Dans le monde entier les introductions d'espèces dans de nouvelles régions constituent une préoccupation écologique croissante ; ces introductions peuvent conduire à des modifications drastiques des écosystèmes, entre autres du fait de la compétition avec des espèces indigènes et également par la modification des réseaux de flux d'énergie dans les écosystèmes. La moule verte Perna viridis est une espèce récemment introduite dans les eaux côtières américaines et qui s'est rapidement disséminée le long des côtes du Sud-Est des États-Unis. Cependant, il n'existe pour le moment que très peu d'informations concernant la structure des populations, et leur dynamique en réponse à la variabilité environnementale locale. Les efflorescences de marées rouges formées par le dinoflagellé toxique Karenia brevis sont fréquentes le long des côtes de Floride bordant le Golfe du Mexique, et la tolérance de P. viridis à l'égard de ces événements et des brévitoxines (PbTx) associées n'est pas connue. En outre, comme P. viridis est une espèce invasive, la potentielle concurrence (ressources trophiques, espace, …) avec des bivalves indigènes comme l'huître Crassostrea virginica, est une préoccupation majeure dans les systèmes côtiers de Floride. Cette étude vise à caractériser la dynamique des populations établies de P. viridis populations établies et leur réponse aux efflorescences naturelles de K. brevis. Les effets des efflorescences à K. brevis ont été évalués à partir des résultats d'un suivi de la croissance, de la mortalité, du recrutement, de la gamétogenèse et de la composition biochimique des tissus (protéines, glycogène et lipides) durant trois ans. En outre, les concentrations en PbTx dans les tissus ont été analysées afin de déterminer l'absorption, l'accumulation et des taux d'élimination de ces toxines. Par ailleurs, les données recueillies sur le terrain et des informations de la littérature ont été utilisées pour élaborer un modèle énergétique individuel DEB pour modéliser la croissance et la reproduction de P. viridis. Avant l'apparition de la première efflorescence à K. brevis, P. viridis présentait des taux de croissance rapide (6-11 mm mois-1) et un taux de survie élevé (mortalité <1%). Au cours des efflorescences à K. brevis, le taux de croissance a chuté de façon significative et une bioaccumulation de PbTx dans les tissus mous a été observée. Les concentrations élevées en PbTx dans les tissus ont persisté longtemps après la dissipation de l'efflorescence et les taux de mortalité élevés se sont maintenus, ce qui a réduit fortement l'abondance de P. viridis. À la fin de l'efflorescence, la concentration en PbTx dans les moules était presque le double de celle relevée chez l'huître indigène Crassostrea virginica pour des individus prélevés à la même période ; chez P. viridis, la concentration en PbTx est restée supérieure à la limite réglementaire pour la consommation humaine pendant 16 semaine, alors qu'elle est revenue en dessous de ce seuil en 2 ½ semaines chez C. virginica.La composition biochimique des tissus et la reproduction n'ont pas parues affectées par ces évènements ; P. viridis réalise sa gamétogénèse durant toute l'année et a mis en place une stratégie de ponte intermittente partielle ; elle présentait durant toute l'année une grande stabilité de la concentration en composés de réserve. L'absence de cycle saisonnier marqué de la composition biochimique suggère que la ressource trophique est suffisante pour soutenir la gamétogenèse tout au long de l'année. Cependant, la première année du suivi, deux évènements majeurs de ponte et de recrutement ont été observés au printemps et à l'automne. Au cours de la deuxième année de suivi, l'analyse histologique montre que le même patron de ponte massive est observé au printemps ; cependant, à cette période, les efflorescences toxiques ont persisté et le recrutement a été inhibé, ce qui suggère que la fécondation et / ou le développement et la survie des larves […] / Worldwide, introductions of exotic species to new regions is of rising concern which can lead to catastrophic ecosystem alterations through competition with native species and disruption in energy flow.Perna viridis is a recently introduced bivalve species to US coastal waters and has vigorously spread throughout the southeastern US. However, little information regarding population structure and response to local environmental factors has been reported. Red tide blooms formed by the toxic dinoflagellate Karenia brevis are frequent along the Gulf coast of Florida and as a recently introduced species, it is unclear what tolerance P. viridis has toward these events and associated brevetoxins (PbTx). Further, as an invasive species ecological concerns have risen regarding potential for spread and competition with native bivalve species, particularly the eastern oyster Crassostrea virginica.This study aimed to characterize the population dynamics of established P. viridis populations and their response to naturally occurring K. brevis blooms. This was completed through monitoring of growth, mortality, juvenile recruitment, gametogenesis and biochemical composition (protein, glycogen and lipid) throughout a three year monitoring period to evaluate the effects of K. brevis blooms. Additionally, tissue PbTx concentrations were analyzed to determine uptake, accumulation and elimination rates. Data collected from the field and information reported in the literature were used to create a functional DEB model to predict individual growth and reproduction of P. viridis under environmentally realistic conditions.Prior to onset of the first K. brevis bloom event, P. viridis showed rapid growth rates (6 – 11 mm month-1) and high survival (mortality <1%). However, during K. brevis blooms growth rate dropped significantly and bioaccumulation of PbTx in the soft tissue was observed. High tissue PbTx concentrations persisted long after bloom dissipation and high rates of mortality ensued, severely reducing population densities. PbTx in mussels nearly doubled that of oysters sampled during the same time and remained above the regulatory limit for significantly longer, 2 ½ weeks and 16 weeks, respectively.Biochemical composition and reproduction appeared unaffected, exhibiting year round gametogenesis with a partial, intermittent spawning strategy and stability in reserves. A lack of significant seasonal cycles in biochemical composition suggests sufficient food and energy availability to support the observed year round gametogenesis. While continuous spawning capabilities were evident two major peaks in spawning and recruitment were observed (spring and fall), suggesting reduced fertilization and / or larval development and survival due to the presence of K. brevis and associated ichthyotoxins and hemolysins.These results indicate that while high tissue PbTx concentrations may lead to reduced growth in P. viridis, gametogenesis is not inhibited, allowing the population to survive K. brevis bloom exposure and reproduce, even while individual mortality was high. Prolonged bioconcentration of PbTx may lead to increased threat of post bloom trophic transfer, resulting in negative impacts on other important fisheries and higher food web implications. While it cannot be conclusively determined that the cause of reduced growth, survival and recruitment is due to red tide events, the parallels observed suggest that K. brevis is an important factor in the drastic changes in population structure.Through the work presented here, population dynamics of locally established P. viridis populations were characterized through monthly monitoring and the development of a DEB model to accurately predict the growth and reproduction under dynamic environmental conditions. This work aims to synthesize our knowledge on the individual bioenergetics of P. viridis and to aid in understand population dynamics and potential for competition with local C. virginica [...]

<p>Målet med den här studien är att förhindra effektivitetssänkningar i moderna biologiska reningsanläggningar för skogsindustriella avloppsvatten. Biologiska processer är vanligtvis effektiva när det gäller att reducera lättnedbrytbart organiskt material. Eftersom den utgörs av levande mikroorganismer (MO) är tekniken känslig. Toxiska ämnen kan döda en kultur av MO. Innan de har ökat i antal igen kommer reduktionseffektiviteten att vara påverkad för en ansenlig tid framöver. I ett pappers- och massabruk finns många typer av vätskor som oavsiktligt kan hamna i reningsanläggningen. I den här studien har svartluts inverkan på reduktionsgraden studerats.</p><p>Biologiska reningsverk har använts under en lång tid. De har utvecklats från att vara generella reningsverk till att bli konceptanläggningar i flera steg, där varje steg har designats för sitt eget syfte med specifika MO. I det här arbetet har ett MultiBio-koncept vid Gruvön Bruk studerats. En anläggning i laboratorieskala har byggts för svartlutsförsöken. Resultatet har jämförts mot simulerade värden och värden från bruket.</p><p>När ett spill av svartlut passerar genom en MultiBio späds det ut mellan varje steg. Halten av svartlut är hög i de första stegen vilka påverkas kraftigt. I de första stegen lever snabbväxande organismer som återhämtar sig på ett par dagar. De mer känsliga aktivslamstegen finns längre bak i reningsverket och är skyddade från toxiska koncentrationer av svartlut. Endast vid försök med 24-timmarstillsatser blev koncentrationen av svartlut så hög att den påverkade MO negativt.</p><p>Den biologiska processen i ett reningsverk kan störas om MO förnekas något essentiellt behov. En biologisk process har ett flertal behov, bland annat behöver aeroba MO löst syre. Eftersom syresättning av vattnet är energikrävande och kostsamt är det inte problemfritt att skapa en omgivning som ger hög effektivitet samtidigt som man strävar efter att sänka energiförbrukningen. I avhandlingen beskrivs ett tillvägagångssätt för att studera energieffektiv syresättning.</p> / <p>The aim of this study is to prevent efficiency reduction in modern wastewater treatment plants for forest industry effluents. Biological processes are usually efficient in reducing biodegradable organic material. Since the technique depends on living microorganisms (MO) it is sensitive. Toxic substances can kill the population. It takes considerable time for the MOs to grow in number and the treatment efficiency will be affected accordingly. In a pulp and paper mill, a number of liquors are handled that can reach the treatment plant by accident. In this study the impact of black liquor spills on treatment efficiency has been studied.</p><p>Biological treatment methods have been used for a long time. They have developed from general treatment plants to multiple stage concepts, where each stage is designed for its own purpose with specific MO cultures. In this thesis, a plant with the MultiBio concept, located at Gruvön Mill in Sweden has been studied. A laboratory scale MultiBio plant has been constructed for the trials in which efficiency during black liquor exposure has been measured. The measured laboratory results were evaluated by comparing them with simulated values and a mill case.</p><p>When a shock of toxic black liquor passing through a MultiBio concept, the black liquor is diluted between the compartments. The first compartments that are exposed to high concentrations of black liquor are affected negatively. The MOs in the first compartment are fast growing and recover in a few days. The more sensitive activated sludge compartments are located further on in the plant. A toxic concentration is found in the activated sludge compartments only when the duration of the spill is 24 hours or more.</p><p>Denying the MOs their needs can disturb biological treatments. Among many things, a biological process needs dissolved oxygen. Since aeration is energy consuming and expensive, there is a conflict between gaining high efficiency and, at the same time, decreasing the energy consumption. In this study, an approach to saving energy for aeration is initiated.</p>

Normal endothelial cell function is controlled in part by a tightly regulated balance between angiopoietin-1 and -2 (Ang-1 and Ang-2). Angiopoietin dysregulation (decreased Ang-1 and increased Ang-2) leads to an activated endothelium that is contractile, adhesive, and prothrombotic. Since an activated endothelial phenotype is seen in invasive group A streptococcal infection, E. coli O157:H7-induced hemolytic-uremic syndrome (HUS), and sepsis, we hypothesized that angiopoietin dysregulation might also be present in these syndromes, and to that end, measured angiopoietin levels in several well-characterized patient cohorts. Decreased Ang-1 and/or increased Ang-2 were found in all three syndromes, and were predictive of clinical outcome in HUS and sepsis. The prognostic utility of Ang-2 in sepsis was further enhanced by combination with biomarkers of inflammation. Angiopoietin dysregulation may therefore represent a shared final common pathway to endothelial activation as well as a clinically useful prognostic biomarker in streptococcal toxic shock, HUS, and sepsis.

Normal endothelial cell function is controlled in part by a tightly regulated balance between angiopoietin-1 and -2 (Ang-1 and Ang-2). Angiopoietin dysregulation (decreased Ang-1 and increased Ang-2) leads to an activated endothelium that is contractile, adhesive, and prothrombotic. Since an activated endothelial phenotype is seen in invasive group A streptococcal infection, E. coli O157:H7-induced hemolytic-uremic syndrome (HUS), and sepsis, we hypothesized that angiopoietin dysregulation might also be present in these syndromes, and to that end, measured angiopoietin levels in several well-characterized patient cohorts. Decreased Ang-1 and/or increased Ang-2 were found in all three syndromes, and were predictive of clinical outcome in HUS and sepsis. The prognostic utility of Ang-2 in sepsis was further enhanced by combination with biomarkers of inflammation. Angiopoietin dysregulation may therefore represent a shared final common pathway to endothelial activation as well as a clinically useful prognostic biomarker in streptococcal toxic shock, HUS, and sepsis.

Bakgrund: Fetma är ett folkhälsoproblem som fortsätter att eskalera världen över. En betydande orsak till detta är den så kallade toxiska miljön vilken medför att människor ständigt exponeras för energität mat och dryck, vilket kan påverka ätbeteendet. Denna studie är viktig att genomföra då det saknas studier som undersöker människors egna upplevelser av miljöstimulis inverkan på ätbeteenden. Syfte: Att undersöka människors upplevelser av att exponeras för ett stort utbud av energirik mat och dryck, hur de upplever att denna exponering påverkar deras och andras ätbeteende samt vilka hälsosamma alternativ de upplever finns i deras närmiljö. Metod: Eftersom det som beskrivs i denna studie är upplevelser av miljöstimuli valdes en explorativ kvalitativ ansats. Som urvalsmetod användes variationsurval för att få en så stor variation som möjligt bland deltagarna. Som datainsamlingsmetod användes halvstrukturerade intervjuer. Analysmetoden i denna studie är innehållsanalys enligt Graneheim och Lundman (2004). Femton informanter deltog i denna studie. Resultat: Dataanalysen resulterade i nio kategorier samt ett övergripande tema; En kamp mellan externa miljöstimuli som styr ätbeteendet och en önskan om att ha kontroll över sitt eget ätbeteende. Kategorierna är; exponering, priser, lättillgänglighet, tidsbrist, synergi, seder, kognitiva faktorer, självkontroll och hälsosamma val. Samtliga informanter upplevde en ganska stark påverkan av externa miljöstimuli, både på andras och det egna ätbeteendet. Slutsats: Miljön underlättar för människor att göra ohälsosamma val då det både finns ett stort utbud av ohälsosamma alternativ och stimuli som påverkar folk att välja det ohälsosamma alternativet, medan utbudet för hälsosamma alternativ i miljön är begränsat. Ett av de viktigaste målen med folkhälsoarbete är således att öka kunskapsnivån hos människor i samhället, då ökad kunskap kan frambringa en ökad efterfrågan på hälsosamma produkter. Ett annat viktigt mål med folkhälsoarbete är att skapa hälsofrämjande miljöer, exempelvis via lagstiftning. Det framtida forskningsbehovet är att utvärdera interventioner som syftar till att påverka ätbeteenden. / Background: Obesity is a public health problem that keeps increasing worldwide. One key causal to this epidemic is the “toxic environment” which contributes to exposure to energy-dense food and high-caloric drinks that influence eating behaviour. This study is essential since there is a lack of studies focusing on people’s experiences regarding environmental influences on eating behaviour. Objective: To investigate people’s experiences regarding exposure to highly accessible, energy-dense food and high-caloric drinks, their experiences of environment’s influences on eating behaviour and their experiences of the ability to choose healthy options in their environment. Methods: Since experiences of environmental influences are described in this study, an explorative qualitative approach was chosen. To obtain maximum variation among the participants, the sampling design used is variation sampling. The data collection method used was semi-structured interviews. The method of analysis used in this study is content analysis according to Graneheim and Lundman (2004). Fifteen informants participated in this study. Results: The data analysis resulted in nine categories and a main theme; A struggle between external influences controlling eating behaviour and the desire to control one’s own eating behaviour. The categories are; exposure, prices, accessibility, lack of time, synergy, customs, cognitive factors, self-control and healthy choices. All informants experienced a rather strong influence from external environmental influences, both on others’ and their own eating behaviour. Conclusion: Environment is making the unhealthy choice easier since there are plenty of unhealthy options that are highly accessible while other environmental influences are affecting people to make unhealthy choices. At the same time the accessibility of healthy choices in environment is limited. One important goal of public health work is to increase knowledge in society, since increased knowledge may raise the demand of healthier products. Another important goal with public health work is to create supportive environments, for example through legislation. Future research projects need to evaluate interventions that aim to influence eating behaviour.

Background: Mastitis in dairy cattle is a common ailment worldwide. A cause of mastitis can be bacteria such as Escherichia coli. Mastitis is not a deadly ailment and sometimes the dairy cows show no symptoms but if certain virulence genes are present in the bacteria that cause the mastitis, the bacteria can be transmitted to humans and cause severe diseases. The potential presence of enterohemorrhagic Escherichia coli (EHEC) in particular would be a major concern for human health. Aim: The aim for this study was to analyze the presence of virulence genes known to be present in E.coli strains isolated from dairy cows with mastitis in Sweden. Method: A Qiagen BIO ROBOT EZ1 was used to purify DNA from 90 bacterial cultures. A panel of virulence genes were amplified and biotinylated from the purified DNA by PCR and an E.coli based DNA microarray was used to detect presumed virulence genes in E.coli. Result: There were no samples that had all the genes traditionally used to classify E.coli as EHEC or potential EHEC. 63 samples were analyzed without any problems but 27 samples were not fully analyzed. Conclusion: The DNA based microarray proved to be a reliable method to detect genes from pathogenic bacteria but it needed high concentration of purified DNA which was not always easy to obtain. There were some samples in this study that contained virulence genes.

<p>This dissertation investigates the non-market value of environmental quality in several contexts with attention paid to equilibrium effects. Chapter One contributes to the ongoing debate concerning the effect of various actions taken by the U.S. Environmental Protection Agency under CERCLA, commonly known as the Superfund Program, on housing prices. The study differs from national sample analyses and site-specific analyses by providing policy-relevant estimates of the hedonic price function in a particular region for the average site. Further, an estimate of the effect on housing prices is given for each of the major events that occur under a typical Superfund remediation. Using house and time-varying census tract fixed effects, I find a 7.3% increase in sales price for houses within 3 km of a site that moves through the complete Superfund program. The analysis gives evidence of positive price appreciation for housing markets and serves as a lower bound for measuring remediation benefits. Chapter Two proposes a new dynamic general equilibrium model of residential location choice with social spillovers and uses it to evaluate the equilibrium consequences of changes in pollution exposure. In particular, I investigate the hypothesis of ``minority move-in,'' which postulates that disproportionate exposure to pollution results from minorities and low-income households trading off such exposure for lower housing costs. Second, I address the question of whether economic incentives caused by differences in willingness to pay across socioeconomic status can explain why polluters disproportionately locate near disadvantaged populations in order to minimize expenses from collective action bargaining over the negative externality. Simulations indicate ``minority move-in'' likely does account for some of the imbalance in exposure to pollution across socioeconomic status. Further, general equilibrium estimates reveal that equilibrium sorting behavior widens the gap in willingness to pay for environmental quality between minority and white households, and between high and low-income households. The disparity in general equilibrium willingness to pay to avoid toxic emissions provides economic incentives for polluters to target disadvantaged populations. Chapter Three investigates how information contained in the U.S. Environmental Protection Agency's Toxic Release Inventory program affects prices in the housing market. First, I use a reduction in the reporting requirement threshold in 2001 as a quasi-experiment to determine whether prices change for existing firms who, as a result of the change, must report. Second, the existence of a reporting threshold creates a discontinuity in treatment than can be exploited. I estimate a regression discontinuity model that assumes that site unobservables are balanced in a neighborhood of the discontinuity. Using a difference-in-differences estimator for the first specification, I find that listing a site in the Toxic Release Inventory lowers prices by 3.1% within a three kilometer radius of the site, and that the effect is stronger at shorter distances. The regression discontinuity model produces qualitatively similar results that are smaller in magnitude but still significant. The results suggest that households to capitalize the information contained in the Toxic Release Inventory. However, since the treatment sites under consideration have virtually no emissions, these results do not contradict previous findings in the literature that toxic air emissions are unrelated to prices. Rather, they suggest that households might be concerned about the dangers of toxic chemicals that might result from an emergency or catastrophic accident.</p> / Dissertation

The distribution of butyltin compounds (BTs) in the sediments and seawater, at the river outfalls, fishing ports, shipyards, and industrial zone docks of Kaohsiung Harbor, Taiwan were investigated. Twenty sediment and seawater samples were collected from various locations in the Harbor in 2006, and analyzed for monobutyltin (MBT), dibutyltin (DBT), and tributyltin (TBT). Results showed that the concentration of total BTs varied from 1.5 to 151 ng/g in sediment samples, with TBT being the major component of the sediment samples. This suggests that sediments could be the most possible sink of TBT brought by the sorption mechanism. The concentrations of BTs ranged from 9.7 to 270 ng/L in seawater samples, whereas DBT and MBT, the degradation byproducts of TBT, were mainly the most abundant BT compounds of the seawater samples. This indicates that the abiotic or biotic degradation potential of TBT was significant. Spatially, the highest concentrations of BTs were observed in both water and sediment samples collected from the shipyard and fishing port areas. This indicates that the shipping related activities (e.g., navigation, ship repair, and ship building), would contribute most of BTs in the environment. Results show that the concentrations of degradation products (DBT and MBT) were related closely to temperature, salinity, dissolved oxygen (DO), and chlorophyll-a of the seawater. This implies that seasonal changes of the water parameters controlled the degradation of TBT in seawater. The observed levels of BT compounds in both seawater and sediments were much higher than those required to induce toxic effects on marine organisms suggesting that appropriate TBT control strategies should be taken in Kaohsiung Harbor. Sediment samples were collected from the river outfalls, fishing ports, shipyards, and industrial zone docks of Kaohsiung Harbor, Taiwan to evaluate the distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments. Collected sediment samples from 12 locations were analyzed for 17 different PAHs, organic content, and grain size. The results show that the total PAH concentrations varied from 472 to 16,201 ng/g dry wt, with a mean concentration of 5,764 ng/g dry wt The highest PAH concentrations were from the industrial zone docks situated in south Kaohsiung Harbor, ranging from 8,788 to 16,201 ng/g dry wt Among those sediment samples, the 5-, 6-ring PAHs were predominant PAH congeners in sediments, ranging from 42 to 71%. However, the dominant PAH congeners were 2-, 3-ring PAHs (37 to 42%) collected from steel industrial zone docks. This indicates that the sources for the PAH contamination at steel industrial zone docks were different from the other zones in Kaohsiung Harbor. According to the diagnostic ratios, the possible source of PAHs in the industrial zone dock could be coal combustion while in the other zones it could be petroleum combustion. The total PAH levels were expressed as the total toxic equivalent (TEQcarc). The total TEQcarc varied from 55 to 1,964 ng TEQ/g dry wt. Higher total TEQcarc values were found at industrial zone docks (from 1,404 to 1,964 ng TEQ/g dry wt). As compared with the US Sediment Quality Guidelines (SQGs), the observed levels of PAHs at industrial zone docks exceeded the effects range low (ERL), and could thus cause acute biological damage. However, the lower levels of PAHs at the other zones would not exert adverse biological effects. Results would be helpful in developing strategies for sediment remediation in Kaohsiung Harbor.

In this work, a new approach to optimize facility layout for toxic release, fire and explosion scenarios is presented. By integrating a risk analysis in the optimization formulation, safer assignments for facility layout and siting have been obtained. Accompanying with the economical concepts used in a plant layout, the new model considers the cost of willing to avoid a fatality, i.e. the potential injury cost due to accidents associated with toxic release near residential areas. For fire and explosion scenarios, the building or equipment damage cost replaces the potential injury cost. Two different approaches have been proposed to optimize the total cost related with layout. In the first phase using continuous-plane approach, the overall problem was initially modeled as a disjunctive program where the coordinates of each facility and cost-related variables are the main unknowns. Then, the convex hull approach was used to reformulate the problem as a Mixed Integer Non-Linear Program (MINLP) that identifies potential layouts by minimizing overall costs. This approach gives the coordinates of each facility in a continuous plane, and estimates for the total length of pipes, the land area, and the selection of safety devices. Finally, the 3D-computational fluid dynamics (CFD) was used to compare the difference between the initial layout and the final layout in order to see how obstacles and separation distances affect the dispersion or overpressures of affected facilities. One of the CFD programs, ANSYS CFX was employed for the dispersion study and Flame Acceleration Simulator (FLACS) for the fires and explosions. In the second phase for fire and explosion scenarios, the study is focused on finding an optimal placement for hazardous facilities and other process plant buildings using the optimization theory and mapping risks on the given land in order to calculate risk in financial terms. The given land is divided in a square grid of which the sides have a certain size and in which each square acquires a risk-score. These risk-scores such as the probability of structural damage are to be multiplied by prices of potential facilities which would be built on the grid. Finally this will give us the financial risk. Accompanying the suggested safety concepts, the new model takes into account construction and operational costs. The overall cost of locations is a function of piping cost, management cost, protection device cost, and financial risk. This approach gives the coordinates of the best location of each facility in a 2-D plane, and estimates the total piping length. Once the final layout is obtained, the CFD code, FLACS is used to simulate and consider obstacle effects in 3-D space. The outcome of this study will be useful in assisting the selection of location for process plant buildings and risk management.

Document formatted into pages; contains 78 pages. / Title from PDF of title page. / Thesis (M.S.P.H.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Malathion is a commonly used organophosphate pesticide on field crops, fruits, nut trees, vegetables, livestock, agricultural premises, and land. The approved uses also include mosquito and medfly control. These uses can result in human skin contact. The purpose of this study is to evaluate the human skin absorption of malathion for the purpose of assessing the risks associated with aqueous solution exposures following applications. Aerial applications can result in solubilized malathion in swimming pools and other waters that may be contacted. Human volunteers were selected and exposed to aqueous solutions of malathion at various concentrations. Participants submerged their arms and hands in twenty liters of dilute malathion solution in either a stagnant or stirred environment. The "disappearance method" was applied by measuring malathion concentrations in the water before and after human subject exposure to the water for various periods of time. Malathion was measured using Gas Chromatography. No measurable skin absorption was detected in 42% of the participants. Measurable skin absorption among the remaining 58% of participants resulted in doses that were more than an order of magnitude less than the minimal dose necessary to cause a measurable change in red blood cell acetylcholinesterase (RBC-AChE). Extrapolation of these results to a mathematical model for recreational swimmers and bathers exposed to contaminated swimming pools and surface waters typically detected after bait application again are an order of magnitude below the doses needed to cause a detectable change in RBC-AChE. These data indicate that exposure to aqueous malathion following usual aerial bait applications is not appreciably absorbed, and therefore, it is not a public health hazard. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.