Using reactive thin-film membranes and molecular tools to determine mercury mobility and transformation in the Penobscot River estuary sediment, Maine

PIs: Aria Amirbahman, University of Maine; Melinda Diehl, University of Maine

Mercury in Maine

The inland and coastal waters in Maine have been subject to long term mercury (Hg) loading. Consequently, Maine 's birds, fish, and other species have accumulated some of the highest Hg body burdens in the United States . Mercury is an acute neurotoxin that bioaccumulates and biomagnifies, so that even small amounts of Hg in the environment can be a serious problem.

We are concerned with the biogeochemical cycling of Hg in estuaries, controlled by both biotic and abiotic processes. Tides can cause rapid changes in the chemical composition of water and sediment, resulting in shifts in Hg speciation and mobility. Measuring Hg fluxes in estuaries is difficult due to redox sensitivity, high spatial heterogeneity, and the low concentrations at which Hg is present. We have developed a thin-film membrane that can increase the spatial and temporal resolution of Hg measurements in sediments (see figure). These membranes have shown promising results in laboratory tests, but have yet to be deployed in the environment.

Project Plan

We will deploy the reactive thin-film membranes in the contaminated sediments of the Penobscot River estuary to measure the mobility of sediment Hg and methylmercury (MeHg) pools. Previous research data on Hg in Penobscot sediments will be used to validate the use of the thin-film membranes. After collection, the membranes will be cut into thin slices to capture a profile of Hg dynamics, particularly at the sediment-water interface (SWI). Most biotic transformations of Hg happen close to the SWI, where Hg can diffuse into the overlying water.

Microbes play a very important role in the mobilization and transformation of Hg. Sediment cores will be collected (adjacent to the membranes) to characterize these biotic processes. DNA will be extracted from slices of sediment cores that correspond to the Hg depth profiles obtained from the membranes. Specifically, we will target sulfate and iron reducers that have been implicated in Hg transformations, as well as bacteria carrying genes involved in Hg detoxification and reduction.

By combining geochemical and biological methods we will provide mechanistic insight into the mobility and bioavailability of sediment Hg, two characteristics that affect Hg bioaccumulation.

Contact Information

Melinda Diehl
Department of Civil and Environmental Engineering
320 Boardman Hall
University of Maine 04469

207-581-3401