Source/environmental indicators

Donald R. Baker. It seems to me that your results on the distribution of boron and gallium have important implications for the work of others who have concluded that these elements are depositional environmental indications. I wonder if the enrichment of these elements in nonmarine rocks of Pennsylvanian age in the eastern U.S. may simply reflect their proximity to the source area and not have any real bearing on the depositional environment. And conversely, the lower content of these elements reported for marine shales may be caused by deposition of these facies in areas far removed from the source areas. What is your opinion ... 

Two sets of sulfur oxide emission estimates for the United States, drawn from Environmental Protection Agency sources (I, 2, 3) are presented in Tables I and II. The source categories in the two tables are not consistent nor are the estimates of the total emission, even allowing for a 3-yr difference in the base periods. It is also obvious that certain sources have not been accounted for in the compilations. Nevertheless, the estimates do identify most of the industrial sources and indicate their relative magnitudes. The distributions of sources in other nations are similar to those in the United States in a number of reported instances (4). 

Notes if no accepted standard data appears in this table, then the designers must provide a justified value if the probability used is less than 1. Sometimes data are valid only in special circumstances. For instance, a statistical source may indicate that a specific number of aircraft accidents due to birdstrikes take place every 100,000 or million hours. One may conclude from this data that the probability of a birdstrike is comparatively low. Hidden by the data analysis approach is the fact that at certain airfields, such as Boston, the Midway Islands, and other coastal and insular areas where birds abound, the probability of a birdstrike accident is much higher than the average. This example demonstrates that generalised probabilities will not serve well for specific, localised areas. This applies to other environmental hazards such as lightning, fog, rain, snow, and hurricanes. 

Fig. 4-7. Trend in carbon monoxide air quality indicators. Source U.S. Environmental Protection Agency, 1992.

Overall the results reported in this review indicate that water scarcity might increase metal exposure (due to low dilution), metal uptake (due to higher retention under low flow), and metal toxicity and/or accumulation (depending on the dose and time of exposure), but also might cause opposite effects depending on the source of pollution. In addition, water scarcity will influence nutrient loads and will also modulate the fate and effects of metals. Thus, future studies addressing the role of environmental stress on the effects of toxicants at community scale are key to predict the impact of toxicants in the aquatic ecosystems. 

A more practical, atom-economic and environmentally benign aziridination protocol is the use of chloramine-T or bromamine-T as nitrene source, which leads to NaCl or NaBr as the sole reaction by-product. In 2001, Gross reported an iron corrole catalyzed aziridination of styrenes with chloramine-T [83]. With iron corrole as catalyst, the aziridination can be performed rmder air atmosphere conditions, affording aziridines in moderate product yields (48-60%). In 2004, Zhang described an aziridination with bromamine-T as nitrene source and [Fe(TTP)Cl] as catalyst [84]. This catalytic system is effective for a variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic alkenes, as well as cx,p-unsaturated esters (Scheme 28). Moderate to low stereoselectivities for 1,2-disubstituted alkenes were observed indicating the involvement of radical intermediate. 

A shift in the velocity constant such as is observed in bulk esterification is the exception rather than the rule. A source of more general concern is the enormous increase in viscosity which accompanies polymerization. Both theory and experimental results indicate that this factor usually is of no importance except under the extreme conditions previously mentioned. Consequently, the velocity coefficient usually remains constant throughout the polymerization (or degradation) process. Barring certain abnormalities which enter when the velocity coefficient is sensitive to the environmental changes accompanying the polymerization process, application of the ordinary methods of chemical kinetics to polymerizations and other processes involving polymer molecules usually is permissible. 

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