You have read in this text many times of the major pollution problems resulting from combustion, especially fossil-fuel combustion. In this chapter we see a global issue – destruction of stratospheric ozone – which does not result from combustion. The chemicals responsible are synthetic chemicals, chlorofluorocarbons (CFCs) and halons. Stratospheric ozone is essential to life on Earth. It absorbs more than 95% of the sun's ultraviolet (UV) radiation, which could otherwise destroy most life. Stratospheric-ozone depletion led to the 1987 Montreal Protocol, the first worldwide agreement to protect the environment. Except for smuggled chemicals, the ban of ozone-depleting chemicals is working. The stratospheric-ozone layer is expected to recover, albeit slowly. Section I below examines the stratosphere and provides background on CFC uses and how ozone depletion was detected. In Section II, we see why the greatest ozone depletion occurs over Antarctica, and describe the increases in UV radiation reaching the Earth.

One chemical category poses special concerns: the persistent, bioaccumulative, and toxic (PBT) chemicals. These chemicals also often move among air, water, and land, and cross human boundaries. Section I of this chapter examines general characteristics of PBTs. We see that even at low levels, PBTs can present problems. Section II examines three families of PBTs that are organic chemicals: polychlorinated, polybrominated, and polyfluorinated PBTs. Metal PBTs are discussed in Chapter 15.

SECTION I

About 87 000 chemicals are in commercial use. The US Environmental Protection Agency (a US agency) has identified 53 of these as persistent, bioaccumulative, and toxic (PBT). Of these, 42 are organic chemicals, many polychlorinated. The other eleven are metals. Doubtless others will be identified as additional chemicals are screened. To identify only 53 among 87 000 may seem a small number, but given their potential to cause problems we can be grateful for this relatively small number. Moreover, other chemicals, such as the polychlorinated biphenyls (PCBs), would be classified as PBTs were they still manufactured today. Industrialized countries banned the worst polychlorinated chemicals in the 1970s and 1980s, long enough ago that even though they are persistent, environmental levels have fallen. However, hot spots remain and people are advised not to eat fish caught in the Great Lakes and certain other areas.

All metals are persistent. However, not all metals are PBTs; that is, not all are also defined as bioaccumulative and toxic. Many factors affect whether exposure to a metal poses problems. A higher dose is, of course, more likely to cause adverse effects than a low dose. Another factor, illustrated by the metal, chromium is the chemistry. Chromium(III) has a valence of three. It is a nutrient and, because it is not very soluble, doesn't build up to high concentrations in water. But chromium(VI) has a valence of six, is toxic and is a carcinogen.

• Five nutrient metals are PBTs: copper, chromium, nickel, selenium, and zinc.

• Six non-nutrient metals are also PBTs: antimony, arsenic, beryllium, cadmium, lead, and mercury. The toxicity of these metals too varies with chemical form as illustrated by lead. Elemental lead is toxic, but tetraethyl lead is much more toxic.

Section I of this chapter is a metal primer, providing information on metals regardless of whether they are PBTs. Section II details four especially troublesome metal PBTs: lead, mercury, cadmium, and arsenic.

SECTION I

A metal primer

Metals are elemental and cannot be destroyed. But they do bond to other elements (thus becoming molecules) and then show properties different from the parent metal. Consider three cases.

Twenty-five years ago, the US Environmental Protection Agency (a US agency), working with Harvard University, was studying the sources of various environmental pollutants. They made what was to them a startling observation: regardless of which community they studied – its location; whether rural or urban; lightly or highly industrialized; and regardless of sex, age, smoking habits, and occupation – indoor air pollution was the major source of exposure to many air pollutants. This is perhaps not surprising: most people spend 90% or more of their time indoors, indoor sources emit many of the same pollutants as outdoors sources, and mixing with outdoor air may be slow to occur. In the following years, the Advisory Board of the US Environmental Protection Agency (a US agency) ranked indoor air pollution as a priority environmental health risk. Section I of this chapter reviews specific contaminants that affect indoor air quality: combustion pollutants (including tobacco smoke), volatile organic chemicals (VOCs), radon, and biological pollutants. It briefly overviews too the major impact that combustion particulates have on people in impoverished homes of less-developed countries. Section II delves into hazardous household products and household hazardous waste, and describes two old hazards that remain with us, asbestos and lead paint.

The reality of outdoor air pollution is more than the words “ambient air pollution” can convey (see Box 5.1). It is the eye-stinging pollution surrounding us in a city crowded with motor vehicles, the odor of ozone on a hot hazy day, the choking dust of a heavy dust storm, the smoke coming from wood or coal fires on a winter day, the fumes from an uncontrolled industrial facility, odor from uncontrolled sewage or an open dump. Many living in wealthy countries are spared the worst of these. Not so for the multitudes living in less-developed countries, who are exposed to these and more; see Table 5.1.

In Chapter 5, Section I examines six major air pollutants, which along with volatile organic chemicals (VOCs) account for 98% of US air pollution and similar percentages worldwide. Section II introduces the hazardous air pollutants (HAPs), also called toxic air pollutants. Section III describes massive pollution that can be directly observed or detected from space while sometimes wreaking havoc at ground level – traveling combustion pollutants, major dust storms, and smoke from mammoth fires. Section IV briefly surveys pollution in less-developed countries.

You saw in earlier chapters the major ways that energy use leads to ambient air pollution, and to acid deposition and global climate change. You also saw its contribution to the nitrogen glut and other water and soil pollution problems. This chapter looks specifically at energy production and use, and alternatives to fossil fuels. Section I surveys world energy use past, present, and future. Overviewed in Section II is our great attachment to motor vehicles, the results of that fondness, and how we can reduce some adverse impacts of motor vehicles. Section III examines another major user of energy, electricity generation, and some of the many approaches for reducing the pollution associated with it. Section IV brings us to an examination of alternative fuels. Section V briefly surveys energy use in less-developed countries, while Section VI summarizes sustainable energy generation.

SECTION I

Overviewing world energy use

World energy use is increasing steadily (Figure 13.1). Between 1970 and 1997 consumption nearly doubled. It is projected to rise another 60% between 1997 and 2020. Emissions of carbon dioxide and other pollutants rise in step with energy consumption.

How can we speak of zero waste or zero emissions if, as you learned earlier no process is 100% efficient? The answer is that zero waste is a philosophy, one that says there is no waste: what we call “waste” or “pollutant” is really a useful resource. This philosophy recognizes too that, if we aspire to reduce waste by 100%, we accomplish more than if our goal was 40% or 80%.

Sections I to III below emphasize dematerialization, reducing the quantities of materials we use. Section I asks how well we are doing in reducing waste and pollution, and looks at the waste that the United States produces. Section II discusses industrial ecology, a discipline with the goal of enmeshing industrial society into the environment. It also raises the idea of increasing our efficiency in resource use 4-fold, perhaps as much as 10- to 20-fold. Section III examines tools useful in working toward zero waste, including life-cycle assessment (LCA) and design for the environment (DfE). Other tools too point toward ways to reduce use of resources: servicizing and product stewardship. Section IV takes us to detoxification; that is, changing the chemicals we use and how we produce them, “green chemistry.” The intention is to reduce chemical risk to humans and the environment. Finally, Section V asks, is there progress toward zero waste?

Pesticide use is among the most controversial of topics. Yet, pesticide use is prevalent. Some individuals believe pesticides are necessary to destroy the enemies of human agriculture and health. Others believe we can use organic farming to accomplish these ends without synthetic pesticides. A third group believes pesticides are needed, but recognize their limitations; they work to minimize pesticide use under the rubric of “Integrated Pest Management”. There is no simple “right” answer, but we do need answers. Consider this challenge from the authors of the article, Can green chemistry promote sustainable agriculture? “Human population is increasing. Demand for food is rising … Environmental impacts are worsening. Taken together, few issues reflect the difficulties of sustainable development more than the problem of controlling pests and increasing food production while protecting the environment and conserving natural resources.”

Section I discusses why we use pesticides and who uses them. After briefly addressing three major insecticide families, we consider selective versus broad-spectrum pesticides. Section II looks at pesticides as pollutants, as food contaminants, and their effects on non-target species. We also examine the important phenomenon of pesticide resistance.

Municipal solid waste (MSW) is but one of many wastes. There are also construction and demolition debris, municipal sludge, combustion ash, mining and drilling debris, agricultural wastes, industrial-process wastes including some sludge, hazardous waste, and others. Altogether the United States alone produces about 10.1 billion tons (9.2 billion tonnes) of waste each year. MSW is barely 3% of that gigantic stream, but it is important: each of us is intimately associated with it. Its composition and amount is the result of our behavior. Moreover, if we move back one step, the businesses producing the products going into MSW generate much of those billions of pounds of waste. In Section I we ask why we generate so much waste. We examine municipal solid waste, what is in it, and why it is of concern. Section II looks at setting priorities in how we manage waste – the waste-management hierarchy (WMH). Pollution prevention is at the top of the WMH, but this section also examines reuse and recycling, incineration, and landfilling. Section III moves onto international MSW issues starting with wealthy societies, and examines the major problems that wastes pose in developing and impoverished societies. It ends with the example presented by the city of Curitiba, Brazil.

Before discussing the formation of the major geological units of the solid Earth, we should review the internal structure of our planet as described by seismic wave studies (Fig. 8.1). The most important discontinuities observed by seismologists down to the base of the mantle are:

• The base of the crust (called the Mohorovičić discontinuity or Moho), 40 km below the continents, but only 5–7 km beneath the oceans.

• The base of the lithosphere, on average 80 km below the oceans, and deeper still beneath the continents. This is the lower boundary of the rigid tectonic plates. The softer part of the upper mantle underneath the lithosphere is called the asthenosphere.

• The 440 km discontinuity corresponding to a change in olivine structure (spinel or ringwoodite phase).

• The 660 km discontinuity corresponding to the transformation of all minerals into perovskite and minor Fe-Mg oxide (magnesio-wüstite). This is the base of the upper mantle.

• The mantle–core boundary at about 2900 km. Above this boundary is a seismically abnormal layer some 200 km thick, known as the D″ layer.

The core is divided into a liquid outer core, responsible for the Earth's magnetic field, and a solid inner core. The core is metallic and composed mostly of iron and nickel.

Plate tectonics is a powerful theory that unifies the geological expression of crustal and upper mantle geodynamics (Fig. 8.2).

Modern geochemistry is a discipline that pervades nearly all of Earth science, from measuring geological time through tracing the origin of magmas to unravelling the composition and evolution of continents, oceans and the mantle, all the way to the understanding of environmental changes. It is a comparatively young discipline that was initiated largely by Goldschmidt in the 1930s, but its modern development and phenomenal growth started only in the 1950s. Although there are many journals dedicated to geochemical research, there have been remarkably few general geochemical textbooks that cover more than a limited segment of the full scope of modern geochemistry. This is one reason why Francis Albarède's new book is most welcome. It is written by the author of the authoritative and widely acclaimed Introduction to Geochemical Modeling (Cambridge University Press, 1995), and it is intended as an undergraduate introductory course in geochemistry. Its scope is large, though not all-inclusive, concentrating on the inorganic chemistry of the condensed part of our planet. Although it started out as a translation from the original French book, the new English-language edition is much more than just a translation. The entire text has been substantially revised and in some parts expanded, and it is really a new book. Yet it retains a distinctly French flavor, particularly in the way many subjects are addressed via mathematical description. This approach is entirely normal for a student of the French Ecole Normale or a French university, but it will surprise many American teachers and students of geology alike.

The theory of element transport is a way of representing the spatial changes in geochemical properties in various contexts, such as movement in the ocean or mantle, the migration of geological fluids or magmatic liquids within a rock matrix, or the attainment of chemical and isotopic equilibrium among minerals within the same rock, etc. It is, in fact, a set of rather complex theories involving some heavyweight mathematics, which we can only touch lightly upon in this book.

The essential concepts forming the core of this theory are those of conservation, flux, sources, and sinks. A conservative property is additive and can only be altered by addition or subtraction at the system boundaries or by the presence of sources and sinks. Mass or number of moles are conservative properties; concentration is not: if a mole of salt is added to a solution already containing one mole, the resulting solution will contain two moles, however the salt is added and whatever the volume of the system. In contrast, two solutions of one mole per liter combine to form a solution of one mole per liter. A flux is a quantity of something (mass, moles, energy, etc.) crossing a unit surface per unit time. The most familiar of these fluxes is volume flow, which is quite simply the velocity v (in cubic meters per square meter per second). Mass flux is the mass content of volume flow, i.e. ρv, where ρ is the density of the medium.