that Boolean search were included, as the key
point of the initial search was to guide the determination of which sections to include in the
review. Because climate change, mercury, and wildlife are global phenomena, papers cited
in this review are intercontinental and cover the Americas, Europe, East Asia, Oceania, and

Land 2025,14, 856 5 of 22
the Artic in general. However, the case study presented in this review is from the United
States, based on the physical location of the researchers. Additional articles outside of the
literature review (usually from earlier years) were included for context, to further explain
an idea or topic, or because a paper from 2020 to 2024 referenced that paper as a source for
a specific idea we wanted to include that required further explanation.
3. Results
3.1. Effects of Increasing Global Temperatures
Since 1850, global average temperatures have increased 1.59
±
0.25
◦
C on land and
0.88
±
0.2
◦
C in the ocean. Despite efforts to curb this warming, the most conservative
models (SSP1-1.9) predict that by 2100, the temperature will still be 1.5
◦
C greater than
1850–1900 levels [28].
3.1.1. Increases in Ocean Temperatures
As ocean temperatures rise, we can expect to see increases in MeHg at all trophic
levels. Ocean deoxygenation associated with increased ocean temperatures leads to hypoxic
and anoxic conditions that select for Hg-methylating microbes, increasing the amount
of MeHg that is bioavailable [
29
]. Increases in ocean water temperatures were linked
to increased MeHg production in marine ecosystems and subsequent increased MeHg
uptake in clams (Ruditapes philippinarum), which resulted in higher cellular damage [
30
]. In
predatory fish, ecosystem models investigating the impacts of a 1
◦
C increase in seawater
temperature showed increases in MeHg contamination. Based on historical data, Atlantic
cod
(Gadus morhua)
MeHg is predicted to increase 32%, Spiny dogfish (Squalus acanthias)
MeHg is predicted to increase 70%, and Atlantic Bluefin tuna (Thunnus thynnus) MeHg is
predicted to increase 56% [31].
3.1.2. Increases in Land Temperatures
Increased plant productivity from warmer environments could help sequester Hg into
soils, as Hg deposition from litterfall would increase [
1
,
19
,
32
,
33
]. In fact, global reforestation
on non-cropland and where forests are ecologically possible was modeled to increase Hg
sequestration by 98 Mg yr
−1
[
34
]. However, if paired with increases in precipitation and
subsequent increased runoff, more Hg will flow into aquatic systems, the primary place of
Hg methylation [
35
]. Additionally, despite potential increases in Hg sequestration in soils, a
review of Hg accumulation from the Holocene to the present showed a distinct correlation
between Hg accumulation and colder global temperatures, not warmer temperatures [
19
].
3.1.3. Increased Cryosphere Melting [28]
Permafrost is a long-term reservoir of Hg. As the permafrost thaws, the Hg stored is
released back into the biogeochemical mercury cycle [
36
]. Wetlands (and their downstream
freshwaters) associated with permafrost melt had significantly higher concentrations of
MeHg than upstream areas and wetlands not created by permafrost melt [36,37].
Glaciers and sea ice are already melting and will continue to melt [
28
]. Glaciers, sea
ice, and snowpack are known sinks of atmospheric Hg [
38
]. While photochemical reactions
often re-emit the Hg stored in ice back into the atmosphere, some remain in the meltwater
as MeHg and are transported into nearby environments [
1
,
38
]. In the Arctic, melting
snowpack leads to high MeHg input to coastal seawaters, which is bioaccumulated in the
marine food web [39].

Land 2025,14, 856 6 of 22
3.1.4. Increases in Temperatures in Freshwater Systems [28]
As land temperatures increase, landlocked freshwater systems will also see increased
temperatures. Extended periods of warm temperatures in lakes increased Hg methyla-
tion and decreased demethylation rates [
40
]. Anoxic waters and sediments promote the
methylation of Hg, usually via sulfate-reducing microorganisms [
41
]. Increases in water
temperatures generally decreased mixing, increased stratification, or raised the thermo-
cline, increasing the area of anoxic environments in lakes, which leads to increased MeHg
production [42].
Additionally, increased productivity in riparian zones can impact MeHg production
surrounding freshwater systems. In lakes with low productivity, increasing DOM input
stimulated microbial activity, which led to increased MeHg concentrations [
43
]. In a
gradient of lakes with increasing nearshore conifer cover, concentrations of Hg in fish
increased with tree cover percent because of increased organic carbon inputs [44].
3.1.5. Changing Climate Oscillations
As temperatures over both the ocean and land increase, climate oscillations will
continue to change [
45
]. In multiple species of arctic biota, yearly variation in the Hg
burden was related to time-lagged Arctic and North American Oscillations (AO/NAO), two
large-scale climate oscillations that influence climate and weather in North America [
46
].
These climate and weather patterns impact mercury cycling and bioavailability, as well as
influence biotic interactions. For example, they often influence the presence/absence of sea
ice during specific seasons, which in turn can influence the trophic level that pagophilic (ice-
loving) consumers feed at during that time [
47
]. As these climate oscillations are projected to
change in the coming decades, the cascading effects of these oscillations will likely change
Hg bioavailability and burdens in organisms. However, evidence of and the direction
of these changes may not be immediately clear, given the time-lag in the relationship
between the Hg burden and the AO/NAO, further complicating our understanding of
this relationship.
3.1.6. Sea Level Rise
Since 1901, the mean sea level has increased by 0.2
±
0.05 m, inundating coastal areas,
and the mean sea level will continue to increase as more glaciers melt [
28
]. In coastal Brazil,
increased MeHg concentrations are linked to the combined effects of sea level rise and
drought. Drought has reduced the flow of freshwater and new sediments through coastal
estuaries, while sea level rise has increased seawater intrusion into these estuaries. This
traps sediments in estuaries, creating anoxic environments, which methylate Hg. This has
resulted in increased MeHg production and increased MeHg concentrations in shrimp,
crab, and fish living in the estuary [
48
]. In tidal marsh songbirds, MeHg contamination can
interact with nest flooding probability to reduce songbird survival. Rising sea levels will
continue to flood tidal marshes, and if MeHg production in the marsh remains the same or
increases, the combined effect will reduce further tidal marsh songbird fitness [49].
3.1.7. Increase in Heavy Precipitation and Storms
Even at the lowest modeled change in global temperatures (+1.5
◦
C), heavy precipita-
tion, storm frequency and intensity, and associated flooding are predicted to increase [
28
].
Changes, including climate-induced changes, to hydrologic systems have an incredible
ability to moderate MeHg production [
23
]. In upland boreal and temperate forests, flooding
increased net MeHg production in nearby freshwater systems and MeHg bioaccumulation
in fish [50–52].

Land 2025,14, 856 7 of 22
3.2. Effects of Increasing Drought Conditions
Increased rates of evapotranspiration resulting from increased land temperatures will
lead to increases in drought conditions in some parts of the world [28].
3.2.1. Increase in Wildfire Intensity
Higher temperatures and drought frequency produce favorable conditions for wild-
fires, and wildfire size and frequency are expected to continue increasing under climate
change [
28
]. In geologic records, elevated mercury input into ecosystems is often linked to
increased forest fires [
1
], likely due to greater Hg and MeHg input into freshwater systems
via postfire runoff events [
53
–
55
]. Not only is MeHg directly introduced into these systems,
but also microbial Hg methylation in anaerobic sediments can be stimulated by wildfire
runoff inputs [
56
]. However, fire has also resulted in lower soil, litterfall, throughfall, and
stream water Hg due to volatilization and loss of organic soil horizon [
57
]. Changes to
water chemistry, like DOC and pH, from wildfire runoff can mediate or enhance micro-
bial methylation rates [
53
,
58
,
59
]. Additionally, wildfire-related changes in primary and
secondary productivity and associated trophic level shifts can impact the bioaccumulation
in freshwater wildlife more than total Hg and MeHg inputs into the system do [59].
3.2.2. Drying of Freshwater Systems
Increases in evaporation because of higher temperatures, drought conditions, and
altered precipitation regimes will affect the wetting and drying patterns of freshwater [
60
].
In some scenarios, this will lead to freshwater systems drying at faster rates and for longer
time periods than currently experienced. Lower lake levels due to drying events were
correlated with increased herring gull (Larus sp.) egg Hg concentrations [
61
]. The authors
speculated that this could be due to warmer, less oxygenated waters that promoted Hg
methylation or a correlation with dry weather and increased wildfires in the surrounding
areas, which are also known to increase Hg input into the ecosystem [
61
]. Overall, research
suggests that changes in hydrologic systems and sediment sources can impact Hg levels in
freshwater [
23
,
62
]. While droughts and decreased water flows may reduce point source
Hg pollution from nearby anthropogenic sources, it can also increase anoxic environments
where inorganic Hg is more readily methylated [62].
3.3. Other Co-Factors Influencing Mercury in Fish and Wildlife
3.3.1. Human Land Use Change
As climate change transforms the landscape around us, humans may have to turn to
the intensification of agriculture and resource extraction to meet our needs [
63
]. Human
land use and potential climate-related changes can also impact wildlife exposure to Hg [
64
].
Forests sequester and store a large amount of unmethylated Hg globally. For example, in
the Amazon rainforest, forested soils sequestered 138
µ
g Hg m
−2
yr
−1
and stored 9100
µ
g
Hg m
−2
in the top 5 cm, compared to areas deforested for mining, which only sequestered
8.6
µ
g Hg m
−2
yr
−1
and only stored 7100
µ
g Hg m
−2
in the top 5 cm [
64
]. If deforestation
of the Amazon continues at the same rate as in 2021, an additional 3.0 Mg Hg yr
−1
would
be released from soils [
65
]. Global models estimated that deforestation in 2015 released
217 Mg Hg yr
−1
, about 10% of all anthropogenic Hg emissions [
34
]. Deforestation for
logging, mining, or agriculture can also emit Hg back into the environment as legacy
emissions [
66
,
67
]. Research has documented links between deforestation and increased Hg
exposure for fish and wildlife, such as a study that found that MeHg burden was higher
for northern pike (Esox lucius) in lakes around logged areas than reference lakes [59].

Land 2025,14, 856 8 of 22
3.3.2. Overfishing
The impacts of overfishing are exacerbated by changes in oceans due to climate change,
which impact not only fish populations but also fish exposure to pollutants like Hg [
59
].
Overfishing can induce changes in marine trophic levels, thus affecting MeHg exposure
of predatory fish. Historical data and modeling show that the overfishing of herring
(Clupea sp.) led to species-specific trophic responses. In Atlantic cod (Gadus morhua),
herring overfishing decreased MeHg concentrations as cod switched from consuming large
herring with high MeHg body burdens to smaller herring with lower MeHg body burdens.
However, the overfishing of herring increased MeHg in Spiny dogfish (Squalus acanthias), as
dogfish switched from consuming herring to consuming cephalopods, which have higher
concentrations of MeHg [
68
]. Similarly, a multi-decadal study of sea bird MeHg burden
showed that the impact of overfishing and climate change on prey fish species led to a diet
shift, causing increased MeHg exposure in birds [31].
3.3.3. Other Pollutants
Other pollutants can interact with landscape characteristics to promote or prevent
the deposition and methylation of mercury. For example, sulfate deposition, especially in
sulfur-limited environments, can increase the number of sulfur-reducing bacteria, which in
turn can methylate mercury into MeHg, increasing the concentration of bioavailable Hg
and increasing the levels of Hg accumulated in aquatic invertebrates [69].
4. Discussion
The biomagnification of mercury in wildlife is a culmination of dietary consumption
of MeHg and physiological processes that govern the bioaccumulation of MeHg within
the body [
64
,
70
,
71
]. In a study on arctic fish and invertebrates, only long-lived predators
were at risk for mercury toxicity, highlighting the importance of an organism’s life history
for mediating the risk of lethal and sublethal effects of mercury [
72
]. Wildlife managers
will want to pay special attention to the condition and population health of high trophic
level predators that feed in aquatic or marine environments since these species are the most
likely to be exposed to high levels of mercury through their diet. At the same time, there
are fewer studies of some lower trophic level organisms and evidence from broad spatial
scale studies (e.g., [73]), which documents the relative importance of other factors such as
biogeochemistry, landscape characteristics, and food web characteristics [
74
], pointing to
the value of assessing multiple trophic levels as part of monitoring plans.
4.1. Case Study: The National Wildlife Refuge System
The United States National Wildlife Refuge System (NWRS) is the world’s largest
network of lands and waters (~346 million hectares) set aside for the conservation of fish,
wildlife, and their habitats [
75
]. NWRS units can be found in every state and all territories
of the United States, from Alaska to the Caribbean, providing a continental scale system
of conservation lands throughout North America. The system consists of 573 National
Wildlife Refuges, 38 Wetland Management Districts, and 5 Marine National Monuments,
which are managed under the purview of the United States Fish and Wildlife Service
(USFWS). These areas serve as vital habitats for fish and wildlife that , support high levels
of biodiversity and ecological integrity, and provide essential ecosystem services such as
water filtration and purification. Many at-risk species rely on these lands, with research
indicating that one-third of federally threatened or endangered species inhabit or depend
on these areas ([76], Figure 2).

Land 2025,14, 856 9 of 22
Land 2025, 14, x FOR PEER REVIEW 9 of 23
water filtration and purification. Many at-risk species rely on these lands, with research
indicating that one-third of federally threatened or endangered species inhabit or depend
on these areas ([76], Figure 2).
Figure 2. The U.S. National Wildlife Refuge System (NWRS) is the largest network of protected
lands and waters dedicated to conserving fish, wildlife, and their habitats. Spanning diverse ecosys-
tems across North America, many NWRS units (e.g., refuges) also include federally designated wil-
derness areas, such as Georgia’s Okefenokee National Wildlife Refuge (a). Refuges support rich bi-
odiversity and provide critical habitat for imperiled species like the endangered black-footed ferret
(Mustela nigripes); (b). Despite their protected status, these ecosystems remain vulnerable to airborne
and waterborne pollutants, with some refuges posting associated warnings (c). This has important
implications for human health, as many refuges are popular for hunting and fishing, such as Kirwin
National Wildlife Refuge in Kansas (d), underscoring the need for a One Health approach to con-
servation. Photo credits: (a,c) = Jennifer Wilkening, USFWS, (b) = Kimberly Fraser, USFWS, (d) =
USFWS.
Lands are managed for the continuing benefit of the American people according to
the National Wildlife Refuge System Administration Act of 1966 (16 U.S.C. 668dd-668ee)
and the National Wildlife Refuge System Improvement Act of 1997 (P.L. 105–57). This
legislation identifies conservation as the fundamental mission of the NWRS and ensures
that the biological integrity, diversity, and environmental health of these areas are main-
tained. Additionally, the legislation recognizes compatible wildlife-dependent recreation,
including hunting and fishing, as appropriate uses, with some areas designating these
activities as priorities.
Although NRWS units are designated as protected areas, pollutants can still infiltrate
via airways or waterways beyond their boundaries. While Hg has not been consistently
or comprehensively studied across the NWRS, some research has been conducted. At
Lostwood National Wildlife Refuge in North Dakota, researchers examined mercury con-
centrations in the eggs and nestlings of tree swallows (Tachycineta bicolor). Their findings
indicated that mercury concentration was higher in eggs collected near seasonal wetlands
when compared to semi-permanent wetlands or lakes, but no significant differences were
observed in nestlings [77]. Additional research at the same location found that seasonal
Figure 2. The U.S. National Wildlife Refuge System (NWRS) is the largest network of protected
lands and waters dedicated to conserving fish, wildlife, and their habitats. Spanning diverse ecosys-
tems across North America, many NWRS units (e.g., refuges) also include federally designated
wilderness areas, such as Georgia’s Okefenokee National Wildlife Refuge (a). Refuges support rich
biodiversity and provide critical habitat for imperiled species like the endangered black-footed
ferret
(Mustela nigripes)
; (b). Despite their protected status, these ecosystems remain vulnerable to
airborne and waterborne pollutants, with some refuges posting associated warnings (c). This has
important implications for human health, as many refuges are popular for hunting and fishing, such
as Kirwin National Wildlife Refuge in Kansas (d), underscoring the need for a One Health approach
to conservation. Photo credits: (a,c) = Jennifer Wilkening, USFWS, (b) = Kimberly Fraser, USFWS,
(d) = USFWS.
Lands are managed for the continuing benefit of the American people according
to the National Wildlife Refuge System Administration Act of 1966 (16 U.S.C. 668dd-
668ee) and the National Wildlife Refuge System Improvement Act of 1997 (P.L. 105–57).
This legislation identifies conservation as the fundamental mission of the NWRS and
ensures that the biological integrity, diversity, and environmental health of these areas
are maintained. Additionally, the legislation recognizes compatible wildlife-dependent
recreation, including hunting and fishing, as appropriate uses, with some areas designating
these activities as priorities.
Although NRWS units are designated as protected areas, pollutants can still infiltrate
via airways or waterways beyond their boundaries. While Hg has not been consistently
or comprehensively studied across the NWRS, some research has been conducted. At
Lostwood National Wildlife Refuge in North Dakota, researchers examined mercury con-
centrations in the eggs and nestlings of tree swallows (Tachycineta bicolor). Their findings
indicated that mercury concentration was higher in eggs collected near seasonal wetlands
when compared to semi-permanent wetlands or lakes, but no significant differences were
observed in nestlings [
77
]. Additional research at the same location found that seasonal and
semi-permanent wetlands consistently had the highest MeHg concentrations [
78
]. Mean-
while, a study at the nearby Glacial Ridge National Wildlife Refuge in Minnesota revealed
that while wetland sediment samples contained typical total Hg concentrations, MeHg
concentration was twice as high as those collected from locations outside the NWRS [79].

Land 2025,14, 856 10 of 22
Wildlife studies have revealed that alligators (Alligator mississippiensis) with elevated
Hg concentrations have lower body condition at Merritt Island National Wildlife Refuge in
Florida [
80
]. Similarly, Hg tissue concentrations for largemouth bass
(Micropterus salmoides)
were significantly correlated with body condition for fish from Crystal Reservoir at
Ash Meadows National Wildlife Refuge in southern Nevada [
81
]. Some studies have
documented Hg decline over time, such as a long-term study on saltmarsh sparrows
(Ammodramus caudacutus)
at Rachel Carson National Wildlife Refuge in Maine that found
blood Hg concentrations decreased from 2000 to 2017 [82].
Studies documenting elevated Hg concentrations on NWRS units have important
ramifications for human health, as hunting and fishing are available on over 400 NWRS
units. These areas are often known as “duck farms” since many complex water management
processes are carried out to enhance resources (e.g., nesting habitats and food) specifically
for waterfowl. An estimated 10–12 million waterfowl and migratory birds are harvested
annually across North America, with about 3 million originating from NWRS units [
83
].
Importantly, many of these harvested fish and wildlife are consumed by visitors to these
protected lands, creating a direct connection between Hg in these aquatic systems and
humans. This reiterates the importance of addressing Hg concerns within a One Health
framework, as wildlife managers have opportunities to engage with hunters and anglers
on potential risks and ways to minimize contamination. This engagement can also lead to
local communities participating in Hg monitoring programs.
4.2. Effects of Mercury on Wildlife Related to Physiology and Behavior
4.2.1. Dosing Studies
Dosing studies have estimated the median lethal dose (LD
50
24 h) of MeHg over 24 h to
be 11.9 mg/kg for rats, 22.4 mg/kg for hamsters (Cricetus cricetus), and over 17 mg/kg for
squirrel monkeys [
84
]. While doses below the LD
50
range may not be enough to outright kill
animals, there are sublethal effects to wildlife that can harm immune systems, neurologies,
endocrine functions, and behaviors that can ultimately cause populations to decline [
85
–
87
].
4.2.2. Immunosuppression
MeHg exposure is a strong immunosuppressor in wildlife [
88
,
89
]. The prevalence of
avian flu in various duck species increased with increased exposure to Hg [
90
]. North-
ern elephant seal (Mirounga angustirostris) mercury burdens were negatively correlated
to the antibody immunoglobulin M levels and inflammatory response regulator cytokine
IL-6 levels [91]
. In harbor seals (Phoca vitulina), increased MeHg concentration was as-
sociated with reduced numbers of lymphocytes.
In vitro
exposure to MeHg increased
cell mortality and decreased DNA, RNA, and protein synthesis [
92
].
In vitro
lymphocyte
growth and proliferation were reduced when exposed to HgCl
2
in brown watersnakes
(Nerodia taxispilota) [93]
. Newborn barnacle goslings (Branta leucopsis) exposed to Hg had
reduced levels of natural antibodies and Hg-induced inflammatory effects [
94
]. Bird em-
bryos with mercury contamination showed potential relationships with four different liver
tissues’ gene expression, suggesting that Hg exposure may also impact organisms on an
epigenetic level [95].
4.2.3. Endocrine Disruption
Mercury exposure is known to impact endocrine function in wildlife [
88
]. Thyroid
hormones play significant roles in moderating life history events, and disruptions to
the endocrine systems in juvenile wildlife can have permanent impacts on individuals
as adults [
95
]. Adrenocortical and thyroid hormone responses to elevated MeHg con-
centrations have been documented in both tree swallow (Tachycineta bicolor) nestlings
and rainbow trout (Oncorhynchus mykiss), although those responses depend on exposure

Land 2025,14, 856 11 of 22
amount, duration, and species [
96
–
98
]. Responses to exposure may not be linear. In
river otters
(Lontra canadensis)
, cortisol production decreases after a specific threshold of
Hg is accumulated [
99
]. In pagophilic (ice-loving) diving sea birds, MeHg blood levels
influenced a thyroid hormone associated with underwater foraging duration and depth.
When the sea birds were stressed due to early sea-ice breakage, this reduced the time
that the sea birds foraged underwater compared to years when sea-ice broke up when
expected [
100
]. This demonstrates that mercury-induced physiological changes occur in
the context of environmental change, which can elicit other hormonal changes, like stress
hormone production.
4.2.4. Reproduction
Mercury contamination can affect individual-level reproduction. For example, sex
hormone production was reduced in brown bullhead (Ameiurus nebulosus) exposed to
Hg [
98
]. Increases in Hg cause decreases in prolactin, a reproductive hormone in common
eiders (Somateria mollissima) [
101
]. When whole populations are exposed, this can cause
an entire population to decline. In arctic birds, Hg exposure reduced reproductive output
and threatened the entire population of the exposed species [
89
]. Increased Hg burdens
were associated with loon (Gavia immer) and zebra finch (Taeniopygia guttata) reproductive
output [
102
,
103
]. Without routine monitoring to determine that Hg concentrations were
affecting the cause of population decline, this could not be accurately determined, and
conservation efforts would continue to be undermined.
4.3. Changes in Mercury Exposure Related to Habitat
4.3.1. Migration
Migrating wildlife both import and export MeHg from systems, such as
salmon [104,105]
and sea birds [
106
,
107
]. Migrating individuals may also experience different exposure rates
than their resident counterparts because different spatial locations, even in the same biome,
have different mercury concentrations [
108
]. The Bicknell’s thrush (Catharus bicknelli) is ex-
posed to higher concentrations of MeHg in their wintering location than in their breeding
grounds [
85
]. In migratory birds, mercury exposure changes throughout the year, influenced
by changes in diet and trophic position, environmental mercury levels, and energy expendi-
ture [
109
,
110
]. In common eiders (Somateria mollissima), mercury concentrations were higher
in migratory populations than resident populations, and researchers hypothesized this was
because migratory eiders had access to and consumed higher trophic level prey than resi-
dents [
111
]. If patterns of migration change due to climate change (e.g., staying in wintering
locations for longer or shorter periods of time or not migrating at all), MeHg exposure for
migratory organisms may change.
4.3.2. Range and/or Diet Shifts
Northward range shifts because of climate change mean consumer-resource patterns
are disrupted, which can alter trophic patterns. This may induce changes in an organism’s
trophic level (increasing or decreasing it) or switching to a prey source with either higher
or lower Hg exposure than the prey usually eaten. It is hard to predict what exactly will
occur and how (and if) food webs may be rearranged [
47
]. However, it is well documented
that shifts in diet lead to shifts in MeHg exposure [
112
]. For example, researchers proposed
that changes in food webs in New York State lakes, either from environmental recovery
from acid deposition or from stocking and the introduction of invasive species, lead to
longer trophic chains and higher Hg concentrations in yellow perch (Perca flavescens; [
113
]).
Similarly, the invasion of dreissenid mussels (Dreissena polymorpha and Dreissena bugensis)
and declines in amphipod prey species in the Great Lakes caused predatory fish to switch

Land 2025,14, 856 12 of 22
from consuming zooplankton to small fish, thus feeding at a higher trophic level with
higher MeHg concentrations [114].
4.4. Co-Exposure to Mercury and to Other Stressors
4.4.1. Other Contaminants
Organisms will likely be exposed to more than one pollutant, leading to
in vivo
interactions and complex interactions between contaminants. For example, exposure to
both chlorpyrifos and MeHg increased MeHg accumulated in amphipods, as opposed
to exposure to just MeHg alone [
115
]. Exposure to PCBs and MeHg had a synergistic
increase on hepatic porphyria (genetic disorders that inhibit liver functioning) in quails
(Coturnix japonica; [
116
]) and a synergistic decrease in dopamine concentrations on rat brain
cells [
117
]. However, some interactions may be more positive and may mediate the effects
of Hg. Selenium (Se) reduces the risk of mercury toxicity in organisms by binding to Hg to
form the biologically inactive HgSe [
118
]. For example, leopard seals (Hydrurga leptonyx)
with higher Se:Hg molar ratios had lower Hg concentrations than leopard seals with a lower
Se:Hg molar ratio, demonstrating the importance of adequate Se in the diet to help counter
a high Hg burden [
119
]. Because of the strong association between Se:Hg molar ratios and
the risk of Hg toxicity, measuring levels of both contaminants may be useful for assessing
Hg toxicity risk [120]. The Hg burdens of long nosed fur seals (Arctocephalus forsteri) were
negatively associated with Se burdens, and Hg levels were strongly correlated with levels of
the heavy metals Cadmium (Cd), Vanadium (V), and Silver (Ag), although no physiological
effects attributed to those co-occurrences were recorded [
121
]. A negative relationship
between arsenic (As) and mercury levels was recorded in freshwater fish, attributed to
differences in the environmental conditions that promote the production of MeHg and the
conditions that facilitate the form of As that bioaccumulates. No physiological effects of
this interaction were observed [122].
4.4.2. Other Stressors
Beyond interactions between contaminant exposures, wildlife also face interactions
among Hg toxicity and other stressors, such as climate change-induced effects on nest-
ing [
123
], diseases and parasites, climate change-induced physiological stress [
99
], and
changes to migratory habitats [
89
,
106
,
109
,
124
,
125
]. These interactions can exacerbate the
already sublethal physiological effects of Hg exposure, further harming wildlife [123].
4.5. Management Actions That Could Potentially Alleviate the Effects of Mercury Exposure
We recommend four priorities for consideration when using a One Health framework
to help mitigate the effects of Hg on wildlife (Figure 3). The One Health framework recog-
nizes the inherent links between environmental health, wildlife health, and human health.
It emphasizes collaboration, communication, and coordination across historically siloed
sectors, including medical and public health, agriculture, environmental conservation, and
wildlife management [126,127]. Our suggestions include prioritizing the investigating (1),
monitoring (2), engagement (3), and prevention (4) of Hg in management actions and
plans related to wildlife resources to help maintain and mitigate the harmful effects on the
environment, wildlife, and humans (Figure 3). We recognize that wildlife managers are
already juggling multiple responsibilities, and our intent is not to add to their workload.
Instead, our suggestions build on routine activities to optimize their efforts in conserving
fish, wildlife, and their habitats.

Land 2025,14, 856 13 of 22
Land 2025, 14, x FOR PEER REVIEW 13 of 23
managers are already juggling multiple responsibilities, and our intent is not to add to
their workload. Instead, our suggestions build on routine activities to optimize their ef-
forts in conserving fish, wildlife, and their habitats.
Figure 3. Intersecting management priorities, often carried out by wildlife managers, for reducing
the impact of mercury (Hg) exposure on humans and on wildlife.
4.5.1. Investigating
Investigating dead organisms when feasible, through necropsies or tissue sampling,
can provide wildlife managers with a deeper understanding of individual body condition
and can help predict population demographics, which are critical for conservation success
[128]. Wildlife managers can send tissue samples from carcasses out for contaminant test-
ing, especially high trophic level aquatic predators, since contamination is often sublethal
and not observable to the eye. For example, on two separate occasions, managers discov-
ered Hg contamination in river oer (Lutra lutra) individuals through necropsy and tissue
testing [128,129]. This can help managers estimate Hg exposure rates and determine if
there is cause for concern. Additionally, managers can collaborate with hunters and an-
glers to identify wildlife carcasses and determine which should be sent out for testing.
4.5.2. Monitoring
Wildlife managers can engage in Hg monitoring as part of other routine management
activities, regularly testing either invertebrates or fish for Hg concentrations when feasible
and making sure these assessments include standardization for body size and species
[130,131]. Time series data from monitoring combined with experimental analyses can
Figure 3. Intersecting management priorities, often carried out by wildlife managers, for reducing
the impact of mercury (Hg) exposure on humans and on wildlife.
4.5.1. Investigating
Investigating dead organisms when feasible, through necropsies or tissue sampling,
can provide wildlife managers with a deeper understanding of individual body condition
and can help predict population demographics, which are critical for conservation suc-
cess [
128
]. Wildlife managers can send tissue samples from carcasses out for contaminant
testing, especially high trophic level aquatic predators, since contamination is often sub-
lethal and not observable to the eye. For example, on two separate occasions, managers
discovered Hg contamination in river otter (Lutra lutra) individuals through necropsy and
tissue testing [
128
,
129
]. This can help managers estimate Hg exposure rates and determine
if there is cause for concern. Additionally, managers can collaborate with hunters and
anglers to identify wildlife carcasses and determine which should be sent out for testing.
4.5.2. Monitoring
Wildlife managers can engage in Hg monitoring as part of other routine manage-
ment activities, regularly testing either invertebrates or fish for Hg concentrations when
feasible and making sure these assessments include standardization for body size and
species [
130
,
131
]. Time series data from monitoring combined with experimental analyses
can shed light on how Hg and its interactions with other stressors impact wildlife popula-
tions [
87
]. Moreover, investigating spatial patterns of Hg contamination can help determine
potential point sources for Hg pollution that may be affecting nearby wildlife [
132
], and
this information can be used to help limit pollution in the future. Monitoring how Hg
concentrations change over time and across space can help researchers determine the
relationship between different biological, physical, and climate factors and Hg exposure in

Land 2025,14, 856 14 of 22
ecosystems, with the intent to help predict where and what wildlife and humans may be at
risk for Hg toxicity [119,133,134].
One example is the Dragonfly Mercury Project (DMP), a national-scale program that
uses dragonfly larvae as bio sentinels for Hg relative risk in national parks, wildlife refuges,
forests, and other public lands [
73
]. More easily collected and analyzed than fish, imma-
ture aquatic dragonflies provide site-specific impairment indices developed by relating
dragonfly Hg to other aquatic and amphibian biota, which provide long-term assessment
of changes in Hg using a simple, standardized sampling protocol [
73
]. By monitoring
these interactions across space and time through a One Health lens, we can utilize histori-
cally siloed surveillance programs to proactively understand where future increases in Hg
levels might appear, thereby resulting in a predictable impact on environment, wildlife,
and human health [
135
]. It may be that a local medical community could be the first to
notice an unusual uptick in Hg-related conditions among patients, prompting cross-sector
collaboration to identify a potential source and collaborate on solutions.
4.5.3. Engagement
Wildlife managers regularly engage with local hunters and anglers and can leverage
these relationships to ask about the observed health and behavior of individuals, especially
high trophic level predators that primarily feed in aquatic systems [
136
]. Additionally,
wildlife managers can continue advising hunters and anglers on mercury levels to help
prevent human exposure to Hg. Mercury advisory signage and outreach are commonly
found near bodies of water that may expose fish-consumers to MeHg by consuming
contaminated fish species (Figure 4). Assessing the effectiveness of these outreach efforts is
paramount as we invest time and resources in public health education and prevention. Such
studies have found, however, that Hg advisories can fall short of reaching their intended
audience or desired goal [
137
–
139
]. Further, these advisories often focus on the impacts of
MeHg exposure on human health and rarely speak to the health of wildlife itself.
Land 2025, 14, x FOR PEER REVIEW 15 of 23
Figure 4. A common example of mercury advisory signage warning against the human health im-
pacts of consuming contaminated fish.
4.5.4. Prevention
Finally, wildlife managers can help prevent future Hg exposure by collaborating with
partners to mitigate exposure at the source when feasible. Managers often partner with
local regulatory agencies to re-evaluate permiing of high Hg emiing industries, even
when the source is beyond their direct authority, to prevent point source Hg pollution.
Additionally, wildlife managers and their governing agencies can choose to invest in non-
Hg creating energy sources when these options are available. Coal-based power plants
are the largest atmospheric Hg emiers in the United States [142]. Moving away from
coal-based power sources and choosing to power any infrastructure with non-Hg emiing
energy can reduce the Hg footprint of areas under the jurisdiction of a wildlife manager
(e.g., wildlife refuges or habitat management areas).
5. Conclusions
Climate change will invariably influence the mercury cycle, which in turn affects the
exposure of wildlife to Hg through a combination of abiotic and biotic interactions. The
direction and magnitude of this change will be dependent on the degree to which climate
change progresses, the climatic regime in each location, biogeochemical impacts on the
Hg cycle, the species affected, and the ecosystem in which this plays out. Additionally,
Hg exposure is mediated by human activities, like land use change and overfishing, other
contaminants, and other stressors that may change under a changing climate. At the high-
est risk for increased Hg exposure are long-lived, high trophic level predators that feed in
Figure 4. A common example of mercury advisory signage warning against the human health impacts
of consuming contaminated fish.
One Health-oriented messaging can help to remind audiences about the intercon-
nections between human health, environmental health, and wildlife health. For some

Land 2025,14, 856 15 of 22
audiences across the United States, this uplifting of the value and rights of wildlife informs
individual decisions (see mutualist, [
140
]). There is further evidence that emphasizing
moral norms and a responsibility to steward the landscape in outreach materials can
positively influence recreationists’ behavior [
141
]. Cross-disciplinary collaborations with
landscape ecologists and the public health sector, for example, can aid wildlife managers
in designing effectively tailored messaging to reach a variety of audiences. Investment in
building relationships with local hunters and anglers can broaden understanding of the
impact of wildlife health and disease, which in turn can inform outreach efforts.
4.5.4. Prevention
Finally, wildlife managers can help prevent future Hg exposure by collaborating with
partners to mitigate exposure at the source when feasible. Managers often partner with local
regulatory agencies to re-evaluate permitting of high Hg emitting industries, even when the
source is beyond their direct authority, to prevent point source Hg pollution. Additionally,
wildlife managers and their governing agencies can choose to invest in non-Hg creating
energy sources when these options are available. Coal-based power plants are the largest
atmospheric Hg emitters in the United States [
142
]. Moving away from coal-based power
sources and choosing to power any infrastructure with non-Hg emitting energy can reduce
the Hg footprint of areas under the jurisdiction of a wildlife manager (e.g., wildlife refuges
or habitat management areas).
5. Conclusions
Climate change will invariably influence the mercury cycle, which in turn affects the
exposure of wildlife to Hg through a combination of abiotic and biotic interactions. The
direction and magnitude of this change will be dependent on the degree to which climate
change progresses, the climatic regime in each location, biogeochemical impacts on the
Hg cycle, the species affected, and the ecosystem in which this plays out. Additionally,
Hg exposure is mediated by human activities, like land use change and overfishing, other
contaminants, and other stressors that may change under a changing climate. At the highest
risk for increased Hg exposure are long-lived, high trophic level predators that feed in
marine and freshwater systems. Wildlife managers, who play a vital role in conserving
these organisms, can proactively plan and adapt to address these emerging challenges.
We suggest that managers continue to engage with local hunters and anglers to track
changes in populations, monitor mercury levels, investigate deaths of these high trophic
level predators, and engage in preventative measures. Wildlife managers can mediate
Hg exposure in wildlife by understanding the current pattern of Hg trends and making
strategic decisions to prevent further Hg contamination in the face of climate change.
Author Contributions: Conceptualization, J.L.W., J.M. and A.L.K.; methodology, A.L.K., J.L.W. and
J.M.; investigation, A.L.K.; data curation, A.L.K.; writing—original draft preparation, A.L.K., J.L.W.,
K.G., D.A.L., S.J.N. and J.M.; writing—review and editing, A.L.K., J.L.W., K.G., D.A.L., S.J.N. and
J.M.; visualization, K.G., D.A.L. and S.J.N.; supervision, J.L.W. and J.M.; funding acquisition, J.L.W.
and J.M. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: No new data were created.
Acknowledgments: The findings and conclusions in this article are those of the authors and do not
necessarily represent the views of the U.S. Fish and Wildlife Service.
Conflicts of Interest: The authors declare no conflicts of interest.

Land 2025,14, 856 16 of 22
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