Roadmap to Understanding Factors Influencing Mercury Exposure and Adverse Health Effects

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In a comprehensive overview, scientists explain that human and wildlife exposure and toxicological responses to mercury are dependent on factors that operate across global, individual, and molecular scales. They provide a roadmap for unified research to facilitate a better understanding of human and wildlife health risks from mercury exposure.

Mercury exposure is perceived as a threat to ecosystems and human welfare worldwide.  Mercury exposure can affect multiple organ systems and manifests as diverse adverse health outcomes in humans, fish, and wildlife. Risks posed by mercury exposure seldom follow a simple path from mercury releases to adverse health outcomes. Instead, external and internal factors at global, individual, and molecular scales interact and influence exposure and health outcomes.

Conceptual model for evaluating interactions between mercury exposure

Conceptual model for evaluating interactions between mercury exposure and key extrinsic and intrinsic drivers on adverse health outcomes in humans and wildlife (Diagram modified from Eagles-Smith and others, 2018)

The interaction of these factors is not well quantified, and that gap results in uncertainty regarding the connection between mercury releases and adverse health effects to humans and other organisms. Efforts to reduce mercury emissions hinge on the assumption that reductions in mercury will reduce exposure and effects. If other complex processes interfere, reductions may appear to be more or less effective than they actually are.

To address this need, the USGS Ecologically-Driven Exposure Pathways Science Team scientists, in collaboration with an international team of experts, provided a roadmap outlining the interaction of key external and internal factors operating across global to molecular scales to influence mercury exposure and health effects. Their goal was to integrate information from multiple scientific disciplines to provide a unified strategy for quantifying mercury exposure and potential effects.

This paper demonstrates that the context within which mercury exposure occurs in the environment is a critical aspect that can influence the risk of exposure and adverse health outcomes. The researchers identified land use change, hydrologic alterations, invasive species, food chain bioaccumulation, and socioeconomic factors as key external global factors that can influence mercury pathways in the environment and thus alter the availability of mercury for uptake. They also identified individual and molecular internal factors such as genetics, nutrition, interactions with the microbiome, and co-exposure to other chemical or microbial contaminants that modify mercury toxicity once exposure has occurred.

The scientists on the USGS Ecologically-Driven Exposure Pathways Science Team are continuing to develop tools that facilitate integration of global, individual, and molecular factors to foster an accurate understanding of health risks associated with mercury exposure. These tools are critical to understanding the effectiveness of mercury-reduction efforts in reducing health risks to humans and other organisms.

This study was funded by the USGS Contaminant Biology Program.

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