Skip Navigation

Michigan State University

Maintenance notice: We are currently addressing issues with broken links due to recent major website changes. We apologize for any inconvenience and appreciate your patience. Please contact for assistance.

Superfund Research Program

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

Project Leader: Stephen A. Boyd
Grant Number: P42ES004911
Funding Period: 2006-2021

Project-Specific Links

Project Summary (2013-2021)

Due to their exceptionally low water solubilities polychlorinated dibenzodioxin 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 clays, amorphous organic matter, and carbonaceous materials, and the fractional distribution among these geosorbents is hypothesized to change with the total PCDD/F load. Because PCDD/Fs are 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 knowledge of sorption of individual PCDD/F isomers by component geosorbents can be extended to whole soils/sediments by predicting and measuring site-specific domains for PCDD/F sequestration in a series of dioxin contaminated ball clays, and the corresponding PCDD/F bioaccessibilites
  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/Fs bioavailability in soils/sediments are few and inconsistent, hence most risk assessment models for exposure to environmental PCDD/Fs make generic and high (e.g. 100%) assumptions of bioavailability irrespective of soil/sediment characteristics. The results of this 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
  2. Establishing the importance of clay-facilitated PCDD/F formation as an on-going 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 by-products of biofuels/C-sequestration technologies, were shown to be effective as soil/sediment amendments to diminish bioavailability of PCDD/Fs.

Current risk assessment models typically assume 100% bioavailability of PCDD/Fs in soils. The ability to assign scientifically informed values for PCDD/F bioavailability, that account for soil composition, represents a major advance in understanding the exposure risk of PCDD/F contaminated soils/sediments. Formulating safe and realistic remediation endpoints based on available contaminant concentrations instead of total ones allows limited remediation funds to be better prioritized and needless remediation attempts avoided.

to Top