Modulators of mercury risk to wildlife and humans in the context of rapid global change

Abstract

Environmental mercury (Hg) contamination is an urgent global health threat. The complexity of Hg in the environment can hinder accurate determination of ecological and human health risks, particularly within the context of the rapid global changes that are altering many ecological processes, socioeconomic patterns, and other factors like infectious disease incidence, which can affect Hg exposures and health outcomes. However, the success of global Hg-reduction efforts depends on accurate assessments of their effectiveness in reducing health risks. In this paper, we examine the role that key extrinsic and intrinsic drivers play on several aspects of Hg risk to humans and organisms in the environment. We do so within three key domains of ecological and human health risk. First, we examine how extrinsic global change drivers influence pathways of Hg bioaccumulation and biomagnification through food webs. Next, we describe how extrinsic socioeconomic drivers at a global scale, and intrinsic individual-level drivers, influence human Hg exposure. Finally, we address how the adverse health effects of Hg in humans and wildlife are modulated by a range of extrinsic and intrinsic drivers within the context of rapid global change. Incorporating components of these three domains into research and monitoring will facilitate a more holistic understanding of how ecological and societal drivers interact to influence Hg health risks.

Keywords: ASGM; Biomagnification; Fisheries; Immunotoxicity; Invasive species; Microbiome; Selenium.

Fig. 1

Conceptual model of mercury (Hg) pathways through the ecosphere, and the domains of drivers that influence the risk of Hg exposure and related adverse health effects. The gray arrows represent the combined physical, chemical, and biological processes that influence movement from one category to another, and the domains represent key drivers that interact with those processes to influence outcomes in the receiving categories. Global extrinsic drivers affecting methylmercury (MeHg) bioaccumulation in Domain 1 include hydrologic alteration, land-use change, invasive species, and climate change (see Fig. 2). Global extrinsic drivers that influence human exposure to inorganic Hg and MeHg in Domain 2 include changes in socioeconomic aspects of subsistence and luxury fish consumption and ASGM, whereas individual- and molecular-level intrinsic drivers within this domain include genetic variability and gastrointestinal assimilation (see Fig. 3). Extrinsic and intrinsic drivers modulating adverse health outcomes of MeHg and inorganic Hg exposure in humans and other animals in Domain 3 include exposure to pathogens and infectious disease, and variations in nutrients and co-contaminants, the microbiome, and genetics

Fig. 2

Major extrinsic drivers of global change (hydrologic alteration, land use change, invasive species, and climate change) indirectly (dashed arrow) influence methylmercury (MeHg) bioaccumulation and biomagnification through their direct effects (solid arrow) on key ecological mechanisms underlying MeHg bioaccumulation (primary productivity, habitat use, bioenergetics, and food web structure)

Fig. 3

Domain 2 represents extrinsic and intrinsic drivers that influence mercury (Hg) exposure in human populations. Domain 2 is influenced by the extrinsic drivers discussed in Domain 1 as they relate to human exposure to methylmercury through the consumption of Hg-contaminated fish

Fig. 4

Relationship between international gold prices, Hg imports, and extent of ASGM mining are in Peru. Reprinted from Swenson et al. (2011)

Fig. 5

Conceptual model for Domain 3, evaluating interactions between Hg exposure and key extrinsic and intrinsic drivers on adverse health outcomes in humans and wildlife