Dioxins such as the potent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are persistent environmental contaminants, exposure to which results in a number of toxic effects in several species. In mice, TCDD-induced hydronephrosis of the kidney is among the most sensitive of developmental abnormalities. It is widely accepted that the toxic effects of dioxins such as TCDD are mediated by the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor expressed in virtually all tissues. Though it is known that activation of the AHR during development is likely the first step in TCDD-induced hydronephrosis, genetic events occurring downstream of AHR activation remain to be elucidated. To this end, we investigated the effect of TCDD on gene expression during development of the mouse kidney through use of expression arrays. Our analysis indicates that TCDD alters the expression of genes involved in the developmentally-critical Wnt signaling pathway and genes involved in cell cycle and cell proliferation. Further investigation of the effect of TCDD on Wnt pathway gene expression using an mRNA expression time course and in situ hybridization to characterize localized mRNA changes suggests that TCDD inhibits canonical Wnt signaling in the developing kidney. Consistent with our expression array finding that TCDD downregulates genes involved in cell proliferation, we also report a decrease in cell proliferation that coincides with regions of the kidney where inhibitors of canonical Wnt signaling are induced in response to TCDD. TCDD-induced disruption of Wnt pathway gene expression is not limited to the kidney, and alteration of Wnt gene expression is tissue-specific with varying effects observed in the heart, lung, liver, skin, and brain. Preliminary evidence also indicates that exposure to TCDD during development can alter the expression of microRNAs predicted to target Wnt pathway genes, suggesting a new mechanism for TCDD-induced disruption of gene expression. Taken together, our findings suggest that TCDD may disrupt an important pathway that is critical to the normal development of several organs in numerous species.

Dioxins such as the potent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are persistent environmental contaminants, exposure to which results in a number of toxic effects in several species. In mice, TCDD-induced hydronephrosis of the kidney is among the most sensitive of developmental abnormalities. It is widely accepted that the toxic effects of dioxins such as TCDD are mediated by the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor expressed in virtually all tissues. Though it is known that activation of the AHR during development is likely the first step in TCDD-induced hydronephrosis, genetic events occurring downstream of AHR activation remain to be elucidated. To this end, we investigated the effect of TCDD on gene expression during development of the mouse kidney through use of expression arrays. Our analysis indicates that TCDD alters the expression of genes involved in the developmentally-critical Wnt signaling pathway and genes involved in cell cycle and cell proliferation. Further investigation of the effect of TCDD on Wnt pathway gene expression using an mRNA expression time course and in situ hybridization to characterize localized mRNA changes suggests that TCDD inhibits canonical Wnt signaling in the developing kidney. Consistent with our expression array finding that TCDD downregulates genes involved in cell proliferation, we also report a decrease in cell proliferation that coincides with regions of the kidney where inhibitors of canonical Wnt signaling are induced in response to TCDD. TCDD-induced disruption of Wnt pathway gene expression is not limited to the kidney, and alteration of Wnt gene expression is tissue-specific with varying effects observed in the heart, lung, liver, skin, and brain. Preliminary evidence also indicates that exposure to TCDD during development can alter the expression of microRNAs predicted to target Wnt pathway genes, suggesting a new mechanism for TCDD-induced disruption of gene expression. Taken together, our findings suggest that TCDD may disrupt an important pathway that is critical to the normal development of several organs in numerous species.

Dioxins are among the most toxic substances known to man. Dioxins are hydrophobic organic molecules that accumulate in the food chain and can cause cancer and reproductive difficulties for both animals and humans. A common method for remediating contaminated soil is excavation and transporting the masses to a landfill site. That leads to large waste piles that occupy a lot of space and clean soil must be transported to the remediation area. By treating the contaminated soil, pure soil can remain untouched. The contaminated area can be treated at the spot (in-situ or on-site) and risks such as spread of polluted soil can be reduced, and transports can be reduced so the environment can be better protected. The purpose of this study is to evaluate remediation methods that is done in-situ or on-site for dioxin-contaminated areas and to make proposals for appropriate remediation methods for some selected dioxin-contaminated areas. For the remediation methods available to treat dioxin in-situ, soil washing seems to be an option. This method involves washing the soil with solvents to release the dioxin molecules from the organic material that it binds tightly to. The contaminated fluid is later pumped up to get disposed. Chemical oxidation, which is another method, is like soil washing but treats decontaminated pollutants that are in the groundwater. With the help of Fenton's reaction, the dioxin molecules can be destroyed, and no excavation is needed. Two other methods that have the potential to reduce the spread of dioxin contamination are stabilization / solidification and containment / barrier technology. These two are enclosing the pollution so it cannot be spread further in the soil. Thermal desorption is a method that can be used in conjunction with soil washing as a final step in destroying the dioxins. It can also be used separately and then heating rods are lowered into the ground which causes the dioxin to change to gas form. This method has also two other alternatives to heat up the pollution in the ground. By using hot water vapor thru the rods in the ground or by using electricity in predrilled holes in the ground and then suck the gas up thru pipes.  The gas with the pollutants is later sucked up to be purified through filters or by letting the pollutants pass through a combustion. When a contaminated area is going to be evaluated, there are some things that needs to be considered before making the choice of remediation method. It can be briefly summarized as a plan for what the area after decontamination will be used for and what is at the site today. These may be ancient remains, red-listed species that may affect the choice of remediation method. Likewise, the choice of method can be influenced if contaminated masses are to be driven to a remediation plant as it should be at an acceptable distance from the contaminated area, to reduce the climate impact. Both Bestorps f.d. sågverk and BT kemi in Teckomatorp who were studied, chose to excavate, and transport to an incineration plant (ex-situ). In this report it has emerged that the social, economic, and environmental aspects should be considered to achieve the best possible effect when choosing a remediation method, such methods are usually in-situ or on-site. Bestorps f.d. kemi and BT kemi in Teckomatorp could have been decontaminated by using soil wash and thermical treatment for the construction parts, such as the old warehouses, and then partly be treated in-situ and on-site and then tribute to reach some of the Swedish Miljökvalitetsmål.

No description available.

This thesis examines the discourses of human health and synthetic chemicals that emerged in New Zealand, focusing specifically on the 1970s dioxin controversy. Dioxins were highly toxic contaminants in the herbicide 2,4,5-T, one of the country’s most widely used agricultural chemicals from 1948 to 1987. The theoretical framework of the thesis is grounded in poststructural notions about power/knowledge and ideas from sociology and science studies that highlight the inevitable uncertainties that surround human exposure to chemicals. Archival material from the Agricultural Chemicals Board and the Department of Health, chemical industry publications and a range of other textual materials were analysed using a discourse methodology that focused on intertextuality. To better understand the discursive construction of dioxins in New Zealand, the role of the chemical industry, government and opposition groups in constructing, resisting and politicising dioxins is described. The thesis reconceptualizes environmental (in)justices as not exclusively local, but as boundless, discursive and socio-historic in character. It also reflects on how resolving contemporary dioxin injustices in New Zealand, themselves the result of historical exposures, are problematically still being approached primarily through a reductionist approach to health and chemicals.

Dioxins are environmental contaminants that raise concern because they are potent and persistent. The most potent dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), causes a wide variety of biochemical and toxic effects in laboratory animals and in humans. Major toxicities of TCDD are initiated by their binding to the AH receptor (AHR), a ligand-activated transcription factor that regulates expression of numerous genes. However, the specific genes whose dysregulation leads to major toxicities such as wasting, hepatotoxicity, and lethality are unknown. The objective of this thesis research was to identify the molecular mechanisms by which dioxins cause lethality. To this end, a powerful genetic rat model was utilized – the Han/Wistar (Kuopio) rat which is highly resistant to dioxin toxicity due to a major deletion in the AHR’s transactivation domain (TAD) leading to 3 potential AHR variant transcripts. We found that insertion-variant transcripts (IVs) are the dominant forms of AHR expressed in H/W rats, constitutively and after TCDD treatment. Gene expression array analysis revealed that the total number of TCDD-responsive genes in liver was significantly lower in H/W rats (that carry the TAD deletion) than in dioxin-sensitive rats (that carry wildtype AHR). Genes that are well-known to be AHR-regulated and dioxin-inducible  such as CYP1 transcripts  remained responsive to TCDD in H/W rats; thus the TAD deletion selectively interferes with expression of a subset of hepatic genes rather than abolishing global AHR-mediated responses. Genes that differed in response to TCDD between dioxin-sensitive rats and dioxin-resistant rats are integral parts of pathways known to be disrupted by dioxin treatment such as protein synthesis/degradation, fatty acid transport/metabolism, and apoptosis. These genes are worthy candidates for further mechanistic studies to test their role in major dioxin toxicities. Numerous differentially-regulated genes were downregulated; however, microRNAs, which downregulate mRNA levels in other systems, likely play no role in downregulation of mRNAs by dioxins in adult liver and are unlikely to be involved in hepatotoxicity. Findings in this research support the hypothesis that H/W rats are resistant to TCDD lethality because the TAD deletion prevents the AHR from dysregulating specific mRNA transcripts but not hepatic miRNAs.

Many physiological responses to dioxin-like compounds (DLCs), including polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are mediated by the aryl-hydrocarbon receptor (AhR). In birds, activation of the AhR stimulates the transcription of cytochrome P4501A (CYP1A) genes, including CYP1A4 and CYP1A5, and ultimately leads to expression of biotransformation enzymes, including ethoxyresorufin-O-deethylase (EROD). It is well established that potencies of different DLCs range over several orders of magnitude. There is also a wide variation among birds in their responsiveness to DLCs both in efficacy and threshold for effects. A molecular basis for this differential sensitivity has been suggested. Specifically, a comparison of the AhR ligand-binding domain (LBD) indicated that key amino acid residues are predictive of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) sensitivity. Based on sequencing of the AhR LBD from numerous avian species a sensitive classification scheme has been proposed (in order of decreasing sensitivity, chicken (type I; sensitive) > Common pheasant (type II; moderately sensitive) > Japanese quail (type III; insensitive)). A series of egg injection studies with White-leghorn chicken (<i>Gallus gallus domesticus</i>), Common pheasant (<i>Phasianus colchicus</i>) and Japanese quail (<i>Coturnix japonica</i>) were performed to determine whether molecular and biochemical markers of exposure to DLCs are predictive of the proposed classification scheme. In addition, I was interested in determining whether this classification scheme applies to other DLCs, specifically dibenzofurans. Determining which species are "chicken- like", "pheasant-like" and "quail-like" in their responses to DLCs should allow more refined risk assessments to be conducted as there would be less uncertainty about the potential effects of DLCs in those species for which population-level studies do not exist.<p> Several concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) (triolein vehicle) were injected into the air cells of Japanese quail, Common pheasant and chicken eggs. Liver from 14 d post-hatch chicks was harvested for analysis of CYP1A4 and CYP1A5 mRNA abundance by quantitative real-time PCR (Q-PCR), and EROD activity. Lowest observed effective concentration (LOEC) and relative potency (ReP) values for CYP1A mRNA abundance and EROD activity were determined and used to make comparisons of sensitivity between each species and DLC potency within each species.<p> The TCDD is widely considered to be the most potent DLC and this is supported by the rank order of LOEC values for CYP1A5 mRNA abundance in White-leghorn chicken (TCDD > PeCDF > TCDF). CYP1A4 mRNA abundance and EROD activity in White-leghorn chicken were significantly increased in the lowest dose exposure groups of each of the three DLCs, so the potency of these compounds based on these endpoints was not established. Interestingly, TCDD was not the most potent DLC in Common pheasant and Japanese quail. In Common pheasant, PeCDF is the most potent as a CYP1A4 mRNA inducer, followed by TCDD and TCDF. However, TCDF was the most potent EROD activity inducer for Common pheasant, followed by PeCDF, and then TCDD. No significant increases were found in CYP1A5 mRNA abundance in pheasant within the tested dose ranges for all the three DLCs. No significant increases in either CYP1A5 mRNA abundance or EROD activity were found in Japanese quail. In addition, PeCDF and TCDF, but not TCDD, significantly increased CYP1A4 mRNA abundance.<p> According to the predicted relative sensitivity by comparing the AhR LBD amino acid sequences, the White-leghorn chicken is more responsive to DLCs than the Common pheasant which is more responsive than the Japanese quail. By comparing the relative sensitivity calculated based on the LOEC values from my study, the sensitivity order to TCDD and TCDF support the proposed molecular based species sensitivity classification scheme (chicken > pheasant > quail), while pheasant is almost as sensitive as chicken to PeCDF ( pheasant ¡Ý chicken > quail).<p> Taken together, the data suggest that TCDD is the most potent DLC in White-leghorn chicken, but not in Common pheasant, or or Japanese quail. The data suggest that in type II avian species PeCDF may be more potent than TCDD. In addition, I found in my study that different biomarkers have different responses, which depends on species and chemicals as well. These data provide further insight into avian sensitivities to DLCs.</p>

Dioxins are environmental contaminants that raise concern because they are potent and persistent. The most potent dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), causes a wide variety of biochemical and toxic effects in laboratory animals and in humans. Major toxicities of TCDD are initiated by their binding to the AH receptor (AHR), a ligand-activated transcription factor that regulates expression of numerous genes. However, the specific genes whose dysregulation leads to major toxicities such as wasting, hepatotoxicity, and lethality are unknown. The objective of this thesis research was to identify the molecular mechanisms by which dioxins cause lethality. To this end, a powerful genetic rat model was utilized – the Han/Wistar (Kuopio) rat which is highly resistant to dioxin toxicity due to a major deletion in the AHR’s transactivation domain (TAD) leading to 3 potential AHR variant transcripts. We found that insertion-variant transcripts (IVs) are the dominant forms of AHR expressed in H/W rats, constitutively and after TCDD treatment. Gene expression array analysis revealed that the total number of TCDD-responsive genes in liver was significantly lower in H/W rats (that carry the TAD deletion) than in dioxin-sensitive rats (that carry wildtype AHR). Genes that are well-known to be AHR-regulated and dioxin-inducible  such as CYP1 transcripts  remained responsive to TCDD in H/W rats; thus the TAD deletion selectively interferes with expression of a subset of hepatic genes rather than abolishing global AHR-mediated responses. Genes that differed in response to TCDD between dioxin-sensitive rats and dioxin-resistant rats are integral parts of pathways known to be disrupted by dioxin treatment such as protein synthesis/degradation, fatty acid transport/metabolism, and apoptosis. These genes are worthy candidates for further mechanistic studies to test their role in major dioxin toxicities. Numerous differentially-regulated genes were downregulated; however, microRNAs, which downregulate mRNA levels in other systems, likely play no role in downregulation of mRNAs by dioxins in adult liver and are unlikely to be involved in hepatotoxicity. Findings in this research support the hypothesis that H/W rats are resistant to TCDD lethality because the TAD deletion prevents the AHR from dysregulating specific mRNA transcripts but not hepatic miRNAs.

Many physiological responses to dioxin-like compounds (DLCs), including polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are mediated by the aryl-hydrocarbon receptor (AhR). In birds, activation of the AhR stimulates the transcription of cytochrome P4501A (CYP1A) genes, including CYP1A4 and CYP1A5, and ultimately leads to expression of biotransformation enzymes, including ethoxyresorufin-O-deethylase (EROD). It is well established that potencies of different DLCs range over several orders of magnitude. There is also a wide variation among birds in their responsiveness to DLCs both in efficacy and threshold for effects. A molecular basis for this differential sensitivity has been suggested. Specifically, a comparison of the AhR ligand-binding domain (LBD) indicated that key amino acid residues are predictive of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) sensitivity. Based on sequencing of the AhR LBD from numerous avian species a sensitive classification scheme has been proposed (in order of decreasing sensitivity, chicken (type I; sensitive) > Common pheasant (type II; moderately sensitive) > Japanese quail (type III; insensitive)). A series of egg injection studies with White-leghorn chicken (<i>Gallus gallus domesticus</i>), Common pheasant (<i>Phasianus colchicus</i>) and Japanese quail (<i>Coturnix japonica</i>) were performed to determine whether molecular and biochemical markers of exposure to DLCs are predictive of the proposed classification scheme. In addition, I was interested in determining whether this classification scheme applies to other DLCs, specifically dibenzofurans. Determining which species are "chicken- like", "pheasant-like" and "quail-like" in their responses to DLCs should allow more refined risk assessments to be conducted as there would be less uncertainty about the potential effects of DLCs in those species for which population-level studies do not exist.<p> Several concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) (triolein vehicle) were injected into the air cells of Japanese quail, Common pheasant and chicken eggs. Liver from 14 d post-hatch chicks was harvested for analysis of CYP1A4 and CYP1A5 mRNA abundance by quantitative real-time PCR (Q-PCR), and EROD activity. Lowest observed effective concentration (LOEC) and relative potency (ReP) values for CYP1A mRNA abundance and EROD activity were determined and used to make comparisons of sensitivity between each species and DLC potency within each species.<p> The TCDD is widely considered to be the most potent DLC and this is supported by the rank order of LOEC values for CYP1A5 mRNA abundance in White-leghorn chicken (TCDD > PeCDF > TCDF). CYP1A4 mRNA abundance and EROD activity in White-leghorn chicken were significantly increased in the lowest dose exposure groups of each of the three DLCs, so the potency of these compounds based on these endpoints was not established. Interestingly, TCDD was not the most potent DLC in Common pheasant and Japanese quail. In Common pheasant, PeCDF is the most potent as a CYP1A4 mRNA inducer, followed by TCDD and TCDF. However, TCDF was the most potent EROD activity inducer for Common pheasant, followed by PeCDF, and then TCDD. No significant increases were found in CYP1A5 mRNA abundance in pheasant within the tested dose ranges for all the three DLCs. No significant increases in either CYP1A5 mRNA abundance or EROD activity were found in Japanese quail. In addition, PeCDF and TCDF, but not TCDD, significantly increased CYP1A4 mRNA abundance.<p> According to the predicted relative sensitivity by comparing the AhR LBD amino acid sequences, the White-leghorn chicken is more responsive to DLCs than the Common pheasant which is more responsive than the Japanese quail. By comparing the relative sensitivity calculated based on the LOEC values from my study, the sensitivity order to TCDD and TCDF support the proposed molecular based species sensitivity classification scheme (chicken > pheasant > quail), while pheasant is almost as sensitive as chicken to PeCDF ( pheasant ¡Ý chicken > quail).<p> Taken together, the data suggest that TCDD is the most potent DLC in White-leghorn chicken, but not in Common pheasant, or or Japanese quail. The data suggest that in type II avian species PeCDF may be more potent than TCDD. In addition, I found in my study that different biomarkers have different responses, which depends on species and chemicals as well. These data provide further insight into avian sensitivities to DLCs.</p>

The Port of Houston and the Houston Ship Channel (HSC) are highly industrialized areas along Galveston Bay, Texas. The HSC is highly polluted with a host of persistent organic pollutants, including dioxins. The main objective of this study was to determine the potential for in situ bioremediation in the HSC sediments. Our study focused on the bacterial group Dehalococcoides, since it is the only known group to reductively dechlorinate dioxins. Culture independent methods were used to determine the presence or absence of Dehalococcoides in HSC sediments. Molecular methods including PCR, cloning, restriction enzyme digest, and sequencing were used to determine the diversity of Dehalococcoides as well as total bacterial diversity in HSC sediments. The metabolically active members of the microbial community in HSC sediments were also determined using the same molecular methods as described above. Dehalococcoides was detected in every sediment core and at various depths within each core. Depths ranged from 1cm (SG-6) to 30cm (11261). Dehalococcoides diversity was centered on Dehalococcoides ethenogenes strain 195 and Dehalococcoides sp. strain CBDB1. Overall bacterial diversity in HSC sediments was dominated by Proteobacteria, especially Deltaproteobacteria, and Chloroflexi, which include Dehalococcoides. Total bacterial diversity at a wetlands control site was dominated by Betaproteobacteria and Acidobacteria. Deltaproteobacteria and Chloroflexi were determined to be the major metabolically active groups within the HSC sediments. These findings indicate that the HSC sediments have great potential for successful in situ bioremediation. These results also support the use of Dehalococcoides as a biological proxy for dioxin contamination.