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Harvard School of Public Health

Superfund Research Program

Geochemical Processes Affecting Temporal Variability in Soil Metal Bioaccessibility

Project Leader: James P. Shine
Co-Investigators: Colleen Hansel (Harvard University), Daniel J. Brabander (Wellesley College)
Grant Number: P42ES016454
Funding Period: 2010-2015
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Project Summary (2010-2014)

The study of toxic heavy metals in the environment is challenging because metals are a natural component of our environment. As such, they have distinct biogeochemical cycles that govern their mobility, fate, and toxicity. A failure to understand these biogeochemical cycles will lead to a failure to adequately assess adverse impacts. Current risk assessment techniques for metals via the oral ingestion route are based on operationally defined tests which mimic the release of metals from soil in the human digestive system. The goal of this project is to be able to define the bioaccessibility of metals in geochemical terms, not based on operationally defined extraction methods. This goal is tested through a combination of laboratory and in situ studies of metal-contaminated soils and mining wastes to characterize the interplay of processes that increase metal bioavailability over time and those that decrease metal bioavailability over time. Through these experiments, researchers are testing whether the bioaccessibility of metals through oral ingestion can be predicted from the underlying speciation of metals and the characteristics of the soil itself. This study bridges the current gap between geology and toxicology. Current risk assessment methods can determine if metals in a soil may exert risk, but not why. It is the intent to show that through the incorporation of a modest amount of geochemical analysis, researchers can greatly improve risk assessment for metals in soils by showing why some soils exert risk while other soils with similar levels of metals do not exert risk. In addition, with a similarly modest understanding of the temporal cycling of metals, researchers can show that bioaccessibility of metals in soils is not time invariant. With this knowledge, risk assessment can be proactive in understanding the nature of both current and future risks.

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