Superfund Research Program
Historical Exposure Assessment
Project Leader: James R. Hunt
Grant Number: P42ES004705
Funding Period: 2000 - 2006
- Project Summary
Final Progress Reports
Contaminants from industrial, municipal, mining and agricultural activities accumulate within the sediments of estuaries. Estuaries are recognized for their importance in maintaining the health of coastal ecosystems through the filtering of sediments and nutrients, and providing a nursery for some marine organisms. These benefits are limited by the accumulation of toxic substances, and human health can be impacted through the consumption of fish that concentrate contaminants.
Assessment and remediation of contaminated estuarine sediments is a challenge because the contamination is widespread but varies dramatically with depth. This unique distribution has resulted from the interplay between wind, waves, tides, freshwater inflow, and the accumulation of fine sediments. In this project the Drs. Hunt and Stacy have developed and applied new analytical methods to determine the three-dimensional distribution of contaminants within two contaminated sediment sites.
They collected over twenty sediment cores of at least a meter depth at each site. These cores have been age-dated using tracers deposited from the atmosphere following nuclear weapons testing. The investigators then developed maps of the sediment surface contamination levels expected historically. At the former Alameda Naval Air Station on San Francisco Bay, this analysis revealed that one of the contaminants in the Seaplane Lagoon used in luminescent paints, Radium-226, was predominately released during World War II, accumulated very close to the outfall discharge location, and has not migrated within the sediment column. These results demonstrated burial and isolation, and the data are being used by the responsible party and the regulatory community to guide the selection of remedial approaches. At the other site, waste from the Gambonini Mercury Mine accumulated in the Walker Creek Delta on Tomales Bay, north of San Francisco Bay. Age-dated sediment cores in the delta revealed recent accumulations of mercury from the mine are found in only selected locations. This analysis revealed that the mine significantly increased the discharge of mercury into the ecosystem and provided an inventory of total mercury in the delta that is needed in considering longer term recovery or possible remediation upstream.
Quantifying historical discharges from Superfund sites is important in understanding prior human exposures since many diseases take a long time to manifest symptoms. Through the development of new analytical instrumentation for sediment characterization, conducting detailed sediment collection efforts, and applying appropriate models for data interpretation, the investigators have demonstrated the ability to reconstruct historical sediment contamination levels at superfund sites.