Types of toxic chemicals

Types of toxic chemicals  [c.67]







Outside of carbon monoxide for which the toxicity is already well-known, five types of organic chemical compounds capable of being emitted by vehicles will be the focus of our particular attention these are benzene, 1-3 butadiene, formaldehyde, acetaldehyde and polynuclear aromatic hydrocarbons, PNA, taken as a whole. Among the latter, two, like benzo [a] pyrene, are viewed as carcinogens. Benzene is considered here not as a motor fuel component emitted by evaporation, but because of its presence in exhaust gas (see Figure 5.25).  [c.260]

Personnel Selection and Training. The quaHty of operating personnel is of paramount importance to the safe operation of a chemical plant. Operators must be intelligent and emotionally stable. Excessive use of alcohol and dmgs affects reHabiHty and can thereby render workers more susceptible to certain types of toxic exposure. Thorough medical screening is essential to avoid damaging exposures to susceptible individuals, eg, people with respiratory ailments should not be employed in areas where corrosive atmospheres could occur.  [c.101]

List and describe the types of dry chemical feeders that are in common use. Go to the Web and develop a list of major vendors for these equipment.  [c.122]

Make a list of chemical flocculating agents and relate each of these chemicals to the specific types of contaminants they are best suited to handle in wastewater. Obtain MSDS (Material Safety Data Sheets) for each of these chemicals.  [c.267]

In recent years, the rate of information available on the use of ion-exchange resins as reaction catalysts has increased, and the practical application of ion-exchanger catalysis in the field of chemistry has been widely developed. Ion-exchangers are already used in more than twenty types of different chemical reactions. Some of the significant examples of the applications of ion-exchange catalysis are in hydration [1,2], dehydration [3,4], esterification [5,6], alkylation [7], condensation [8-11], and polymerization, and isomerization reactions [12-14]. Cationic resins in form, also used as catalysts in the hydrolysis reactions, and the literature on hydrolysis itself is quite extensive [15-28], Several types of ion exchange catalysts have been used in the hydrolysis of different compounds. Some of these are given in Table 1.  [c.775]

These are supplied as separate components which are mixed together and then applied. The paints cure by chemical reaction —a process which also occurs in the can and so limits the time available for application after mixing. The films are tough and have good chemical resistance. There are three main types of these coatings  [c.640]

Figure 11.2 Various types of scrubbers can be used to treat air pollution from solid particles. (Reproduced with permission from Stenhouse, Pollution Control in Teja, Chemical Engineering and the Environment, Blackwell Scientific Publications, Oxford, U.K., 1981.) Figure 11.2 Various types of scrubbers can be used to treat air pollution from solid particles. (Reproduced with permission from Stenhouse, Pollution Control in Teja, Chemical Engineering and the Environment, Blackwell Scientific Publications, Oxford, U.K., 1981.)
Separation of families by merely increasing the resolution evidently can not be used when the two chemical families have the same molecular formula. This is particularly true for naphthenes and olefins of the formula, C H2 , which also happen to have very similar fragmentation patterns. Resolution of these two molecular types is one of the problems not yet solved by mass spectrometry, despite the efforts of numerous laboratories motivated by the refiner s major interest in being able to make the distinction. Olefins are in fact abundantly present in the products from conversion processes.  [c.50]

Before entering the detailed discussion of physical and chemical adsorption in the next two chapters, it is worthwhile to consider briefly and in relatively general terms what type of information can be obtained about the chemical and structural state of the solid-adsorbate complex. The term complex is used to avoid the common practice of discussing adsorption as though it occurred on an inert surface. Three types of effects are actually involved (1) the effect of the adsorbent on the molecular structure of the adsorbate, (2) the effect of the adsorbate on the structure of the adsorbent, and (3) the character of the direct bond or local interaction between an adsorption site and the adsorbate.  [c.582]

Physical adsorption may now, in fact, be seen as a preamble to chemisorption in heterogeneous catalysis, that is, as a precursor state (see Section XVIII-4). Physical adsorption is not considered to involve chemical bond formation, however, and the current theoretical approaches deal mainly with the relatively long range electrostatic and van der Waals types of forces. The quantum mechanics of chemical bonding is thus largely missing although aspects of it appear in the treatment of physisorption on metal surfaces. Steele [8] provides an extensive review of molecular interactions in physical adsorption generally, and for the case of molecules adsorbed on the graphite basal plane in particular [95].  [c.634]

Surface photochemistry can drive a surface chemical reaction in the presence of laser irradiation that would not otherwise occur. The types of excitations that initiate surface photochemistry can be roughly divided into those that occur due to direct excitations of the adsorbates and those that are mediated by the substrate. In a direct excitation, the adsorbed molecules are excited by the laser light, and will directly convert into products, much as they would in the gas phase. In substrate-mediated processes, however, the laser light acts to excite electrons from the substrate, which are often referred to as hot electrons . These hot electrons then interact with the adsorbates to initiate a chemical reaction.  [c.312]

Equation (B2.4.33) and equation (B2.4.34) are the basic equations for a time-domain description. For instance, they say that any time-domain NMR signal is the sum of decaying oscillations. This is obvious from the fact that it is described by a first-order differential equation, but (B2.4.34) gives a way of calculating the values of these exponentials for any system, static or dynamic. The distinctions amongst different types of spectrum lie in the eigenvalues and eigenvectors of the Liouville matrix iL-tR-tK. equation (B2.4.34) describes static spectra, spin relaxation and spectra showing the effects of chemical exchange or relaxation, in a single, unified picture.  [c.2101]

The reactivity of size-selected transition-metal cluster ions has been studied witli various types of mass spectrometric teclmiques [1 ]. Fourier-transfonn ion cyclotron resonance (FT-ICR) is a particularly powerful teclmique in which a cluster ion can be stored and cooled before experimentation. Thus, multiple reaction steps can be followed in FT-ICR, in addition to its high sensitivity and mass resolution. Many chemical reaction studies of transition-metal clusters witli simple reactants and hydrocarbons have been carried out using FT-ICR [49, 58].  [c.2394]

We shall describe some of tire common types of chemical patterns observed in such experiments and comment on tire mechanisms for tlieir appearance. In keeping witli tire tlieme of tliis chapter we focus on states of spatio-temporal chaos or on regular chemical patterns tliat lead to such turbulent states. We shall touch only upon tire main aspects of tliis topic since tliere is a large variety of chemical patterns and many mechanisms for tlieir onset [2,3, 5,31].  [c.3064]

The phase change of the total polyelectronic wave function in a chemical reaction [22-25], which is more extensively discussed in Section in, is central to the approach presented in this chapter. It is shown that some reactions may be classified as phase preserving (p) on the ground-state surface, while others are phase inverting (i). The distinction between the two can be made by checking the change in the spin pairing of the electrons that are exchanged in the reaction. A complete loop around a point in configuration space may be constmeted using a number of consecutive elementaiy reactions, starting and ending with the reactant A. The smallest possible loop typically requires at least three reactions two other molecules must be involved in order to complete a loop they are the desired product B and another one C, so that the complete loop is A B C A. Two types of phase inverting loops may be constructed those in which each reaction is phase inverting (an i loop) and those in which one reaction is phase inverting, and the other two phase preserving (an ip loop). At least one reaction must be phase inverting for the complete loop to be phase inverting and thus to encircle a conical intersection and lead to a photochemical reaction. It follows, that if a conical intersection is crossed during a photochemical reaction, in general at least two products are expected, B and C. A single product requires the existence of a two-component loop. This is possible if one of the molecules may be viewed as the out-of-phase combination of a two-state system. The allyl radical (Section IV, cf. Fig. 12) and the triplet state are examples of such systems. We restrict the discussion in this chapter to singlet states only.  [c.329]

Having settled on a definition of chemoinformatics - the use of informatics tools to solve chemical problems - we have to address the question of how informatics can assist in answering a chemist s fundamental questions, as outlined in Section 1.2. In essence, these fundamental questions all boil down to having to predict a property, be it physical, chemical, or biological, of a chemical compound or an ensemble of compounds, such as the starting materials of a chemical reaction. In order to make predictions one has to have passed through a process of learning. There exist two different types of learning deductive and inductive.  [c.6]

The most important feature of editing software is the option to save the structure in standard file formats which contain information about the structure (e,g., Mol-filc. PDB-filc). Most of these file formats arc ASCII text files (which can be viewed in simple text editors) and cover international standardized and normalized specifications of the molecule, such as atom and bond types or connectivities (CT) (see Section 2,4). Thus, with these files, the structure can be exchanged between different programs. Furthermore, they can seiwe as input files to other chemical software, e.g, to calculate 3D structures or molecular properties.  [c.138]

Compounds need not to be represented by only one spectrum. Several different types of spectra can be used simultaneously to represent a chemical compound, thus taking advantage of the different information they contain.  [c.431]

Potential-step teclmiques can be used to study a variety of types of coupled chemical reactions. In these cases the experiment is perfomied under diffrision control, and each system is solved with the appropriate initial and boundary conditions.  [c.1929]

Use. Owing to inherent physical characteristics, chemical agents can be adapted to a variety of munitions, including grenades, mines, artillery shells, bombs, bomblets, spray tanks, rockets, and missiles. Tactically, chemical agents have defensive and offensive capabiUties in limited or general wars. Toxic chemical agents may be used alone or in conjunction with other types of weapons. Chemical weapons do not destroy matHriel but allow physical preservation of industrial complexes and other faciUties. Incapacitating agents may also be used to preserve life and avoid permanent injury.  [c.399]

Another important class of random copolymers are the ethylene—propylene elastomers. The saturated hydrocarbon backbone provides good ozone resistance and better weathering and aging characteristics than diene mbbers. Even though these materials are synthesized by Ziegler—Natta catalysts, they do not exhibit much stereospecificity. There are basically two types of these copolymers, ethylene—propjiene (EPM) and ethylene—propjiene—diene (EPDM) materials (67). EPM materials are completely saturated if vulcanization is requited, it is carried out by means of free-radical generators (ie, organic peroxides). These copolymers are typically polymerized in an organic solvent or by using the Hquid phase of the monomer itself. Copolymers containing from 40 to 60 mol % of ethylene are most desirable more ethylene leads to crystalline block stmctures. EPDM materials contain 3 to 10 wt % of one of the following nonconjugated dienes ethyHdene norbornene (ENB) 1,4-hexadiene (HD) or dicyclopentadiene (DCPD). Similarly, these random terpolymers are made in a solution process where the solvent is organic or the monomer itself is in the Hquid phase. Suspension processes have also been developed. Because these materials contain unsaturation, they are easily vulcanized with either common mbber accelerators and sulfur or with organic peroxides. Important producers of EP elastomers include Copolymer Rubber and Chemical (EP syn), Du Pont (Nordel), Exxon Chemical (Vistalon), Polysar Inc. (Polysar EPM and EPDM), and Unicoyal (Royalene). The U.S. production of EPM and EPDM in 1990 was 295,000 t (68).  [c.184]

The human body and other biological systems have a tremendous capacity to take in all types of chemicals and either utilize them to support some bodily function or eliminate them. As analyhcal capabihhes have improved, lower and lower concentrations of chemicals have been observed in various parts of the body. Some of these chemicals enter the body by inhalation.  [c.101]

When discussing how to support a worker s task by interface design, it is useful to have a simple framework for the types of task involved, because different design principles are relevant to different types of the overall task. The skill-rule-knowledge (SRK) framework of human performance (see Chapter 2) can be useful in classifying the types of tasks involved in navigating through a computer-based display system and in controlling the chemical process itself. These tasks can be classified as follows  [c.328]

This could provide method to distinguish between the different types of nuclei but it is of minor interest to the physical chemist. On the other hand, if the experiment is conducted using spectrometers witji strong, very uniform magnetic fields, and if the spectrometer is equipped with a very precise frequency synthesizer, it is possible to detect frequency differences for a given isotope. These differences are on the order of 10 , 10 with respect to the nominal frequency and are due to the chemical environment surrounding the nucleus. They are called chemical shifts and are expressed in parts per million, ppm, of the base frequency giVenDy the resonance of a refere,nce, material. There are two ways to find the resonance, by exciting in succession the different types of nuclei continuous wave NMR, by exciting all the nuclei of an isotope at the same time and extracting the resonances of each chemical species from the signal obtained by pulsed NMR, often called Fourier transform NMR .  [c.64]

In the case of ion exchangers, the primary ions are chemically bonded into the ftamework of the polymer, and the exchange is between ions in the secondary layer. A few illustrations of these various types of processes follow.  [c.412]

While there was a general recognition of tire similarity of various types of critical phenomena, the situation was greatly clarified in 1970 by a seminal paper by Griffiths and Wlieeler [21], In particular the difference between variables that are fields and those that are densities was stressed. A field is any variable that is the same in two phases at equilibrium, (e.g. pressure, temperature, chemical potential, magnetic field). Conversely a density is a variable that is different in the two phases (e.g. molar volume or density, a composition variable like mole fraction or magnetization). The similarity between different kinds of critical phenomena is seen more clearly when the phase diagram is shown exclusively with field variables. (Examples of this are figure A2.5.1 and figure A2.5.11 )  [c.649]

One of the major tasks in chemoinformatics is to represent chemical structures and to transfer the various types of representation into application programs. A first and basic step to teaching computer chemistry is to transfoim the molecular structure into a language amenable to computer representation and manipulation. Basically, computers can only handle bits of 0 and 1. Thus, coding is the basis for transferring data. In general, coding is considered as a form of ciphering with the help of different symbols in a certain system under observed rules. Writing is such a system of symbols, which permits the spoken natural language to be reprocessed again and again. Thus, writing is a kind of coding of the language. More about ontology and taxonomy can be found in Ref. [1].  [c.16]

Boranes are typical species with electron-deficient bonds, where a chemical bond has more centers than electrons. The smallest molecule showing this property is diborane. Each of the two B-H-B bonds (shown in Figure 2-60a) contains only two electrons, while the molecular orbital extends over three atoms. A correct representation has to represent the delocalization of the two electrons over three atom centers as shown in Figure 2-60b. Figure 2-60c shows another type of electron-deficient bond. In boron cage compounds, boron-boron bonds share their electron pair with the unoccupied atom orbital of a third boron atom [86]. These types of bonds cannot be accommodated in a single VB model of two-electron/ two-centered bonds.  [c.68]

Toxic effects are measured through a wide variety of tests. Roughly, one can distinguish two types in vivo and in vitro tests. In vivo tests are carried out with organisms such as rodents, fish, water fleas, earthworms, and algae. In-vitro tests are done mostly with single cells, organelles like mitochondria, or even just enzymes that are affected by a toxicant. The dassical" in vivo test for acute toxicity of a chemical is the LCso-value. This is the concentration at which 50% of the test spedes are lolled by the toxic effects of a compound in a given time period. Until now this has also been one of the most common values to be predicted with QSAR equations.  [c.504]

Figure 10.1-7 shows that there is a strong correlation between hpophilicity and toxicity for these types of compounds. Although the compounds are not congeneric they can all be modeled just by the hpophilicity term of Eq. (15). A multitude of quantitative models have been published over the last 20 years, initiated by Konemann, who proposed a linear relationship between log P and LC50 of guppies (Pocilia reticulata) for a similar data set with 50 compoimds with log P ranging from -1 to 6 [40], Equations of this type can be appUed to model many common industrial chemicals successfiilly. Figure 10,1-8, however, shows that reality is a little more complicated. Now all compounds of the previously mentioned data set are shown [39], The data set was actually compiled with the aim of having highly diverse compounds and also a high diversity of toxic effects. All the effects on targets of major importance in acute toxicity are covered - plus receptor-mediated effects through environmental estrogens. These effects can be grouped into modes of action (MOA). A MOA can be defined as a common set of physiological and behavioral signs characterizing a type of adverse biological response, while a toxic mechanism is defined as the biochemical process underlying a given MOA [41],  [c.506]

A di awback is that the evaluation scheme for modeling the course of chemical reactions, as set up by the initial developer, is difficult to change as any alteration might have unexpected consequences for other types of reactions. Thus, it is a beautiful edifice that has basically not been changed since the early Nineties.  [c.549]

During the first centiuy of organic chemistry the chemist s view was focused on the structure of organic compounds and their transformations. Reactions were grouped according to the types of compounds which undeiTvent the reaction thus reaction types were defined such as ester condensation, substitution of aromatic compounds, or glycol cleavage. The view was focused on the direction of the chemical change in a chemical reaction, i.e., from reactants to products. The focus of a rctrosynthctic approach, on the other hand, is centered on the perception  [c.569]

Thus, computers will continue to penetrate every aspect of chemistry and we have to prepare the next generation of chemists for this process. In fact, we will see that the various types of computer applications in chemistry will increasingly be used in concert to solve chemical problems. Therefore, a unified view of the entire field is needed the various approaches to using computers in chemistry have to be ordered into a common framework, into a disdpline of its own Chemoinfor-matics.  [c.672]

The chemical environment foran atom m a molecule is probably niiit iie to th at molecule. Chem istry tries to find unify in g concepts an d the atom type Is on e of those unifying con cepts. For example, the AMBER force field defines five atom types for oxygens  [c.169]

See pages that mention the term Types of toxic chemicals : [c.112]    [c.301]    [c.781]    [c.819]    [c.1450]    [c.1453]    [c.1944]    [c.2495]    [c.2777]   
See chapters in:

Hazardous chemicals handbook Изд.2  -> Types of toxic chemicals