Herbert M. Clark

The earth's crust

The present structure of the earth consists of a largely molten core composed chiefly of iron and nickel, surrounded by lighter rocks. The outer few miles, the crust, is the only portion of the earth that is accessible, and is the source of most of the substances used in a technological society. This chapter describes the structure, composition, and evolution of earth crust, and the processes that take place in it. The volume of material to be mined and processed, the energy requirements, and the waste disposal problems clearly set economic and environmental restrictions on the minimum concentration that can be employed for large-scale use of any substance but the society generally uses atypical, high concentration sources for most of its mineral needs. Bacteria can also be used for recovery of metals from low-grade sources in an economical way through microbial mining. Surface rocks are subject to breakup and chemical change by several weathering processes including physical disintegration, chemical reactions, and biological effects that lead to soil formation. Soil is a vital substance but its degradation is of serious concern in terms of its impact on future food needs. Human activity frequently causes degradation of soil in ways that range from loss of nutrients to changes in physical character of the soil to contamination with toxic materials to loss of the soil itself. Different types of soils, their composition and process of formation, soil contamination, and methods of decontamination such as bioremediation, are also presented in the chapter.

Soaps, synthetic surfactants, and polymers

This chapter reviews the chemical nature, synthesis, and environmental problems associated with biodegradable and nonbiodegradable organic compounds. Most of the polymers and surfactants in the detergents are made mainly from the chemicals derived from petroleum, and contain segments of linear or lightly branched hydrocarbon chains. Both soaps and synthetic detergents have similar structures, and their mechanisms of cleansing are also similar; however, zeolites of the detergents have environmental problems and they promote surface algal blooms. Microorganisms in the environment can utilize the energy of oxidation released by some hydrocarbons, soaps, and surfactants through β-oxidation. The chapter illustrates the microbial metabolism of hydrocarbons, soaps and synthetic detergents, and proposes guidelines to facilitate the understanding of microbial degradation of detergents. Although progress has been made in the synthesis of biodegradable polymers, these materials cost more, and in general, their properties are not as useful as those prepared from petroleum feedstock. A potential problem associated with biodegradable surfactants is the eutrophication of lakes that results from microbial degradation. The biodegradable replacements have solved the environmental problems associated with nonbiodegradable surfactants, and it is likely that biodegradable polymers assume an increasingly larger percentage of the polymer market.

Water systems and water treatment

This chapter discusses the major water systems, composition of various water bodies, factors that influence the composition and properties of water, and methods of water treatment. The composition of natural water bodies depends upon the gain, and loss of solutes through both chemical reactions and physical processes. The oxides of sulfur, and nitrogen that enters into the atmosphere from automobiles, other combustion sources, smelting, and some natural sources dissolve in raindrops and decrease the pH of rain water; resulting in acid rain. It affects the weathering reactions, solubility, and biological processes in lakes, rivers, and soils whose pH values are reduced as a consequence. The ecological effects of acid deposition include disruption of species distribution and food chains in lakes, as lower organisms disappear, and potential toxic effects on vegetation. Large scale water treatment is necessary in two general circumstances; for water taken into distribution systems for household or industrial use, and for wastewater that must meet particular standards for pollution control. Industrial waste water may require specialized treatments that depend on contaminants while treatment of domestic waste involves more general procedures. Several methods of water treatment for domestic waste water for household use like chlorination, use of activated charcoal, irradiation with ultraviolet light, are discussed in the chapter. Depending upon the final water-quality desired, treatment may be at the primary, secondary, or tertiary level. Clean water is a vital commodity, and the usage now is so extensive that waste-waters must be repurified to avoid destruction of aquatic ecosystems and because, often, the water will be reused.

Solid waste disposal and recycling

Safe disposal of solid wastes is a serious problem and with our culture, which generates ever larger amounts of disposable materials and an increasing population density, we can no longer simply throw things away. This chapter highlights the problems associated with solid waste materials such as plastic, rubber, glass, and metals, and several methods of solid waste disposal. Some waste materials can be disposed of by burning but combustion of many substances can generate toxic products that are released into the atmosphere; special incinerators and scrubbers may be necessary. Recycling is an alternative to the waste disposal methods and will reduce the amount of material to be disposed of. Some solid wastes can be recycled in a variety of ways to make useful object also. However, recycling has its own problems of collection, sorting, and cost. Composting of degradable organic materials also reduces disposal while producing a useful product, while anaerobic digestion is a possible source of methane fuel. A mix of these processes will be needed in future solid-waste handling techniques.

The nuclear environment

This chapter contains introductory discussions of the following topics: • Natural and anthropogenic sources of ionizing radiation in the environment

The environmental chemistry of some important elements

The naturally occurring elements that are present in high abundance, determine the nature of the environment as a whole through the properties, or behavior of themselves or their compounds. This chapter describes the chemistry of some of the most important elements that is related to the properties of the environment and to the biological effects. Many of these inorganic systems, play vital organic/biochemical roles; sometimes essential for life, and sometimes toxic to it. The biological availability of an element, and its ultimate effect on an organism, may depend on the chemical form in which the element is encountered. The elements are distributed through the environment in geochemical or bio-geochemical cycles, and these cycles involve processes that transfer substances from rocks and soils to the atmosphere; to oceans through weathering and runoff and through precipitation, and back to rocks through incorporation into sediments and subsequent geological transformations. The chapter discusses bio-geochemical cycles of important elements such as carbon, nitrogen, sulfur, and other elements of environmental interest.

Principles of photochemistry

Photochemical reactions are some of the most important processes taking place in the human environment that occur at high altitudes in the mesosphere and stratosphere, and are essential for the maintenance of thermal and radiation balance at the surface of the earth. This chapter describes the basic principles of light absorption, electronic excitation, and subsequent photochemical and photophysical processes. According to the principle of photochemistry, for light to be effective in producing photochemical transformations, the photon must not only possess sufficient energy to initiate the reaction, but also be absorbed. Photochemistry is generally limited to absorption in the visible, near-ultraviolet, and far-ultraviolet spectral regions. Absorption in the low-energy radio, microwave, or infrared spectral regions results in no direct photochemistry unless very-high intensity laser radiation is used. The chapter also discusses the properties of light, the kinetics of photochemical processes, and the deleterious physiological effects from overexposure to radiations.

Petroleum, hydrocarbons, and coal

Organic compounds are the basis of life on earth, and hydrocarbons are considered to be the parent compounds for organic materials. This chapter reviews petroleum and coal as major sources of hydrocarbons, the air pollution problems, and the toxic effects of these hydrocarbons on terrestrial and marine life. Crude oil is the predominant source of hydrocarbons used for internal combustion and industrial processes, and is also a major source of environmental pollution. Petroleum contains sulfur, oxygen, nitrogen, and other metal derivatives, and when burned, compounds containing these elements are emitted that contribute to the major environmental effects of petroleum. While automobile emissions cause atmospheric problems, catastrophic oil spills can have dramatic local environmental effects. Coal is another important source of hydrocarbons that contains a variety of inorganic ions. Several methods to obtain hydrocarbons from coal such as coal gasification, coal liquefaction, and direct conversion of coal to hydrocarbons are discussed in the chapter. The chapter also addresses the problems associated with oil spills and automobile emissions, hydrocarbon production from coal, and various approaches to mitigate them, such as use of skimmers or boats, and bioremediation.

Haloorganics and pesticides

Halo-organic compounds have many uses, such as pharmaceutical agents, fibers, building materials, agricultural chemicals, solvents, and cleaning agents. This chapter reviews the chemistry, reactivity, and environmental problems due to several types of halo-organics. Because many chloroorganics are pesticides, a discussion of general pesticides and other methods of pest control, is also included. The chapter explains many environmental processes such as oxidation, photolysis, or hydrolysis that may cause the degradation of haloorganics and other organic compounds, and subsequently may result in their being converted to nontoxic or in some instances more toxic compounds. Biodegradation is the key to destruction of organic compounds in the environment, and is usually carried out by a cooperating group of microorganisms through various pathways, such as reductive degradation and oxidative degradation. The toxicity associated with some haloorganics is of chronic type and have many deleterious health effects other than causing cancer; low levels can cause endocrine, immune, and neurological effects. Most of the chlorofluorocarbons and perhalogenated organics, so-called halons, are nontoxic, stable, colorless, and nonflammable; ideal substances for a variety of industrial applications. However, these compounds impose two major environmental problems, global warming and destruction of ozone layer. The chapter entails some biochemical methods that are increasingly used as an alternative to, or in conjunction with the application of synthetic pesticides.

Chemistry in aqueous media

This chapter provides an overview of the main principles that explain the chemical behavior of natural and unnatural environmental processes occurring in aqueous media. Chemical interactions in aqueous systems make up an important area of environmental chemistry, and the properties of water determine the behavior observed in solution. The structure and density properties of water are largely determined by the hydrogen bonding of water molecules with one another. Density differences, along with wind effects, lead to ocean-current circulation patterns that are analogous to circulation in the atmosphere. Besides the unusual density properties that water exhibits as a result of hydrogen bonding, it also has high values for several thermodynamic properties such as specific heat and enthalpy of vaporization that are important factors in climate. In aqueous systems, water is the most abundant ligand. The behavior of elements present in large amounts in an aqueous system is controlled by the rules of solubility, acid-base equilibria, and complexation, but the behavior of trace substances is largely controlled by adsorption on solid surfaces. The chapter provides a discussion on several properties of water, such as solubility, acid-base behavior, pH and solubility of compounds, adsorption and ion exchange, and effects of temperature and pressure on equilibrium reactions.