Mercury is a toxic metal that is negatively impacts the health of humans and wildlife that consume fish throughout the northeastern United States. Humans have increased the loading of mercury to aquatic ecosystems in this region through combustion of coal, incineration of waste, and other industrial processes. Soils act as a strong accumulator and ‘natural barrier’ preventing much of the human-derived mercury from entering lakes and rivers. However, exotic and invasive earthworm species threaten the stability and retention of mercury in the forest soils.
Invasive and exotic earthworms can bioaccumulate mercury by consuming soils with elevated concentrations. Invasive earthworm populations experience nearly complete winter mortality. The fate of the mercury taken up by the earthworms is unclear; the earthworm-derived organic materials (EDOM) may or may not stabilize mercury in soil. I conducted a decomposition experiment to quantify the retention rate of mercury and identify chemical properties of EDOM promoting mercury retention.
The Graduate Alumni Research Award allowed for the preparation of soil thin-sections containing EDOM and travel to the Stanford Linear Accelerator Center (SLAC). At SLAC, my collaborators and I analyzed EDOM in soil using micro X-ray fluorescence (μXRF) and X-ray absorption spectroscopy (XAS). We created spatial maps of mercury in soil and its relationship with other elements using the μXRF instrument. In addition, XAS was used to quantify the chemical species of lighter elements responsible for stabilization of mercury. This research will determine if EDOM can stabilize mercury in soil and give insight on the molecular mechanisms responsible. Our results will help inform scientists and forest managers about potential in-direct hazards from invasive earthworms.