1º Parcial – Inglés II
1) HAZARDS FROM CHEMICAL AND RADIOACTIVE POLLUTION IN WATER
When present above a certain level and ingested in water, some chemical pollutants (e.g., nitrates, arsenic and lead) may constitute a direct toxic hazard, not posed by other water constituents, such as fluorides, which are beneficial, and may be essential to health in small concentrations ( although toxic when taken in larger amounts. Certain other substances or chemical characteristics may affect the acceptability of water for drinking purposes, including substances causing odours or tastes, acidity or alkalinity, anionic detergents and naturally occurring salts of magnesium and iron. Both international and national criteria and standards have been established, so that a basis for the control of human exposure to many of these substances through ingestion of polluted water can be provided.
Ingestion is, however, only one possible pathway to exposure, since man can be exposed to water pollutants through other types of direct contact that would include recreation or the use of water for personal hygiene. The possible health implications these non-drinking uses of water (including agricultural and industrial uses) would pose are less well understood, no international criteria or guidelines (based on the actual intake of drinking water and the body burden resulting from other sources) existing for the control of such exposure.
Since chemical water pollutants –at the level now existing in water bodies- may influence man´s health indirectly by disturbing the aquatic ecosystems or by accumulating in aquatic organisms used in human food, it would be advisable to analyse public health aspects of water pollution related to substances such as compounds of toxic metals and organochlorine pesticides.
The various chemical and biochemical transformations that pollutants may undergo in the aquatic environment also deserve attention, as chemical change may affect their biological availability or toxicity, which may be either enhanced or reduced. Although essential to the understanding of the health implications of chemical water pollution, these physical, chemical and biological processes and their mechanisms have not been completely understood.
1)Haga la traducción de este texto
2)Elabore un resumen del mismo
3)Responda las siguientes preguntas:
a)¿De qué formas puede el ser humano entrar en contacto con sustancias contaminantes provenientes del agua?
b)Mencione algunos tipos de sustancia que suelen contaminar el agua.
c)¿Qué efectos pueden producir algunos de ellos en el agua?
d)¿Qué aspectos deberían tenerse en cuenta si se elaboraran normas internacionales para regular la exposición a contaminantes a través del agua?
e)¿Qué tipo de transformaciones pueden sufrir los contaminantes en el agua y cuáles aspectos de estos compuestos pueden ser afectados?
2) EFFECT OF TEMPERATURE ON MICROBIAL GROWTH
Factors determining temperature limits for growth
The numerical values of cardinal temperatures (those at which microorganism growth is minimal, optimal and maximal) and the range of temperatures over which growth is possible, vary widely among bacteria. Some which have been isolated from hot springs are able to grow at temperatures as high as 95ºC, while others, isolated from cold environments, can grow at temperatures as low as -10ºC. On the basis of the temperature range of growth, bacteria are frequently divided into three broad groups: termophiles, which grow at elevated temperature (above 55ºC); mesophiles, which grow well in the midrange of temperature (20 to 45ºC); and psychrophiles, which grow well at 0ºC.This tripartite classification of temperature response does not take fully into account the variation among bacteria with respect to the extent of the temperature range over which growth is possible.
Represente gráficamente la información brindada por este texto, de manera que se vea claramente la relación entre los grupos de bacterias y sus rangos correspondientes de temperatura.
The factors determining the temperature limits for growth have been revealed by both comparisons of the properties of organisms with widely different temperature ranges and analyses of the properties of temperature-sensitive mutants, the temperature range of which has been decreased by a single mutational change.
Studies on the kinetics of thermal denaturation of not only enzymes but also cell structures containing proteins (e.g., flagella, ribosomes) have shown that many specific proteins of thermophilic bacteria are considerably more heat stable than their homologues from mesophilic bacteria. It is also possible to make an approximate determination of the overall thermal stability of soluble cell proteins by measuring the rates at which the protein in a cell-free bacterial extract becomes insoluble as a result of heat denaturation at several different temperatures. It can be clearly demonstrated that virtually all the proteins of a thermophilic bacterium remain in the native state after a heat treatment, this denaturing virtually all the proteins of a related mesophile. It therefore follows that the adaptation of a thermophilic microorganism to its thermal environment can be achieved only through mutational changes, which are able to affect the primary structures of most cell proteins.
Although the evolutionary adaptations which have produced thermophiles must have involved mutations which increased the thermal stability of their proteins, most of the mutations affecting the primary structure of a specific protein decrease the thermal stability of that protein, even though many of these mutations could have little or no effect on its catalytic proteins. Consequently, in the absence of counterselection by a thermal challenge, the maximal temperature for growth of any microorganism should decline progressively as a result of random mutations that affect the primary structure of its proteins. This inference is supported by the observation that psychrophilic bacteria isolated from antarctic waters contain a large number of exceptionally heat-labile proteins.
Diga si las siguientes afirmaciones son verdaderas o falsas (marque los segmentos de texto donde ha encontrado su respuesta)
a) Las proteínas de las bacterias mesófilas son más resistentes al calor que las de las
termófilas.
b) Las proteínas que han sido objeto de mutaciones generalmente muestran mayor estabilidad al
calor.
c) Lo más común, es que después de varias mutaciones la temperatura máxima de un
microorganismo disminuya.
d) Las proteínas de las bacterias halladas en lugares fríos son muy sensibles al calor.
e) Podemos decir que la mayor o menor estabilidad al calor de las proteínas es lo que determina
la supervivencia de un microorganismo a diferentes temperaturas.
3) ACID RAIN
I Sometimes more acidic than lemon juice, acid rain is a threat to trees, rivers, lakes, fish, and wildlife, interfering with photosynthesis in trees and other green plants, converting lakes into acid baths that cannot support life, leaching toxic metals (primarily aluminium) from the soil and carrying them to lakes, killing fish even when the acidity by itself is not dangerously high; attacking marble and limestone ( it can literally deface statues and buildings that have suffered less harm in their first 2000 years of existence than in their last 50).
II Natural rainfall is water containing enough dissolved carbon dioxide to produce a slightly acidic solution with a pH of about 5.6. When the pH of rainfall drops to lower values, however, the environment is adversely affected. “Acid rain” is a generic term describing rainfall or snow whose pH is less than 5. Today, it is a well known fact that the average pH of rainfall in northeastern United States is 4.4, and values less than 2 have been recorded. For comparison, note the pH of vinegar is 2.5.
III Acid rain results from the presence of sulfur oxides, and to a lesser extent nitrogen oxides, in the atmosphere. Small amounts of these oxides arise naturally, from volcanic activity, lighting, and forest fires, but the major sources are associated with modern industrial societies. Although metal-ore smelting and chemical manufacturing contribute, the chief culprit is the combustion of coal, which can contain up to 5 % sulfur. During the combustion process, the sulfur is converted to SO2, which, unless removed from the flue gases, is released into the atmosphere.
IV Once in the atmosphere, SO2 is converted to SO3, which reacts with water to produce H2SO4, which falls as acid rain. What is complex and not fully understood is the conversion mechanism of SO2 to SO3. The direct reaction SO2 + ½ O2 SO3 is too slow to account for the formation of acid rain. Dust particles, from both human and natural sources, may well provide a surface upon which the reaction can take place more rapidly. Another possibility is hydroxyl radical (OH •), a molecular fragment produced by the action of sunlight on mixtures of NO2, H2O, and O2. Sulfur dioxide reacts readily with OH • : SO2(g) + 2 OH •(g) SO3(g) +H2O(g).
V Pollutants can travel far from their point of origin, and this is one of the reasons why tracing the source of acid rain is not an easy task. The smokestacks of many power-generating plants are 1000 feet high, where prevailing winds can disperse pollutants over a wide area. Today, specially equipped aircraft - flying laboratories – are used to track chemically tagged smokestack plumes.
VI Making our rainfall safe again will not be cheap. Before burned, a great deal of sulfur can be removed from coal by several different techniques.. Alternatively, SO2 can be removed from the flue gases by reaction with CaO and O2 to form CaSO4(s). In addition, it is possible to counteract the effect of acid rain in lakes by neutralising them with massive annual doses of air-dropped CaCO3(s).
VII The problem continues generating conflicts. Some say tough new restrictions are needed immediately to reduce SO2 emissions. Others call for more research, arguing that effective environmental policies must be based on a clear understanding of the problem.
ACID RAIN
A)Realice un resumen esquemático del texto. Para ello tenga en cuenta las siguientes cuestiones
- Problemas que acarrea la lluvia ácida (párrafo I)
- Definición de “lluvia ácida” (párrafo II)
- Causas de la lluvia ácida (párrafo III)
- Posibles reacciones (párrafo IV)
- Causas de la dificultad de determinar las fuentes (párrafo V)
- Alternativas para evitar la lluvia ácida (párrafo VI)
- Popuestas sugeridas (párrafo VII)
B)Decida si las siguientes afirmaciones son verdaderas (V) o falsas (F)
- La lluvia normal es una solución ácida
- Cuando el pH de la lluvia es inferior a 5, la misma produce efectos perjudiciales sobre el medio ambiente
- Los óxidos de nitrógeno son la causa principal de la lluvia ácida
- La existencia de estos gases se debe fundamentalmente a causas naturales
- La producción de H2SO4 es una reacción sobre la cual no se conoce mucho
C)Traduzca los párrafos II, III, y VII
2º Parcial – Inglés II
1) DIOXIN EMISSIONS FROM COMBUSTION PROCESSES
As more has been learned about the toxic effects of dioxin on human health and the environment, preventing dioxin emissions has become a key environmental goal. Despite its singular form, the term “dioxin” actually refers to 210 compounds – 75 dioxins and 135 furans – with similar structures and properties, the principal problems being 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and 2,3,7,8-tetradichlorodibenzofuran (TCDF).
Some of the compounds are extremely toxic, having been implicated in some of this century’s most infamous environmental accidents such as Yusho, Japan (1968); Times Beach, Mo. (1971); and Seveso, Italy (1976). Governments around the world have established strict regulations intending to decrease dioxin’s impact on the environment.
In Europe, the European Union Directive 94/67/CE mandates that dioxin emissions from incinerators be reduced to 0.1 ng toxic equivalent value (TEQ/Nm3 per 6-8 h period (Table 1). The toxic equivalent value of any mixture is known to be the sum of the TEQs of individual compounds which are calculated based on their concentrations and specific toxic equivalent factors (TEFs). The regulation became law through most of Europe in 1996.
Although the chemical process industries (CPI) emit dioxins, and they were once believed to be their primary source, the compounds have since been traced to combustion processes. Primary sources of dioxins include municipal and industrial waste incinerators, internal combustion vehicle, coal combustion, and metal processing plants. Figure 1 shows the leading sources of dioxins in the U.S in 1994.
The four factors favouring dioxin formation in waste combustion processes are: Previous presence of dioxins in the residue; incomplete incineration of the waste; a temperature ranging between 200º C and 400º C, and the presence of heavy metals or cupric chloride (CuCl2). Chlorine and some of its derivatives, such as polyvinyl chloride, chlorobenzenes, chlorophenols, chlorotoluenes or sodium chloride, have all been identified as likely dioxin precursors, the scientific evidence being, so far, inconclusive.
Several methods are available to reduce or eliminate dioxin emissions. Primary control measures, applied during the combustion process, include maintaining an adequate residence time in the postcombustion chamber at temperatures of 850º C for longer than 2 s; controlling the oxygen component of the combustion air so that it contains more than 6% oxygen; maintaining a high degree of turbulence, providing a homogeneous mixture of gases. Turbulence helps avoid “cold points”, or temperatures under 400º C, where dioxin formation is favored, and “lean points” with less than 6% vol. of oxygen, to maximize the partial oxidation of chlorine-containing species. In addition, should rapid cooling, from 850º to 200º C, be applied, the formation of dioxins in the range 200-400º C will be prevented. For that purpose to be achieved, a boiler is provided.
Secondary dioxin-decomposition methods include catalytic decomposition and adsorption by activated carbon. In catalytic systems, dioxins and furans are destroyed via catalytic oxidation, as follows: Dioxin + O2 CO2 + H2O + HCl
DIOXIN EMISSIONS FROM COMBUSTION PROCESSES
1)Decida en cada caso cuál es la opción correcta e indique la parte del texto donde encontró la información para resolver el ejercicio.
a)La reducción de las emisiones de dioxinas es un objetivo ambiental clave porque:
- Cada vez se conoce más sobre los efectos tóxicos de las dioxinas
- Es necesario conocer más sobre los efectos tóxicos de las dioxinas
- Ninguna de estas razones
b)El término dioxina hace referencia a:
- Los compuestos TCDD y TCDF
- Compuestos derivados del TCDD y TCDF
- Dioxinas y furanos con propiedades y estructuras similares
c)La pincipal fuente de dioxinas en los Estados Unidos es:
- Las industrias de procesos químicos
- Los incineradores de residuos hospitalarios
- La combinación de varias de estas fuentes.
2)Responda las siguientes preguntas
a)¿Cómo se calcula el TEQ de una mezcla?
b)¿Qué papel juega el cloro y sus derivados en la formación de dioxinas?
c)¿Qué valor de concentración de oxigeno es el indicado y qué ocurre por debajo del mismo?
d)En el texto se indica que una temperatura entre 200 y 400 C favorece la formación de dioxinas. ¿Qué se propone para evitar que esto suceda?
e)¿En qué se diferencian los métodos secundarios de los primarios?
3)Traduzca los párrafos 4, 5 y 6.
2) SEPARATION AND PURIFICATION TECHNIQUES
2.2. Recrystallization
Crystallization is the deposition of crystals from a solution or melt of a given material. During the process of crystal formation, a molecule will tend to become attached to a growing crystal composed of the same type of molecules because of a better fit in a crystal lattice for molecules of the same structure than for other molecules. If the crystallisation process is allowed to occur under near-equilibrium conditions, the preference of molecules to deposit on surfaces composed of like molecules will lead to an increase in the purity of the crystalline material. Thus the process of recrystallisation is one of the most important methods available to the chemist for the purification of solids. Additional procedures can be incorporated into the recrystallisation process to remove impurities. These include filtration to remove undissolved solids and adsorption to remove highly polar impurities.
Recrystallisation depends on the differential solubility of a substance in a hot and cold solvent. It is desirable that the solubility of the substance be high in the hot solvent and low in the cold solvent to facilitate the recovery of the starting material. The solution remaining after crystals have deposited is known as the mother liquor. The proper choice of solvent is critical and may require trial tests with small quantities of the material in a variety of solvents or solvent pairs (combinations of two solvents)
Recrystallisation procedures
The solvent, or solvent pair, to be used in the recrystallisation of a substance is chosen in the following manner. A small amount of the substance is placed in a small test tube and a few drops of solvent are added. The test tube is gently heated to see if the sample dissolves in the heated solvent. In general, one should first use a nonpolar solvent, for example, hexane or petroleum ether. If the sample does not dissolve, try using a more polar solvent such as ethanol or acetone. Should the sample completely dissolve in any solvent, chill the solution to see whether crystals will form (sometimes it is necessary to chill the solution using a Dry Ice-acetone bath in order to cause crystallisation). If no crystals appear, the material is too soluble in that solvent, and that solvent should not be used for the recrystallisation. If no single solvent provides suitable results, a mixture of two solvents can be employed, one of the solvents being a good solvent for tthe sample, and the other being a poor solvent for the sample. The sample is first dissolved in the solvent in which the sample is most soluble, and then small portions of the other solvent are added until a cludiness is formed upon addition of the second solvent. A small amount of the better solvent is added to remove the cludiness, and the solution is allowed to cool. The correct proportion of the two solvents must be determined by trial and error. Once the proper solvent has been chosen, the remainder of the sample is recrystallized.
For gram- or multigram-scale recrystallisations, the material to be recryustallised is placed in a suitable container such as an Erlenmeyer flask.
1)Traducir la sección del texto que se indica.
2)Decidir si estas afirmaciones, RELACIONADAS CON EL TEXTO TRADUCIDO, son verdaderas o falsas.
a)Para seleccionar el solvente más adecuado, se puede trabajar con el total de la muestra (F)
b)Al seleccionar el solvente más adecuado se empieza a probar con los más polares. (F)
c)Cuando con uno solo de los solventes no se logran los resultados deseados se recurre al uso de dos solventes (V)
d)Si se usan dos solventes, la muestra se disuelve primero en aquel en el que es menos soluble. (F)
e)Existe una fórmula precisa que permite calcular las proporciones en que deben agregarse los dos solventes. (F)
3)Las siguientes preguntas se refieren a las secciones QUE NO ESTÁN INCLUÍDAS EN LA TRADUCCIÓN del texto. Respóndalas.
a)¿Por qué se produce el proceso de cristalización?
b)¿Para qué sirve este proceso?
c)¿Con qué otros métodos puede combinarse y para qué se recurre a ellos?
d)¿Cuál es el fundamento del proceso de recristalización?
e)¿Qué se define en el texto como “mother liquid”