Oral Bioavailability of Polychlorinated Dibenzo-p-Dioxins/Dibenzofurans in Industrial Soils

ABSTRACT

In this study, the oral bioavailabilities of numerous 2,3,7,8-PCDD/F congeners were evaluated in soil samples from an industrial site. The purpose of this study is several-fold: (1) to compare the soil bioavailability results of the different PCDD/F congeners; (2) to evaluate the consistency of the bioavailability results with those obtained in an in vitro bioaccessibility study with simulated GI tract fluids; and (3) to develop quantitative bioavailability measurements that are appropriate for use in a health risk assessment for this site. Soil samples containing PCDD/F toxic equivalent (TEQ) concentrations ranging from 0.53–45.2 ng/g were administered to female Sprague Dawley rats via oral gavage. Reference formulations of PCDD/Fs were administered intravenously or by oral gavage. The overall relative bioavailability of PCDD/Fs in the soil samples on a TEQ basis ranged from 17 to 51%, with a mean of 38%. The results of the in vitro bioaccessibility study were consistent with the bioavailability results (mean extracted TEQ of 22%). Because of the clear relationship between increasing chlorination and decreasing bioavailability and bioaccessibility observed in this study, we suggest that simply extrapolating results from one congener to another may be associated with a high degree of uncertainty.

Key Words:

• dioxin
• TEQ
• soil contaminant
• PCDD/F bioavailability
• bioaccessibility

ACKNOWLEDGEMENTS

Funding for the conduct of this study, the preparation of this article, and other consulting services was provided to ChemRisk, Inc. by U.S. Magnesium, the operator of the facility that was the subject of this study.

Notes

^a Total toxic equivalent (TEQ) concentration of soil sample based on 2005 WHO toxic equivalency factors.

^a Total toxic equivalent (TEQ) concentration of soil sample based on 2005 WHO toxic equivalency factors.

^a Samples 1, 2, 6, 7, 8 were sieved to the < 250-μ m particle size fraction prior to analysis.

^b Samples 4 and 5 were sieved to the < 500-μ m particle size fraction prior to analysis. Sample 3 was not sieved.

^c Based on 2005 WHO toxic equivalency factors.

^a Samples 1, 2, 6, 7, 8 were sieved to the < 250-μ m particle size fraction prior to analysis.

^b Samples 4 and 5 were sieved to the < 500-μ m particle size fraction prior to analysis. Sample 3 was not sieved.

^c Based on 2005 WHO toxic equivalency factors.

^a Total toxic equivalent (TEQ) concentration in liver at time of sacrifice based on 2005 WHO toxic equivalency factors.

^a Based on 2005 WHO toxic equivalency factors.

^a Based on 2005 World Health Organization toxic equivalency factors.

^b Reference group dose level used as the basis of bioavailability determinations.

* Currently at Tetra Tech EM, Inc., 135 Main Street, Suite 1800, San Francisco, CA 94105.

**Currently at Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080.