PNNL

Abstract

Seven polychlorinated dibenzo-p-dioxins (PCDDs), ten polychlorinated dibenzofurans (PCDFs) as well as twelve polychlorinated biphenyls (PCBs) are collectively referred to as dioxin-like compounds. The World Health Organization toxic equivalency factors (TEFs) for these persistent chlorinated organic compounds and their measured concentrations are used to produce the toxic equivalency quotient (TEQ) of a sample. TEF values are partially based on a common mechanism involving binding of the chemical to the aryl hydrocarbon receptor (AhR). Biological methods for the determination of TEQs are based on the assumption that all dioxin-related compounds act through the Ah receptor signal transduction pathway. Based on the biochemical response of CYP1A activation via the AhR, in vitro systems that utilize a reporter gene under transcriptional control of CYP1A have been developed. Several investigations have reported on the success of utilizing biological test systems to detect PCDDs, PCDFs, PCBs in environmental samples. The P450 Human Reporter Gene System assay (EPA Method 4425) utilizes a human hepatoma cell line (HepG2) in which a plasmid containing the human CYP1A1 promoter and 5'-flanking sequences with three xenobiotic responsive elements (XREs) fused to the luciferase reporter gene. The enzyme luciferase is produced in the presence of compounds that bind the XREs, and can be detected by a simple assay that measures relative light units with a luminometer. Method 4425, used by Columbia Analytical Services (CAS), has gained acceptance as a rapid and inexpensive approach for screening solvent extracts of environmental samples of soil, sediment, tissue, and water to detect compounds that activate the AhR. Investigations in the U. S. and Japan comparing the results of 4425 and standard high-resolution GC/MS (HRGC/HRMS) will be reported here. The purpose of making these comparisons is to determine if risk assessments for large dioxin sites both before and after remediation can be safely evaluated by the combination of analyses over a wide area by Method 4425 and confirmation of selected samples by HRGC/HRMS. Such an approach would allow a more comprehensive evaluation of a site, while saving considerable time and costs.