Pathways of Metal Transfer from Mineralized Sources to Bio-receptors

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Project Summary

The mid 1800s marked the beginning of a long and colorful history of mining in the western US that has left a legacy of approximately 11,000 abandoned hard rock mine sites.  At many of these sites, historical mining activities resulted in adverse impacts to the quality of water and sediment and to the health of humans and other biota.  Successful management of these ecosystems requires an understanding of the processes that are responsible for the distributions, concentrations, and bioavailability of potentially toxic elements, such as arsenic (As), cadmium (Cd), lead (Pb), mercury (Hg), selenium (Se), and zinc (Zn), in the environment.  Such understanding is used to identify and target those processes or pathways that have the greatest immediate and long-term impact on the environment and health of biota, and is the scientific foundation for making decisions, developing strategy, and assessing mitigation and remediation alternatives by local, state, and other federal agencies charged with minimizing the environmental and health impacts of the elements.  The Pathways Project is focused on improving our understanding of how elements are mobilized from mineralized sources, transported through the environment, and become available to humans and other biota.

Project Objectives & Strategy

The major objectives of the Pathways Project are to:

1. advance our understanding of the physical and biogeochemical processes responsible for the cycling of potentially toxic elements in large-scale ecosystems impacted by mineralized deposits and mine wastes,
2. develop conceptual and quantitative transport and reaction models that link the concentrations and distributions of elements to processes, and
3. identify those pathways that have the greatest chronic or adverse impact to the environment and health of biota.

To meet these objectives, work within the Pathways Project examines the behavior of various potentially toxic elements in different ecosystems and addresses several inter-related questions:

1. How does the speciation of dissolved and particulate elements affect their geochemical mobility and bioavailability?
2. What are the relationships among different types of microbial communities, processes that transform elements between various chemical forms, and the availability of elements to biota?
3. How do processes at physical and geochemical boundaries affect element speciation, mobility, and bioavailability?
4. How are the interactions and availability of elements with metal oxyhydroxide and oxyhydroxysulfate minerals affected by precipitation and aging of the minerals?
5. How do ecosystem conditions (for example, arid versus wet or vegetated versus non-vegetated) influence the transport and dispersion of elements?
6. Can conceptual and quantitative models be developed and used to link element concentrations and distributions in mineralized ecosystems to specific physical and biogeochemical processes and to understand the possible impact of natural and anthropogenic changes on element distributions in these systems?

View Understanding metal pathways in mineralized ecosystems: by Balistrieri, L.S., Foster, A.L., Gough, L.P., Gray, Floyd, Rytuba, J.J., and Stillings, L.L., 2007, U.S. Geological Survey Circular 1317, 12 p.