Screening assay for dioxin-like compounds based on competitive binding to the murine hepatic Ah receptor. 2. Application to environmental samples

AH receptor agonist activity in human blood measured with a cell-based bioassay: evidence for naturally occurring AH receptor ligands in vivo

In the present study, an aryl hydrocarbon receptor (AHR)-driven reporter gene bioassay was used to measure the activity, measured as an induction equivalent (IEQ) as compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), or IEQ concentration in human blood samples from 10 volunteers under different dietary regimens. Blood concentrations of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs), as determined by analytical chemistry (HR-GC/MS), and expressed as toxic equivalents (TEQs) with the use of TCDD equivalency factors (TEFs), were within a range that has been reported in the general US population, ranging from 0.022 to 0.119 ppt (whole blood basis). However, the human blood IEQ measured directly via bioassay ranged from 13.4 to 218 ppt (whole blood basis). These order of magnitude greater IEQs compared to the TEQs for dioxins, furans, and certain PCBs suggests that human blood contains a relatively high level of AHR agonists able to activate the CYP1A1 dioxin response element (DRE)-linked reporter gene bioassay and that this AHR activity is not accounted for by PCDDs/Fs and dioxin-like PCBs based on standard HR-GC/MS and TEF analysis. When study participants switched from a "baseline" to a high-vegetable diet, increases in bioassay IEQ were observed that were statistically significant (P<0.05). In addition, IEQ activity was elevated above levels observed following dietary intervention in two subjects given indole-3-carbinol (I3C) supplements. We conclude that a substantial portion of the IEQ activity occurred as a result of the increased intake of natural AHR agonists (NAHRAs) present in many fruits, vegetables. and herbs. Our findings also suggest that dietary NAHRAs constitute a substantial daily dietary intake of AHR-active compounds, and these NAHRAs could influence AHR status in humans and play a role in a basal level of AHR activation.

Biomarkers and bioassays for detecting dioxin-like compounds in the marine environment

The presence of toxic chemical contaminants in some marine organisms, including those consumed by humans, is well known. Monitoring the levels of such contaminants and their geographic and temporal variability is important for assessing and maintaining the safety of seafood and the health of the marine environment. Chemical analyses are sensitive and specific, but can be expensive and provide little information on the actual or potential biological activity of the contaminants. Biologically-based assays can be used to indicate the presence and potential effects of contaminants in marine animals, and therefore, have potential for routine monitoring of the marine environment. Halogenated aromatic hydrocarbons (HAHs) such as chlorinated dioxins, dibenzofurans, and biphenyls comprise a major group of marine contaminants. The most toxic HAHs (dioxin-like compounds) act through an intracellular receptor protein, the aryl hydrocarbon receptor, which is present in humans and many, but not all, marine animals. A toxic equivalency approach based on an understanding of this mechanism provides an integrated measure of the biological potency or activity of HAH mixtures. Biomarkers measured in marine animals indicate their exposure to these chemicals in vivo. Similarly, in vitro biomarker responses measured in cell culture bioassays can be used to assess the concentration of 'dioxin equivalents' in extracts of environmental matrices. Here, I have reviewed the types and relative sensitivities of mechanistically-based, in vitro bioassays for dioxin-like compounds, including assays of receptor-binding, DNA-binding and transcriptional activation of native (CYP1A) or reporter (luciferase) genes. Examples of their use in environmental monitoring are provided. Cell culture bioassays are rapid and inexpensive, and thus have great potential for routine monitoring of marine resources, including seafood. Several such assays exist, or are being developed, for a variety of marine contaminants in addition to the dioxin-like chemicals. A battery of cell culture bioassays might be used to rapidly and sensitively screen seafood for the presence of contaminants of concern, including dioxin-like compounds as well as other contaminants such as natural toxins, hormonally active agents, and heavy metals. Such a battery of mechanism-based, in vitro bioassays could be incorporated into monitoring efforts under recently adopted hazard analysis and critical control point (HACCP) programs.

Melting and incineration plants of municipal waste. Chemical and biochemical diagnosis of thermal processing samples (emission, residues)

Control of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in emissions and thermal residues from incinerators has been a cause of public concern for more than one decade. Recently, several studies showed that other persistent organic pollutants (POPs) such as coplanar polychlorinated biphenyls (co-PCBs) also have dioxin-like activity and are released from incinerators. Therefore, the present study was aimed at making a risk assessment about dioxin-like activity in extracts of thermal waste residues (e.g. combustion gas; fly ash, slag) from incineration and melting processes in Germany and Japan. For this purpose, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), coplanar polychlorinated biphenyls (co-PCBs), polychlorinated naphthalenes (PCNs) and polyaromatic hydrocarbons (PAHs) were analyzed by chemical analysis. Additionally, 2, 3, 7, 8-TCDD equivalents (EROD-TEQs) were determined by in vitro Micro-EROD bioassay using rat H4IIE hepatoma cells. EROD-TEQs could be correlated to I-TEQ values (from PCDD/Fs/co-PCBs) analyzed by chemical analysis resulting in a maximal sixfold higher estimate. Our study indicates minor influences of co-PCBs, PAHs and PCNs to the sum of dioxin-like toxicity in the extracts of thermal waste residues as determined here. Furthermore, we showed that the levels of dioxins and co-PCBs contained in slag from melting processes and bottom ashes from incineration processes were lower by 1-2 orders of magnitude than that in fly ash.

Combinatorial bio/chemical analysis of dioxin and dioxin-like compounds in waste recycling, feed/food, humans/wildlife and the environment

The present review describes international activities using bioassays/biomarkers in combination with chemical analysis to measure the effects of dioxin and dioxin-like compounds (DLCs) in the environment. The above authors reviewed already the state-of-art bioanalytical detection methods (BDMs) for dioxins and DLCs [Environ Int (2001)]. The aim of this study will be to review applications of these bioassays/biomarkers to evaluate potential dioxins and DLCs. The present literature study lists relative potencies (REPs) of polyhalogenated dibenzo-p-dioxins and -furans (PXDD/Fs; X = Cl, Br, F), their thio analogues polychlorinated dibenzothiophenes (PCDTs) and thianthrens (PCTAs), polyhalogenated biphenyls (PXBs), polychlorinated naphthalenes (PCNs) and other Ah receptor agonists measured by several biodetectors (Tier 3 screening). The authors will discuss some examples of the applications of some of these biodetectors in biomonitoring programmes and recently occurred dioxin crisis in feed/food. The diagnosis of the biopotency of these pollutants in technical processes like thermally treated waste, waste water treatment, landfill leachate treatment, commercial PCB-mixtures, the release into the environment (soil, air and water) and the final intake into wildlife and humans will be reviewed.

Bioanalytical screening methods for dioxins and dioxin-like compounds a review of bioassay/biomarker technology

Determination of environmental pollutants utilizing biodetectors such as bioassays, biomarkers, enzyme immunoassays (EIAs), or other bioanalytical tools is a continuously growing area. The present literature review describes the principles and advantages/limitations of several bioanalytical detection methods (BDMs) for the screening and diagnosis of dioxin and dioxin-like compounds. This study characterizes briefly the family of dioxin and dioxin-like compounds, discusses potential Ah receptor (AhR) ligands and cytochrome P-450 (CYP) 1A1-enzyme-inducing compounds. 'Milestones' in the development of BDMs are summarized and explained in detail for a number of bioanalytical tools that can be used to detect these classes of dioxin-like persistent bioaccumulative toxicants (PBTs). The design of a screening profile with a battery of bioassays/biomarkers coupled with the chemical analysis is evaluated. The relative potencies (REPs) to 2,3,7,8-TCDD for dioxin-like compounds are reviewed for various BDMs and the differences are noted.

Dietary and tissue residue analysis and contaminant intake estimations in rats consuming diets composed of Great Lakes salmon: a multigeneration study

To further characterize the toxicological risk associated with chemical contaminants in Great Lakes fish, a multigeneration rat reproduction study was designed. Mature chinook salmon (Oncorhynchus tsawytscha), collected during the Fall 1991 spawning runs from Sydenham River, Lake Huron, and Credit River, Lake Ontario, were filleted, lyophilized, and incorporated into standard rat diets at 25% (w/w) or 100% (w/w) of the normal protein compliment [casein, 20% (w/w)]. This resulted in diets composed of 5 or 20% (w/w) lyophilized fish and estimated daily fish intakes by the rats at levels approximately 15- and 60-fold greater, respectively, than the current estimate for the Canadian public for all fish and seafood. Both fresh and lyophilized fish were analyzed for the following groups of contaminants: halogenated aromatic hydrocarbons [polychlorinated biphenyls, dibenzodioxins, and dibenzofurans (PCBs, PCDDs, PCDFs)], polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, metals, volatile organics, and other extractable organics (chlorinated phenols and benzenes). In general, only minor site differences existed for the specific types of contaminants detected; however, fish from the Credit River contained slightly greater amounts of PCBs (2- to 3-fold), dioxin toxic equivalencies (TCDD TEQs; 1.5- to 2.0-fold), DDT and metabolites (1. 5-fold), and appreciably higher amounts of mirex (15-fold). This general pattern of contaminant differences continued when the various diets were prepared using the lyophilized fish. Tissue samples (adipose, liver) were taken from the animals at various stages of the study and also analyzed for the same groups of contaminants. In general, adipose tissue was the major reservoir for organochlorine (OC) pesticides and PCBs, while "dioxin-like" PCDD/DF congeners and mercury were found preferentially in the liver. Contaminant intake calculations and tissue residue levels are provided.

Gas chromatographic analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans are toxic compounds formed during natural processes and human activities. The extraction and clean-up for these compounds from various environmental and biological sources has been described. The gas chromatographic analysis of polychlorinated dibenzo dioxins/furans with different columns and detectors has been reviewed. The advantages of using a mass detector in the analysis are discussed.