No description available.

Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) have been introduced in radiation therapy to achieve highly conformal dose distributions around the tumour while minimizing dose to surrounding normal tissues. These techniques have increased the need for comprehensive quality assurance tests, to verify that customized patient treatment plans are accurately delivered during treatment. In vivo dose verification, performed during treatment delivery, confirms that the actual dose delivered is the same as the prescribed dose, helping to reduce treatment delivery errors. In vivo measurements may be accomplished using entrance or exit detectors. The objective of this project is to investigate a novel entrance detector designed for in vivo dose verification. This thesis is separated into three main investigations, focusing on a prototype entrance transmission detector (TRD) developed by IBA Dosimetry, Germany. First contaminant electrons generated by the TRD in a 6 MV photon beam were investigated using Monte Carlo (MC) simulation. This study demonstrates that modification of the contaminant electron model in the treatment planning system is required for accurate patient dose calculation in buildup regions when using the device. Second, the ability of the TRD to accurately measure dose from IMRT and VMAT was investigated by characterising the spatial resolution of the device. This was accomplished by measuring the point spread function with further validation provided by MC simulation. Comparisons of measured and calculated doses show that the spatial resolution of the TRD allows for measurement of clinical IMRT fields within acceptable tolerance. Finally, a new general research tool was developed to perform MC simulations for VMAT and IMRT treatments, simultaneously tracking dose deposition in both the patient CT geometry and an arbitrary planar detector system, generalized to handle either entrance or exit orientations. It was demonstrated that the tool accurately simulates dose to the patient CT and planar detector geometries. The tool has been made freely available to the medical physics research community to help advance the development of in vivo planar detectors. In conclusion, this thesis presents several investigations that improve the understanding of a novel entrance detector designed for patient in vivo dosimetry.

The effect of engineered nanoparticles (ENPs) mixture consisting of silver oxide, (Agg0[Silver Oxide Nanopartical], 20 nm), titanium dioxide, (TiO2[Titanium dioxide], 30-40 nm) and zinc oxide, (ZnO, 20 nm) compared with their bulk metal salts was evaluated against unspiked activated sludge (control) using 3 parallel pilot-scale treatment plants. The total concentration of the ionic species of Ag+ Ti[Silver + Titanium] and Zn(2+) in the effluent of the ENP spiked activated sludge (AS) was below limits of detection and> 99% of the spiked ENP were found in the waste activated sludge (WAS), whereas 39 – 58 % of Ag0[Silver Oxide Nanopartical], 51 – 63 % and 58 – 74 % of ZnO ion concentrations were recovered in the anaerobic digestate (AD) cake suggesting higher affinity of ENPs to WAS than to anaerobic digestate. ENPs induced a 2-fold increase of the microbial community specific oxygen uptake rate (SOUR) compared with the control and > 98 % of ammonia and 80 % of COD were removed from the AS suggesting that the heterotrophic biomass retained their ability to nitrify and degrade organic matter at the spiked ENP concentration. The floc size and cultivable microbial abundance was reduced in the ENP spiked AS with no apparent disruption of the overall AS process efficiency. However, scanning electron microscopic analysis clearly showed damage to specific microbial cells. The lipid fingerprint and 16S rRNA gene-based pyrosequencing evidenced the dominance of Proteobacteria, Firmicutes, and Bacteriodetes with a clear temporal shift in microbial community structure. The prominent nano-tolerant bacterial species identified were Acidovorax, Rhodoferax, and Comamonas whereas Methanocorpusculum and Methanosarcina were recovered in AS and were the dominant Archaea in the AD with 99 and 98 % similarities to the closest culturable relative. Their presence in the AS suggests tolerance to ENPs and oxygen-dependent respiration. V. fisheri activity was not sensitive to the ionic concentrations of the ENP or metal salt mixture in the digestate samples and illustrates the need to develop bioassay using indigenous wastewater microorganisms to detect the potential effect of ENP. Overall, unlike other xenobiotic compounds, ENPs can hasten the natural selection of microbial species in activated sludge and anaerobic digestion processes.

Despite indications that they are potential contaminant transport systems and threats to groundwater quality, very little effort has been invested in comparing contaminant transport behavior of natural environmental nanocolloids and their corresponding macrocolloid fractions in the presence of As, Se, Pb, and Cu contaminants. This study involved physico-chemical, mineralogical, stability and contaminant-transport characterizations of nano- (< 100 nm) and macro-colloids (100-2000 nm) fractionated from three Kentucky soils and one biosolid waste. Particle size was investigated with SEM/TEM and dynamic light scattering. Surface reactivity was estimated using CEC and zeta potential. Mineralogical composition was determined by XRD, FTIR, and thermogravimetric analyses. Sorption isotherms assessed affinities for Cu2+, Pb2+, AsO3-, and SeO4-2 contaminants, while settling kinetics experiments of suspensions at 0, 2 and 10 mg/L contaminants determined stability and transportability potential. Undisturbed 18x30 cm KY Ashton Loam soil monoliths were also used for transport experiments, involving infusion of 50 mg L-1 colloid suspensions spiked with 2 mg L-1 mixed contaminant loads in unsaturated, steady state, unit gradient downward percolation experiments. Overall, nanocolloids exhibited greater stability over corresponding macrocolloids in the presence and absence of contaminants following specific mineralogy trends. Physicochemical characterizations indicated that extensive organic carbon surface coatings and higher Al/Fe:Si ratios may have induced higher stability in the nanocolloid fractions, in spite of some hindrance by nano-aggregation phenomena. In the transport experiments, nanocolloids eluted significantly higher concentrations of colloids, total, and colloid-bound metals than corresponding macrocolloids. Contaminant elutions varied by colloid type, mineralogy and contaminant, with the following sequences: soil-colloids>bio-colloids, smectitic>mixed≥kaolinitic>biosolid, and Se>Pb/Cu≥As. Our findings demonstrate that even though they behave more like nano-aggregates rather than individual nano-particles, nanocolloids may exhibit significantly higher mobility and contaminant transport potential over great distances in subsoil environments than their corresponding macrocolloid fractions.

Over 7.8 km of seismic reflection data and 2 km of electrical resistivity data were acquired, processed, and interpreted during this multi-method geophysical study. Objectives included the definition of geologic conditions underlying a contaminant plume in McCracken County, western Kentucky, and the determination of the potential for structural control on the rate and direction of plume migration. Both geophysical methods indicate the presence of multiple high-angle normal faults outlining a series of asymmetric grabens ranging in width from 160 m to almost 300 m and striking between N40°E and N45°E. There was agreement between the two methods on fault location and degree of near-surface offset, with offsets of 1 to 2 m observed at 10 to 20 m below ground surface and 3 to 8 m observed at 20 to 30 m depth. Bedrock displacement was generally 2 to 3 times larger, with offsets of 10 to 26 m observed. The faults appear to have originated in the Paleozoic with predominantly normal reactivation occurring as recently as the Pleistocene. The fault strikes generally approximate the orientation of the northwestern contaminant plume. Observed offset of the Regional Gravel Aquifer may form a preferential flow path for contaminant migration.

Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) have been introduced in radiation therapy to achieve highly conformal dose distributions around the tumour while minimizing dose to surrounding normal tissues. These techniques have increased the need for comprehensive quality assurance tests, to verify that customized patient treatment plans are accurately delivered during treatment. In vivo dose verification, performed during treatment delivery, confirms that the actual dose delivered is the same as the prescribed dose, helping to reduce treatment delivery errors. In vivo measurements may be accomplished using entrance or exit detectors. The objective of this project is to investigate a novel entrance detector designed for in vivo dose verification. This thesis is separated into three main investigations, focusing on a prototype entrance transmission detector (TRD) developed by IBA Dosimetry, Germany. First contaminant electrons generated by the TRD in a 6 MV photon beam were investigated using Monte Carlo (MC) simulation. This study demonstrates that modification of the contaminant electron model in the treatment planning system is required for accurate patient dose calculation in buildup regions when using the device. Second, the ability of the TRD to accurately measure dose from IMRT and VMAT was investigated by characterising the spatial resolution of the device. This was accomplished by measuring the point spread function with further validation provided by MC simulation. Comparisons of measured and calculated doses show that the spatial resolution of the TRD allows for measurement of clinical IMRT fields within acceptable tolerance. Finally, a new general research tool was developed to perform MC simulations for VMAT and IMRT treatments, simultaneously tracking dose deposition in both the patient CT geometry and an arbitrary planar detector system, generalized to handle either entrance or exit orientations. It was demonstrated that the tool accurately simulates dose to the patient CT and planar detector geometries. The tool has been made freely available to the medical physics research community to help advance the development of in vivo planar detectors. In conclusion, this thesis presents several investigations that improve the understanding of a novel entrance detector designed for patient in vivo dosimetry.

The fate and bioaccumulation of a contaminant entering the marine environment through wastewater outfalls depends on the contaminant’s persistence and affinity for particles. The physical characteristics of the receiving environment, e.g. current velocity, sedimentary processes, and the availability of organic carbon are also important. However, these latter effects are not usually evaluated quantitatively. This thesis investigates the near-field accumulation in sediment and biota of particle-reactive polybrominated diphenyl ethers (PBDEs) entering coastal waters via two municipal outfalls: one discharging into a high energy, low sedimentation environment near Victoria, B.C., Canada; the other into a low energy, high sedimentation environment near Vancouver, B.C. We used 210Pb profiles in sediment box cores together with an advection-diffusion model to determine surface mixing and sedimentation rates, and to model the depositional history of PBDEs at these sites. A particularly important finding of this study is that the very high energy environment to the southeast of the Victoria outfall accumulates PBDEs despite not having net sediment accumulation. Although the discharge of PBDEs was much lower from the Victoria outfall than from Vancouver, some sediment PBDE concentrations were higher near Victoria. Most PBDEs were dispersed beyond the near-field at both sites, but a greater proportion was captured in the sediment near the Vancouver outfall where rapid burial was facilitated by inorganic sediment supplied from the nearby Fraser River. Clearly, treating wastewater to the same level, regardless of local oceanographic conditions, will not result in a uniform environmental footprint. Total PBDE concentrations in benthic invertebrate communities were higher near Vancouver than Victoria, despite lower concentrations in sediments, and correlated with organic carbon normalized sediment concentrations. Principal Components Analysis suggested uptake of individual PBDE congeners was determined by sediment properties (TOC, grain size), whereas PCB congener uptake was governed by physico-chemical properties (octanol-water partitioning coefficient). Our results suggest that sediment quality guidelines for PBDEs and likely PCBs may be more relevant if corrected to TOC content in sediment. In addition, where enhanced wastewater treatment increases the ratio of PBDEs to particulate organic carbon in effluent, nearfield benthic invertebrates may face increased PBDE accumulation. This underlines the need for source control of persistent organic contaminants, which cannot be broken down by conventional wastewater treatment. / Graduate

Chemical and biological contaminants can enter a drinking water distribution system through one of the many access points to the network and can spread quickly affecting a very large area. This is of great concern, and water utilities need to consider effective tools and mitigation strategies to improve water network security. This work presents two components that have been integrated into EPA’s Water Security Toolkit, an open-source software package that includes a set of tools to help water utilities protect the public against potential contamination events. The first component is a novel water quality modeling framework referred to as Merlion. The linear system describing contaminant spread through the network at the core of Merlion provides several advantages and potential uses that are aligned with current emerging water security applications. This computational framework is able to efficiently generate an explicit mathematical model that can be easily embedded into larger mathematical system. Merlion can also be used to efficiently simulate a large number of scenarios speeding up current water security tools by an order of magnitude. The last component is a pair of mixed-integer linear programming (MILP) formulations for efficient source inversion and optimal sampling. The contaminant source inversion problem involves determining the source of contamination given a small set of measurements. The source inversion formulation is able to handle discrete positive/negative measurements from manual grab samples taken at different sampling cycles. In addition, sensor/sample placement formulations are extended to determine the optimal locations for the next manual sampling cycle. This approach is enabled by a strategy that significantly reduces the size of the Merlion water quality model, giving rise to a much smaller MILP that is solvable in a real-time setting. The approach is demonstrated on a large-scale water network model with over 12,000 nodes while considering over 100 timesteps. The results show the approach is successful in finding the source of contamination remarkably quickly, requiring a small number of sampling cycles and a small number of sampling teams. These tools are being integrated and tested with a real-time response system.

ABSTRACT The tropical and subtropical nearshore marine environments of Queensland, Australia sustain diverse and unique marine wildlife. Continuous population growth and land-use changes along the Queensland coastline are known to exert numerous anthropogenic pressures on these marine ecosystems, including the delivery of high sediment loads. Sediments also provide a transport pathway for persistent organic pollutants (POPs) from rural and urban catchments into the marine environment. While such pollutants are known to be elevated in marine sediment and biota from nearshore areas in Queensland, their input and distribution pathways, as well as exposure and associated risks to wildlife populations are only partially understood. Mounting evidence suggests that POPs may contribute to population declines in marine wildlife species; however, limited information is available regarding the accumulation and effects of these contaminants in endangered or threatened marine turtles. This study aimed to redress some of these information gaps using a case study approach in marine turtle habitats of Moreton Bay, and other embayments in Queensland. Among persistent organic pollutants (POPs), dioxins (polychlorinated dibenzo-p-dioxins; PCDDs) and to some extent also dioxin-like PCBs (polychlorinated biphenyls; PCBs) were found to be widespread and often present at elevated (ppb) levels in surface sediments from Moreton Bay. However, while PCDD/F toxic equivalencies (TEQs) are above international (Canadian) sediment quality guidelines at numerous sites in Moreton Bay, in general TEQs across the Bay are relatively low compared to those from contaminated locations near dense industrial activities. POP contamination in surface sediments across Moreton Bay was investigated by a combination of GIS spatial mapping, geostatistical and traditional statistical modalities. High spatial variability and complex spatial distribution patterns were revealed. High resolution GIS kriging model outputs from the mid to southern Bay facilitated identification of distinct sediment contamination zones, with highest PCB and PCDD/F levels present in nearshore locations, associated with nearby river systems. While primarily governed by organic carbon, a multitude of physical, chemical and hydrological factors were identified to influence the spatial variance of PCDD/F concentrations. The main parameters governing PCDD/F spatial distribution were identified as sediment geochemistry, water depth and anthropogenic alterations of the physical environment and, together, all quantifiable explanatory variables (including hydrodynamic flushing) explained ≈75% of spatial PCDD/F variance. Together, the interaction of these parameters results in complex distribution patterns and highly variable concentrations even among neighbouring sites of 1-3 km resolution. These results suggest that prediction models of POP distributions in the nearshore marine environment may require high-resolution validation, and highlights that the design of low resolution monitoring strategies can have profound impacts on the reliability of contaminant information or any subsequent extrapolations. This knowledge and methodology can be utilised to optimise on-going and future near-shore sediment monitoring programs both locally and in other regions around the world. Using the spatial distributions of dioxin-like contaminants within sediments, this study provided an opportunity to assess field-based relationships between habitat contamination and local marine biota contamination. Detectable levels of PCDD/Fs and dioxin-like PCBs were measured in all green, hawksbill, loggerhead and flatback marine turtle tissues. POP concentrations in sediments were found to significantly correlate with those in the herbivorous green turtle from different sediment contamination zones. These findings demonstrate that sediments represent an important secondary contaminant source and lead to redistribution of POPs to the marine food chain. POP concentrations and TEQs clearly increased from sediment to turtles as well as with increasing trophic levels in marine turtle species. The results from this study demonstrate that the extent of sediment contamination within foraging habitats governs marine turtle exposure, while, trophic status and to some extent age influence contaminant exposure within a particular contamination zone. Despite the relatively low TEQ in sediments from Moreton Bay, TEQ levels in green turtle sub-populations foraging from near-shore locations and higher trophic loggerhead and flatback turtles are similar or elevated compared to those reported for other marine wildlife from Moreton Bay and elsewhere, even compared to higher trophic species from locations impacted by dense industrial activities. High bioaccumulation potential of 2,3,7,8-PCDD/F and dioxin-like PCBs compounds were estimated for green turtles using biota to sediment accumulation factors. Selective accumulation of toxicologically more potent (i.e. lower chlorinated) PCDD/Fs was observed for higher trophic marine turtles, resulting in increasing TEQs for the carnivorous species. Biomagnification was also observed for some non-2,3,7,8-substituted dioxin congeners which typically do not accumulate in most biota. These results are proposed to be due to relatively high accumulation efficiency and/or low metabolic capacity for these POP compounds in marine turtles. These findings are also hypothesised to reflect temperature dependant, greater bioavailability of hydrophobic chemicals in sub-tropical and shallow marine systems. An additional pilot study revealed that in contrast to PCDD/Fs and PCBs, levels of persistent flame retardants (polybrominated diphenyl ethers; PBDEs) were relatively low in marine turtles and other marine species (dugong, fish and shellfish) from Moreton Bay. This suggests relatively low level input of these more recent industrial products into the marine environment. However, as elevated levels of PBDEs have been reported in blood from the general population of Australia, ongoing transport from the terrestrial to the marine system and redistribution of these contaminants, similar to PCDD/F and PCBs, would be expected to occur into the future. Limited information is available regarding the sensitivity of reptiles to and effects of POPs, however, studies have shown that reptiles are sensitive to POPs albeit with uncharacterised relative potency. In the absence of robust toxicological information for reptiles or marine turtles, the potential risks associated with PCDD/F and PCB exposure of Queensland turtle populations was evaluated using toxicity for sensitive biological endpoints observed in mammals and birds. Using probabilistic methodology for marine turtles from Queensland, the body burden of up to 31% and 55% of green and loggerhead turtles, respectively, are above the threshold levels where the most sensitive physiological effects are observed in mammals and birds. While this evaluation illustrates that the contaminants investigated have the potential to impact on the health of marine turtle populations, it must be highlighted that it is compromised by the lack of species-specific (and in this case, class-specific) information, the uncertainty of which is often considered to represent a factor of at least 10. The findings of the present study indicate that exposure to POPs has the potential to adversely affect the health of Queensland’s marine turtle populations, and highlight the need for robust information on reptile specific sensitivity to these compounds.

[pt] Este trabalho tem como objetivo apresentar uma avaliação da mobilidade do chorume no solo do aterro Sanitário de Sauípe, no município de Entre Rios, BA. O estudo se baseia em resultados de ensaios de laboratório e em dados encontrados na literatura, os quais foram utilizados para prever o transporte do contaminante e os principais mecanismos de interação entre este e o solo.Foi utilizado um equipamento desenvolvido para a realização de ensaios de transporte em laboratório, que permite a determinação dos parâmetros de transporte do contaminante no solo. / [en] The purpose of this thesis is to present an evaluation of the mobility of leachate in the soil of Sauípe s Sanitary Landfill, located in the municipality of Entre Rios, in the State of Bahia. The study is based on experimental laboratory results and on literature data, which have been used for predicting the contaminant transport and the main mechanisms of its interaction with the soil. To carry out the laboratory tests has been used an equipment developed for this purpose, which allows the determination of the transport parameters of the contaminant in the soil.