Oxidant concentrations, exposure

Environmental water samples to be analyzed for metals are best stored in quartz or Teflon containers. However, because these containers are expensive, polypropylene containers are often used. Borosilicate glass may also be used, but soft glass should be avoided because it can leach traces of metals into the water. If silver is to be determined, the containers should be light absorbing (dark colored). Samples should be preserved by adding concentrated nitric acid so that the pH of the water is less than two. The iron in well water samples, for example, will precipitate as iron oxide upon exposure to air and would be lost to the analysis if not for this acidification. 

Holland et al. studied 14 subjects under conditions of short-term exposures to irradiated automobile exhaust. The environmental conditions simulated the moderate smog episodes in the Los Angeles air basin. Oxidant concentrations were reported as 0.22 0.27 ppm (on the basis of the alkaline potassum iodide method). No significant changes attributed to exposure were found in reaction time, vital capacity, work performance, or oxygen consumption. 

Heagle and associates found a reduction in yield of sweet com and soybean after exposure to ozone at 0.10 ppm for 6 h/day over much of the growing season. These exposures were carried out in field chambers set over soybean plots in the field. They suggested that a threshold for measurable effects on these crops would lie between ozone (oxidant) concentrations of 0.05 and 0.10 ppm for 6 h/day. These values are realistic in terms of growing-season averages in the eastern United States. More of these studies could help to clarify dose-response relationships for economically important crops. Table 11-5 summarizes these long-term, chronic studies. 

Even that kind of information is not available for forest species. Other than chronic injury to white pine (associated with ozone, sulfur dioxide, and their mixtures), no clearly defined examples of chronic injury from ozone have been reported for eastern forests, and no information is available on PAN. It is of interest that both Virginia and jack pine appear more sensitive than white pine to acute ozone exposures, but chronic symptoms have not been observed in either species. The relationship between oxidant dose and injury in the San Bernardino Mountains area suggests that ponderosa pine is moderately to severely injured in areas that receive oxidant at above 0.08 ppm for 12-13 h each day (Chapter 12). Ponderosa pine seems to be the most sensitive western pine, but in some areas Jeffrey pine is about as sensitive. White fir, incense cedar, and sugar pine all appear more tolerant, even to the high oxidant concentrations in the San Bernardino Mountains. PAN may play some role in the chronic responses noted in the western forest species, particularly by broadleaf deciduous trees and some shrubs. 

The bioassay technique was developed to reduce the uncertainties associated with the use of native vegetation or cultivated crops. Plants can be started under controlled conditions and exposed under standardized conditions. Species and cultivars can be selected for oxidant sensitivity and symptom characteristics. The two studies just noted were the most closely controlled. Similar work has not been repeated. However, many investigators have grown plants under known cultural conditions and then transplanted them to field sites where they received special care. These plants can then be read for foliar symptoms throughout a given period, and the symptoms related to oxidant concentrations. The lack of apparent correlation in the two early studies could be due to the lack of specificity for the monitored oxidants, the presence of different concentrations of interacting oxidants at different times, or variations in cultural conditions between exposure times. 

Another subject of recent interest has been the question of indoor-outdoor oxidant concentrations. Available measurements and models suggest that indoor exposures may be substantially reduced by appropriate choices of ventilation sterns, air filters, and interior surface materials. The cost-benefit relationships coming from these studies may well have a great impact on future devious based on atmospheric concentrations of oxidant pollutants. 

Chromosomal aberrations, from ozone exposure, 8, 342, 363-64 Chromotrophic acid procedure, to measure oxidant concentration, 185 Cigarette-smoking... 

The peak in the derivative of the 5-phase resonance does not change drastically in intensity upon oxidation. The /8-phase resonance, however, does change considerably in intensity in the intermediate concentration range (0.5-3.6 wt. %) upon oxidation. Upon exposure of reduced chromia-on-alumina samples of low concentration to air at room temperature, a rapid color change from blue to green occurs and the EPR characteristic of the 7-phase immediately appears, although reduced in intensity in comparison to the 7-phase resonance intensity after oxidation at 600°. 

In an evaluation of epidemiological studies to date, it was concluded that most of the respiratory cancer seen among the nickel refinery workers could be attributed to exposure to a mixture of oxidic and sulfidic nickel at very high concentrations. Exposure to large concentrations of oxidic nickel in the absence of sulfidic nickel was also associated with increased lung and nasal cancer risks. There was also evidence that soluble nickel exposure increased the risk of these cancers and that it may enhance risks associated with exposure to less soluble forms of nickel. There was no evi-... 

NICKEL. [CAS 7440-02-0]. Chemical element, symbol Ni, at. no. 28. at. wt. 58.69, periodic table group 10, mp 1453rC, bp 2732°C. density 8.9 g/cm3 (solid, 20"C>. 9.04 g/cnr (angle crystal). Elemental nickel has a face-centered cubic crystal structure. Nickel is a silver-white metal, harder than iron, capable of taking a brilliant polish, malleable and ductile, magnetic below approximately 360°C. When compact, nickel is not oxidized on exposure to air at ordinary temperatures. The metal is soluble in HNO3 (dilute), but becomes passive in concentrated HNO3. The... 

Heat the solvent to 250F/121C in a water bath, such as a double boiler with the top part covered to prevent condensation of water vapor into the developer concentrate. It won t boil, but some steam may be given off if there is any water in the solvent mixture. Steam will arise when the powdered ingredients are added, which I presume to be water produced in the reaction between the ascorbic acid and part of the TEA. Once the powders have dissolved they will remain in solution and as long as water is kept out of the stock it will not oxidize by exposure to air. 

Annual Exposure to Oxidant Concentrations. Air monitoring was not done during winter because conditions then result in much less confinement of air pollutants by the marine temperature inversion in the adjacent basin below the forest, less oxidant synthesis during shorter days, and less frequent transport of polluted air to the forest. 

Amorphous silicon oxidizes upon exposure to air, at a rate which depends on the microstructure of the film. Columnar material (see Section 2.1.1) oxidizes rapidly along the surface of the columns because the intercolumnar regions are porous. The surface area of the columns is so large that an effective oxygen concentration of 10-20 at%... 

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