2. Penobscot River Mercury Study Panel - Radiochemical

2. Penobscot River Mercury Study Panel - Radiochemical analyses of sediment
cores from the Penobscot River and Estuary, Peter H. Santschi, PI, Bryce
Johnson, Kathleen Schwehr, Patrick Louchouarn, co-PIs, 2009-2011 ($330,400).
This court mandated collaborative project between USM, TAMUG and the Flett Laboratory will
evaluate the potential of natural attenuation of the mercury contaminated Penobscot River and
Estuarine System in Maine through determination of sedimentation and sediment mixing rates.
Summary:
This court mandated collaborative project between USM, TAMUG and the Flett Laboratory will
evaluate the potential of natural attenuation of the mercury contaminated Penobscot River and
Estuarine System in Maine through determination of sedimentation and sediment mixing rates.
The gradual reduction of surface sediment mercury concentrations by deposition of cleaner
particulates should lead to a gradual reduction in the rate of methyl mercury (MeHg) production
in the ecosystem, which would be followed by lower MeHg concentrations in biota. This natural
attenuation option would obviously also be very cost effective because it would require no active
remediation.
Methods to measure sediment accumulation rates are very well established. The age of sediments
can be determined by the use of several radioisotopes that have been deposited from past
atmospheric nuclear testing events (cesium-137, plutonium-239, 240) as well as ongoing
deposition of naturally occurring radioisotopes (beryllium-7, lead-210). The concentration
profiles of these isotopes versus depth is used to determine the rate of long term sediment
accumulation. These isotopes can also be used to identify locations where sediments, which are
resuspended often by currents as they move down the river, are being temporarily deposited.