Chemicals in the air

Atmospheric chemistry influences human health, climate, food production, and through its impact on visibility, our view of the world. Chemicals in the air affect us with each breath we take. Suspended particulate matter that form from gas-phase reactions affect the amount of solar energy reaching the earth s surface. 

Air heaters in industrial environments require corrosion-protective finishes that are capable of protecting the coil and case from damage by condensation, acid vapors, or aggressive chemicals, in the air or the primary medium. If air washers are used with coils placed after them, copper or other noncorroding metal tubes should be used. 

Singh HB, Salas LJ, Stiles RE. 1983a. Selected man-made halogenated chemicals in the air and oceanic environment. J Geophys Res 88 3675-3683. 

A third way to gain some knowledge about the concentrations of chemicals in the environment involves some type of modeling. Scientists have had, for example, fair success in estimating the concentrations of chemicals in the air in the vicinity of facilities that emit those chemicals. Information on the amount of chemical emitted per unit time can be inserted into various mathematical models that have been designed to represent the physical phenomena governing dispersion of the chemical from its source. Certain properties of the chemical and of the atmosphere it enters, together with data on local weather conditions, are combined in these models to yield desired estimates of chemical concentrations at various distances from the source. These models can be calibrated with actual measurement data for a few chemicals, and then used for others where measurement data are not available. 

If the oral route is to be used, the chemical may be mixed with the diet, dissolved in drinking water, or delivered by a tube to the stomach (gavage). An inhalation exposure requires special equipment to create the desired concentration of the chemical in the air to be breathed by the animal. In any case, the analytical chemist must be called on to measure the amount of the chemical in these various media after it has been added to guarantee that the dose is known with accuracy. Some chemicals decompose relatively quickly, or errors are made in weighing or mixing the chemical to achieve the desired diet, water, or air concentrations, so chemical analysis of these media is essential throughout the study. 

In the past (prior to 1974), exposure of humans to heptachlor and heptachlor epoxide was directly related to the application of heptachlor as an insecticide. However, because of the persistence and bioaccumulation of heptachlor and heptachlor epoxide, exposure of the general population can occur through ingestion of contaminated food (especially cow s or maternal human milk), inhalation of vapors from contaminated soil and water, or direct contact with residual heptachlor from pesticide application. People whose homes have been treated may continue to be exposed to these chemicals in the air over long periods. Occupational exposure can occur in the manufacture of the chemical or from use of heptachlor to control fire ants. The most likely routes of exposure at hazardous waste sites are unknown. Heptachlor has been found infrequently in soil and groundwater at hazardous waste sites. Children who eat contaminated soil or people who obtain tap water from wells located near hazardous waste sites might be exposed to heptachlor. Also, since both compounds can volatilize from soil, people living near hazardous waste sites may be exposed to the compounds in the air. 

Dichlorobenzidine is not a volatile chemical. In the air, it may exist as dust particles or boimd to particulate matter. The absorption of 3,3 -dichlorobenzidine from such respirable particles into the body depends, in part, on the size of the particle. Large particles tend to deposit in the upper airways and are subsequently cleared by ciliary action with little absorption across limg tissues. However, the ciliary action transports the particles to the epiglottis where they are often swallowed, leading to gastrointestinal absorption. Smaller particles can penetrate more deeply into the respiratoiy tree, where 3,3 -dichloro-benzidine absorption may be significant. 

For systemic effects observed in inhalation smdies, the determining factor for effects to occur at the systemic target is generally the total dose rather than the concentration of the chemical in the air. In such cases, a tolerable intake (expressed as mg/kg body weight per day, or mg/m depending on the standard to be derived, i.e., a tolerable intake in its strict meaning, or a tolerable concentration) is estabhshed from the NOAEC, or LOAEC, derived in the inhalation smdy and adjusted for continuous exposure. 

For substances with local effects on the respiratory tract, no general approach for interspecies scaling can be given. Anatomical and physiological differences in the airways between experimental animals and humans contribute to interspecies differences in local effects observed between animals and humans, see Section 4.7.8. It should be noted, however, that for local effects the determining factor for effects to occur in the respiratory tract is generally the concentration of the chemical in the air rather than the total dose and thus allometric scaling is not relevant. 

ENVIRONMENTAL CHEMISTRY. That aspect of chemistry concerned with air and water pollution, pesticides, and chemical and radioactive waste disposal. A random selection of specific areas of research includes. (l)Lead and other toxic chemicals in the air. 

Exposure levels of hazardous chemicals in the air of work environments are mandated by OSHA as exposure limit values. The studies necessary to establish these limits are carried out by NIOSH. However, the more complete list of the better-known threshold limit values (TLVs) is established by the American Conference of Governmental Industrial Hygienists. Although TLVs are not binding in law, they are an excellent guide to the employer. In fact they are often adopted by OSHA as exposure limit values. The concentrations thus expressed are the weighted average concentrations normally considered safe for an exposure of 8 h/day, 5 days/week. Absolute upper limits (excursion values) may also be included. Some exposure limits are shown in Table 23.1. 

To understand any extraction technique it is first necessary to discuss some underlying principles that govern all extraction procedures. The chemical properties of the analyte are important to an extraction, as are the properties of the liquid medium in which it is dissolved and the gaseous, liquid, supercritical fluid, or solid extractant used to effect a separation. Of all the relevant solute properties, five chemical properties are fundamental to understanding extraction theory vapor pressure, solubility, molecular weight, hydrophobicity, and acid dissociation. These essential properties determine the transport of chemicals in the human body, the transport of chemicals in the air water-soil environmental compartments, and the transport between immiscible phases during analytical extraction. 

The mechanism of olfaction has many theories but is not fully understood and is still the subject of research. The nose is the human organ that detects smell (Fig. 5.9). It extends from the face to the end of the palate. In its simplest explanation the two nasal cavities are lined with a mucous membrane, kept moist by the secreted substance mucus. Chemicals in the air entering the nose must dissolve in this mucus before they can be detected. A small area - about the size of a small postage stamp - in the upper part of the nasal cavity contains olfactory cells, which are sensitive to the chemicals in the mucus solution. For a molecule to be detected it must bind specifically to the sensitive cells that act as sensory receptors. The sensory receptors situated in the olfactory epithelium (epithelium is the name given to the outer layer of covering cells) are believed to bind specifically with substances according to the shape of their molecules. 

In all the experiments, direct measurements of the concentrations of the chemicals in the air in the treated plots were made by drawing known volumes of air through adsorbing samplers placed at various heights within the plots. Details of the treatments and sampling procedures varied somewhat from experiment to experiment and have been described elsewhere ( 1 > 2, 3, 5..) only the more relevant... 

Based in this information difference between the NOEL and human exposure or the risk at a given exposure is determined. Humans may be exposed to chemicals in the air, water, food, or on the skin. From the concentrations of a chemical in these different compartments the external daily exposure is estimated. The response to the chemical depends upon duration and route of exposure, the toxicokinetics of the chemical, the dose-response relationship and the susceptibility of the individual. Thus, the precise definition of the terms hazard, exposure, and risk is essential to understand toxicological evaluations (details on data requirements and procedures for risk assessment are given subsequently). 

Henry s Law Constant and Air- Water Partitioning (Ka ) Air-water partitioning is described by the Henry s Law constant (//), which is defined as the ratio of the partial pressure (j>) of a chemical in the air to its mole fraction (or molar concentration) dissolved in water (Cw) at equilibrium, according to... 

Therefore, the general differential eqnation of the chemical in the air compartment for a single room with room materials j, snch as floor, walls and ceiling, is expressed as follows ... 

You can exposed to 1,1 -dichloroethane by breathing air containing its vapors in the outdoor air or in your workplace, or by drinking water contaminated with it. Release from industrial processes are the main source of this chemical in the air. Some members of the general population may be exposed to... 

An interesting use of iridium involves the official world standard for the kilogram. The standard, kept at the International Bureau of Weights and Measures in Paris, France, is a piece of platinum-iridium metal stored in an airtight jar. The standard is made of platinum and iridium to protect it from reacting with oxygen and other chemicals in the air. In this way, the standard s weight will always remain exacdy the same. 

Chemicals present in blood that are gases or possess a high degree of volatility diffuse passively into the alveolar air of the lung until they reach equilibrium. The concentration of these chemicals in the air phase is directly proportional to their concentration in blood, and the latter in turn is in equilibrium with the concentration of the chemicals in the tissues. This phenomenon can be applied to noninvasively monitor the presence and the concentration of gases and volatile substances in blood. A practical example of such application is the indirect measurement of alcohol present in blood by analyzing for ethanol in exhaled air with an instrument known as the Breathalyzer. 

If mixing height, L, is low enough so that it restricts the ascension of a plume, it may be appropriate to assume that the plume becomes fully mixed vertically beneath L and spreads only horizontally. In this case, the concentration of a chemical in the air can be estimated as... 

The U.S. EPA is charged with addressing air pollution under the Clean Air Act. The poor air quality found in California has led the state of California to establish the California Air Resources Board (ARB), which also addresses this subject. EPA has established a list of hazardous air pollutants anci ARB has established a Toxic Air Contaminant (TAC) Identification List. 4 Numerous other literature references identify still other known air pollutants. Table 7.1, toxic chemicals in the air, which was compiled from these sources, shows the range of pervasive toxic chemicals that are found in the air we breathe. 

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