Examples of Pollutants

Metals that are of environmental concern fall into three classes (1) metals that are suspected carcinogens, (2) metals that move readily in soil, and (3) metals that move through the food chain. 

Mercury. In Japan in the 1950s and 1060s, wastes from a chemical and plastics plant containing mercury were discharged into Minamata Bay. The mercury was converted to the readily absorbed methylmercury by bacteria in the aquatic sediments. Consumption of fish and shellfish by the local population resulted in numerous cases of mercury poisoning, or Minamata disease. By 1970, at least 

107 deaths had been attributed to mercury poisoning, and 800 cases of Minamata disease were confirmed. Even though the mothers appeared healthy, many infants bom to these mothers who had eaten contaminated fish developed cerebral palsy-like symptoms and mental deficiency. 

Pesticides are also a major source of concern as water and soil pollutants. Because of their stability and persistence, the most hazardous pesticides are the organochlorine compounds such as DDT, aldrin, dieldrin, and chlordane. Persistent pesticides can accumulate in food chains for example, shrimp and fish can concentrate some pesticides as much as 1000- to 10,000-fold. This bioaccumulation has been well documented with the pesticide DDT, which is now banned in many parts of the world. In contrast to the persistent insecticides, the organophosphorus (OP) pesticides, such as malathion, and the carbamates, such as carbaryl, are short-lived and generally persist for only a few weeks to a few months. Thus these compounds do not usually present as serious a problem as the earlier insecticides. Herbicides, because of the large quantity used, are also of concern as potential toxic pollutants. Pesticides are discussed in more detail in Chapter 5. 

Nitrates and phosphates are two important nutrients that have been increasing markedly in natural waters since the mid-1960s. Sources of nitrate contamination include fertilizers, discharge from sewage treatment plants, and leachate from septic systems and manure. Nitrates from fertilizers leach readily from soils, and it has been estimated that up to 40% of applied nitrates enter water sources as runoff and leachate. Fertilizer phosphates, however, tend to be absorbed or bound to soil particles, so that only 20% to 25% of applied nitrates are leached into water. Phosphate detergents are another source of phosphate, one that has received much media attention in recent years. 

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Table 1. Examples of Pollution Prevention Practices in the Chemical Process ndustries.

Some OPs are prime examples of pollutants that are highly toxic but of low persistence, and serve as useful models for other compounds of that ilk that have been less well investigated. Because of their limited persistence, toxic effects are expected to be localized and of limited duration. As the compounds degrade quickly in tissues. 

Although general air and water pollution and controls are affected by the chemical industry, these problems and solutions are not unique to our industry. Certainly the area of toxic chemicals is unique. Because this problem is so diverse it is by itself a series of complex pollution problems. We have discussed some of these already (see Table 25.1). We now attempt to summarize these and other toxic chemical problems in chronological order. This includes many examples of pollution caused more specifically by the chemical industry or a closely allied industry as well as the laws and controls that have been enacted by governments and the industry to solve some of these unique problems. 

We will also see that residence time distribution notions lead to some interesting examples of pollution reactions, biological populations, and environmental modeling. 

Chemistry of the Environment focuses on the role of chemistry in environmental issues, including air and water pollution, solid wastes, and the relatively new field of green chemistry. The term pollution refers to the release of harmful or ohjectionahle substances into the environment, most commonly as the result of human activities. Some of the most obvious examples of pollution are smoke produced by industrial operations, carbon dioxide and other gases released into the atmosphere as a by-product of burning fuels, silt and sediment washed off land by rainwater, and garbage dumped on land. 

Figure 2.3 Illustration of the definition of environmental chemistry by the example of pollutant sulfuric acid formed by the oxidation of sulfur dioxide generated during the combustion of sulfur-containing coal. 

Section I provides an introduction to green chemistry and green engineering. Section II provides examples of pollution prevention heuristics for chemical processes. Heuristics of the two most important unit operations, reactors and separators, are covered. Section III introduces readers to the concept of environmental fate and transport and prediction of environmental fate properties. Understanding of environmental fate and transport is important for exposure assessment and also is essential for evaluating environmental performance of processes and products during process development and design. 

FIGURE 1-4 An example of pollutant advectlon and diffusion in the atmosphere. Smoke from multiple burning oil wells in Kuwait is carried downwind by advection. At the same time, the plumes of smoke widen because of diffusive transport, one of the major Fickian transport processes. Imagery courtesy of Space Imaging, Thornton, Colorado, USA. 

Give three examples of pollution sources for (a) water (b) air (c) soil. 

See examples of pollution control devices at http //www.epa.gov/ebtpages/treapollutioncontrol.html or http //cn.wikipedia.org/wiki/air polution/control devices. 

Fig. 26.1 Examples of pollutions entering the aquatic environment. Pollutions may originate from a point source, discharge from a factory, and non-point sources with activities connected to agriculture, i.e. pesticide spraying, fertilizing and cattle. Drawing by Jorge A. Varela Ramos...

Process combustion vaporization mechanical comminution Examples of pollutants emitted NO, NO2, CO, soot, SO2 hydrocarbons coarse particles, e.g. dusts, sea spray... 

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