Unit Eight. The Living Environment
38. Human Influences on the Living World
The girl gazing from this now-classic National Geographic photo faces an uncertain future. An Afghani refugee, the whims of war destroyed her home, her family, and all that was familiar to her. Her expression carries a message about our own future: The problems humanity faces on an increasingly unstable, overcrowded, and polluted earth are no longer hypothetical. They are with us today and demand solutions. This chapter provides an overview of the problems and then focuses on solutions—on what can be done to address very real problems. As a concerned citizen, your first task must be to clearly understand the nature of the problem. You cannot hope to preserve what you do not understand. The world’s environmental problems are acute, and a knowledge of biology is an essential tool you will need to contribute to the effort to solve them. It has been said that we do not inherit the earth from our parents—we borrow it from our children.
We must preserve for them a world in which they can live. That is our challenge for the future, and it is a challenge that must be met soon. In many parts of the world, the future is happening right now.
Our world is one ecological continent, one highly interactive biosphere, and damage done to any one ecosystem can have ill effects on many others. Burning high-sulfur coal in Illinois kills trees in Vermont, while dumping refrigerator coolants in New York destroys atmospheric ozone over Antarctica and leads to increased skin cancer in Madrid. Biologists call such widespread effects on the worldwide ecosystem global change. The pattern of global change that has become evident within recent years, including chemical pollution, acid precipitation, the ozone hole, the greenhouse effect, and the loss of biodiversity, is one of the most serious problems facing humanity’s future.
The problem posed by chemical pollution has grown very serious in recent years, both because of the growth of heavy industry and because of an overly casual attitude in industrialized countries. In one example, a poorly piloted oil tanker named the Exxon Valdez ran aground in Alaska in 1989 and spilled oil over many kilometers of North American coastline, killing many of the organisms that live there and coating the land with a thick layer of sludge. If the tanker had been loaded no higher than the waterline, little oil would have been lost, but it was loaded far higher than that, and the weight of the abovewaterline oil forced thousands of tons of oil out the hole in the ship’s hull. Why do policies permit overloading like this?
Chemicals are released into both the air and into water; therefore, their effects are far reaching.
Air Pollution. Air pollution is a major problem in the world’s cities. In Mexico City, oxygen is sold routinely on corners for patrons to inhale. Cities such as New York, Boston, and Philadelphia are known as gray-air cities because the pollutants in the air are usually sulfur oxides emitted by industry. Cities such as Los Angeles, however, are called brown-air cities because the pollutants in the air undergo chemical reactions in the sunlight to form smog.
Water Pollution. Water pollution is a very serious consequence of our casual attitude about pollution. “Flushing it down the sink” doesn’t work in today’s crowded world. There is simply not enough water available to dilute the many substances that the enormous human population produces continuously. Despite improved methods of sewage treatment, lakes and rivers throughout the world are becoming increasingly polluted with sewage. In addition, fertilizers and insecticides also get washed from the land to the water in great quantities.
The spread of “modern” agriculture, and particularly the Green Revolution, which brought high-intensity farming to developing countries, has caused very large amounts of many kinds of new chemicals to be introduced into the global ecosystem, particularly pesticides, herbicides, and fertilizers. Industrialized countries like the United States now attempt to carefully monitor side effects of these chemicals. Unfortunately, large quantities of many toxic chemicals, although no longer manufactured, still circulate in the ecosystem.
For example, the chlorinated hydrocarbons, compounds that include DDT, chlordane, lindane, and dieldrin, have been banned in the United States, where they were once widely used. They are still manufactured in the United States and exported to other countries, where their use continues. Chlorinated hydrocarbon molecules break down slowly and accumulate in animal fat tissue. Furthermore, as they pass through a food chain, they become increasingly concentrated in a process called biological magnification. Figure 38.1 shows how a minute concentration of DDT in plankton increases to significant levels as it is passed up through this aquatic food chain. In the United States and elsewhere, DDT caused serious ecological problems by leading to the production of thin, fragile eggshells in many predatory bird species, such as peregrine falcons, bald eagles, osprey, and brown pelicans. In the late 1960s, DDT was banned in time to save the birds from extinction. Chlorinated compounds have other undesirable side effects and exhibit hormonelike activities in the bodies of animals.
Figure 38.1. Biological magnification of DDT.
Because DDT accumulates in animal fat, the compound becomes increasingly concentrated in higher levels of the food chain.
Key Learning Outcome 38.1. All over the globe, increasing industrialization is leading to higher levels of pollution.