Neste trabalho foi avaliado o impacto na simulação dos poluentes fotoquímicos do uso de diferentes parametrizações da Camada Limite Planetária (CLP) para a Região Metropolitana de São Paulo, utilizando o modelo de mesoescala não-hidrostático Weather Research and Forecasting (WRF) com o acoplamento dos módulos químicos (WRF/Chem). Para análise da acurácia dos resultados obtidos com o modelo, foram utilizadas as medições realizadas pelas estações automáticas da CETESB em superfície, e a validação do perfil vertical da concentração de O3 com base nos dados do experimento de lançamento de ozoniosondas realizado dentro do contexto de um projeto de políticas públicas (recursos FAPESP) realizado durante o período de estudo. A motivação para a realização do presente trabalho foi a grande dificuldade de representação da estrutura da CLP em especial durante o período noturno sobre áreas urbanas. O estudo contou com a utilização inédita do modelo on-line para simulação da composição química da atmosfera da RMSP, e por fim analisou o impacto do acoplamento com o modelo urbano Urban Canopy Model (UCM), com o modelo WRF-Chem. A área de estudo é a Região Metropolitana de São Paulo e adjacências, e o período estudado foi de 28/10 a 01/11/2006. As variações anuais da temperatura do ar, velocidade do vento e radiação solar para o ano de 2006, mostraram que o mês de outubro foi marcado por grande disponibilidade de radiação solar, altos valores de temperatura do ar e ventos intensos. As simulações com casos idealizados mostraram que o esquema numérico de CLP, YSU (Yonsei University) representou melhor a variação da Camada Limite na área urbana, o que influenciou diretamente na dispersão dos poluentes. Já para as simulações de casos reais os resultados mostraram uma boa correlação entre simulado e observado para as concentrações superficiais de O3 e CO e uma grande dificuldade do modelo em representar o perfil vertical da concentração de O3, quando utilizada a versão 2.1 do modelo WRF/Chem. Problema este parcialmente resolvido (podendo melhorar ainda mais) quando é utilizada uma versão mais recente do modelo WRF-Chem, como o caso da versão 3, acoplada com o modelo urbano UCM. Os experimentos realizados para estimar o impacto do tipo do uso do solo sobre a variação da altura da CLP e conseqüente relação com a composição química da atmosfera, mostraram que a altura da CLP é mais alta sobre áreas urbanas em comparação com áreas rurais, portanto influenciando de forma efetiva na dispersão dos poluentes. No presente trabalho foi mostrado o transporte de poluentes existente entre as regiões metropolitanas de São Paulo, Campinas e Sorocaba, devido principalmente a topografia que atua canalizando o vento na direção de Campinas e Sorocaba. A proximidade com as fontes de emissão mostrou ser um fator importante para o nível de concentração de O3, pois à medida que se afasta das fontes de emissão tanto vertical quanto horizontalmente a concentração de O3 aumenta. E devido a sua relativa proximidade com o Oceano Atlântico, a RMSP é beneficiada com a formação da Brisa Marítima que auxilia na dispersão dos poluentes emitidos e formados na RMSP. / This work evaluated the parameterizations´ sensibility of the Planetary Boundary Layer (PBL) in the simulation of photochemical pollutants above the Metropolitan Region of São Paulo, by using the Weather Research and Forecasting (WRF) non-hydrostatic mesoscale model, with the coupling of chemical modules (WRF/Chem). In order to analyze the accuracy of the results obtained with the model, there will be used the measurements made by the automatic air quality stations from CETESB on surface, and the validation of the O3 vertical profile, will be based on ozonesoundings experiments conducted during the period of the study. The motivation for this study was the great difficulty in representing the PBLs structure specially during the night, witch is an new utilization of an on-line model to simulate the chemical composition of the atmosphere of the MASP, and finally, to analyze the impact of the coupling with the Urban Canopy Model (UCM). The study area is the Metropolitan Region of São Paulo and surroundings, and the period was between 10/28 11/01/2006. The annual variations of the air temperature, wind speed and solar radiation for 2006, showed that the month of October was marked by wide availability of solar radiation, high values of air temperature and intense winds. The simulations with idealized cases showed that the PBLs order of height based on the numerical scheme is YSU, MYJ, BOULAC and UCM, which influences directly the dispersion of pollutants with lower concentrations of the CO for YSU and higher for UCM respectively, and for the concentrations of the O3, the scheme YSU shows lower concentrations but unlike the CO, the other schemes are equal. However, for the simulations of real cases, the results showed a good correlation between simulated and observed for the surface concentrations of the O3 and CO, and a great difficulty of the model on the vertical profiles representation of the concentration of O3, when the 2.1 version of the WRF/Chem model is used. This problem was partially solved (can be better improved) when used with the latest version, as version 3, and coupled with the Urban Canopy Model. The experiments performed to estimate the impact of the land use type on the variation of the PBL height and consequent relationship with the chemical composition of the atmosphere, showed that the PBL height is higher on the urban areas compared to rural areas, thus influencing effectively in the dispersal of pollutants, and a lower PBL height was associated with higher concentrations due to lower dispersion of pollutants. This work has demonstrated the transport of pollutants between the metropolitan regions of São Paulo - Campinas and São Paulo - Sorocaba, due to topography that acts targeting the wind in the direction of Campinas. The proximity of emission sources has been important for the level of concentration of O3, as it moves away from sources of emissions both vertically and horizontally increases its concentration. Due the proximity with the Atlantic Ocean, the formation of Sea Breeze helps dispersion of pollutants emitted and formed in the MASP.

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-08-21T15:13:55Z No. of bitstreams: 1 gabriellerabeloquadra.pdf: 2085169 bytes, checksum: 5108ddde0dcf7f981be518facd560aa1 (MD5) / Rejected by Adriana Oliveira (adriana.oliveira@ufjf.edu.br), reason: on 2017-08-24T11:31:31Z (GMT) / Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-08-24T13:21:00Z No. of bitstreams: 0 / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-30T12:29:16Z (GMT) No. of bitstreams: 0 / Made available in DSpace on 2017-08-30T12:29:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-02-24 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / - / Aquatic ecosystems provide many services to humanity, despite this; water pollution is one of the most serious environmental problems worldwide. Reservoirs, including ones used for water supply, receive from tributaries, or directly, several effluents from human activities that contain a pool of pollutants. Reservoir sediments work as sink or source for pollutants depending on environmental conditions. Therefore, pollutants present in these aquatic compartments can return to the water column or transfer through the food chain, where they can be toxic to biota and even to humans. Contaminants in the environment can cause mutagenic effects that can accumulate in DNA and harm a whole population. Then, genotoxicity tests, such as Allium cepa assay, may be used to evaluate the extent of environmental pollution, since synergistic effects might occur and physicochemical analysis just provide the presence of pollutants. Studies focusing on the presence of chemical compounds in reservoirs sediments and their toxicity are crucial. In this context, the study aimed to investigate contamination in sediments by metals in Brazilian reservoirs, as well as potential ecological risk and potential to cause cytogenotoxicity in A. cepa. Copper, chromium, cadmium, lead, zinc and iron were measured in sediment samples from six Brazilian reservoirs. Besides that, the surface layer of sediment was submitted to a resuspension simulation to the water column, and sediment solution was submitted to Allium cepa assay and metals analysis. Our findings showed that these reservoirs seem to be influenced by agricultural, industrial and domestical effluents because of the presence of copper, cadmium, and zinc above threshold effect levels in some samples and a potential ecological risk was observed. More than that decrease mitotic index and increase chromosomal aberrations in all treatments (except Furnas reservoir) showed cytogenotoxic effects. The presence of metals and other possibly inorganic and organic pollutants may be answerable for cytogenotoxic effects observed. In this sense, just chemical analyses were not enough to evaluate the extent of environmental pollution in sediments and its impact. We need to use more tools combined with chemical analysis to provide a better understand of pollution in aquatic ecosystems. It is important to implement law and regulations that are more efficient, intensive monitoring, sewage treatment and reforestation of riparian zones to protect these systems, including preventing public health problems.

M.Sc. / Natural Organic Matter (NOM) is a complex of organic material present in a natural surface water. Odour, taste and acidity are some of the problems associated with NOM in water systems. Futhermore, it causes the yellow or brown colour of water, whic is aesthetically unpleasant to consumers. NOM is also the energy source of bacterial re-growth and aids in the transportation of metal ions in the distribution system.Moreover, NOM in water can react with disinfectants, e.g. chlorine, to form disinfection by products (DBPs) such as trihalomethanes (THMs) and habacetic acids (HAAs). DBPs have recently been found to have adverse effects in humans. This study was undertaken in order to assess the effectiveness of some of the water treatment techniques employed by selected water supplying companies in dealing with NOM. To achive this, the water treatment processes used by these companies to reduce NOM and metal ions were coagulation, sand filtration, the use of granular activated carbon, ozonation and chlorination. In addition, β-cyclodextrin (β-CD) polyurethanes synthesized in our laboratories were used to remove the DBPs present in the water samples.

The escalating population growth and increased forestry, mining, agricultural and industrial development in the catchment areas over past years has had a profound effect upon water quality and quantity, resulting in increased pollution levels and a reduction in flow rates. This is cause for concern not only to water users in the upper catchments but also to the down stream user, the Kruger National Park, which is exceedingly dependent on good quality waters in order to maintain and sustain a large variety of ecosystems. This study was therefore aimed at investigating the physicochemical, nutrient and metal concentrations of four major river systems that transect the park, namely the Luvuvhu, Shingwedzi, Letaba and Sabie Rivers. By virtue of its position along South Africa’s eastern border the Kruger National Park (KNP) receives waters from seven major river systems each of which enter via the western boundary, flow eastwards through the park and on into Mozambique. The majority of the catchment areas of these river systems are situated upstream of the park itself making water quality and quantity management an important yet challenging task. Water quality is a significant and powerful determinant of health of aquatic ecosystems. Full assessment of chemical and physical attributes upon the river systems was supported by biological monitoring thus integrating changes in the system over time. Water and sediment samples were collected seasonally between September 2005 to March 2006 at sites outside and inside the borders of the Kruger National Park. Sites outside were located of sufficient distance from the border so as to be regarded as representative of water quality conditions before entering the Park. At each site physico-chemical variables were measured in the water. Two metal bioaccumulation indicator species (Labeobarbus marequensis and Barbus radiatus) were also sampled during this time period. These samples as well as water and sediment samples were analysed for Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Physico-chemical analyses of water and sediment allowed for the separation of the rivers into two distinct groups. The Luvuvhu and Sabie Rivers grouped together showing little deviations from normal water quality guidelines. On the other hand the Shingwedzi and Letaba Rivers deviated from normal values sometimes by large degrees. This was particularly true for the Letaba 1a site for all physico-chemical variables barring temperature. Nutrient concentrations correlated with these findings. Nitrates and Sulphates can be identified as possible problem nutrients; however historic data suggest levels to be acceptable for these river systems. Multivariate analysis of sites with regards to physico-chemical and nutrient concentrations produced three major clusters. Determining factors were conductivity, nitrates, organic content and grain size of 53 μm. Fish were utilised as bioindicator organisms in order to quantify the levels of metals available within each river system. These organisms accumulate metals in their tissues and thus provide not only instantaneous data but rather a time integrate of measure of the bioavailability of metals. Although metal concentrations within water, sediment and fish were not consistently high within one system, three distinct trends were observed. Firstly metal levels were generally found to occur in slightly higher concentrations during the high flow periods when waters were turbid; this could be attributed to increased run off from the surrounding lands as well as increased exposure to sediment bound chemicals released back into the systems. Secondly a trend of high concentrations of Cr, Cu, Fe, Pb, Mn, Ni and Zn was found occurring at the Luvuvhu 1, Luvuvhu 2 and Shingwedzi 1 sites during the high flow sampling. Metal levels at these sites were consistently higher than those recorded at other sampling sites. The last trend noted was that the Sabie River on a whole showed lower metal readings with regard to water, sediment as well as fish samples. In order to integrate bioaccumulation data and metal concentrations in the different phases of the water and sediments an equilibrium partitioning (EP) technique was implemented. Toxic effect-derived quality data is the lowest for Al, Cr, Cu, Pb and Zn, whilst product standard-based criteria produce the lowest values for Fe, Mn and Ni. Cadmium values were found to be similar for both criteria. Results indicate that current water quality guidelines are over protective for Al and Fe, whilst those for Ni and Mn are too lenient. The EP method has not been utilised extensively in South Africa and was carried out for the first time upon these river systems, it is thus essential that further research be carried out. Recommendations are made as to the continued monitoring of these diverse systems. It is suggested that each river be looked at in greater detail and that the development of a field biomonitoring programme should be implemented in order to determine the impacts upon the biological components and the aquatic ecosystem as a whole. Future studies should also look at incorporating the use of aquatic macroinvertebrates (SASS 5) as well as other available techniques in order to supply a more detailed assessment. / Prof. V. Wepener Dr. T. Gyedu-Ababio Prof. J.H.J. Van Vuren

In our environment there are many compounds which can negatively influence humans and wildlife. Every day, a vast number of environmental pollutants are released into our environment and there is no way to avoid their exposure. Some of these compounds can even mimic endogenous hormones and interfere with our endocrine system (so called endocrine disruptors), which is the key regulatory system controlling almost all physiological processes in human and animal bodies. Also the reproductive system is largely regulated by various hormones, and their proper function is crucial for gamete formation, fertilization and embryo development. Environmental pollutants are therefore considered as one of the possible causes of increased infertility in human population. This prompted us to study the effect of two endocrine disruptors (tetrabromobisphenol A - TBBPA, and zearalenone - ZEA) on the male mouse reproductive system in vivo. According to our results, TBBPA is able to induce apoptosis as well as changes in the expression of selected testicular genes and sperm protamination. Our results also suggest that permanent exposure to TBBPA slightly enhances its effect in the next generation, depending on whether the parents have been affected or not. We hypothesized that differential protamination of the sperm DNA...

Persistent organic pollutants such as polychlorinated biphenyls (PCBs), DDT and polybrominated diphenyl ethers (PBDEs) tend to accumulate in biota and are transferred through the aquatic food web, which result in a high accumulation in marine mammals. In recent years various novel flame retardants (nBFRs), which have replaced the banned PBDEs, have also started to occur in the environment. These nBFRs have similar properties as PBDEs, such as long-range transport and accumulation in biota. The purpose with this study was to evaluate a method by using pre-packed silica columns for quantification of PCBs, DDT, PBDEs and nBFRs in seal blubber, in order to facilitate the pre-treatment and decrease the time. To elute the different POPs from the pre-packed silica column; hexane, toluene and dichloromethane were used in different stages. By using this method levels of PCB and DDT were determined. For DDT the concentration was 8.28 ng/g lipid and 8.94 ng/g lipid for the two samples that was analysed, and the analysis of the PCBs showed a higher trend for the higher chlorinated PCBs. As the pre-packed silica columns are a relative new method. Further studies are therefore needed on these columns to further improve the sample clean-up and fractionation of the different POPs in environmental samples.

[pt] Atualmente, vem ocorrendo um notável aumento de investimentos no setor de gás natural no Brasil. A utilização do gás natural para a geração de energia tem importantes atrativos como, por exemplo, a diversidade de oferta do gás e sua queima mais limpa em relação a outros combustíveis fósseis. Existe um crescente interesse em projetos, idéias e opções alternativas para melhorar a performance e reduzir as descargas poluentes de equipamentos de combustão industrial para o meio ambiente. A necessidade de processos mais eficientes e menos poluentes tem acelerado a busca por desenvolvimento tecnológico. No projeto desenvolvido, foi investigada a performance de um modelo baseado na formulação de volumes finitos, incluindo o modelo k-e de turbulência, o modelo generalizado de taxas finitas de Arrhenius e Magnussen para o cálculo das reações químicas, e o modelo de radiação por transferência discreta, para simular o processo de combustão em fornalhas industriais através da utilização do pacote comercial Fluent (versão 4.4). O principal objetivo do estudo foi o de investigar a performance deste modelo em simular a combustão e prever a formação de NO e CO em chamas industriais de gás natural através da comparação com dados experimentais. Para a simulação da combustão foram testados dois modelos, o primeiro correspondendo a uma única reação global de oxidação do metano (1 etapa), e o segundo composto por duas reações (2 etapas). Uma sensível evolução foi obtida empregando-se o modelo em duas etapas em comparação com o em uma etapa. Para a simulação da formação de NO foram testados sete casos diferentes. Nestes casos, foram principalmente investigados os mecanismos - thermal NOx -,- prompt NOx - e o método PDF para a representação da interação química- turbulência. Percebeu-se que o método PDF permitiu uma evolução na predição da formação de NO na fornalha. Além disso, o - prompt NOx - foi o mecanismo dominante e portanto faz-se necessária uma investigação mais aprofundada sobre as características desse mecanismo para melhores resultados na predição de NO. Apesar da evolução dos modelos empregados e de seus resultados durante o trabalho, são necessárias novas investigações para detectar possíveis melhorias em tais modelos que possibilitem previsões mais realistas para a formação de NO. / [en] Nowadays, a strong raise in investments is occurring in the natural gas segment in Brazil. The natural gas application for energy generation is very attractive due to many reasons, like the offering diversity and the cleaner burning in comparison with other fossil combustibles. There is an increasing interest in projects, ideas and alternative options for the improvement of the performance and reducing the pollutants discharges of industrial combustion equipments to the environment. The need for more efficient and less polluters processes has accelerated the search for technological development. In the present work, it was investigated the performance of a model based in the finite volume formulation including the k-e model of turbulence, the generalized finite rate model of Arrhenius and Magnussen for the chemical reactions calculations, and the discrete transfer radiation model for simulating the combustion processes in natural gas industrial flames using the commercial code Fluent (version 4.4). The main goal of the inquiry was to investigate the performance of such modeling approach in predicting NO and CO formation inside the furnace by the comparison with the experimental data. For the combustion modeling, two mechanisms were simulated. The first corresponding to an unique global reaction for the oxidation of methane (1 step), and the second corresponding to two reactions (2 steps). An evident evolution was obtained using the two steps model. Seven different cases were tested to predict the NO formation. In these cases, the main investigations were concentrated on the mechanisms -thermal NOx-, -prompt NOx- and on the PDF method for representing the interaction between chemistry and turbulence. The PDF method improved the prediction for the NO formation within the furnace. The -prompt NOx- was the dominating mechanism and therefore it is necessary a deeper investigation on the characteristics of this mechanism for better results in estimating the NO concentrations. Although the models, mechanisms and results have improved along the present research, new investigations are necessary for more accurated predictions for the NO formation. / [es] Atualmente, ha ocurrido un notable aumento de inversiones en el sector de gas natural en Brasil. La utilización del gas natural para la generación de energía tiene importantes atractivos como, por ejemplo, la diversidad de oferta del gas y su quema más limpia en relación a otros combustibles fósiles. Existe un cresciente intereés en proyectos, ideas y opciones alternativass para mejorar la calidad y reducir las descargas poluentes de equipos de combustión industrial para el medio ambiente. La necesidad de procesos más eficientes y menos poluentes ha acelerado la búsqueda del desarrollo tecnológico. En el proyecto desarrollado, se investigó la performance de un modelo basado en la formulación de volumes finitos, incluyendo el modelo k-e de turbulencia, el modelo generalizado de tasas finitas de Arrhenius y Magnusen para el cálculo de las reacciones químicas, y el modelo de radiación por transferencia discreta, para simular el proceso de combustión en hornos industriales a través de la utilización del software comercial Fluent (versión 4.4). El objetivo principal de este estudio fue el de investigar la performance de este modelo al simular la combustión y preveer la formación de NO y CO en llamas industriales de gas natural a través de la comparación con datos experimentales. Para la simulación de la combustión se provaron dos modelos, el primeiro corresponde a una única reacción global de oxidación del metano (1 etapa), y el segundo compuesto por dos reacciones (2 etapas). Se obtiene una sensible evolución al utilizar el modelo en dos etapas envés del modelo con una etapa. Para la simulación de la formación de NO se probaron siete casos diferentes. En estos casos, se ivestigaron principalmente los mecanismos - thermal NOx -,- prompt NOx - y el método PDF para la representación de la interacción química-turbulencia. Se observa que el método PDF permite una evolución en la predicción de la formación de NO en el horno. Además, el - prompt NOx - fue el mecanismo dominante y por lo tanto se hace necesario una investigación más profunda sobre las características de ese mecanismo para mejorar los resultados en la predición de NO. A pesar de la evolución de los modelos empleados y de sus resultados durante el trabajo, se necesitan nuevas investigaciones para detectar posibles mejorías que hagan posible previsiones más realistas para la formación de NO.

M.Sc. / Drinking water treatment plants in South Africa rely almost entirely on surface water sources, which are often compromised due to high return flows and indirect reuse. The typical treatment plants focus on the removal of physical and microbial contaminants which include turbidity, colour, chemical compounds and micro-organisms. A relatively new alarm to this list is natural organic matter (NOM) which has become a major concern in potable water treatment due to its recent regulation. Conventionally, the drive to remove NOM from potable water would be the desire to remove colour from public water supplies. However, more problems in drinking water treatment associated with NOM have been recently identified. These include taste and odour, its tendency to foul membranes, interference with the removal of other contaminants and its potential to contribute to corrosion and slime growth in distribution systems. Moreover, it causes high demands for coagulants and disinfectants. The NOM is also the main precursor for disinfection by-products (DBPs) formed when it interacts with disinfectants such as chlorine during water disinfection. In this study, different raw water samples, of different NOM composition were collected from selected sources across the country and assessed for the removal of dissolved organic carbon (DOC) and UV absorbance at a wavelength of 254 nm (UV 254) using enhanced coagulation (EC). The efficacy of EC, which can be employed as a practical technology in the removal of both turbidity and NOM, was evaluated in these raw water sources. Jar tests were conducted with ferric chloride as the coagulant, and specific pH values were chosen as target values guiding the different coagulant dosages for the jar tests. The pH of the low-alkalinity (<60 mg/ℓ CaCO3) raw waters were adjusted and raised by the addition of sodium carbonate. Algorithms for finding the optimum coagulant dosage for both turbidity and UV 254 removal were developed and consistently applied to all the results in independent v batch tests, in which residual amounts of UV 254, DOC and turbidity were measured. The raw water parameters and results obtained from these tests were used to develop feed-forward multiplicative models predicting the performance of EC using ferric chloride. The results showed that the raw waters chosen were, indeed, representative of the different water types present in South Africa, and that the general water characteristics were affected by seasonal variations. The EC procedure developed was able to reduce turbidity to levels low enough for removal by subsequent treatment steps in the water treatment train. The residual UV 254 values were in all cases lower than 6 m-1, which theoretically corresponds to about 3.5 mg/ℓ DOC. This was confirmed by the residual DOC values which were found to be lower than 4 mg/ℓ. Generally, the waters of South Africa were found to be amenable to coagulation. In almost all cases, the costs for EC were comparable to those for conventional coagulation, hence EC could be employed as a NOM removal strategy in the South African context.

M.Sc.

M.Ing. (Civil Engineering) / Natural organic matter (NOM) is a complex mixture of organic compounds resulting from the decay of plants and animals. When not properly removed, NOM reacts with disinfectants to form disinfection by-products, of which some are known to be carcinogenic. Regulations have become more and more stringent about the maximum level of NOM in drinking water. Different water treatment processes can be applied to remove NOM. However, because each process targets specific fractions of NOM, this results in the existence of recalcitrant NOM fractions that are not removed, for each treatment process. The main objective of the study was thus to investigate NOM removal by using three advanced water treatment processes alone and in combination. The processes used were enhanced coagulation, granular activated carbon adsorption and ion exchange resin processes. Strong and weak base ion exchange resins were used. Although NOM removal methods have been investigated intensively, little attention is given to a so-called “multi-barrier” approach of NOM removal through enhanced coagulation, granular activated carbon adsorption and ion exchange resin that could be applied in practice. In order to take the seasonal and geographical variability of NOM into account, water samples were collected at eight geographical areas over five to seven seasons from 2010 to 2013. Results showed that different treatment processes remove different NOM fractions with different efficiency. Results also confirmed that EC performs better than the adsorptive treatment processes. But the literature shows that NOM removal by EC is difficult for water with high alkalinity and low SUVA values, which is common with SA waters. The adsorptive processes used for NOM removal revealed that they are not viable options, because even low percentage of NOM removal would require high adsorbent dosages, which removes this approach as a practical option.