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Project 6

Geochemical Controls on the Sorption, Bioavailability, Formation and Long-term Environmental Fate of Polychlorinated Dibenzo-p-Dioxins (PCDDs) 

Due to their exceptionally low water solubilities polychlorinated dibenzodioxins and furans (PCDD/Fs) are strongly and extensively bound to soil and sediment particles.  Sorbed PCDD/Fs are distributed among the primary component geosorbents, namely char-like carbonaceous materials, amorphous organic matter, and clays, and the fractional distribution among these geosorbents is hypothesized to change with the total PCDD/F load.  Since PCDD/Fs are also highly resistant to decomposition, sorption is a primary determinant of their environmental fates and impacts.  Importantly, sorption to soil/sediment particles may modify the bioavailabilities and toxicities of PCDD/Fs in unknown ways, and bioavailability is expected to be geosorbent-specific. 

The major goals are:

  1. to advance fundamental understanding of PCDD/F sorption by the dominant geosorbents comprising soils/sediments, especially at very low environmentally relevant (ppt-ppb) concentrations where carbonaceous materials (e.g. chars) are hypothesized to control soil-water distribution
  2. to determine the differential bioaccessibilities/bioavailabilities of PCDD/Fs sorbed to each key geosorbent type using physiologically based extraction fluid, and mammalian models
  3. to test the hypothesis that mechanistic knowledge of sorption/desorption reactions for PCDD/Fs with individual component geosorbents can be extrapolated to predict site-specific bioaccessibilites and bioavailabilities for contaminated whole soils/sediments
  4. to evaluate the clay-facilitated formation of PCDD/Fs, and corresponding predioxins/furans, from precursor chlorophenols, and elucidate the underlying mechanistic basis for these reactions

Estimates of PCDD/F bioavailability in soils/sediments are few and inconsistent, hence most risk assessment models for exposure to environmental PCDD/Fs make generic assumptions of 100% bioavailability, irrespective of soil/sediment characteristics.  The results of the proposed research will provide the basis for (1) a more mechanistic understanding of the relationship between soil/sediment composition and the human and ecological risks posed by a given total PCDD/F load in soil/sediment, and (2) understanding the prevalence of clay-facilitated PCDD/F formation as an ongoing in-situ process leading to unexpected PCDD/F accumulations that threaten human health.  Further, it would be of great economic and environmental benefit if certain chars, such as those produced as intentional byproducts of biofuels/C-sequestration technologies, were shown to be effective as soil/sediment amendments to diminish bioavailability of PCDD/Fs.

Stephen BoydStephen A. Boyd, Ph.D.
Project Leader
Michigan State University

Cliff JohnstonCliff T. Johnston, Ph.D.
Purdue University

Hui Li
Hui Li, Ph.D.
Michigan State University

Brian TeppenBrian J. Teppen, Ph.D.
Michigan State University