We are reminded in Section 4.1 that a hazardous chemical is a risk only if there is exposure to it. Section 4.2 summarizes the ongoing studies of the US Centers for Disease Control and Prevention (CDC) on human exposure to more than 300 chemicals. Section 4.3 introduces epidemiology, a discipline that studies possible relationships between human exposure to a particular chemical and its possible adverse health effects. We see the many difficulties posed in doing a good epidemiological study, but that they are important. Section 4.4 introduces chemical risk assessment, which is done to calculate a dose that is safe for human exposure; the four steps of an assessment are explained. Box 4.1 describes the use of factors of 10. An example of how risk assessment can lead to controversy is explained in Box 4.2. Section 4.5 explains that the purpose of risk management is reducing exposure to the chemical in question. Regulatory methods are often used, but other approaches are also noted. Section 4.6 describes why reducing risk to children has special importance. It also looks at chemical risks in less-developed countries versus developed countries. Section 4.7 discusses how chemical risk assessment continues to be done in animals; however, that may rapidly change with Tox21, a major effort that is radically changing chemical risk assessment. This uses automated means of testing chemical toxicity and does so rapidly and without animals. Section 4.8 concludes the chapter.

This chapter deals with a global issue – the destruction of stratospheric ozone – that results from ozone-depleting chemicals, of which chlorofluorocarbons (CFCs) and halons are best known. Depletion of stratospheric ozone by these chemicals led to increasing amounts of the Sun’s ultraviolet (UV) light reaching Earth’s surface. This problem led to the 1987 Montreal Protocol, the first worldwide agreement to protect the environment. The ban on ozone-depleting chemicals is largely working. Problems continue to arise that need resolving, but the “ozone hole” is slowly recovering (see Table 1.3).1

Section 13.1 describes the characteristics of hazardous waste (HW), the US law governing it, the history of HW site development, and those who currently generate HW. In Section 13.2 we see the cradle-to-grave tracking of HW and major means of treating it. In Section 13.3 we see how Superfund came into being and examine two sites, Love Canal and a huge mining site; we see a great number of HW sites that the government itself created. Section 13.4 portrays the evaluation of HW sites, and how exposure to those sites and their health risks are evaluated. Section 13.5 briefly looks at cleaning up HW sites; we learn the good potential for reuse of brownfield sites. In Section 13.6 we see how HW has been irresponsibly transported into poor countries and the passage of the Basel Convention to reduce illegal dumping. In Section 13.7 we see the major problems associated with waste electronics (e-waste), and that e-waste can become HW when “recycled” in countries unable to handle it. We also see that e-waste can be properly recycled, but at a cost; electronics are not designed for recycling, and even disassembly can be difficult. However, the EU has a directive that requires extended producer responsibility (EPR). Electronics production requires large quantities of resources, including 10 percent of the world’s gold; these factors may lead to more responsible e-waste recycling. Section 13.8 presents the chapter conclusions.

Metals rank among the agents posing the greatest hazards to humans.1 Many are nutrients and exposure to normal levels of these is not toxic. However, none of the persistent, bioaccumulative, toxic (PBT) or other hazardous metals – also called heavy metals – is a nutrient. PBT and other heavy metals can be toxic even at low concentrations. Three metals – lead, methylmercury, and cadmium – are PBTs.2 All metals are found in nature, but at low concentrations. A metal’s toxicity, as will be seen in this chapter, can vary depending on its chemical form.3

Recall persistent organic pollutants (POPs) from Chapter 1 (see Box 1.4). A POP is a chemical that persists and bioaccumulates in the environment1 – that is, a chemical accumulates in a particular living creature faster than it can be eliminated. And the chemical is toxic.2 In this chapter, PBT (persistent, bioaccumulative, toxic) is used synonymously with POP because all POPs are PBTs. However, the opposite is not true: In Chapter 15 you will see three metal PBTs, so not all PBTs are POPs.3

Climate change is nothing new. About 18,000 years ago, Earth was experiencing the last of many ice ages, from which it only emerged about 10,000 years ago.1 More recently, approximately between the years 1300 and 1870, portions of the Earth passed through a little ice age. The role of greenhouse gases (GHGs), especially water vapor and carbon dioxide (CO2),2 in affecting the Earth’s temperature is also ancient, and indeed has long served life on Earth well. Radiation from the sun reaches and warms the Earth’s surface. Earth absorbs about half of this radiation and, in turn, emits radiant heat (infrared radiation) back toward space; part of this is captured by heat-trapping water vapor and GHGs. Without the “greenhouse effect” to trap this warmth, the Earth could be colder by 35°C (95°F), and unable to support life as we know it. However, the last century has brought greater warming than can be accounted for by natural causes, and warming that is occurring at a faster rate.3 This is what we examine in this chapter. Moreover, another impact due to carbon dioxide has been occurring – ocean acidification, another impact with serious implications.