Browsing by Subject "polycyclic aromatic hydrocarbons"

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    Biomarkers of Exposure to Foodborne and Environmental Carcinogens: Enterosorbent Intervention in a High Risk Population
    (2011-10-21) Johnson, Natalie Malek
    The need to assess human exposures to foodborne and environmental carcinogens, particularly in populations at high risk for cancer and disease, has led to the development of chemical-specific biomarkers. Sensitive biomarkers for aflatoxin and polycyclic aromatic hydrocarbons (PAHs) have been useful in providing information on population exposure and reducing associated public health impacts. Aflatoxins are fungal metabolites found in a variety of foods. Among these toxins, aflatoxin B1 (AFB1) is the most predominant and hepatocarcinogenic. Acutely, AFB1 can cause disease and death, necessitating safe and effective intervention strategies. Inclusion of NovaSil (NS) clay in the diet represents a practical, sustainable approach. NS has been shown to prevent aflatoxicosis in multiple animal species by binding aflatoxins in the gastrointestinal tract, reducing toxin bioavailability. Co-exposure to PAHs, hazardous environmental contaminants, has been shown to increase the risk for hepatocellular carcinoma (HCC). Therefore, objectives of this research were to utilize biomarkers to assess aflatoxin and PAH exposures in susceptible populations in Ghana and the U.S. and to evaluate the safety and efficacy of NS intervention in Ghana (a population at risk for aflatoxicosis). After 3-month intervention with 3.0g NS/day, median aflatoxin M1 (an AFB1 metabolite) was significantly reduced (up to 58 percent) compared to the placebo group. Furthermore, no significant differences were found in levels of nutrient minerals between NS and placebo groups at baseline and 3-months suggesting NS can be used to effectively sorb AFB1 without affecting serum concentrations of important minerals. PAH biomarker results showed participants in Ghana were significantly exposed to high levels of PAHs based on the presence of 1-hydroxypyrene (1-OHP) in the majority of urines (98.9 percent). NS treatment had no effect on 1-OHP levels, further confirming the preferential binding of aflatoxins by NS. U.S. population data from a Hispanic community in Texas with an elevated incidence of HCC demonstrated a lower percentage and level of aflatoxin and PAH biomarkers. Aflatoxin M1 excretion, however, was associated with increased consumption of certain foods prone to aflatoxin contamination; thus, some individuals may be more vulnerable to exposure and associated interactions that increase the risk for HCC (e.g., PAHs or hepatitis infection).
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    Chemical and biological methods for the analysis and remediation of environmental contaminants frequently identified at Superfund sites
    (Texas A&M University, 2004-11-15) Wiles, Melinda Christine
    Substantial environmental contamination has occurred from coal tar creosote and pentachlorophenol (C5P) in wood preserving solutions. The present studies focused on the characterization and remediation of these contaminants. The first objective was to delineate a sequence of biological changes caused by chlorinated phenol (CP) exposure. In Clone 9 cells, short-term exposure to 10 ?M C5P decreased pH, GJIC, and GSH, and increased ROS generation. Long-term exposure caused mitochondrial membrane depolarization (25 ?M), increased intracellular Ca2+ (50 ?M), and plasma membrane depolarization (100 ?M). Cells were affected similarly by C5P or 2,3,4,5-C4P, and similarly by 2,3,5-C3P or 3,5-C2P. Endpoints were affected by dose, time, and the number of chlorine substituents on specific congeners. Thus, this information may be used to identify and quantify unknown CPs in a mixture to be remediated. Due to the toxic effects observed due to CP exposure in vitro, the objective of the second study was to develop multi-functional sorbents to remediate CPs and other components of wood preserving waste from groundwater. Cetylpyridinium-exchanged low pH montmorillonite clay (CP-LPHM) was bonded to either sand (CP-LPHM/sand) or granular activated carbon (CP-LPHM/GAC). Laboratory studies utilizing aqueous solution derived from wood preserving waste indicated that 3:2 CP-LPHM/GAC and CP-LPHM/sand were the most effective formulations. In situ elution of oil-water separator effluent indicated that both organoclay-containing composites have a high capacity for contaminants identified in wood preserving waste, in particular high molecular weight and carcinogenic PAHs. Further, GAC did not add substantial sorptive capacity to the composite formulation. Following water remediation, the final aim of this work was to explore the safety of the parent clay minerals as potential enterosorbents for contaminants ingested in water and food. Calcium montmorillonite and sodium montmorillonite clays were added to the balanced diet of Sprague-Dawley rats throughout pregnancy. Based on evaluations of toxicity and neutron activation analysis of tissues, no significant differences were observed between animals receiving clay supplements and control animals, with the exception of slightly decreased brain Rb in animals ingesting clay. Overall, the results suggest that neither clay mineral, at relatively high dietary concentrations, influences mineral uptake or utilization in the pregnant rat.
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    Using Sediment Records to Determine Sources, Distribution, Bioavailability, and Potential Toxicity of Dioxins in the Houston Ship Channel: A Multi-proxy Approach
    (2012-07-16) Seward, Shaya M.
    Urban centers are major sources of contaminants to the surrounding air, water and soils. Above all, combustion-derived carbonaceous aerosols, especially black carbon (BC) and associated polycyclic aromatic hydrocarbons (PAHs), make significant contributions to the pollution in these systems. Here sedimentary records are used to produce a series of historical reconstructions of such contaminants to the Houston Ship Channel (HSC) system and compare these to point source inputs of hydrophobic organic contaminants (HOC). Analytical data on total organic carbon (TOC), BC, PAHs, dioxins and lignin (likely discarded from a pulp and paper mill along the Channel) were determined. This multi-proxy approach revealed that over the last several decades, HOC inputs to the system have been derived from a complex mixture of combustion processes, industrial point-sources, and oil spills. In particular, widespread dioxin contamination was observed throughout the study region with a particular site of the HSC showing total concentrations over 20,000 pg/g and 5000 pg toxic equivalent (TEQ)/g dry weight of sediment. Using two models based on sorption constants of total OC and BC, porewater concentrations were estimated to be lower than expected, at 20 pg/L and 5 pg TEQ/L. These values, however, are recognized as being extremely high for freely dissolved concentrations in porous media. The pulp and paper waste pit has recently been declared a Superfund site based on dioxin concentrations alone. The relationship between lignin biomarkers and dioxins observed in these sediments confirms that discharges of pulp and paper effluents were responsible for such high dioxin levels. Concentrations of BC, amorphous OC, and TOC were then used to calculate sediment binding of dioxins in sediments of the HSC. Our study found BC to be extremely low in HSC sediments (0.04 to 0.20%) indicating minimal dioxin sorption capacity. This suggests strong potential for fluxes of dioxins from sediments to the water column both through passive diffusion and physical mixing during natural and anthropogenic sediment remobilization events in this shallow system (hurricanes, storms, and dredging). The purposeful addition of BC to these sediments might be promising as a remediation strategy.