Mercury in Tree Rings

Objective/Intended Use

Develop an assessment tool for quantifying mercury in stemwood tissue and provide a preliminary assessment of historical trends in mercury deposition around a contaminated site as revealed by dendrochemical analysis.

Abstract

Contamination caused by release of mercury into the environment is a growing concern. This release occurs due to a variety of anthropogenic activities and natural sources. After release, mercury undergoes complicated chemical transformations. The inorganic forms of mercury released into the environment can be converted, by naturally occurring biological processes, into the highly toxic methylmercury species. This species is known to bioaccumulate in fish and animal tissue and human exposure to methylmercury has been associated with serious neurological and developmental effects. Historical trends in deposition of mercury into the terrestrial and aquatic environments is not well known. Trees have been shown to be good indicators and integrators of air and ground-water quality. Spatiotemporal trends in mercury around contaminated sites can be assessed using the historical record of elemental concentrations captured in the annual rings of trees. Knowledge of the regional spatiotemporal distribution of mercury deposition as reflected in tree rings can augment fate-and-transport modeling efforts. Temporal trends in mercury as revealed in tree rings can shed light on the effectiveness of on-going site clean-up and source emission reduction strategies.

Project Status

On-going. This study was initiated in the second quarter of FY03. A one-year no-cost extension was authorized in April 2004. Test tree cores have been collected for use in methods development. Tree cores around a chloralkali plant in North Carolina were sampled in summer 2003 for PIXE and ICP-MS analysis. This project is expected to be completed in the last quarter of FY05.

Project Start Date

05/14/2003

Project Completion Date (Actual/Projected)

05/31/2006